NanoWiki - Brukerbidrag [nb]

Utveksling

2017-02-05T19:38:51Z

Birgela: /* Utvekslingssteder */

== Standard ting ==

Det kan være greit å finne ut hvor man vil, og hva man vil ved å dra ut.
Når man vet hvor, så er det litt greiere å finne ut hva man vil; lære et språk, finne et sted med bedre kompetanse, høste kulturerfaring, unngå Trondheimsklimaet, skaffe kontakter eller bare få seg et år borte fra de andre på linja.

Uansett er det visse ting man må finne ut:

*Noe om universitetet: Gå på hjemmesida til universitet, eller søk etter informasjon hos [http://www.ntnu.no/studier/studier_i_utlandet/land internasjonal seksjon].
*Få [http://www.ntnu.no/eksternweb/multimedia/archive/00031/Forh_ndsgodkjennings_31079a.pdf godkjenning] hos fakultetet når du har funnet ut av fagene.
*Søk om støtte hos [http://www.lanekassen.no/templates/Page____5505.aspx Lånekassa] og hos [https://www.intersek.ntnu.no/soknadsskjema/ Internasjonal seksjon].

Ellers er Internajsonalt Hus på Gløshaugen et sted å gå for å få mer informasjon og det finner du på [http://www.ntnu.no/ntnukart//no/gloshaugen.gif dette kartet] (øverst i venstre hjørne).

Ved utveksling utenom 4. året, da med tanke på masteroppgaven, eventuelt Ph.D, så er det viktigste å kontakte faglærere og finne ut av hvem som har kontakter hvor, for da går det mye på hvem som kjenner hvem.

== Praktiske ting ==

Det kan i mange tilfeller være greit å være litt tidlig ute med følgende ting:
*Forsikring - skaff en spesialforsikring for studenter i utlandet enten via ANSA eller ditt forsikringsselskap
*Enkelte steder er det knot å få seg en plass i faget, men bare besøk professorens kontor, etter litt korrespondanse via mail, og snakk med ham/henne så ordner slikt seg.
*Velg deg ut en hel haug med fag! Er ikke alltid du er like heldig med fagvalgenes ledighet og tilgjengelighet...
*Kom ned litt tidlig slik at du har tid til å skaffe bolig, da det er litt kjedelig å bo på hostell når du begynner med undervisninga. Dette kan selvfølgelig i noen tilfeller ordnes hjemme fra Norge, men det er greiere å se hva du får før du sier ja.

== Utvekslingssteder ==

Her er en oversikt over noen forslag til universiteter rundt om i verden, en del av dem med tanke på at de bedriver litt med nanoteknologi på noen av sine fakulteter og muligens har programmer for utdanning innen vårt fagfelt:

{| class="wikitable sortable"
|-
! Institusjon
! Land
! Beliggenhet
! Avtale med NTNU
|-
| [[Universitetet i Oslo]]
| Norge
| Oslo
| ?
|-
| [[University of California, Berkeley]]
| USA
| Berkeley, California
| Delvis
|-
| [[University of California, Santa Barbara]]
| USA
| Santa Barbara, California
| Delvis
|-
| [[University of Waterloo]]
| Canada
| Waterloo, Ontario
| Ja
|-
| [[California Institute of Technology]]
| USA
| Pasadena, California
| Nei
|-
| [[Seoul National University]]
| Korea
| Seoul
| Ja
|-
| [[Osaka Prefecture University]]
| Japan
| Osaka
| Ja
|-
| [[Tokyo Instuitute of Technology]]
| Japan
| Oookayama, Tokyo
| Ja
|-
| [[Waseda University]]
| Japan
| Shinjuku, Tokyo
| Ja
|-
| [[University of Alberta]]
| Canada
| Edmonton, Alberta
| Ja
|-
| [[Cornell University]]
| USA
| Ithaca, New York
| Nei
|-
| [[University of California, San Diego]]
| USA
| San Diego, California
| Ja(?)
|-
| [[University of Guelph]]
| Canada
| Guelph, Ontario
| Nei
|-
| [[Penn State University]]
| USA
| Centre County, Pennsylvania
| Ja (Bare lærerutdanning?)
|-
| [[Korea Advanced Institute of Science and Technology]] (KAIST)
| Korea
| Yuseong, Deajeon
| Ja
|-
| [[TU Delft]]
| Nederland
| Delft
| Ja, Erasmus
|-
| [[University of Twente]]
| Nederland
| Enschede
| Ja, Erasmus
|-
| [[Massachusetts Institute of Technology (MIT)]]
| USA
| Cambridge, Massachusetts
| Nei
|-
| [[Rice University]]
| USA
| Houston, Texas
| Nei
|-
| [[University of Colorado at Boulder (CU Boulder)]]
| USA
| Boulder, Colorado
| Nei
|-
|[[Institut National de Polytechnique (INP Grenoble)]]
| Frankrike
| Grenoble, Rhône-Alpes
| Ja
|-
|[[Institut National des Sciences Apliquées (INSA Lyon)]]
| Frankrike
| Lyon
| Ja
|-
|[[Université Montpellier II (UM2)]]
| Frankrike
| Montpellier
| Ja
|-
|[[Eidgenössische Technische Hochschule (ETH Zürich) ]]
| Sveits
| Zürich
| Ja
|-
|[[Universitat de Barcelona (UB)]]
| Spania
| Barcelona, Catalonia
| Ja (kun innen nanoteknologi)
|-
|[[Technische Universität München (TUM)]]
| Tyskland
| München
| Ja, Erasmus
|-
|[[Indian Institute of Technology (IIT)]]
|India
|Kanpur, Uttar Pradesh
| Nei
|-
|[[Universiteit Gent]]
| Belgia
| Gent
| Ja, Erasmus
|-
|[[National University of Singapore]]
| Singapore
| Singapore
| Ja, ca to plasser
|}

Det at NTNU har avtale med universitet kan bety litt forskjellig. Det kan variere fra at man får totalt fritak av betaling av skolepenger til at man bare får et lite avslag i prisen. For mer informasjon bes det tas kontakt med Internasjonal Seksjon.

== Finansiering av utdanning ==

* [http://www.lanekassen.no/templates/Page____9098.aspx Lånekassen]
* [https://www.intersek.ntnu.no/soknadsskjema/ Stipend fra NTNU]
* [http://www.legathandboken.no/ Legathåndboken]
* [http://www.fulbright.no/Fulbright_Grants/Norwegians_to_the_US/Fulbright+stipend+for+norske+studenter+til+USA.E3p1MY7.ips Fullbright-stipend (kun USA)]
* [http://www.noram.no/index.php?side_id=75&vis=1 NORAM-stipend (kun USA og Canada)]

== Utvekslingsrapporter ==
Mange studenter fra NTNU får utvekslingsstipend fra Internasjonal Seksjon. For å få utbetalt stipendet må man skrive en rapport som legges inn i [https://www.intersek.ntnu.no/rapport/FMPro?-db=Rapport.fp5&-lay=www&-format=search.htm&-view database]. Nedenfor er ei liste med utvekslingsrapporter skrevet av nanoteknologistudenter.

===Tyskland===
[https://www.intersek.ntnu.no/rapport/FMPro?-db=rapport.fp5&-format=record%5fdetail.htm&-lay=www&-sortfield=-none-&-op=cn&City=M%fcnchen&-op=cn&Fakultet%20hjemme=NT&-op=cn&Utvekslingsperiode=H%f8st%20og%20v%e5r%202014%2f15&-max=10&-recid=48245&-find= Technische Universität München] høst og vår 2014/2015, skrevet av Ane Tefre Eide, [[Bionanoteknologi]]
===Nederland===
===Singapore===
[https://www.intersek.ntnu.no/rapport/FMPro?-db=rapport.fp5&-format=record%5fdetail.htm&-lay=www&-sortfield=created&-sortorder=descend&-op=cn&Land=Singapore&-max=2147483647&-recid=43067&-find= National University of Singapore (NUS)] høst og vår 2011/2012, skrevet av Sara Westrøm, [[Bionanoteknologi]]

[https://www.intersek.ntnu.no/rapport/FMPro?-db=rapport.fp5&-format=record%5fdetail.htm&-lay=www&-sortfield=created&-sortorder=descend&-op=cn&Land=Singapore&-max=10&-recid=48506&-find= National University of Singapore (NUS)] høst og vår 2014/2015, skrevet av Marie Hernes, [[Nanoelektronikk]]

===Sveits===
===USA===
[https://www.intersek.ntnu.no/rapport/FMPro?-db=rapport.fp5&-format=record_detail.htm&-lay=www&-sortfield=-none-&-op=cn&City=Boulder&-max=10&-recid=40002&-find= University of Colorado at Boulder] vår 2010, skrevet av Sigmund Østtveit Størset, [[Bionanoteknologi]]

[https://www.intersek.ntnu.no/rapport/FMPro?-db=rapport.fp5&-format=record%5fdetail.htm&-lay=www&-sortfield=-none-&-op=cn&Land=USA&-op=cn&Vertsinstitusjon=UC%20Berkeley&-op=cn&City=Berkeley&-op=cn&Hjemmeinstitution=NTNU&-op=cn&Fakultet%20hjemme=NT&-op=cn&Utvekslingsperiode=H%f8st%20og%20v%e5r%202009%2f2010&-max=10&-recid=39770&-find= University of California Berkeley], Høst/Vår 2009/2010, [[Nanomaterialer]]

== Nyttige lenker ==

*[http://www.ntnu.no/studier/studier_i_utlandet Internasjonal seksjon, NTNU]
*[http://www.ntnu.no/intersek/tilutlandet123 Til utlandet på 123]
*[http://www.ansa.no/ Mye nyttig informasjon om utdanning i utlandet fra ANSA]
*[http://ed.sjtu.edu.cn/ARWU-FIELD2008/ENG2008.htm De 100 beste teknologiuniversitetene]
*[http://www.ifs.tuwien.ac.at/~silvia/research-tips/times_top100_technologie_2005.pdf Times rangering av de 100 beste tekniske universitetene]
*[http://colleges.usnews.rankingsandreviews.com/college Rangeringer inne mange kategorier i USA]
*[http://www.ntnu.no/international/usa/visa.pdf Informasjon om prosedyren for å søke visum til USA]
*[http://www.ntnu.no/international/recommendations Informasjon om letters of recommendation]
*[http://www.ntnu.no/international/statementofpurpose.pdf Informasjon om å skrive statement of purpose (motivasjonsbrev)]
*[http://www.ansa.no/upload/Dokumenter/Infosenteret/Landbrosjyrer/usa07.pdf ANSA's brosjyre om utdanning i USA]

[[Kategori:Utveksling]]

University of Twente

2017-02-05T19:35:04Z

Birgela: /* Struktur */

{{Infobox
|Fakta
|*'''Land:''' Nederland
*'''Beliggenhet:''' Enschede
*'''Studenter:''' 9614
*'''Nettsted:''' [https://www.utwente.nl/en/ utwente.nl/en]
}}

== Hvordan søke ==
Siden UTwente har Erasmusavtale med NTNU kan man søke på vanlig måte via NTNU. Søknadsfristen er 4 måneder før semesterstart (1. mai for start 1. september, 1. oktober for start 1. februar). Gå til [http://www.ntnu.no/studier/studier_i_utlandet Internasjonal Seksjon] for mer informasjon om søknadsprosedyrer. Ellers, se [https://www.utwente.nl/en/education/international-students/exchange-students/ UTwentes sider for utvekslingsstudenter]. For nordmenn er det ikke nødvendig med engelsktest.

== Hva koster det ==

Hvis man har Erasmus stipend betaler man ikke skolepenger. Man betaler semesteravgiften til NTNU og får 350€ i måneden når man er i utlandet. (2016/17)

Bolig er billligere enn i norge dersom man klarer å få gjennom skolen. Hvis man leier privat kan det svinge litt. Mer om det når vi har fått oss bolig.
Twente har veldig bra informasjon rettet mot utvekslingsstudenter på sidene sine, så det anbefales å sjekke der.

== Fagtilbud ==

[https://osiris.utwente.nl/student/OnderwijsCatalogusZoekCursus.do Full oversikt over alle fag.]

=== Nanoteknologi master ===
Twente har et 2-årig masterprogram i Nanoteknologi som er relevant for bio og elektro:
https://www.utwente.nl/en/education/master/programmes/nanotechnology/

Angående fag: klikk på de forskjellige lenkene [https://www.utwente.nl/nt/program/ her], det er en MYE bedre oversikt enn fagvelgeren som er lenket til fra NTNUs side om Twente. Man kan også se en kjapp oversikt [https://www.utwente.nl/en/education/master/programmes/nanotechnology/programme/courses/ her].

=== Molecular and material engineering master ===
De har også et 2-årig masterprogram i Chemical engineering, som også inkluderer Molecular and material engineering som er relevant for material:
https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/

En mer detaljert fagoversikt finnes [https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/course-descriptions/#elective-courses her].

=== K-emner ===
Vi har ikke helt funnet ut hvordan det funker med K-emner og studiepoeng. Teorien er at når man har droppen TekLed i tredje, så må vi ha 15 poeng (altså tre fag) K-emner i løpet av året. BMS-fakultetet arrangerer en del slike kurs. Det kan være lurt å ta kontakt med dem før man melder seg opp i kurset ettersom de tydeligvis ikke er like snille som naturfakultetet på å la en ta alle fag.

=== Struktur ===
Twente har et system bygget på 60 studiepoeng (Elective Credits) per år, hvor hvert år er delt opp i fire terminer. ([https://www.utwente.nl/ces/planning-roosters/en/ timeplan]) Fagene er mindre enn vi er vant til fra NTNU med stort sett 5 poeng per fag. Det vil si at man tar tre fag i terminen. Hvis du ser et fag som er verdt 15 poeng er det sannsynligvis en Bachelor-modul som vil si at det også er bakt inn grunnleggende kunnskap i faget (det kan fort bli bortkastet tid). Så langt har ingen her tatt en slik modul.

De har en del vekt på vurderinger underveis, så det er mye mer spredning i vurderingsformene enn på NTNU. Noen fag har 100% eksamen, som vi er vant med og noen har bare øvinger/prosjekter/presentasjoner som vurderingsgrunnlag. Vanligst er en kombinasjon med rundt 50% eksamen og 50% innleveringer.

== Erfaringer ==
=== Bolig ===
Hvis du skal på utveksling fra høsten er det veldig stort press på boligmarkedet. Dette gjelder visst for hele Nederland ettersom de har begynt å ta inn ekstra mange internasjonale studenter. Heldigvis prioriteres internasjonale studenter i søknadskøen, så bare vær tidlig ute og søk som du vil få beskjed om, så ordner det seg sannsynligvis. Vi fikk svar på boligsøknaden i juni-juli. Det virker som om det er litt flere ting som er tilgjengelig for dem som begynner på våren. Sjekk facebooksidene "University of Twente - Marketplace" og "University of Twente - International" for ledige rom i tillegg til sidene som står i heftet til universitetet. Vær obs på scam til og med på disse modererte sidene og ikke gjør noe dumt som å sende masse penger ut av landet.

Skal du bo i byen eller på campus?
Fordelen med campus er at det tar maks 5 min fra du går ut døra til du er i forelesningen. Mye av sportene er også basert på campus og studentforeningene er selvfølgelig også her.

Hvis du tror at du kommer til å dra på byen eller nyte andre kulturelle aktiviteter flere ganger i uka lønner det seg naturligvis å bo i byen. Det er også en type lesesaler i byen, så man må ikke reise til universitetet for å få studiero. Det tar forresten 10-20 minutter å sykle fra campus til byen avhengig av hvor rask (full) du er og hvor på campus/i byen du skal.

