A thesis submitted to the Faculty of Science,
University of the Witwatersrand, Johannesburg,
in fulfilment of the requirements for the degree of
Doctor of Philosophy. Johannesburg, 29 May 2018. / The relatively unknown resin-gel synthesis technique has the potential to form multi-mode mixed metal oxide nanoparticles with differing stoichiometries. These oxides can be employed in a plethora of applications. In order to exploit these benefits, the mechanism of nanoparticle formation must be understood. To this end, this study embarked on a parametric investigation to gain insights on the formation of the less stable anatase and more stable rutile (titanium dioxide) using resin-gel synthesis. By adjusting parameters such as the type of polymer, solvent, acid, and metal ion precursor, and by varying other parameters such as the polymer chain length, polymer stoichiometry, and heating rate, a model for nanoparticle formation was developed and refined. This model considered the formation of hydroxylated metal ion species following the addition of a metal ion precursor to a hydroxyl-containing solvent. These species were protected and stabilised by the remaining fragments of solvent components. In addition, the size of the ligands attached to the metal ion precursor governed the amount of protection and stabilisation afforded to the hydroxylated species by the precursor. These complexes were coordinated to polymer chains that underwent degradation during the course of heating and ignition. Polymer degradation produced polymer reaction chambers. The formation, action, and interaction of these chambers with developing titania crystallites are a novel finding of this work. The sizes of these chambers were controlled largely by the quantity of polymer present in the reaction. The number of accessible oxygen sites on the precursor determined the degree of association between the metal ion complexes and the reaction chambers. If the association was intimate, the polymer reaction chambers served to stabilise and protect the newly nucleated anatase particles. If the combination of protection effects afforded by the solvent components, precursor ligands, and association of reaction chambers of appropriate sizes was insufficient to stabilise nucleated anatase, it readily converted into the rutile phase. Anisotropic growth along [0 0 1] then caused rutile to form nanorods. Rutile mesocrystals developed following sufficient polymer degradation. The association of nanoparticles with polymer fragments was viewed using TEM. Additionally, TEM investigations revealed the presence of polymer-derived superstructures containing reaction chambers. Reaction chambers presented with various morphologies and were composed of crystalline carbon. / LG2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/26059 |
| Date | January 2018 |
| Creators | Narrandes, Ashvir Ashwin |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (li, 464 leaves), Online resource (li, 464 leaves), application/pdf |
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