Advanced nanomaterial synthesis for catalysis applications
Creators: name: Pearson, Andrew
Publisher: name: RMIT University
Year: 2024

description: Currently, almost all industrial processes employ some form of catalyst to increase economic viability, from fuel cells to refineries, catalysts are prevalent everywhere. The aim of this research project was to develop novel nanostructured materials for the purpose of enhancing catalytic processes such as the photocatalytic degradation of organic dyes and the enhancement of the catalytic processes of direct methanol fuel cells.<br><br>The work undertaken in this thesis has been split into three distinct streams. While the three streams concentrated on distinctly different material systems, common themes of galvanic replacement and the use of different solvents to achieve different structures intertwine and link the different chapters of the thesis.<br><br>Firstly when galvanic replacement of Ag nanospheres with [AuBr<sub>4</sub>]- ions were compared in an aqueous solvent and an ionic liquid, structures with remarkably different morphologies were observed in these two solvents. This study highlighted the significantly different replacement reaction kinetics in ionic liquid than that seen in aqueous solutions, thereby leading to markedly different reaction products in these two solvent systems. This study revealed for the first time the significant role that solvents may play during galvanic replacement reactions.<br><br>Secondly the reaction between semiconductor microrods of CuTCNQ and [AuBr<sub>4</sub>]- ions was explored in both acetonitrile and aqueous solutions whereby the reactions were found to be redox in nature and proceed by a galvanic replacement mechanism wherein the surface of the CuTCNQ microrods is replaced with metallic Au nanoparticles. It was established that given the difference in solubility and stability of reactant species generated during the galvanic replacement reaction in different solvents, the reactions in acetonitrile and aqueous solution proceed along two very different mechanisms wherein two different reaction products were obtained by simply modifying the reaction medium. This work established for the first time that metal-organic semiconducting, charge transfer complexes such as CuTCNQ can not only be galvanically replaced by metal salts, these materials also possess photocatalytic properties.<br><br>Lastly in an attempt to improve the photocatalytic efficiency of TiO<sub>2</sub> based nanomaterials, a facile, generalised and highly localised reduction approach was demonstrated for the decoration of TiO<sub>2</sub> surfaces with a range of metal nanoparticles including Cu, Ag, Pt and Au. This was achieved by employing a TiO<sub>2</sub> surface bound Keggin ion, 12-phosphotungstic acid, as a highly localised UV-switchable reducing agent, which specifically reduced metal ions into their nanoparticulate form directly and only onto the TiO<sub>2</sub> surface. Notably this led to the metal contaminant free synthesis of TiO<sub>2</sub>-Keggin ion-metal nanocomposites which is a significant advantage of the proposed approach. The study further demonstrated that as Keggin ions are regenerable photoactive molecules of considerable electron transfer ability, the deposition of the metal nanoparticles on the TiO<sub>2</sub>@Keggin ions cocatalytic surface can have a dramatic effect on the overall photocatalytic performance of the composite system.<br>