=== Forelesere ===
Det virker som om de fleste professorene er ganske flinke. Noe av det ligger i at fag på masternivå er mer spesialiserte og foreleserne derfor kan ha fag i det de kan best. Forelesere her har også mer kontroll over faget, så de kan legge det opp som de vil uten å tenke så mye på godkjenning fra eksamenskontoret og liknende. Alle forskningsgrupper tilbyr noe som heter Capita Selecta. Dette er et fag som ofte er litteraturstudie, men som også kan være eksperimentelt. Så hvis du liker en foreleser/fag veldig godt kan man gjøre et dypdykk ved å ta ett av diss fagene.

=== Fag ===
Fagene blir organisert sånn per halvår, så det er ikke sikkert at alle fagene du hadde tenkt deg går det rette kvartalet, eller går i det hele tatt. En rask guide er som følger: 1A, 1B, 2A, 2B er terminene fra høst til sommer. JAAR betyr at faget enten er individuelt eller at det bare går når nok studenter har vist interesse. Send mail til foreleseren og hør hva som er greia. De fleste fag har en resit, så man får to forsøk på å stå. Karakterskalaen er 1-10 med 5.5 som ståkarakter. 9 er i praksis høyeste karakter og 10 får man bare dersom man har absolutt alt rett og har imponert foreleseren. Eksamener er ikke anonyme, men vi har ikke funnet ut om dette er i hovedsak positivt eller negativt.

== Annet ==
* Siden de ikke har bachelorutdannelse for nano, starter alle i en ny "nano-klasse", som gjør det lett å bli inkludert i klassemiljøet.
* Ulempen med dette er at de på master i nano har mange "basic" nanofag som vi allerede har hatt.
* Twente har [https://www.utwente.nl/mesaplus/ Mesa+]

== Hvem har vært der ==
'''Kull 13:''' Birger, Jonathan, Ruth

'''Kull Danmark:''' Halvor

'''Kull 10:''' Simen (tar PhD)

== Nyttige linker ==
* [https://www.intersek.ntnu.no/socrates/ Erasmus NTNU]
* [http://siu.no/no/Programoversikt/EU-program/Erasmus Erasmus, info]
* [http://www.ntnu.no/portal/page/portal/ntnuno/tre-spalter?selectedItemId=25330&rootItemId=22934&sectionId=11052 Utveksling i EU-land]
* [http://www.stexx.eu/search/?q=ca-1,2,3,4,5,6,7,8,9|cl-positive,negative,neutral,advice|elv-ba,ma,other|ge-m,f|mt-exchange|tor-16 Anmeldelser på studyportals]
[[Kategori:Utveksling]]

University of Twente

2017-02-05T19:32:30Z

Birgela: /* Molecular and material engineering master */

{{Infobox
|Fakta
|*'''Land:''' Nederland
*'''Beliggenhet:''' Enschede
*'''Studenter:''' 9614
*'''Nettsted:''' [https://www.utwente.nl/en/ utwente.nl/en]
}}

== Hvordan søke ==
Siden UTwente har Erasmusavtale med NTNU kan man søke på vanlig måte via NTNU. Søknadsfristen er 4 måneder før semesterstart (1. mai for start 1. september, 1. oktober for start 1. februar). Gå til [http://www.ntnu.no/studier/studier_i_utlandet Internasjonal Seksjon] for mer informasjon om søknadsprosedyrer. Ellers, se [https://www.utwente.nl/en/education/international-students/exchange-students/ UTwentes sider for utvekslingsstudenter]. For nordmenn er det ikke nødvendig med engelsktest.

== Hva koster det ==

Hvis man har Erasmus stipend betaler man ikke skolepenger. Man betaler semesteravgiften til NTNU og får 350€ i måneden når man er i utlandet. (2016/17)

Bolig er billligere enn i norge dersom man klarer å få gjennom skolen. Hvis man leier privat kan det svinge litt. Mer om det når vi har fått oss bolig.
Twente har veldig bra informasjon rettet mot utvekslingsstudenter på sidene sine, så det anbefales å sjekke der.

== Fagtilbud ==

[https://osiris.utwente.nl/student/OnderwijsCatalogusZoekCursus.do Full oversikt over alle fag.]

=== Nanoteknologi master ===
Twente har et 2-årig masterprogram i Nanoteknologi som er relevant for bio og elektro:
https://www.utwente.nl/en/education/master/programmes/nanotechnology/

Angående fag: klikk på de forskjellige lenkene [https://www.utwente.nl/nt/program/ her], det er en MYE bedre oversikt enn fagvelgeren som er lenket til fra NTNUs side om Twente. Man kan også se en kjapp oversikt [https://www.utwente.nl/en/education/master/programmes/nanotechnology/programme/courses/ her].

=== Molecular and material engineering master ===
De har også et 2-årig masterprogram i Chemical engineering, som også inkluderer Molecular and material engineering som er relevant for material:
https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/

En mer detaljert fagoversikt finnes [https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/course-descriptions/#elective-courses her].

=== K-emner ===
Vi har ikke helt funnet ut hvordan det funker med K-emner og studiepoeng. Teorien er at når man har droppen TekLed i tredje, så må vi ha 15 poeng (altså tre fag) K-emner i løpet av året. BMS-fakultetet arrangerer en del slike kurs. Det kan være lurt å ta kontakt med dem før man melder seg opp i kurset ettersom de tydeligvis ikke er like snille som naturfakultetet på å la en ta alle fag.

=== Struktur ===
Twente har et system bygget på 60 studiepoeng (Elective Credits) per år, hvor hvert år er delt opp i fire terminer. ([https://www.utwente.nl/ces/planning-roosters/en/ timeplan]) Fagene er mindre enn vi er vant til fra NTNU med stort sett 5 poeng per fag. Det vil si at man tar tre fag i terminen.

De har en del vekt på vurderinger underveis, så det er mye mer spredning i vurderingsformene enn på NTNU. Noen fag har 100% eksamen, som vi er vant med og noen har bare øvinger/prosjekter/presentasjoner som vurderingsgrunnlag. Vanligst er en kombinasjon med rundt 50% eksamen og 50% innleveringer.

== Erfaringer ==
=== Bolig ===
Hvis du skal på utveksling fra høsten er det veldig stort press på boligmarkedet. Dette gjelder visst for hele Nederland ettersom de har begynt å ta inn ekstra mange internasjonale studenter. Heldigvis prioriteres internasjonale studenter i søknadskøen, så bare vær tidlig ute og søk som du vil få beskjed om, så ordner det seg sannsynligvis. Vi fikk svar på boligsøknaden i juni-juli. Det virker som om det er litt flere ting som er tilgjengelig for dem som begynner på våren. Sjekk facebooksidene "University of Twente - Marketplace" og "University of Twente - International" for ledige rom i tillegg til sidene som står i heftet til universitetet. Vær obs på scam til og med på disse modererte sidene og ikke gjør noe dumt som å sende masse penger ut av landet.

Skal du bo i byen eller på campus?
Fordelen med campus er at det tar maks 5 min fra du går ut døra til du er i forelesningen. Mye av sportene er også basert på campus og studentforeningene er selvfølgelig også her.

Hvis du tror at du kommer til å dra på byen eller nyte andre kulturelle aktiviteter flere ganger i uka lønner det seg naturligvis å bo i byen. Det er også en type lesesaler i byen, så man må ikke reise til universitetet for å få studiero. Det tar forresten 10-20 minutter å sykle fra campus til byen avhengig av hvor rask (full) du er og hvor på campus/i byen du skal.

=== Forelesere ===
Det virker som om de fleste professorene er ganske flinke. Noe av det ligger i at fag på masternivå er mer spesialiserte og foreleserne derfor kan ha fag i det de kan best. Forelesere her har også mer kontroll over faget, så de kan legge det opp som de vil uten å tenke så mye på godkjenning fra eksamenskontoret og liknende. Alle forskningsgrupper tilbyr noe som heter Capita Selecta. Dette er et fag som ofte er litteraturstudie, men som også kan være eksperimentelt. Så hvis du liker en foreleser/fag veldig godt kan man gjøre et dypdykk ved å ta ett av diss fagene.

=== Fag ===
Fagene blir organisert sånn per halvår, så det er ikke sikkert at alle fagene du hadde tenkt deg går det rette kvartalet, eller går i det hele tatt. En rask guide er som følger: 1A, 1B, 2A, 2B er terminene fra høst til sommer. JAAR betyr at faget enten er individuelt eller at det bare går når nok studenter har vist interesse. Send mail til foreleseren og hør hva som er greia. De fleste fag har en resit, så man får to forsøk på å stå. Karakterskalaen er 1-10 med 5.5 som ståkarakter. 9 er i praksis høyeste karakter og 10 får man bare dersom man har absolutt alt rett og har imponert foreleseren. Eksamener er ikke anonyme, men vi har ikke funnet ut om dette er i hovedsak positivt eller negativt.

== Annet ==
* Siden de ikke har bachelorutdannelse for nano, starter alle i en ny "nano-klasse", som gjør det lett å bli inkludert i klassemiljøet.
* Ulempen med dette er at de på master i nano har mange "basic" nanofag som vi allerede har hatt.
* Twente har [https://www.utwente.nl/mesaplus/ Mesa+]

== Hvem har vært der ==
'''Kull 13:''' Birger, Jonathan, Ruth

'''Kull Danmark:''' Halvor

'''Kull 10:''' Simen (tar PhD)

== Nyttige linker ==
* [https://www.intersek.ntnu.no/socrates/ Erasmus NTNU]
* [http://siu.no/no/Programoversikt/EU-program/Erasmus Erasmus, info]
* [http://www.ntnu.no/portal/page/portal/ntnuno/tre-spalter?selectedItemId=25330&rootItemId=22934&sectionId=11052 Utveksling i EU-land]
* [http://www.stexx.eu/search/?q=ca-1,2,3,4,5,6,7,8,9|cl-positive,negative,neutral,advice|elv-ba,ma,other|ge-m,f|mt-exchange|tor-16 Anmeldelser på studyportals]
[[Kategori:Utveksling]]

University of Twente

2017-02-05T19:29:41Z

Birgela:

{{Infobox
|Fakta
|*'''Land:''' Nederland
*'''Beliggenhet:''' Enschede
*'''Studenter:''' 9614
*'''Nettsted:''' [https://www.utwente.nl/en/ utwente.nl/en]
}}

== Hvordan søke ==
Siden UTwente har Erasmusavtale med NTNU kan man søke på vanlig måte via NTNU. Søknadsfristen er 4 måneder før semesterstart (1. mai for start 1. september, 1. oktober for start 1. februar). Gå til [http://www.ntnu.no/studier/studier_i_utlandet Internasjonal Seksjon] for mer informasjon om søknadsprosedyrer. Ellers, se [https://www.utwente.nl/en/education/international-students/exchange-students/ UTwentes sider for utvekslingsstudenter]. For nordmenn er det ikke nødvendig med engelsktest.

== Hva koster det ==

Hvis man har Erasmus stipend betaler man ikke skolepenger. Man betaler semesteravgiften til NTNU og får 350€ i måneden når man er i utlandet. (2016/17)

Bolig er billligere enn i norge dersom man klarer å få gjennom skolen. Hvis man leier privat kan det svinge litt. Mer om det når vi har fått oss bolig.
Twente har veldig bra informasjon rettet mot utvekslingsstudenter på sidene sine, så det anbefales å sjekke der.

== Fagtilbud ==

[https://osiris.utwente.nl/student/OnderwijsCatalogusZoekCursus.do Full oversikt over alle fag.]

=== Nanoteknologi master ===
Twente har et 2-årig masterprogram i Nanoteknologi som er relevant for bio og elektro:
https://www.utwente.nl/en/education/master/programmes/nanotechnology/

Angående fag: klikk på de forskjellige lenkene [https://www.utwente.nl/nt/program/ her], det er en MYE bedre oversikt enn fagvelgeren som er lenket til fra NTNUs side om Twente. Man kan også se en kjapp oversikt [https://www.utwente.nl/en/education/master/programmes/nanotechnology/programme/courses/ her].

=== Molecular and material engineering master ===
De har også et 2-årig masterprogram i Chemical engineering, som også inkluderer Molecular and material engineering som er relevant for material:
https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/

En mer detaljert fagoversikt finnes [https://www.utwente.nl/che/education/curriculum/Molecular%20%26%20Materials%20Engineering/ her].

=== K-emner ===
Vi har ikke helt funnet ut hvordan det funker med K-emner og studiepoeng. Teorien er at når man har droppen TekLed i tredje, så må vi ha 15 poeng (altså tre fag) K-emner i løpet av året. BMS-fakultetet arrangerer en del slike kurs. Det kan være lurt å ta kontakt med dem før man melder seg opp i kurset ettersom de tydeligvis ikke er like snille som naturfakultetet på å la en ta alle fag.

=== Struktur ===
Twente har et system bygget på 60 studiepoeng (Elective Credits) per år, hvor hvert år er delt opp i fire terminer. ([https://www.utwente.nl/ces/planning-roosters/en/ timeplan]) Fagene er mindre enn vi er vant til fra NTNU med stort sett 5 poeng per fag. Det vil si at man tar tre fag i terminen.

De har en del vekt på vurderinger underveis, så det er mye mer spredning i vurderingsformene enn på NTNU. Noen fag har 100% eksamen, som vi er vant med og noen har bare øvinger/prosjekter/presentasjoner som vurderingsgrunnlag. Vanligst er en kombinasjon med rundt 50% eksamen og 50% innleveringer.

== Erfaringer ==
=== Bolig ===
Hvis du skal på utveksling fra høsten er det veldig stort press på boligmarkedet. Dette gjelder visst for hele Nederland ettersom de har begynt å ta inn ekstra mange internasjonale studenter. Heldigvis prioriteres internasjonale studenter i søknadskøen, så bare vær tidlig ute og søk som du vil få beskjed om, så ordner det seg sannsynligvis. Vi fikk svar på boligsøknaden i juni-juli. Det virker som om det er litt flere ting som er tilgjengelig for dem som begynner på våren. Sjekk facebooksidene "University of Twente - Marketplace" og "University of Twente - International" for ledige rom i tillegg til sidene som står i heftet til universitetet. Vær obs på scam til og med på disse modererte sidene og ikke gjør noe dumt som å sende masse penger ut av landet.

Skal du bo i byen eller på campus?
Fordelen med campus er at det tar maks 5 min fra du går ut døra til du er i forelesningen. Mye av sportene er også basert på campus og studentforeningene er selvfølgelig også her.

Hvis du tror at du kommer til å dra på byen eller nyte andre kulturelle aktiviteter flere ganger i uka lønner det seg naturligvis å bo i byen. Det er også en type lesesaler i byen, så man må ikke reise til universitetet for å få studiero. Det tar forresten 10-20 minutter å sykle fra campus til byen avhengig av hvor rask (full) du er og hvor på campus/i byen du skal.

=== Forelesere ===
Det virker som om de fleste professorene er ganske flinke. Noe av det ligger i at fag på masternivå er mer spesialiserte og foreleserne derfor kan ha fag i det de kan best. Forelesere her har også mer kontroll over faget, så de kan legge det opp som de vil uten å tenke så mye på godkjenning fra eksamenskontoret og liknende. Alle forskningsgrupper tilbyr noe som heter Capita Selecta. Dette er et fag som ofte er litteraturstudie, men som også kan være eksperimentelt. Så hvis du liker en foreleser/fag veldig godt kan man gjøre et dypdykk ved å ta ett av diss fagene.

