Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In an attempt to produce active catalysts for the oxidation of alkanes, hydrophobic dendritic
micelle encapsulated gold nanoparticles were prepared. Dendrimers are well suited as
templates for the encapsulation of metal nanoparticles as they can control the size and
distribution of the particles. Using hydrophobic dendritic micelles it was found that the mode
of encapsulation is driven by the solubility of the metal ions and not complexation of these
ions, as is the case with conventional dendrimers. The dendritic micelles also provide the
possibility of producing the dendrimer encapsulated nanoparticles in organic solvents,
simplifying the encapsulation process as well as their subsequent application in catalysis.
With this in mind, two types of dendritic micelles were synthesized. The first type, based on
commercially available DAB PPI dendrimers, contained a diaminobutane core while the
second type, containing a PAMAM interior architecture, has a cyclam core. Three
generations of DAB PPI dendrimers were modified on their periphery with palmitoyl chloride
to give the alkyl chain terminated hydrophobic DAB PPI dendritic micelles. The
PAMAM-type cyclam-cored dendrimers were synthesized from the core outwards to produce
two generations of cyclam-cored amine-terminated dendrimers. Their periphery could then be
modified with palmitoyl chloride to produce two generations of alkyl chain terminated
hydrophobic cyclam-cored dendritic micelles.
The dendritic micelles were used as templates for the encapsulation of gold nanoparticles and
these were fully characterized by UV/Vis spectroscopy and HR-TEM. Au13, Au31 and Au55
nanoparticles were encapsulated in each dendrimer template by varying the dendrimer to gold
ratio. HR-TEM results indicate relatively uniform particles with an average particle size
falling in the range of 4-6 nm.
Finally, the dendrimer encapsulated nanoparticles (DENs) were applied as catalysts in the
oxidation of n-octane. To the best of our knowledge DENs have not been applied as catalysts
in the oxidation of linear alkanes. High substrate conversions, falling in the range of 70-90%,
were achieved with all of the catalysts. Longer reaction times and lower catalyst loadings
resulted in higher conversions with the optimum condition determined to be 0.1 mol%
catalyst and 72 hours reaction time. It was also concluded that the nanoparticle size has a bigger influence on the conversion than the nature and generation of the dendrimer template.
Overall the gold DENs show great potential as oxidation catalysts. / AFRIKAANSE OPSOMMING: In die poging om aktiewe katalisators vir die oksidasie van alkane te produseer is goud
nanopartikels in die binne ruimtes van hidrofobiese dendritiese miselle ge-enkapsuleer.
Dendrimere is geskikte template vir die enkapsulering van metaal nanopartikels a.g.v die feit
dat dit die grootte en distribusie van die partikels kan beheer. Deur gebruik te maak van
hidrofobiese dendritiese miselle verander die wyse van enkapsulering van kompleksering van
metaal ione (die geval in konvensionele dendrimere) na oplossing gedrewe enkapsulering.
Dendritiese miselle bied ook die moontlikheid om die dendrimer-ge-enkapsuleerde
nanopartikels in organiese oplosmiddels voor te berei wat die enkapsulerings proses sowel as
die toepassing in katalise vergemaklik.
Met hierdie in gedagte is twee verskillende tipe dendritiese miselle gesintetiseer. Die eerste
tipe, gebasseer op kommersieel beskikbare DAB PPI dendrimere, bevat ‘n diaminobutaan
kern, terwyl die tweede tipe, bestaande uit ‘n PAMAM binne-struktuur, ‘n siklaam kern
bevat. Drie generasies van DAB PPI dendrimere was gemodifieer op die periferie met
palmitoïelchloried om alkiel ketting getermineerde hidrofobiese DAB PPI dendritiese miselle
te produseer. Die PAMAM siklaam kern bevattende dendrimere was gesintetiseer van die
kern uitwaarts om twee generasies amien getermineerde dendrimere te produseer. Dit was toe
moontlik om die periferie met palmitoïelchloried te modifieer om twee generasies van alkiel
getermineerde siklaam kern bevattende hidrofobiese dendritiese miselle op te lewer.
Die dendritiese miselle was gebruik as template vir die enkapsulasie van goud nanopartikels
en volledig gekarakteriseer deur UV/Vis spektroskopie en HR-TEM. Au13, Au31 and Au55
nanopartikels was ge-enkapsuleer in elk van die dendrimeer template deur die verhouding
van dendrimeer tot goud te wissel. HR-TEM resultate dui aan dat die partikels goed versprei
is met ‘n gemiddelde partikel grootte tussen 4-6 nm.
Die dendrimeer ge-enkapsuleerde goud nanopartikels (DENs) was as katalisators in die
oksidasie van n-oktaan toegepas. Volgens ons kennis is DENs nog nie toegepas as
katalisators in die oksidasie van lineêre alkane nie. Hoë substraat omskakelings, tussen 70 en
90%, was deur al die katalisators bereik. ‘n Langer reaksie tyd en laer katalisator
konsentrasies het hoër omsettings tot gevolg gehad. Die optimale kondisies sluit ‘n 0.1 mol%
katalisator konsentrasie en 72 uur reaksie tyd in. Die gevolgtrekking was gemaak dat die nanopartikel grootte ‘n groter invloed op die substraat omsetting het as die aard en generasie
van die dendrimeer templaat. Alles in ag geneem, wys die goud DENs groot potensiaal as
oksidasie katalisators.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96790 |
| Date | 04 1900 |
| Creators | Slazus, Ene |
| Contributors | Mapolie, Selwyn Frank, Malgas-Enus, Rehana, Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xx, 86 pages : illustrations (some colour) |
| Rights | Stellenbosch University |
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