=== Fag ===
Fagene blir organisert sånn per halvår, så det er ikke sikkert at alle fagene du hadde tenkt deg går det rette kvartalet, eller går i det hele tatt. En rask guide er som følger: 1A, 1B, 2A, 2B er terminene fra høst til sommer. JAAR betyr at faget enten er individuelt eller at det bare går når nok studenter har vist interesse. Send mail til foreleseren og hør hva som er greia. De fleste fag har en resit, så man får to forsøk på å stå. Karakterskalaen er 1-10 med 5.5 som ståkarakter. 9 er i praksis høyeste karakter og 10 får man bare dersom man har absolutt alt rett og har imponert foreleseren. Eksamener er ikke anonyme, men vi har ikke funnet ut om dette er i hovedsak positivt eller negativt.

== Annet ==
* Siden de ikke har bachelorutdannelse for nano, starter alle i en ny "nano-klasse", som gjør det lett å bli inkludert i klassemiljøet.
* Ulempen med dette er at de på master i nano har mange "basic" nanofag som vi allerede har hatt.
* Twente har [https://www.utwente.nl/mesaplus/ Mesa+]

== Hvem har vært der ==
'''Kull 13:''' Birger, Jonathan, Ruth

'''Kull Danmark:''' Halvor

'''Kull 10:''' Simen (tar PhD)

== Nyttige linker ==
* [https://www.intersek.ntnu.no/socrates/ Erasmus NTNU]
* [http://siu.no/no/Programoversikt/EU-program/Erasmus Erasmus, info]
* [http://www.ntnu.no/portal/page/portal/ntnuno/tre-spalter?selectedItemId=25330&rootItemId=22934&sectionId=11052 Utveksling i EU-land]
* [http://www.stexx.eu/search/?q=ca-1,2,3,4,5,6,7,8,9|cl-positive,negative,neutral,advice|elv-ba,ma,other|ge-m,f|mt-exchange|tor-16 Anmeldelser på studyportals]
[[Kategori:Utveksling]]

University of Twente

2017-02-05T19:28:52Z

Birgela: /* Hvem har vært der */

{{Infobox
|Fakta
|*'''Land:''' Nederland
*'''Beliggenhet:''' Enschede
*'''Studenter:''' 9614
*'''Nettsted:''' [https://www.utwente.nl/en/]
}}

== Hvordan søke ==
Siden UTwente har Erasmusavtale med NTNU kan man søke på vanlig måte via NTNU. Søknadsfristen er 4 måneder før semesterstart (1. mai for start 1. september, 1. oktober for start 1. februar). Gå til [http://www.ntnu.no/studier/studier_i_utlandet Internasjonal Seksjon] for mer informasjon om søknadsprosedyrer. Ellers, se [https://www.utwente.nl/en/education/international-students/exchange-students/ UTwentes sider for utvekslingsstudenter]. For nordmenn er det ikke nødvendig med engelsktest.

== Hva koster det ==

Hvis man har Erasmus stipend betaler man ikke skolepenger. Man betaler semesteravgiften til NTNU og får 350€ i måneden når man er i utlandet. (2016/17)

Bolig er billligere enn i norge dersom man klarer å få gjennom skolen. Hvis man leier privat kan det svinge litt. Mer om det når vi har fått oss bolig.
Twente har veldig bra informasjon rettet mot utvekslingsstudenter på sidene sine, så det anbefales å sjekke der.

== Fagtilbud ==

[https://osiris.utwente.nl/student/OnderwijsCatalogusZoekCursus.do Full oversikt over alle fag.]

=== Nanoteknologi master ===
Twente har et 2-årig masterprogram i Nanoteknologi som er relevant for bio og elektro:
https://www.utwente.nl/en/education/master/programmes/nanotechnology/

Angående fag: klikk på de forskjellige lenkene [https://www.utwente.nl/nt/program/ her], det er en MYE bedre oversikt enn fagvelgeren som er lenket til fra NTNUs side om Twente. Man kan også se en kjapp oversikt [https://www.utwente.nl/en/education/master/programmes/nanotechnology/programme/courses/ her].

=== Molecular and material engineering master ===
De har også et 2-årig masterprogram i Chemical engineering, som også inkluderer Molecular and material engineering som er relevant for material:
https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/

En mer detaljert fagoversikt finnes [https://www.utwente.nl/che/education/curriculum/Molecular%20%26%20Materials%20Engineering/ her].

=== K-emner ===
Vi har ikke helt funnet ut hvordan det funker med K-emner og studiepoeng. Teorien er at når man har droppen TekLed i tredje, så må vi ha 15 poeng (altså tre fag) K-emner i løpet av året. BMS-fakultetet arrangerer en del slike kurs. Det kan være lurt å ta kontakt med dem før man melder seg opp i kurset ettersom de tydeligvis ikke er like snille som naturfakultetet på å la en ta alle fag.

=== Struktur ===
Twente har et system bygget på 60 studiepoeng (Elective Credits) per år, hvor hvert år er delt opp i fire terminer. ([https://www.utwente.nl/ces/planning-roosters/en/ timeplan]) Fagene er mindre enn vi er vant til fra NTNU med stort sett 5 poeng per fag. Det vil si at man tar tre fag i terminen.

De har en del vekt på vurderinger underveis, så det er mye mer spredning i vurderingsformene enn på NTNU. Noen fag har 100% eksamen, som vi er vant med og noen har bare øvinger/prosjekter/presentasjoner som vurderingsgrunnlag. Vanligst er en kombinasjon med rundt 50% eksamen og 50% innleveringer.

== Erfaringer ==
=== Bolig ===
Hvis du skal på utveksling fra høsten er det veldig stort press på boligmarkedet. Dette gjelder visst for hele Nederland ettersom de har begynt å ta inn ekstra mange internasjonale studenter. Heldigvis prioriteres internasjonale studenter i søknadskøen, så bare vær tidlig ute og søk som du vil få beskjed om, så ordner det seg sannsynligvis. Vi fikk svar på boligsøknaden i juni-juli. Det virker som om det er litt flere ting som er tilgjengelig for dem som begynner på våren. Sjekk facebooksidene "University of Twente - Marketplace" og "University of Twente - International" for ledige rom i tillegg til sidene som står i heftet til universitetet. Vær obs på scam til og med på disse modererte sidene og ikke gjør noe dumt som å sende masse penger ut av landet.

Skal du bo i byen eller på campus?
Fordelen med campus er at det tar maks 5 min fra du går ut døra til du er i forelesningen. Mye av sportene er også basert på campus og studentforeningene er selvfølgelig også her.

Hvis du tror at du kommer til å dra på byen eller nyte andre kulturelle aktiviteter flere ganger i uka lønner det seg naturligvis å bo i byen. Det er også en type lesesaler i byen, så man må ikke reise til universitetet for å få studiero. Det tar forresten 10-20 minutter å sykle fra campus til byen avhengig av hvor rask (full) du er og hvor på campus/i byen du skal.

=== Forelesere ===
Det virker som om de fleste professorene er ganske flinke. Noe av det ligger i at fag på masternivå er mer spesialiserte og foreleserne derfor kan ha fag i det de kan best. Forelesere her har også mer kontroll over faget, så de kan legge det opp som de vil uten å tenke så mye på godkjenning fra eksamenskontoret og liknende. Alle forskningsgrupper tilbyr noe som heter Capita Selecta. Dette er et fag som ofte er litteraturstudie, men som også kan være eksperimentelt. Så hvis du liker en foreleser/fag veldig godt kan man gjøre et dypdykk ved å ta ett av diss fagene.

=== Fag ===
Fagene blir organisert sånn per halvår, så det er ikke sikkert at alle fagene du hadde tenkt deg går det rette kvartalet, eller går i det hele tatt. En rask guide er som følger: 1A, 1B, 2A, 2B er terminene fra høst til sommer. JAAR betyr at faget enten er individuelt eller at det bare går når nok studenter har vist interesse. Send mail til foreleseren og hør hva som er greia. De fleste fag har en resit, så man får to forsøk på å stå. Karakterskalaen er 1-10 med 5.5 som ståkarakter. 9 er i praksis høyeste karakter og 10 får man bare dersom man har absolutt alt rett og har imponert foreleseren. Eksamener er ikke anonyme, men vi har ikke funnet ut om dette er i hovedsak positivt eller negativt.

== Annet ==
* Siden de ikke har bachelorutdannelse for nano, starter alle i en ny "nano-klasse", som gjør det lett å bli inkludert i klassemiljøet.
* Ulempen med dette er at de på master i nano har mange "basic" nanofag som vi allerede har hatt.
* Twente har [https://www.utwente.nl/mesaplus/ Mesa+]

== Hvem har vært der ==
'''Kull 13:''' Birger, Jonathan, Ruth

'''Kull Danmark:''' Halvor

'''Kull 10:''' Simen (tar PhD)

== Nyttige linker ==
* [https://www.intersek.ntnu.no/socrates/ Erasmus NTNU]
* [http://siu.no/no/Programoversikt/EU-program/Erasmus Erasmus, info]
* [http://www.ntnu.no/portal/page/portal/ntnuno/tre-spalter?selectedItemId=25330&rootItemId=22934&sectionId=11052 Utveksling i EU-land]
* [http://www.stexx.eu/search/?q=ca-1,2,3,4,5,6,7,8,9|cl-positive,negative,neutral,advice|elv-ba,ma,other|ge-m,f|mt-exchange|tor-16 Anmeldelser på studyportals]
[[Kategori:Utveksling]]

University of Twente

2017-02-05T19:27:32Z

Birgela:

{{Infobox
|Fakta
|*'''Land:''' Nederland
*'''Beliggenhet:''' Enschede
*'''Studenter:''' 9614
*'''Nettsted:''' [https://www.utwente.nl/en/]
}}

== Hvordan søke ==
Siden UTwente har Erasmusavtale med NTNU kan man søke på vanlig måte via NTNU. Søknadsfristen er 4 måneder før semesterstart (1. mai for start 1. september, 1. oktober for start 1. februar). Gå til [http://www.ntnu.no/studier/studier_i_utlandet Internasjonal Seksjon] for mer informasjon om søknadsprosedyrer. Ellers, se [https://www.utwente.nl/en/education/international-students/exchange-students/ UTwentes sider for utvekslingsstudenter]. For nordmenn er det ikke nødvendig med engelsktest.

== Hva koster det ==

Hvis man har Erasmus stipend betaler man ikke skolepenger. Man betaler semesteravgiften til NTNU og får 350€ i måneden når man er i utlandet. (2016/17)

Bolig er billligere enn i norge dersom man klarer å få gjennom skolen. Hvis man leier privat kan det svinge litt. Mer om det når vi har fått oss bolig.
Twente har veldig bra informasjon rettet mot utvekslingsstudenter på sidene sine, så det anbefales å sjekke der.

== Fagtilbud ==

[https://osiris.utwente.nl/student/OnderwijsCatalogusZoekCursus.do Full oversikt over alle fag.]

=== Nanoteknologi master ===
Twente har et 2-årig masterprogram i Nanoteknologi som er relevant for bio og elektro:
https://www.utwente.nl/en/education/master/programmes/nanotechnology/

Angående fag: klikk på de forskjellige lenkene [https://www.utwente.nl/nt/program/ her], det er en MYE bedre oversikt enn fagvelgeren som er lenket til fra NTNUs side om Twente. Man kan også se en kjapp oversikt [https://www.utwente.nl/en/education/master/programmes/nanotechnology/programme/courses/ her].

=== Molecular and material engineering master ===
De har også et 2-årig masterprogram i Chemical engineering, som også inkluderer Molecular and material engineering som er relevant for material:
https://www.utwente.nl/en/education/master/programmes/chemical-engineering/specialization/molecules-and-materials-engineering/

En mer detaljert fagoversikt finnes [https://www.utwente.nl/che/education/curriculum/Molecular%20%26%20Materials%20Engineering/ her].

=== K-emner ===
Vi har ikke helt funnet ut hvordan det funker med K-emner og studiepoeng. Teorien er at når man har droppen TekLed i tredje, så må vi ha 15 poeng (altså tre fag) K-emner i løpet av året. BMS-fakultetet arrangerer en del slike kurs. Det kan være lurt å ta kontakt med dem før man melder seg opp i kurset ettersom de tydeligvis ikke er like snille som naturfakultetet på å la en ta alle fag.

=== Struktur ===
Twente har et system bygget på 60 studiepoeng (Elective Credits) per år, hvor hvert år er delt opp i fire terminer. ([https://www.utwente.nl/ces/planning-roosters/en/ timeplan]) Fagene er mindre enn vi er vant til fra NTNU med stort sett 5 poeng per fag. Det vil si at man tar tre fag i terminen.

De har en del vekt på vurderinger underveis, så det er mye mer spredning i vurderingsformene enn på NTNU. Noen fag har 100% eksamen, som vi er vant med og noen har bare øvinger/prosjekter/presentasjoner som vurderingsgrunnlag. Vanligst er en kombinasjon med rundt 50% eksamen og 50% innleveringer.

== Erfaringer ==
=== Bolig ===
Hvis du skal på utveksling fra høsten er det veldig stort press på boligmarkedet. Dette gjelder visst for hele Nederland ettersom de har begynt å ta inn ekstra mange internasjonale studenter. Heldigvis prioriteres internasjonale studenter i søknadskøen, så bare vær tidlig ute og søk som du vil få beskjed om, så ordner det seg sannsynligvis. Vi fikk svar på boligsøknaden i juni-juli. Det virker som om det er litt flere ting som er tilgjengelig for dem som begynner på våren. Sjekk facebooksidene "University of Twente - Marketplace" og "University of Twente - International" for ledige rom i tillegg til sidene som står i heftet til universitetet. Vær obs på scam til og med på disse modererte sidene og ikke gjør noe dumt som å sende masse penger ut av landet.

Skal du bo i byen eller på campus?
Fordelen med campus er at det tar maks 5 min fra du går ut døra til du er i forelesningen. Mye av sportene er også basert på campus og studentforeningene er selvfølgelig også her.

Hvis du tror at du kommer til å dra på byen eller nyte andre kulturelle aktiviteter flere ganger i uka lønner det seg naturligvis å bo i byen. Det er også en type lesesaler i byen, så man må ikke reise til universitetet for å få studiero. Det tar forresten 10-20 minutter å sykle fra campus til byen avhengig av hvor rask (full) du er og hvor på campus/i byen du skal.

=== Forelesere ===
Det virker som om de fleste professorene er ganske flinke. Noe av det ligger i at fag på masternivå er mer spesialiserte og foreleserne derfor kan ha fag i det de kan best. Forelesere her har også mer kontroll over faget, så de kan legge det opp som de vil uten å tenke så mye på godkjenning fra eksamenskontoret og liknende. Alle forskningsgrupper tilbyr noe som heter Capita Selecta. Dette er et fag som ofte er litteraturstudie, men som også kan være eksperimentelt. Så hvis du liker en foreleser/fag veldig godt kan man gjøre et dypdykk ved å ta ett av diss fagene.

=== Fag ===
Fagene blir organisert sånn per halvår, så det er ikke sikkert at alle fagene du hadde tenkt deg går det rette kvartalet, eller går i det hele tatt. En rask guide er som følger: 1A, 1B, 2A, 2B er terminene fra høst til sommer. JAAR betyr at faget enten er individuelt eller at det bare går når nok studenter har vist interesse. Send mail til foreleseren og hør hva som er greia. De fleste fag har en resit, så man får to forsøk på å stå. Karakterskalaen er 1-10 med 5.5 som ståkarakter. 9 er i praksis høyeste karakter og 10 får man bare dersom man har absolutt alt rett og har imponert foreleseren. Eksamener er ikke anonyme, men vi har ikke funnet ut om dette er i hovedsak positivt eller negativt.

== Annet ==
* Siden de ikke har bachelorutdannelse for nano, starter alle i en ny "nano-klasse", som gjør det lett å bli inkludert i klassemiljøet.
* Ulempen med dette er at de på master i nano har mange "basic" nanofag som vi allerede har hatt.
* Twente har [https://www.utwente.nl/mesaplus/ Mesa+]

== Hvem har vært der ==
Kull 13:
Birger
Jonathan
Ruth

Kull Danmark:
Halvor

Kull 10:
Simen (phD)

== Nyttige linker ==
* [https://www.intersek.ntnu.no/socrates/ Erasmus NTNU]
* [http://siu.no/no/Programoversikt/EU-program/Erasmus Erasmus, info]
* [http://www.ntnu.no/portal/page/portal/ntnuno/tre-spalter?selectedItemId=25330&rootItemId=22934&sectionId=11052 Utveksling i EU-land]
* [http://www.stexx.eu/search/?q=ca-1,2,3,4,5,6,7,8,9|cl-positive,negative,neutral,advice|elv-ba,ma,other|ge-m,f|mt-exchange|tor-16 Anmeldelser på studyportals]
[[Kategori:Utveksling]]

Etterspurte artikler

2016-11-04T15:21:38Z

Birgela: /* Artikler som bør opprettes */

Er det en artikkel du savner? Skriv artikkelnavnet/temaet og bakgrunnen for ønsket (slik at det er lettere å tilpasse artikkelen til behovet) under. Se også [[Spesial:Ønskede_sider]] (Dette er en oversikt over alle internlenker som ikke har fått en artikkel ennå - altså alle røde lenker i wikien).

==Artikler som bør opprettes==
* [[Læringsressurser]] (samleside)
* [[TMM4100 - Materialteknikk]]
* [[TKT4146 - Nanomekanikk]]
* [[TMM4162 - Atomistisk modellering av brudd i materialer]]
* [[TKP4180 - Bioenergi og fiberteknologi]]
* [[TMT4166 - Eksperimentell material- og elektrokjemi]]
* [[Referansegruppe]]
* [[Fordypninger på MTNANO]]
* [[:Category:Faglige notater|Kompendium/notater]] (skrevet av MTNANO-studenter fra ulike år. Bør passordbeskyttes?)

==Artikler som bør utvides eller oppdateres==
* [[MATLAB]]
* [[Forskningsgrupper]]
* [[Master]]
* [[Prosjektoppgave]]
* [[NTNU Nanolab]]
* [[Eksperter i team]]
* [[Utveksling]]
** Utvekslingsrapporter for flere land enn USA
*[[TFY4250]]
**Faget trenger en ordentlig beskrivelse. (Undervisast ikkje lenger, erstatta med FY2045.)
*[[TKP4190]]
**Masse bra fagstoff, men bør puttes i eget kompendie.
*[[TBT4135]]
**Masse bra fagstoff, men bør puttes i eget kompendie.

==Artikler som bør slettes eller revolusjoneres==
* [[FE8116]]

Nyttige sider

2016-11-04T15:20:59Z

Birgela: /* Faglig */

===Faglig===
*[[Fagtabell|Fagtabell for MTNANO]]
*[[Fagoversikt|Komplett fagoversikt]]
*Hvordan skrive en god [[rapport]]
**[[Rapport#LaTeX_rapportmal|LaTeX rapportmal]]
* [[:Category:Faglige notater|Kompendium/notater]]

===Nanowiki===
*[[Nanowiki]]
*[[Retningslinjer for nanowiki]]
*[[Opprette fagside]]
*[[Eksempel på fagside]]
*Mal for [[fagmal|fagsider]]
*[[Etterspurte_Artikler|Etterspurte artikler]]
*[[Artikler som bør oppdateres ofte]]

===Diverse===

*[[Utveksling]]

*[[Forskningsgrupper]]

*[[Romreservasjon NTNU]]

*[[Ekskursjon]]

Nyttige sider

2016-11-04T15:19:37Z

Birgela: /* Faglig */

===Faglig===
*[[Fagtabell|Fagtabell for MTNANO]]
*[[Fagoversikt|Komplett fagoversikt]]
*Hvordan skrive en god [[rapport]]
**[[Rapport#LaTeX_rapportmal|LaTeX rapportmal]]
* Faglige notater

===Nanowiki===
*[[Nanowiki]]
*[[Retningslinjer for nanowiki]]
*[[Opprette fagside]]
*[[Eksempel på fagside]]
*Mal for [[fagmal|fagsider]]
*[[Etterspurte_Artikler|Etterspurte artikler]]
*[[Artikler som bør oppdateres ofte]]

===Diverse===

*[[Utveksling]]

*[[Forskningsgrupper]]

*[[Romreservasjon NTNU]]

*[[Ekskursjon]]

Nyttige sider

2016-11-04T15:18:27Z

Birgela: /* Faglig */

===Faglig===
*[[Fagtabell|Fagtabell for MTNANO]]
*[[Fagoversikt|Komplett fagoversikt]]
*Hvordan skrive en god [[rapport]]
**[[Rapport#LaTeX_rapportmal|LaTeX rapportmal]]
*[[Faglige_notater|Kompendier/notater]]

===Nanowiki===
*[[Nanowiki]]
*[[Retningslinjer for nanowiki]]
*[[Opprette fagside]]
*[[Eksempel på fagside]]
*Mal for [[fagmal|fagsider]]
*[[Etterspurte_Artikler|Etterspurte artikler]]
*[[Artikler som bør oppdateres ofte]]

===Diverse===

*[[Utveksling]]

*[[Forskningsgrupper]]

*[[Romreservasjon NTNU]]

*[[Ekskursjon]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-11-04T15:16:10Z

Birgela:

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Pensumlitteratur=
* Alle bøker er tilgjengelig som e-bok gjennom innsida
* En god del forskningsartikler som blir lastet opp på its-learning
* Pensumoversikten under (sist oppdatert i 2016)
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]

=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
** Each spherically symetric nitrogen helps separate the generations (G)

====Synthesis====
* Divergent (bottom-up)
** Large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
* Convergent (top-down)
** Max 4G, more economically viable, limited by steric constraints

====Properties===
* Monodispersity
* Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

====Biocompatibility====
Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

==Functionalization of metallic nanoparticles==
* Metallic nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles

===Langmuir adsoption isotherm===
The Langmuir adsorption isotherm describes how many molecules (often surfactants) that bind to the surface at a given concentration. You get the '''fractional surface coverage''' <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>
This equation must be derived.

The assumptoins of the Langmuir model are
* Only monolayer formation
* Completely reversible adsorption
* Homogenous and flat surface
* No surface diffusion after adhesion
* Adsorption independent on surface coverage (no latteral interaction)

=== Macromolecular adsorption===
Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

Macromolecules, such as polymers and proteins may not comply with the Langmuir assumptions due to
* Strong interactions between polymers (H-bonds, hydrophobic interactions) can lead to
** More layers forming
** Interactions with neighbours by blocking active sites
* Strong affinity towards surface leads to
** non-reversible adsorption
** spreading on the surface, and thereby latteral diffusion

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Drug delivery==
Pharmacology-pharmacodynamics-pharmacokinetics-pharmacogenetic

The golden rules for Drug Delivery
* '''M'''onodisperse
** To avoid undesired effects
** In general 5nm < L < 200nm
** Desirable size: 10-30 nm for access to nucleus
* '''B'''iocompatible
** Not cytotoxic
** Biodegradable
* '''L'''ong circulation time
* '''T'''arget specific
** Active vs passive targeting
* '''D'''elivery of cargo

The main steps through the body are
* '''A'''dministration
* '''D'''istribution
* '''M'''etabolism
** Encymatic cleavage of the backbone to reduce the size is essential
* '''E'''limination
** Must be 10-15nm in order to go through the kidney

===Targeting mechanisms===
* Passive targeting: Enhanced permeability and retention (EPR)
** Leaky blood channels around infections
** High weight polymers accumulate in solid tumor tissue
**
* Active targeting
** Tumors often have unique receptors / antigens that our vector can bind to

After vectors have aggregatet, they can be heated by photothermal therapy to kill cells. They can also be heated by hyperthermal therapy to get even more local heat.

===New drug delivery vectors===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers as drugs===
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Magnetic Resonance Imaging==
A large magnetic field forces hydrogen proton spins to align. By applying a radifrequency pulse, the proton magnetization can be momentarily switched before it relaxes back to the direction of the magetic field, releasing energy in the process. The relaxation happens by two independent processes
* longitudinal relaxation (T1- recovery)
* transverse relaxation (T2-decay)

The difference between T1 and T2 varies with the surrounding tissue and chemical environment and is what creates the contrast in MRI scanning.

===Contrast enhancement===
In the presence of magnetic NPs, both T1 and T2 will be shortened. Shortening of T1 can be reduced by usinger a thicker coating. T2 can be shortened by using superparamagnetic NPs. With a little signal trick you can get hypointense contrast (which probably means very good contrast).

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]
[[Kategori:Faglige_notater]]

Supramolekylær kjemi

2016-11-04T15:13:14Z

Birgela: /* Host-guest chemistry */

Supramolekylær kjemi er fagområdet som tar for seg interaksjon mellom molekyler som ''ikke'' er basert på kovalente interaksjoner. Dette inkluderer altså alle interaksjoner mellom molekyler, kalt intermolekylære interaksjoner, og hvordan disse kan brukes for å lage nye typer supramolekyler.

=Utvikling av fagfeltet=

Fagfeltet har utviklet seg fra grensesnittet mellom kjemi og biologi og tar mye inspirasjon fra biologiske systemer hvor ikke-kovalente interaksjoner er utrolig viktige. DNA er et kjent eksempel, hvor de to DNA-trådene er holdt sammen med ikke-kovalente hydrogenbånd mellom nukleotidene. For at cellen skal kunne åpne DNA-tråden er det viktig at bindingene er ''reversible'', noe som også ofte kjennetegner supramolekylære bånd.

==Host-guest chemistry==
Den mest kjente typen supramolekylær kjemi er host-guest kjemi. Dette feltet tar for seg syntese og karakterisering av organiske molekyler med et hulrom. I dette hulrommet er det vanligvis først løsemiddel, men hvis den rette gjesten blir tilsatt løsningen vil den ha høy affinitet for hulrommet og derfor foretrekke å være inni verten. Denne affiniteten mellom gjest og vert kommer av at de har bindingssteder som tilsvarer hverandre og at disse er plassert korrekt stereokjemisk. Tenk på en hånd i en hanske, hvor hansken er laget slik at hver finger på hånda (bindingssted på gjest) passer veldig bra inn i hver finger på hansken (komplementært bindingssted på vert). Hånd-i-hanske prinsippet er også kjent fra ensym-verdenen, og ensym-substrat komplekset er faktisk en type host-guest kompleks.

Under er et bilde fra en kjent vert, curcubit-6-uril (lilla). Her med gjesten xylylenediammonium (grå). I dette tilfellet blir gjesten holdt på plass av to krefter: hydrofobe interaksjoner mellom innsiden av curcubit og benzen-ringen midt på verten og elektrostatisk interaksjon mellom polare hydroksyl-grupper over og under curcubiten og de ladede ammonium-gruppene øverst og nederst på gjesten.

https://upload.wikimedia.org/wikipedia/commons/9/98/Cucurbit-6-uril_ActaCrystallB-Stru_1984_382.jpg

Supramolekylær kjemi

2016-11-04T15:12:00Z

Birgela: Ny side: Supramolekylær kjemi er fagområdet som tar for seg interaksjon mellom molekyler som ''ikke'' er basert på kovalente interaksjoner. Dette inkluderer altså alle interaksjoner mellom molek...

Supramolekylær kjemi er fagområdet som tar for seg interaksjon mellom molekyler som ''ikke'' er basert på kovalente interaksjoner. Dette inkluderer altså alle interaksjoner mellom molekyler, kalt intermolekylære interaksjoner, og hvordan disse kan brukes for å lage nye typer supramolekyler.

=Utvikling av fagfeltet=

Fagfeltet har utviklet seg fra grensesnittet mellom kjemi og biologi og tar mye inspirasjon fra biologiske systemer hvor ikke-kovalente interaksjoner er utrolig viktige. DNA er et kjent eksempel, hvor de to DNA-trådene er holdt sammen med ikke-kovalente hydrogenbånd mellom nukleotidene. For at cellen skal kunne åpne DNA-tråden er det viktig at bindingene er ''reversible'', noe som også ofte kjennetegner supramolekylære bånd.

==Host-guest chemistry==
Den mest kjente typen supramolekylær kjemi er host-guest kjemi. Dette feltet tar for seg syntese og karakterisering av organiske molekyler med et hulrom. I dette hulrommet er det vanligvis først løsemiddel, men hvis den rette gjesten blir tilsatt løsningen vil den ha høy affinitet for hulrommet og derfor foretrekke å være inni verten. Denne affiniteten mellom gjest og vert kommer av at de har bindingssteder som tilsvarer hverandre og at disse er plassert korrekt stereokjemisk. Tenk på en hånd i en hanske, hvor hansken er laget slik at hver finger på hånda (bindingssted på gjest) passer veldig bra inn i hver finger på hansken (komplementært bindingssted på vert). Hånd-i-hanske prinsippet er også kjent fra ensym-verdenen, og ensym-substrat komplekset er faktisk en type host-guest kompleks.

Under er et bilde fra en kjent vert, curcubit-6-uril (lilla). Her med gjesten xylylenediammonium (grå). I dette tilfellet blir gjesten holdt på plass av tre krefter: hydrofobe interaksjoner mellom innsiden av curcubit og benzen-ringen midt på verten, π-π stabling mellom curcubit og benzen-ring og elektrostatisk interaksjon mellom polare hydroksyl-grupper over og under curcubiten og de ladede ammonium-gruppene øverst og nederst på gjesten.

https://upload.wikimedia.org/wikipedia/commons/9/98/Cucurbit-6-uril_ActaCrystallB-Stru_1984_382.jpg

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T19:02:59Z

Birgela: /* Drug delivery */

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T18:41:32Z

Birgela: /* Dendrimers as drugs */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Pensumlitteratur=
* Alle bøker er tilgjengelig som e-bok gjennom innsida
* En god del forskningsartikler som blir lastet opp på its-learning
* Pensumoversikten under (sist oppdatert i 2016)
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]

=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
** Each spherically symetric nitrogen helps separate the generations (G)

====Synthesis====
* Divergent (bottom-up)
** Large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
* Convergent (top-down)
** Max 4G, more economically viable, limited by steric constraints

====Properties===
* Monodispersity
* Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

====Biocompatibility====
Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

==Functionalization of metallic nanoparticles==
* Metallic nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles

===Langmuir adsoption isotherm===
The Langmuir adsorption isotherm describes how many molecules (often surfactants) that bind to the surface at a given concentration. You get the '''fractional surface coverage''' <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>
This equation must be derived.

The assumptoins of the Langmuir model are
* Only monolayer formation
* Completely reversible adsorption
* Homogenous and flat surface
* No surface diffusion after adhesion
* Adsorption independent on surface coverage (no latteral interaction)

=== Macromolecular adsorption===
Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

Macromolecules, such as polymers and proteins may not comply with the Langmuir assumptions due to
* Strong interactions between polymers (H-bonds, hydrophobic interactions) can lead to
** More layers forming
** Interactions with neighbours by blocking active sites
* Strong affinity towards surface leads to
** non-reversible adsorption
** spreading on the surface, and thereby latteral diffusion

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Drug delivery==
Pharmacology-pharmacodynamics-pharmacokinetics-pharmacogenetic

The golden rules for Drug Delivery
* '''M'''onodisperse
** To avoid undesired effects
** In general 5nm < L < 200nm
** Desirable size: 10-30 nm for access to nucleus
* '''B'''iocompatible
** Not cytotoxic
** Biodegradable
* '''L'''ong circulation time
* '''T'''arget specific
** Active vs passive targeting
* '''D'''elivery of cargo

The main steps through the body are
* '''A'''dministration
* '''D'''istribution
* '''M'''etabolism
** Encymatic cleavage of the backbone to reduce the size is essential
* '''E'''limination
** Must be 10-15nm in order to go through the kidney

===Targeting mechanisms===
* Passive targeting: Enhanced permeability and retention (EPR)
** Leaky blood channels around infections
** High weight polymers accumulate in solid tumor tissue
**
* Active targeting
** Tumors often have unique receptors / antigens that our vector can bind to

After vectors have aggregatet, they can be heated by photothermal therapy to kill cells. They can also be heated by hyperthermal therapy to get even more local heat.

===New drug delivery vectors===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers as drugs===
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T18:34:00Z

Birgela:

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Pensumlitteratur=
* Alle bøker er tilgjengelig som e-bok gjennom innsida
* En god del forskningsartikler som blir lastet opp på its-learning
* Pensumoversikten under (sist oppdatert i 2016)
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]

=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
** Each spherically symetric nitrogen helps separate the generations (G)

====Synthesis====
* Divergent (bottom-up)
** Large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
* Convergent (top-down)
** Max 4G, more economically viable, limited by steric constraints

====Properties===
* Monodispersity
* Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

====Biocompatibility====
Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

==Functionalization of metallic nanoparticles==
* Metallic nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles

===Langmuir adsoption isotherm===
The Langmuir adsorption isotherm describes how many molecules (often surfactants) that bind to the surface at a given concentration. You get the '''fractional surface coverage''' <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>
This equation must be derived.

The assumptoins of the Langmuir model are
* Only monolayer formation
* Completely reversible adsorption
* Homogenous and flat surface
* No surface diffusion after adhesion
* Adsorption independent on surface coverage (no latteral interaction)

=== Macromolecular adsorption===
Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

Macromolecules, such as polymers and proteins may not comply with the Langmuir assumptions due to
* Strong interactions between polymers (H-bonds, hydrophobic interactions) can lead to
** More layers forming
** Interactions with neighbours by blocking active sites
* Strong affinity towards surface leads to
** non-reversible adsorption
** spreading on the surface, and thereby latteral diffusion

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Drug delivery==
Pharmacology-pharmacodynamics-pharmacokinetics-pharmacogenetic

The golden rules for Drug Delivery
* '''M'''onodisperse
** To avoid undesired effects
** In general 5nm < L < 200nm
** Desirable size: 10-30 nm for access to nucleus
* '''B'''iocompatible
** Not cytotoxic
** Biodegradable
* '''L'''ong circulation time
* '''T'''arget specific
** Active vs passive targeting
* '''D'''elivery of cargo

The main steps through the body are
* '''A'''dministration
* '''D'''istribution
* '''M'''etabolism
** Encymatic cleavage of the backbone to reduce the size is essential
* '''E'''limination
** Must be 10-15nm in order to go through the kidney

===Targeting mechanisms===
* Passive targeting: Enhanced permeability and retention (EPR)
** Leaky blood channels around infections
** High weight polymers accumulate in solid tumor tissue
**
* Active targeting
** Tumors often have unique receptors / antigens that our vector can bind to

After vectors have aggregatet, they can be heated by photothermal therapy to kill cells. They can also be heated by hyperthermal therapy to get even more local heat.

===New drug delivery vectors===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T17:39:25Z

Birgela: /* New drug delivery vectors */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
** Each spherically symetric nitrogen helps separate the generations (G)

====Synthesis====
* Divergent (bottom-up)
** Large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
* Convergent (top-down)
** Max 4G, more economically viable, limited by steric constraints

====Properties===
* Monodispersity
* Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

====Biocompatibility====
Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

==Functionalization of metallic nanoparticles==
* Metallic nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles

===Langmuir adsoption isotherm===
The Langmuir adsorption isotherm describes how many molecules (often surfactants) that bind to the surface at a given concentration. You get the '''fractional surface coverage''' <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>
This equation must be derived.

The assumptoins of the Langmuir model are
* Only monolayer formation
* Completely reversible adsorption
* Homogenous and flat surface
* No surface diffusion after adhesion
* Adsorption independent on surface coverage (no latteral interaction)

=== Macromolecular adsorption===
Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

Macromolecules, such as polymers and proteins may not comply with the Langmuir assumptions due to
* Strong interactions between polymers (H-bonds, hydrophobic interactions) can lead to
** More layers forming
** Interactions with neighbours by blocking active sites
* Strong affinity towards surface leads to
** non-reversible adsorption
** spreading on the surface, and thereby latteral diffusion

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Drug delivery==
Pharmacology-pharmacodynamics-pharmacokinetics-pharmacogenetic

The golden rules for Drug Delivery
* '''M'''onodisperse
** To avoid undesired effects
** In general 5nm < L < 200nm
** Desirable size: 10-30 nm for access to nucleus
* '''B'''iocompatible
** Not cytotoxic
** Biodegradable
* '''L'''ong circulation time
* '''T'''arget specific
** Active vs passive targeting
* '''D'''elivery of cargo

The main steps through the body are
* '''A'''dministration
* '''D'''istribution
* '''M'''etabolism
** Encymatic cleavage of the backbone to reduce the size is essential
* '''E'''limination
** Must be 10-15nm in order to go through the kidney

===Targeting mechanisms===
* Passive targeting: Enhanced permeability and retention (EPR)
** Leaky blood channels around infections
** High weight polymers accumulate in solid tumor tissue
**
* Active targeting
** Tumors often have unique receptors / antigens that our vector can bind to

After vectors have aggregatet, they can be heated by photothermal therapy to kill cells. They can also be heated by hyperthermal therapy to get even more local heat.

===New drug delivery vectors===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

Faglige notater: MOL3018

2016-06-10T17:17:25Z

Birgela:

Faglige notater i faget Toksikologi. Sist oppdatert: ?

= Core Curriculum =
== Toxicokinetics ==

===Definitions===
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.

''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.

''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.

''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.

''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.

''Bolus'': A dosage of X. administered directly into the plasma.

''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.

''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.

''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.

''Enteroheptic circulation'': Absorption from small intestine to blood --> liver --> conjugate --> bile --> small intestine --> hydrolyzed --> parent compound --> reasorbed into blood

''Distribution Equilibrium'': A state where consenstrations of a substanse in different organs are in equilibrium with each other.

===Introduction===
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:
*Blood flow through organs
*Absorption of the small intestine
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation.
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.

===Compartmental models===
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment.

=== Rate constants and elimination ===
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.

An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{f}+k_{ts}-k_{tr}</math>, where <math>f</math> - feces, <math>ts </math>- tubular secretion and <math>tr</math>- tubular reabsorption. Similar models can be made for other organs, both absorbative and eliminative.

The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.

Integrating the formula above gives

<math>C(t)=C_0 e^{-k_{el} t}</math>,

and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.

Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation.

If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:

<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,

where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.

If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time.

=== Toxicokinetic Parameters ===
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.

D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).

Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.

If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C\left(t_{1/2}\right)</math>. Equivalent equations for this is:
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math>

If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time <math>\left(\frac{F \times D}{\tau}\right)</math> with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.

==Metabolism of xenobiotics==
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.

===Phase I reactions===

Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.

=== Phase II reactions ===
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly.

Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation.

''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''

== Risk assessment ==
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans.

The general system for risk assessment is as follows:
*Hazard identification
*Expose assessment to determine total daily exposure (TDE)
*Effect assessment of the TDE
*Risk characterization and action

===Hazard identification===
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.

===Exposure assessment===
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math>
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math>

===Effect assessment===
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:
*Acute toxicity -> dose vs. percentage of test animals dead.
**Dead animals get a full pathology, with target organ and type of toxicity present.
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.
*Irritation/sensitization, often done one guinea pigs or rabbits.
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.

===Risk characterization===
After the exposure and effects have been characterized, the total risk is assessed. This includes:
*Relevance and quality of previous testing
**Choice of animal, are the results applicable to humans?
**Is the toxicokinetic data of sufficient quality?
*Extrapolation of the acquired data
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.

If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.

An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.

[[Kategori:Faglige notater]]

Faglige notater: MOL3018

2016-06-10T17:17:07Z

Birgela:

Faglige notater i faget Toksikologi.

= Core Curriculum =
== Toxicokinetics ==

===Definitions===
''Xenobiotic'' (X.): A chemical that is not native in the body, or is present in much higher concentration than normal.

''Toxic effect'': A change in physiological conditions caused by an effect of xenobiotics on the cellular level creating a decrease in health or behavior.

''Toxicodynamics'': Mechanism of the toxic effect, reactivity, receptors and organ types.

''Toxicokinetics'': Uptake, transport and lingering time/concentration of X.

''Absorption'': Transport from the place of disposition to blood with a rate constant <math>k_a</math>.

''Bolus'': A dosage of X. administered directly into the plasma.

''Elimination'': Biotransformation, exhalation or excretion of X. X. does not need to be removed from the body, only made unavailable in its original form.

''First pass metabolism'': The metabolism of a X that occurs in liver during the first passage.

''Bioavailability (F)'': The fraction of a given dose D (X-parent compound) that reaches circulation in an unchanged form.

''Enteroheptic circulation'': Absorption from small intestine to blood --> liver --> conjugate --> bile --> small intestine --> hydrolyzed --> parent compound --> reasorbed into blood

''Distribution Equilibrium'': A state where consenstrations of a substanse in different organs are in equilibrium with each other.

===Introduction===
There are two main ways to model toxicokinetics: Compartmental models and physiological models. The compartmental models are described more in detail below, and involve modeling organ systems by simple relations without involving physiology, i.e. the rate constants used are acquired from measurements alone. The physiological model looks at theoretical, or physiological, models to predict rate constants of the organs in the body. This involves factors such as:
*Blood flow through organs
*Absorption of the small intestine
**Villi and microvilli in the intestine: These greatly increase the intestinal area, so absorption into the blood for selected X. is greatly enhanced here.
**Active and passive diffusion: Some substances can diffuse directly across tissues, but most require some form of transport proteins. The mechanisms of these proteins determine how effectively and selectively xenobiotics are absorbed.
**There is also metabolism in the intestine, by e.g. the cytochrome P450 3A4 (CYP3A4) enzyme which can activate many prodrugs.
**Drug export from cells via P-glycoprotein is a very important mechanism which greatly reduces the amount of many xenobiotics that are absorbed.
*The portal vein collects blood from the intestine and goes directly to the liver, where many substances are metabolized and their bioavailability is reduced. This is called first-pass metabolism, where the drugs are metabolized before reaching general systemic circulation.
*After being metabolized in the liver many xenobiotics are conjugated and marked for excretion into the bile. The bile is excreted in the small intestine, where the drugs can be un-conjugated and reabsorbed, passing into the liver again. This is called the entero-hepatic circulation, and keeps plasma concentration of xenobiotics low in general.
*Other special barriers, such as the blood-brain barrier and the placenta also greatly effect the distribution of xenobiotics.

===Compartmental models===
A model often used to model toxicokinetics is the compartmental model. In the compartmental model there is a central compartment representing the blood plasma and rapidly equilibrating tissues (e.g. liver and kidney), and side-compartments of more slowly equilibrating tissues. The simplest such model is the one-compartment model. Here there is only one compartment, which means all the modeled tissues are rapidly equilibrating. In this model a bolus will decay exponentially, i.e. measuring the logarithm of the plasma concentration over time gives a linear plot. Conversely, if experimental data holds with this description, it can be modeled by the one-compartment model. The decay is elimination, and elimination happens from the central compartment.

=== Rate constants and elimination ===
There are several rate constants involved in toxicokinetics. There are elimination and absorption rate constant, <math>k_e</math> and <math>k_a</math>, which describes elimination from and absorption into the central compartment (see below) if the dose is administered e.g. orally. In multi-compartment models there are also distribution and redistribution constants, e.g. <math>k_{12}</math> and <math>k_{21}</math>, which describes rates between the compartments.

An example of a rate constant is the excretion rate constant through the kidney, <math>k_r</math>. In the kidney, glomerular filtration has a certain rate, tubular excretion another, and and reabsorption into the tubules a third. Thus, the excretion from the kidneys is given by <math>k_r=k_{f}+k_{ts}-k_{tr}</math>, where <math>f</math> - feces, <math>ts </math>- tubular secretion and <math>tr</math>- tubular reabsorption. Similar models can be made for other organs, both absorbative and eliminative.

The elimination rates can follow different rate laws. Generally, in a one-compartment model, there is a first-order rate law, e.g. <math>-\frac{d C(t)}{dt}=k_e * C(t)</math>. Other rate laws hold if e.g. the elimination system is saturated, then <math>-\frac{d C(t)}{dt}=const.</math>.

Integrating the formula above gives

<math>C(t)=C_0 e^{-k_{el} t}</math>,

and further manipulation gives e.g. the half-life of X. in the blood to be <math>t_{1/2}=\frac{ln 2}{k_e}</math>.

Often the concentration is plotted on a semilogarithmic plot versus time. If this yields a straight line, we have a one-compartment model. <math>k_e</math> can be predicted from the slope, and <math>C_0</math> by extrapolation.

If the semilogarithmic plot of plasma concentration of X. versus time does not yield a straight line, higher compartmental models must be used. In the higher-compartment model the tissues connected to the plasma equilibrate more slowly with the plasma, so the plasma concentration falls off more rapidly in the beginning, in what is called the ''distribution phases'', before the concentration profile again is as for the one-compartment model above. If there are two phases, one distribution phase and one linear phase (the eliminiation phase), we have a two-compartment model, which usually can be modeled by:

<math>C(t)=A e^{-\alpha t}+B e^{-\beta t}</math>,

where <math>\beta</math> corresponds to <math>k_{e}</math> above, and can be treated the same way.

If C is measured for e.g. an orally distributed drug there is also an absorption phase where the concentration increases over a certain time.

=== Toxicokinetic Parameters ===
There are several parameters that can be used to describe the models in more experiment-friendly terms. At the heart is C(t), the plasma concentration of X. at a given time. X is the total amount of X. in the body. The parameter V, called the volume of distribution, which relates X and C. V tells how large a volume is needed to distribute the total amount of the xenobiotic (X), so the concentration of X. in V is the same as in the blood (C). Mathematically, this gives <math>V=\frac{X}{C}</math>.

D is the administered dosage. AUC is the area under the concentration/time curve from 0 to infinity. The bioavailability of X. is given as <math>F=\frac{AUC_{a}}{AUC_{i.v.}}</math>, which gives the fraction in plasma when administered e.g. orally compared to intra venously. This gives another relation: <math>V=\frac{D \times F}{k_{el} \times AUC}</math> for a non-i.v. delivered drug. The denominator term is the plasma concentration. For a one-compartment model this can often be approxomated as <math>V=\frac{D \times F}{C_0}</math>, or <math>V=\frac{X}{C}</math> as above for an i.v. delivered dosage (D=X).

Clearance (Cl) is a term the that describes the volume of plasma that is cleared of X. per unit time, and can be given as the sum of clearances from each of the eliminating organs (<math>Cl_{total}=Cl_{renal}+Cl_{hepatic}+...</math>). The total body clearance is given by <math>Cl=\frac{D_{i.v.}}{AUC}</math>, which gives units of volume/time. Using the relations from above this can be seen to be equivalent to <math>Cl_t=V \times k_{el}</math> for a one-compartment model.

If more than one dose is given, the dosage interval is given by <math>\tau</math>. Giving a dose either continuously, or with a certain interval, allows one to reach a steady state concentration, where there is a balance between absorption and elimination. By definition, this is equal to <math>5 \times C\left(t_{1/2}\right)</math>. Equivalent equations for this is:
*<math>C_{ss}=\frac{F\times D}{Cl_t \times \tau}=\frac{F\times D}{k_e\times V \times \tau}</math>

If the steady state is reached by a dosage D every <math>\tau</math>, there is naturally an oscillation of steady state values, given by <math>\frac{C_{ss}^{max}}{C_{ss}^{min}}=e^{k_e \tau}</math>. By replacing the bioavailable dosage per time <math>\left(\frac{F \times D}{\tau}\right)</math> with an constant infusion rate <math>k_0</math> on obtains <math> C_{ss}=\frac{k_0}{Cl_t}</math>. Often it is desirable to reach steady state concentration as quickly as possible. In this case a bolus dose that immediately gives <math>C_{ss}</math> in the plasma. This dose is then given by <math>D_{bolus}=C_{ss}\times V</math>.

==Metabolism of xenobiotics==
The biotransformation and metabolism of xenobiotics is of great importance in maintaining homeostasis. Some enzymes are very important for these metabolic reactions. There are several types of enzymes, responsible for oxidation, reduction, hydrolysis and conjugation of xenobiotics. These reaction are divided into two phases: Phase I and phase II.

===Phase I reactions===

Phase I reactions are the primary biotransformation of xenobiotics. This includes oxidation, hydrolysis or reduction, and generally introduces or reveals a functional group that increases the hydrophilicity of the xenobiotic a small amount. One very important oxidase is the cytochrome P-450 (CYP) family which are found in most lifeforms. CYP is a heme-containing enzyme family involved in electron transport. The most common reaction is oxidation of an organic substrate by using molecular oxygen as an electron acceptor, i.e. <math>RH + O_2 + 2H^+ + 2e^- \rightarrow ROH + H_2 O</math>. During the oxidation of certain compounds such as aliphatic alkenes and aromatic hydrocarbonds by CYP highly reactive species called epoxides can be formed. This is called activation of the xenobiotic, in which the metabolite form of the xenobiotic is more reactive than the original form. Epoxides can bind to DNA and are possibly mutagenic or carcinogenic. Therefore, in virtually all cells there are CYP-dependent oxidations there is enzyme called ''epoxide hydrolase'' which reacts the epoxide group with water to produce diols. CYP enzymes are especially prevalent in the liver, and play a vital role in regulating the toxicity of a number of compounds that pass trough the liver. Important members of the CYP family are CYP3A4, which metabolises a great variety of compounds, and is present at high concentrations in the liver, CYP1A2 and CYP2D6, which metabolise a many different drugs, among them caffeine. CYP2E1 is less prevalent enzyme, but important since it metabolises small polar molecules such as ethanol.

=== Phase II reactions ===
Conjugation with various groups, such as acetylation, methylation, sulfonation, conjugation with glutathion and glucuronidation are the phase II reactions. In general (with the exception of acetylation and methylation) these cause a large increase in hydrophilicity of the conjugate, which allows the xenobiotic to be easily eliminated. These reactions generally proceed much quicker than the phase I reactions, and can either follow a phase I reaction or proceed directly.

Glucuronidation is a major pathway of biotransformation of xenobiotics in humans. In glucoronidation the xenobiotic is conjugated with the cofactor uride diphosphate-glucuronic acid, creating a highly water soluble molecule, which can be excreted in urine or bile, depending on the total size of the molecule. This reaction is catalyzed by UDP-glucuronosyltransferase, and requires a hydroxyl, carboxyl or thiol group (roughly), so this will often follow a phase I reaction that provides such groups. Other important pathways are glutathione conjugation (catalyzed by glutathione -S-transferase) and GSH (glycine-cysteine-glutamic acid) conjugation.

''GAH, kan noen som faktisk var på denne forelesningen skrive noe her, notatene hans er forferdelige!''

== Risk assessment ==
In addition to the knowledge about toxicokinetics and toxicodynamics, there is a whole greater field of risk assessment to see if a given xenobiotic represents a threat in certain situation. There are two main ways to determine toxicity in general, the epidemiological and toxilogical methods. Epidemology is the study of toxicity of substances in man. The disadvantage of this method is that it only can be performed post-exposure. Toxicology is the study of substances working in cells and animals. This can be done pre-exposure, but requires extrapolations to be applicable to humans.

The general system for risk assessment is as follows:
*Hazard identification
*Expose assessment to determine total daily exposure (TDE)
*Effect assessment of the TDE
*Risk characterization and action

===Hazard identification===
Questions asked: 1. Can people be exposed? This is answered by checking individual habitats, work places, etc to see if there is any exposure risk at all. If yes, the next question is: Can toxic effects occur? This is answered by knowledge of toxicity, structure, like compounds, etc. If the answer is yes, one proceeds to exposure assessment.

===Exposure assessment===
There are standardized rules for TDE depending on form of exposure. Formulas for this can be:
*<math>\text{TDE}_{environment}=\text{inhale} + \text{eat}=\frac{C_{air}[mg/m^3]\times V_{inhale} [20m^3/day]}{W_{body} [70 kg]} + \sum_{i=1}^n \frac{intake/day [kg] \times C_i [mg/kg]}{W}</math>
*<math>\text{TDE}_{work}=\text{inhale} + \text{skin}=\frac{C_{air}[mg/m^3]\times V_{inhale} [0.8m^3/hour]\times WT[8h]}{W_{body} [70 kg]} + \frac{A_{skin}[2000cm^2]\times Th_{matrix}[0.01cm]\times C_{subst. in matrix}[mg/cm^3]\times n}{W}, n=1...10</math>

===Effect assessment===
Firstly, more detailed toxicology data is acquired. For substances that are produced more than one ton per year this data is required, for lesser substances it might not be available. Many tests can be done to acquire this type of data:
*Acute toxicity -> dose vs. percentage of test animals dead.
**Dead animals get a full pathology, with target organ and type of toxicity present.
**The dosage is a single dosage, then wait 14 days and monitor behavior, GI trouble, cramps, etc.
**<math>\text{LD}_{50}</math>is the dose at which 50% of the animals die within 14 days, this is an important number.
*Irritation/sensitization, often done one guinea pigs or rabbits.
*No observed adverse effect limits (NOAELs) are calculated from 28 days repeated administration.
*In vitro testing of cell, genetic testing (Ames test), chromosomal tests and toxicokinetics.
*If the substance has a distribution of more than 1000 tons per year, the studies are larger, including fertility and long term effects.

===Risk characterization===
After the exposure and effects have been characterized, the total risk is assessed. This includes:
*Relevance and quality of previous testing
**Choice of animal, are the results applicable to humans?
**Is the toxicokinetic data of sufficient quality?
*Extrapolation of the acquired data
**Total daily exposure (TDE) compared to acceptable daily input (ADI) over a lifetime
**Calculated by <math>\text{ADI}=\frac{\text{NOAEL}}{\text{Uncertainty factors (UF)}}</math>, where UF is 10 for animal to man and man to man (!). If lowest adverse effect limit (LOAEL) is used instead, another factor of ten is added.
**Certain factor can modify the equation, e.g. if the metabolism of the specific xenobiotic is identical in the animal and human.

If the results give that <math>\text{TDE}\geq \text{ADI}</math>, action is taken to reduce the TDE.

An example of the importance of the quality of data is well known in the case of thalomide, which was tested, but tested on the wrong animals so the extrapolations where not valid. Another example is for <math>\beta</math>-naphthylamine, a drug that caused many cases of urinary bladder infection. In the liver this substance is not particularly harmful, and is oxidised by a CYP enzyme, producing and active and carcinogen form of the drug. But in the liver it is immediately conjugated with glucuronic acid, which makes it soluble and allows it to be secreted into the urine, and does not bind to DNA. In rats and mice this is the end result, and the substance is excreted and no adverse effects are observed. Dogs, on the other hand, contain <math>\beta</math>-glucuronidase, an enzyme in the bladder that hydrolyses the bond to glucuronic acid, redeeming the active and carcinogenic form of the drug. Since there are no UDP glucuronosyltransferase enzymes in the bladder, the drug stays in this activated form and binds to DNA, causing urinary bladder cancer. Initially, this drug was only tested on rats and mice and other animals that do not have <math>\beta</math>-glucuronidase in the bladder, this was not discovered. Humans do have this enzyme, which lead to many cases of urinary bladder cancer due to the use of the "wrong" test animals.

[[Kategori:Faglige notater]]

Faglige notater: TMT4110

2016-06-10T17:14:31Z

Birgela:

Faglige notater i faget kjemi

== Viktige relasjoner ==

'''Ideell gasslov:''' <math> PV = nRT </math>

'''Varmekapasitet:''' <math>C = \frac{q}{\Delta T}</math>

'''Endring i indre energi:''' <math>E = q + w</math>

'''Entalpi:''' <math>H = E + PV</math>

'''Konstant trykk:''' <math>\Delta H = q_{p}</math>

<math>\Delta H</math> ved temperatur T: <math>\Delta H_T^o = \Delta H_{298}^o + \Delta C_p^o \cdot \Delta T</math> (forutsatt <math>\Delta C_p^o</math> konstant)

'''Likevekt ved ulike temperaturer:''' <math>\ln\frac{K_2}{K_1} = \frac{\Delta H}{R}\left( \frac{1}{T_1}-\frac{1}{T_2} \right)</math> (<math>\Delta H</math> og <math>\Delta S</math> konstant)

'''Entropiendring:''' <math>\mathrm{d}S = \frac{\mathrm{d}q_{rev}}{T}</math>

<math>\Delta S</math> ved temperatur T: <math>\Delta S_T^o = \Delta S_{298}^o + \Delta C_p^o \cdot \ln \frac{T}{298,15}</math> (forutsatt <math>\Delta C_p^o</math> konstant)

'''Gibbs fri energi:''' <math>G = H - TS</math>

<math>\Delta G</math> ved konstant T: <math>\Delta G = \Delta H - T \Delta S</math>

<math>\Delta G^o</math> ved temperatur T: <math>\Delta G^o_T = \Delta H^o_{298} - T \Delta S^o_{298}</math> (forutsatt <math>\Delta C_p^o \approx 0</math>)

'''Reaksjon:''' <math>\Delta G = \Delta G^o + RT \cdot \ln Q</math>

'''Likevekt:''' <math>\Delta G^o = -RT \cdot \ln K</math>

'''Fri energi for galvanisk celle:''' <math>\Delta G = - nFE</math>

'''Elektrisk ladning:''' <math>Q = It = n_e F</math>

'''Nernsts likning:''' <math>E = E^o - \frac{RT}{NF}\ln Q = E^o - \frac{0,0592}{n}\log Q</math> (ved 298K)

[[Kategori: Faglige notater]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T17:11:01Z

Birgela: /* Pensum Del III (Sulalit Bandyopadhyay) */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
** Each spherically symetric nitrogen helps separate the generations (G)

====Synthesis====
* Divergent (bottom-up)
** Large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
* Convergent (top-down)
** Max 4G, more economically viable, limited by steric constraints

====Properties===
* Monodispersity
* Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

====Biocompatibility====
Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

==Functionalization of metallic nanoparticles==
* Metallic nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles

===Langmuir adsoption isotherm===
The Langmuir adsorption isotherm describes how many molecules (often surfactants) that bind to the surface at a given concentration. You get the '''fractional surface coverage''' <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>
This equation must be derived.

The assumptoins of the Langmuir model are
* Only monolayer formation
* Completely reversible adsorption
* Homogenous and flat surface
* No surface diffusion after adhesion
* Adsorption independent on surface coverage (no latteral interaction)

=== Macromolecular adsorption===
Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

Macromolecules, such as polymers and proteins may not comply with the Langmuir assumptions due to
* Strong interactions between polymers (H-bonds, hydrophobic interactions) can lead to
** More layers forming
** Interactions with neighbours by blocking active sites
* Strong affinity towards surface leads to
** non-reversible adsorption
** spreading on the surface, and thereby latteral diffusion

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T16:47:52Z

Birgela: /* Synthesis procedures */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==

===Reduction of metallic particles in solution===

==== Turkevich reaction ====
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

====Brust reaction====
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

====Goia reaction====
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===Colloidal templating===
Reverse micelles as spherical nanoreactors.
Two micelle solutions of gold salt and reducing agent respectively. Mixed, and micelles come together by Brownian motion. NP is formed and micelle split into compartments equal to the original size.

A '''rule of thumb''' is that the NP size is controlled by the micelle size. The micelle size can be controlled by varying the water-surfactant ratio. More water gives larger reverse micelles.

===Sol-Gel Method===
Hydrolysis and polycondensation in parallel steps yielding molecular level homogeneity at low processing temperature. (But don't you have to mill it afterwards?)

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using globular proteins
* Using viral templates

===By microorganisms===
It is being done.

===Nucleotide-mediated synthesis===
By using either nucleotides, sugar backbone, DNA, RNA, or synthetic derivatives, selective metal binding can be achieved. The suggested process goes as follows:
* Initiation
* Growth
* Termination
* Passivation
* Solubilization

====SELEX====
"Natural selection" of biomolecules capable of nanoparticles formation by screening millions of peptides at once, and selecting those who adhere to the metal surface. Multiply these, and repeat to select those who bind strongest.

===Electrochemical deposition===
Top-down approach connected to cyclic voltametry

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T16:28:25Z

Birgela: /* One-pot synthesis */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T16:23:28Z

Birgela: /* Optical properties of metallic nanoparticles */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T16:22:02Z

Birgela:

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings
* Red shift = bathochromic shift = higher wavelength and lower energy = larger particles
* Blue shift = hypsochromic shift = lower wavelength and higher energy = smaller particles

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium

===UV-vis===
Intensity through a medium of thickness L is given by '''Beer-Lamberts law''':
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient. [There is missing a concentration in the exponent.]

Beer Lamberts law is only valid for these systems
* The solution is homogenous
* The molecules do not interact
* The molecules do not change by being exposed light
* The molecules should not aggregate and thereby scatter more light

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

==Extinction==
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T15:19:09Z

Birgela: /* Supports */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better dispersion control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || High loading and high dispersion
|}

===Activation===

After being loaded, the catalyst has been through many chemical processes and does not function optimally. '''Calcination''' (heating) is often required to reshape the particles, get rid of oxides, and make them ready for use. Watch out for aggregation and reduced dispersion during this step.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T15:13:52Z

Birgela: /* Loading of support */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefits
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better size control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || high loading and high dispersion
|}

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T15:13:46Z

Birgela: /* Loading of support */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefitsl
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better size control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || high loading and high dispersion
|}

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T15:13:27Z

Birgela: /* Loading of support */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table
{| class="wikitable"
|+ style="text-align: left;" | Loading techniques
|-
! scope="col" | Name !! scope="col" | Used for !! scope="col" | Description !! scope="col" | Benefitsl !! scope="col"
|-
! scope="row" | Wet impregnation
|Large mesoporous support || Dip the support in catalyst solution, dry, and repeat until desired loading || No capillary forces that may break the pore structure
|-
! scope="row" | Dry impregnation (incipient wetness)
| Powder mesoporous support || Drip catalyst solution of desired volume onto the powder, dry and repeat until desired loading || Loading measurable by mass change
|-
! scope="row" |Deposition precipitation
| Small pores || Support is suspended in solution and catalyst is nucleated directly onto the support || Better size control
|-
! scope="row" |Co-precipitaiton
| When you have time || Difficult method where both particle and support are catalyzed simultaneously || high loading and high dispersion
|}

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T14:57:54Z

Birgela:

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Supports==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

===Loading of support===
After the support is fabricated it needs to be loaded with the active catalyst particles.

The different loading techniques are summarized in this table

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T14:56:20Z

Birgela: /* Zeolites */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Support==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

==Zeolites==
Zeolites are made of O, Al and Si. Tetrahedra O-blocks are linked together by alternately Al3+ and Si4+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

===Selectivity mechanisms===
Due to the extremely small pore size, zeolites can function as molecular sieves, where only selected
* reactants are allowed into the network
* products are allowed to leave the network
* transition states are allowed, and the speccificity of the catalyst is therefor enhanced

===Charge compensation===
Zeolites can become basic or acidic when Al3+ replaces Si4+ in the structure. The network ''compensates'' by binding cations or protons, and thus becomes more reactive and can donate or accept groups to weaken or (preferetially) enhance the catalysis process.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T14:42:51Z

Birgela: /* Pensum Del II (Estelle Marie M. Vanhaecke) */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Support==
The support is what the catalyst particles is deposited on. A good support has
* Large specific surface area
* Good mechanical, chemical and thermal stability
* Helps the catalysis by holding particles separated, affect the functionality of the metal, act as a '''co-catalyst'''
* Is easy to manufacture in large quanta

Support materials to know are Alumina, Silica, carbon and zeolites.

===Porosity===
Supports are '''porous''' with the different sizes
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

Mesopores are most common, as too small pores will lead to obstruction and blocking of parts of the porous network

===BET isotherm===
The BET technique is used to find the specific surface area of your support, and is very important to know in detail. It uses '''N2 at 77 K in vacuum at pressures lower that the EQ pressure of N2 (P0)'''.

The machine flows a stream of the probe molecule through the support and measures how much comes out on the other side. This is done at different pressures (driving force for chemisorption), to find where the adsorbed amount of gas is stable. At this point a monolayer is assumed to have been formed, and one can find the number of molecules needed to cover the support. From the area per molecule (16.2 Å2 for N2), the specific surface area is found.

The main assumptions are (and the limitations spring out of this)
* Energy for monolayer formation is lower than energy for subsequent layers (interactions with substrate is stronger than interaction between probe molecules)
* Energy of formation for the subsequent layers are equal
* Rate of adsorption and desorption are equal
* All sites are equivalent
* The surface do not change during adsorption

Measure P and Va and plot it as the '''BET equation:''' P / Va (P0 - P) as a function of P / P0 to get a linear line. Do some exam problems to know this method in and out.

==Zeolites==
Zeolites are made of O, Al and Si. Tetragonal O-blocks are linked together by alternately Al3+ and Si2+ to form '''sodalite cages'''. These cages are self assembled to form large, highly ordered '''microporous''' networks with pore sizes down to 4 Å.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T13:24:47Z

Birgela: /* Carbon */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
CNF are synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure to remove oxides
* Catalyst particles are Ni, Fe, Co...
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

===Catalyst pretreatment===
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst to change it from oxidized to '''metallic state''', which alters both shape and lattice constant.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

CNF is a good support because of
* Good CO tollerance, but very low sulfur tollerance
* High conductivity
* Large electroactive surface area
* 3D mesophorous and good Pt dispersion
* Hydrophobic

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T13:13:28Z

Birgela: /* Particle size */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Pulse chemisorption
** Short pulse of gas through the material. Goes faster, but has higher probability for falsely measuring physisorption (weak bands)
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T13:04:35Z

Birgela: /* 2-D nanostructures */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

===Film crystalinity===
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T13:03:56Z

Birgela: /* 2-D nanostructures */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* CVD
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
** contact angle larger than 0
* Layer growth / Frank-van der Merwe growth
** contact angle equal 0
** '''homoepitaxy''', when lattice constant is equal
* Island layer / Stranski-Krastonov growth
** '''heteroepitaxy''' for slightly different lattice constants
** lattice mismatch induces strain energy that must be included in the free energy of nucleation
** stress is released by forming islands on top of the layer

Growth can produce as a
* single-crystalline film
** high T, low ''impinging flux of growth species'' (flux), clean substrate, good lattice match
* polycrystalline film
** medium T, medium flux
* amorphous film
** low T, very high flux

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:48:54Z

Birgela: /* 1-D nanostructures */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now anisotropic
** Evaporation-condensation growth: Supersaturation driven growth
*** Different facets have different growth rates
*** Dislocations in certain directions
*** Poisoning of impurities (structure-directing agents) on specific facets
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid catalyst particle and upon saturation, selectively crystalized in one direction, growing out from the catalyst.
** Stress-induced recrystallization

* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:41:15Z

Birgela: /* 1-D nanostructures */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
*** Precursor gas or solution is dissolved in liquid metal or oxide particle and upon saturation, selectively crystalized in one direction, growing out from the particle.
** Stress-induced recrystallization
** Structure directing agents
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:37:30Z

Birgela: /* Formation of spherulitic particle */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Mechanism behind spherulitic particles===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:33:52Z

Birgela: /* Growth */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

===Formation of spherulitic particle===
Spherulitic particles are polycrystalline particles. There are two theories for their formation: '''non-classical nucleation''' (nano-aggregation) or by '''classical growth'''.

Requirements to claim non-classical nucleation
* Nucleation rate is fast enough to account for the high number of small nucleus required to build the sperulite crystals.
* These small nucleus should be detectable in solution

According to work by Jens-Petter S is not high enough to form enough nuclei for non-classical nucleation. In addition spherulitic growth was observed by time-resolved SEM microscopy.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:14:40Z

Birgela: /* Induction time */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. As tind is proportional to J-1, a plot of tind can reveal the change in nucleation rate for different parameters.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T12:00:22Z

Birgela: /* Pensum Del I (Jens-Petter Andreassen) */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Nucleation==
===Homogeneous nucleation===
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations.

===Heterogeneous nucleation===
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

===Nucleation rate===
Rate of nucleation can be expressed as an Arrhenius equation:

<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>

J can be changed by gamma-3, T3 and ln(S)2. A is the ''pre-exponential factor'' determined mainly by monomer addition frequency.

J is increased by
* Decreasing gamma
** add surfactant or change solvent
* Increasing T
** Faster monomer diffusion, but watch out for lower S
* Increasing S
** Often preferred because S can be varied by several orders of magnitude

====Induction time====

As counting the number of nucleus in a highly dynamic system is hard, induction time tind is introduced. tind is the time when the system has transitioned from its metastable state. It is an experimental value that varies depending on experimental technique. A plot of tind for different S at constant T and gamma, will allow for determination of A, and thereby the nucleation mechanism as homo or hetero.

==Growth==

===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:30:21Z

Birgela: /* Growth rate limits */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:29:43Z

Birgela: /* Growth determined morphology */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
* '''Low S''' - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
* '''S above critical value for 2D-nucleation''' - Nucleuses form and monomers are added around these.
* '''High S''' - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
* '''Very high S''' - Monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:28:32Z

Birgela: /* Growth rate limits */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1 (diffusion controlled)
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Growth determined morphology===
Low S - Spiral growth dominates by monomer integration at inherent stacking faults in the crystal.
S above critical value for 2D-nucleation - nucleuses form and monomers are added around these.
High S - Surface nucleation happens quickly, leading to diffusion control and dendriting growth. S is consumed at corners and edges, leading to monocrystalline, symmetric, dendriting crystals forming
Very high S - monomer integration is no longer crystallographic and polycrystalline spherulites form

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:17:34Z

Birgela: /* Diffusion controlled growth */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing supersaturation (driving force), increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>

===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:16:25Z

Birgela: /* Heterogeneous nucleation */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed when a solid surface with lower surface energy is awailable. This can also bee seeds in solution.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>
===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:14:10Z

Birgela: /* Heterogeneous nucleation */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed due to availability of a solid surface with different surface energy towards the formed nuclei.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle found by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>
===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:13:55Z

Birgela: /* Heterogeneous nucleation */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed due to availability of a solid surface with different surface energy towards the formed nuclei.

<math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>

theta is the contact angle, as can be determined by Young's equation.

==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>
===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

2016-06-10T11:05:04Z

Birgela: /* Size dependent solubility */

=Faglig innhold=
Emnet tar for seg det termodynamiske grunnlaget og kinetikken for nukleering og vekst av nanopartikler med fokus på felling fra væskesystemer. Ulike mekanismer for nukleering og krystallvekst med tilhørende beregninger av nukleerings- og veksthastigheter gir grunnlag for design av partikkelpopulasjoner og anvendelsen av disse partiklene i i ulike systemer relevant for forskning og industri. Funksjonalisering av overflater vil bli behandlet.

Emnet tar videre for seg metoder for framstilling av katalysator og katalysatorbærere basert på utfelling, samt andre metoder som har spesiell relevans i forhold til katalysatorenes nanostruktur og funksjonalitet, for eksempel sol-gel og kolloidbasert framstilling. Relevante eksempler der stor betydning av partikkel- eller porestørrelse er påvist gjennomgår (Au, Co, Ni- katalysator og karbon nanofibre (CNF)). Det gis også en kort innføring i katalytiske modellsystemer og overflatevitenskap og deres eksperimentelle og teoretiske anvendelse innen katalyse.
=Lenker=
*[http://www.ntnu.no/studier/emner/TKP4190/2013#tab=omEmnet NTNUs fagbeskrivelse]
=Pensum Del I (Jens-Petter Andreassen)=
==Crystallization fundamentals==
'''Morphology''' is the external shape of a crystal. '''Polymorphism''' is the internal crystal structure of a crystal.

====Calcium Carbonate====
CaCO3 has three basic forms, here ordered by decreasing solubility. Calcite is the least soluble, and therefore also most thermodynamically stable.
* Vaterite (hexagonal)
* Aragonite (rod-like)
* Calcite (cubic)

===Supersaturation===
Supersaturation is the driving force for both nucleation and growth
Concentration driving force: <math>\Delta c = c - c^*</math> where c is the solution concentration and c* is the equilibrium saturation at a given temperature.
Supersaturation ratio S is given as <math>S = \frac{c}{c^*}</math> and the relative supersaturation ratio <math>\sigma = \frac{\Delta c}{c^*} = S-1</math>

Supersaturation can be created in three ways
* By dissolving reactant at high temperature, and then owering the temperature
** Only works if solubility is temperature-dependent
* By reduction of ionic precursor in solution
* By evaporating solvent to increase concentration of precursor
* '''By adding antisolvent''' to decrease the solubility of the precursor in the solution

==Homogeneous nucleation==
The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces.
<math>\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v</math>
Here <math>\Delta G_S</math> is the surface excess free energy, <math>\gamma</math> is the interfacial tension between the phases, <math>\Delta G_V</math> is the volume excess free energy and <math>\Delta G_v</math> is the same per unit volume.
At the point where the <math>\Delta G</math>-curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: <math>\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma</math>
 
Inserting <math>-\Delta G_v = \frac{k_B T \ln{S}}{\nu}</math> the critical energy for nucleation is <math>\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}</math>
 
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation: 
<math>J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})</math>
==Heterogeneous nucleation==
Critical energy changed due to availability of a solid surface. <math>\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})</math>
==Growth rate limits==
===Diffusion controlled growth===
Growth as change of particle radius per time is given as <math>\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}</math> where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, <math>C_S</math> is the solubility concentration and <math>V_m</math> is the molecular volume. Solving gives <math>r^2 = 2D(C-C_S)V_mt + r_0^2</math>
* Diffusion controlled growth promotes unisized particles
* Can be obtained by increasing viscosity or introducing a diffusion barrier
 Radius difference between particles decreases with time: <math>\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}</math>
===Surface integration controlled growth===
Growth rate given by <math> G = \frac{dr}{dt}= k_g(S-1)^g</math>
* Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
* 2D Nucleation: g > 2
* Rough growth: g=1
'''Mononuclear growth (layer by layer):''' <math>\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt</math> and radius difference increases with time <math>\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}</math> 
'''Polynuclear growth (multiple layers growing at once):''' <math>\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0</math> and radius difference remains unchanged <math>\delta r = \delta r_0</math>

===Phase stability and size===
'''Ostwald rule of stages''' states that when crystals grow, the polymorph with the fastest growth kinetics will form first. Over time the most thermodynamically stable form will grow by leeching from the other forms. For the CaCO3 system, amorphous calcium will first form, then vaterite, then aragonite followed by calcite, which is the most stable form.

These kinetics can be manipulated in many ways
* Slow the growth rate to have more stable crystals form faster.
* Add structure directing agents that bind selectively to specific sites to stop one polymorph from growing
** Such as alginate G-blocks to Calcium carbonate. (although the mechanism is debated)
* Add additives to alter the stability of different polymorphs
** Such as Mg, which will incorporate into and lower the stability of calcite until aragonite is more stable
* Add capping ligands that stops growth and ostwald ripening alltogether

===Size dependent solubility===
Due to the '''Thomsom-effect''' particles with higher curvature (small radius) will be more soluble than lower curvature particles (large radius). Small particles will therefore dissolve and shrink and large particles will grow larger. This process is called '''Ostwald ripening''' and is generally unwanted because it leads to less monodisperse particles.

==Synthesis of metallic nanoparticles==
* Metal complexes in dilute solutions are reduced
* Stronger reducing agent --> smaller particles
* Polymers used as stabilizers and diffusion barriers
===Mechanisms for formation of spherical crystalline particles===
* Aggregation
* Crystal Growth
===Influences on the synthesis===
* From reducing agents
** Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
** Strong reduction agent: smaller particles.
** The growth rate affects morphology and polymorphism
* From other factors (Very specific examples in the text)
** Chloride ion concentration affects syntehsis of Pt nanoparticles from <math>H_2PtCl_6</math>
** Low concentration of reactant --> decreased reduction rate
* From polymer stabilizers
** Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
** Adsorption of polymer occupies growth sites --> growth reduced
** Diffusion barrier
** May also react with solute, catalyst or solvent

==1-D nanostructures==
===Techniques for growing===
* Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
** Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
** Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
** Stress-induced recrystallization
* Template-based synthesis (Bottom-up)
** Electroplating and electrophoretic deposition
** Colloid dispersion, melt or solution filling
** Conversion with chemical reaction
* Electrospinning (Bottom-up)
* Lithography (Top-down)

==2-D nanostructures==
===Techniques for growing===
* Vapor-phase deposition
** Performed under vacuum
* Liquid based growth

===Initial nucleation===
* Island growth / Volmer-Weber growth
* Layer growth / Frank-van der Merwe growth
* Island layer / Stranski-Krastonov growth

=Pensum Del II (Estelle Marie M. Vanhaecke)=
==Catalysis==
Nobel price winner W. Ostwald defined it as "A catalyst is a substance that enhances the rate of a reaction without itself being consumed."

Note the concept of '''non-functionality''':
* A catalyst ''can not'' change the thermodynamic equilibrium of a reaction, only the rate at which the equilibrium is approached.

Here are some useful concepts for describing a catalyst:

* Activity
** Amount of reactant converted per amount of catalyst per time.
* Selectivity
** Amount of product per amount of reactant converted. If it creates bi-products, it has poor selectivity.
* Lifetime
** How long a catalyst can maintain a certain activity or selectivity.
* Turnover Frequency (TOF)
** # reactant molecules converted / (#sites x time)

===Heterogenous catalysis===
We mainly consider heterogenous catalysis in this course, that is catalyst that are in a different phase than the reactant.

The main steps of heterogenous catalysis are (in order)
* Adsorbtion
** Can be dissocisative or non-dissociative
* Reaction of adsorbed species
** Can be in multiple steps
** At total free energy lower than the product
* Desorption
** If desorption is not fast enough, the catalyst will become saturated and stop functioning.

Note that '''diffusion''' to the catalyst and on the catalyst is also very important.

====Examples of heterogenous catalysis====
You have to remember at least three examples

* Ammonia synthesis
* Oil refineries
* Natural gas production
* Polymer production
* Industrial chemicals
* Exhaust clea-up (Tree-way Catalyst)

===Three-way catalyst (TWC)===
TWC are found in engines an exhaust systems in order to reduce CO, hydrocarbons and NOx to less harmful substanses.

The main '''active phases''' are
* Pt or Pd for CO
* Pt or Pd for hydrocarbons
* Rh or Pd for NOx

As these three reactions are strongly dependent on the amount of oxygen awailable, CeOx (ceria) is also needed as an oxygen buffer. The engine must also be fitted with an electrical system to regulate the oxygen amount (a <math>\lambda</math>-probe).

==Catalyst materials==
'''Catalytically active materials''' are the transition metals.

===Structure===
Solid catalyst particles are metals with a periodic structure characterized by crystal structures.

In this course we mainly consider
* Simple cubic
* Body centered cubic (bcc)
** Fe
* Face centered cubic (fcc)
** Rh, Pd, Pt, Au ++
* Hexagonally close packed (hcp)
** Co
** Note that the 100 plane of hcp has the same packing as the 111 plane of fcc

The bulk structure translates to the surface by exposing certain faces.

====Model systems====
Real catalyst will continously be changing their shape, so when we model it as a single crystal with defined crystal structure, we call this a model system

* A model system is single crystalline
* It has minimized surface free energy, according to the '''Wullf construction'''.
* It is nice for modeling '''structure sensitive reactions''' (reactions that can only occur on specific surfaces or sites)

===Overlayer nomenclature===
Adsobates can position themselves in different positions relative to the atoms on the face of a crystal.

On top, long bridge, bridge, four-fold hollow, three-fold hollow and three-fold hollow hcp.
Adsorbates form a new 2D primitive unit cell that is denoted by using the primitive unit vecors of the crystal face below.
For example: ''insert example''

===Particle size===
Reactions only happen on the surface, so we want to maximize the amount of surface.

'''Dispersion''' is the # of surface atoms per # of atoms in total

Dispersion is measured by
* Gas chemisorption
** Normally H2 (dissociative) or CO (non-dissociative) is floated through the catalyst, and the amount of adsorbed gas is measured.
** There is roughly one surface atom per adsorbed gas molecule.
* Grivmetric analysis
** Basically the same as chemisorption, but the whole system is contiously weighted to monitor the amount of adsorbed species.

==Carbon==
Carbon allotropes include graphite, diamond, carbon black, graphene, carbon nanotubes (CNT), multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF).

Previously carbon formation was associated with decreased performance in catalysators and were unwanted. Now we use the same catalysts to make them on purpose due to their intriguing properties.

===Catalytic decomposition===
The four last are often synthesized using gas precursor and a catalytic particle or substrate in a process called '''catalytic decomposition'''.
* Gass precursors are methane, CO or other more complex structures.
* H2 athmosphere at low pressure
* Catalyst particles are Ni and Fe
* Catalyst substrates are Ni, Cu and Fe

Happens in a CVD. Important parameters are:
* '''Temperature range 500-1000 C'''
* Direction of insertion, rate of insertion, distanse to catalyst, type of catalyst, time for growth, instrument used +++

====Catalyst pretreatment====
Catalyst pretreatment is so important that it requires its own heading. Heating or gas flow over the deposited catalyst can alter both structure and functionality. Catalyst particles must be in a molten or at least semi-molten state to dissolve carbon before redeposition.

===Functionalization===
Functionalization of CNTs are done because they are
* Difficult to disperse
* Insoluble in water and organic solvents
* Hydrophobic (resistant to wetting)
* and to remove the catalyst

It is done by
* Acid/base treatment to remove catalyst metal ('''oxidative purification''')
* Acid treatment to create defects for functional groups to bind to ('''Defect functionalization''')
* Halogenation by F, Cl or N

===Fuel cells (FC)===
Carbon nanostructures can be used as electrocatalyst support and as electrode material. The main goal is (as always) to minimize the Pt used.
Some terms:
* MEA - Membrane Electrode Assembly
* APU - Auxiliary Power Unit
* ESA - Electrochemical Surface Area
* PEMFC - Polymer Electrolyte/Membrane Fuel Cell
* DMFC - Direct Metanol Fuel Cell
** Anode reactions: H2 -> 2 H+ + 2e-
** CH3OH + H2O -> CO2 + 6H+
** Cathode reaction: O2 + 4 H+ + 4 e- -> H2O

Carbon based fuel cells have good CO tollerance, but very low sulfur tollerance.

{| class="wikitable"
|+ style="text-align: left;" | Important fuel cell properties that must be remembered
|-
! scope="col" | Fuel cell type !! scope="col" | Operating temperature [C] !! scope="col" | Operating pressure [bar] !! scope="col" | Anode material !! scope="col" | Catode material
|-
! scope="row" | PEMFC
|80-120 || up to 10 || Pt/C || Pt/C
|-
! scope="row" | DMFC
| 150 || up to 3 || Pt-Ru/C || Pt/C
|-
! scope="row" | Alkaline (classic)
| 100-250 || ~5 || Ni-Al, Pt or Ag || Pt
|}

===Cyclic voltametry===
During cyclic voltametry a potential is raised from a starting level E1 to a final level E2, with a certain rate v. The current is measured as a function of V.

Electrochemists use this to find ESA.

==Micro- meso- and macroporous materials==
* Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
* Macropores: d>50nm
* Mesopore: 2nm<d<50nm
* Micropores: d<2nm

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

=Pensum Del III (Sulalit Bandyopadhyay)=
==Optical properties of metallic nanoparticles==
===LSPR===
* [[Lokalisert overflateplasmonresonans|Localized surface plasmon resonance]]
* Depends on size, morphology, metal, surroundings

===Quasi-static approximation===
* Energy levels treated as a quasi-continuum of states
* Assuming
** <math>D \le \frac{\lambda}{10}</math> for the EM field to be treated as uniform within each spherical particle.
** Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
** D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
** Volume fraction small enough to treat particles as independent
** We can introduce an effective dielectric constant for the medium
*Intensity through a medium of thickness L:
** <math>I_t=I_0\exp(-\alpha L)</math>, where <math>\alpha(\omega)</math> is the absorption coefficient
** For normal medium, <math>\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)</math>
** For a matrix + nanosphere system, <math>\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)</math>, where p is the volume fraction of nanoparticles, and <math>\epsilon_1</math> is the complex dielectric constant of the matrix and <math>\epsilon_2</math> is the complex dielectric constant of the nanoparticles.
** <math>|f(\omega)|^2</math> represents enhancement of <math>E_i</math>. Enhancement occurs when <math>|f(\omega)|^2 > 1</math>, which happens if the contribution to the dielectric constant from conduction electrons is dominant.
** <math>\alpha(\omega)</math> expresses extinction by both absorption and scattering
*** <math>S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2</math> and <math>S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2</math>
*** Ratio varies as volume of nanoparticles: <math>\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3</math>
* If resonance condition <math>\epsilon_1(\Omega_R)+2\epsilon_m =0</math>, SPR frequency is <math>\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}</math>
* SPR shifted towards red with increasing <math>\epsilon_m</math>
** Red shift = bathochromic shift = higher wavelength and lower energy
** Blue shift = hypsochromic shift = lower wavelength and higher energy

===Mechanisms for optical properties===
====Intraband====
* Optical transitions '''without''' change of band
* Due to quasi-free electrons in conduction band
* Described by '''Drude model''': <math>\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}</math> where <math>\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}</math>
* Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
* Dominates in red and infrared
====Interband====
* Optical transitions '''between''' electronic bands
* From filled bands to conduction band or from conduction band to empty bands of higher energy
* Dominates in visible and ultraviolet

===The Mie Model===
* For larger sizes, variations across the size of object must be considered

==Synthesis procedures==
=== Turkevich reaction ===
* Citrate reduction of chloride precursor <math>(HAuCl_4)</math>, aqueous phase
* Citrate acts as reducing agent and passivating ligand
* Most common commercially available method
* Typically at 100 degrees C
* Sizes 2-200nm
* Wide array of surface functionalities through ligand exchange

===Brust reaction===
* <math>BH_4^-</math> reduction of chloride precursor
* 1.5-8nm size
* Very stable particles
* Wide array of surface functionalities through ligand exchange

===Goia reaction===
* Reduction of auric acid with iso-ascorbic acid
* Stabilizer-free, like with citrate
* Room temperature, aqueous phase, rapid nucleation and growth
* Tunable particle size through pH, reaction ratios, concentration
* 30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

===One-pot synthesis===
* Using stimuli-responsive polymers
* Using tiopronin or co-enzyme A
* Using globular proteins
* Using starch-glucose
* Using viral templates

==Functionalization of metallic nanoparticles==
* Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
* Direct functionalization: Reducing agent is passivating ligand
* Post-synthesis functionalization: Passivating ligand added after synthesis
** Can displace or bind to existing ligand

===Adsorption===
* Chemisorption
** Covalent / ionic bonds, high binding energy
** "Irreversible**
** Monolayer
* Physisorption
** van-der-Waals interactions, low binding energy
** Reversible
** Mono or multilayer
* Driven by reduction of free energy
* Surfactant adsorption on hydrophobic surfaces
** Monolayer
** Hemi-micelles
* Surfactant adsorption on hydrophilic surfaces
** At high concentrations: double layer
** Alternatively, close packed micelles
* Fractional surface coverage <math>\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}</math>

===Self-assembled monolayers (SAMs)===
* One head group interacts with substrate, the other determines properties.

=== Macromolecular adsorption===
Entropy of mixing: <math>S=k\ln{\Omega}</math>, where <math>\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}</math>. Given that <math>x_j</math> is the mole fraction of j, we have <math>-\Delta S_{mix} = k[n_a\ln{x_A} + n_B\ln{x_B}]</math>.
Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: <math>\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B</math>. Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.
 Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.
 Adsorption rate: <math>\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)</math> where <math>\Gamma</math> is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, <math>c^s</math> is the subsurface concentration and <math>c^b</math> is the bulk concentration.

==New drug delivery vectors==
* Desirable size: 10-30 nm for access to nucleus
* Active vs passive
=== Approaches===
* Viral: proteines, peptides
** Very efficient
** Not easy to tune, size restricted
** Elicits strong immune responses
** Can mutilate, can be cytotoxic
** Incapable of delivering chemotherapy agents or short oligonucleotides
* Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
** Inefficient
** Challenging to add functions
** Possibly to control immune reactions
** Not infectious, often cytotoxic
** Capable of delivering chemotherapy agents or short oligonucleotides
* Combination vectors: metallic nanoparticle vectors
** Tunable efficiency
** Easy to incorporate different functions
** Size tunable
** Not infectious, controllable cytotoxicity
** Capable of delivering chemotherapy agents or short oligonucleotides

===Gold nanoparticles===
Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.
*Functionalization methodologies:
** Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
** Direct attachment of payload to substrate through thiol chemistry
* Plasmonically heated Au nanoparticles
** LSPR excited nanomaterials are heated by adsorbed light
** Localized increase in temperatures --> hyperthermal therapy
** LSPR should be in near-infrared because body is more transparent there

===Dealing with Cancer===
* Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
* Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
* Core-shell hydrogel swelling can be tuned to within 0.1 pH
** Nanoparticles suspended within gel, and released upon pH changes

===Plant virus nanotechnology===
* Don't inherently target human cells
* Can be used to carry chemotherapeutic agents with little risk
* Biologically degradable

===Dendrimers===
* Superbranched polymers
** Core: chemical species in specific nanoenvironment
** Interior monomer layers: encapsulation of molecular species
** Multifunctional surface: determines macroscopic properties
* Synthesis
** Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
** Convergent (top-down): max 4G, more economically viable, limited by steric constraints
* Properties
** Monodispersity
** Biocompatibility
** Size and shape
** Polyvalency
** Interior compartment
* Advantages
** Uniform tunable size
** Hydrophilic exterior, hydrophobic interior
** More stable than micelles
** Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes. 
Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

====Targeting mechanisms====
* Enhanced permeability and retention (EPR)
** There are increased amounts of biofluids around tumors
** High weight polymers accumulate in solid tumor tissue
** Passive targeting
* Tumor receptor / antigen targeting
** Tumors often have unique receptors / antigens

====Dendrimers as drugs====
* Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
* Antibacterial: Adheres to and damages bacterial cell membranes
* Photodynamic therapy: Photoactivated, generates reactive oxygen species

==Core-shell structures==
===Heteroepitaxial semiconductor core-shell structures===
One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

===Metal-oxide structures===
For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

===Metal-polymer structures===
Prepared by emulsion polymerization or membrane based synthesis.

===Oxide-polymer structures===
Prepared by polymerization at surface or adsorption.

==Fuel cells, batteries==

=Removed from curriculum=

==Basics of membrane materials and separation==
* Microporous membrane: Separation according to selective surface flow - largets molecule permeates
* Dense polymers: Permeability P equal to diffusion times solution, P=DS
** Influenced by state of polymer, type of gas, pressure, temperature
** Other polymeric membranes: SFTM (selective facilitated transport membrane).
* Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
** P=DS but diffusion factor most important
* Basic equations for membrane separation
** <math> P = DS</math> where <math>D [cm^2/s]</math>is diffusivity and <math>S [cm^3(STP)/cm^3 bar]</math> is solubility
** Selectivity <math>\alpha = P_i/P</math>
** Production rate (flux) <math>\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)</math> where <math>A_m</math> is the membrane area, <math>l</math> is the membrane thickness, <math>p_h,p_l</math> are feed and permeate pressures and <math>x_0,y_p</math> are mole fractions of component i.
 
Total feed flow given by material balance, <math>L_f = L_0 + V_p</math>, where <math>L_f</math> is the feed in, <math>L_0</math> is the reject feed out and <math>V_p</math> is the permeate out.

==Selected nanostructured membranes==
===Mixed Matrix Membranes===
* Polymeric matrix with dispersed porous inorganic particles

===Carbon Molecular Sieve Membranes===
* Improved flux and selectivity
* Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

===Glass Membrane===
* Surface of glass pore can be functionalized to improve flux and selectivity

==Types of porous solids==
* Zeolites (crystalline aluminosilicates)
** Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
** Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
* Metal organic frameworks (MOF)
** Low density
** May have permanent porosity if solvent can be removed
** Synthesis: Hydrothermal or solvothermal
** Applications: Gas adsorption and storage
* Ordered mesoporous oxides (Amorphous materials with ordered pores)
** Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
** Size of pores controlled by surfactant size
** Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
* Sol-gel derived oxides (random mesoporous solids)
* Nano-crystalline Titanium Oxide
** Photocatalycic applications (pollutant degradation, water splitting)
* Porous silicon technology
** Preparation: etching
** Applications: sensing technology, support for CNT growth

[[Kategori:Obligatoriske emner]]
[[Kategori:Fag 6. semester]]
[[Kategori:Fag 8. semester]]
[[Kategori:Fag]]