Synthesis and applications of nanostructured metal oxide films

This research project focuses on the creation and optimisation of the nanomaterial films for enhancing their medical and photocatalytic applications. Developing controlled drug delivery systems has been gaining increasing interest. Processing of metal oxides into porous nanostructures has been considered as a promising strategy. In this work, the morphology of TiO2 nanotubes was modified and tubes with a bottle shape were designed and used for controlled drug delivery. It was found that, the drug loading and release kinetics can be controlled by adjusting the nanotubes and nanobottles morphology. Moreover, there is increasing interest of using metal oxides as photocatalyst for capturing solar energy and converting it to chemical energy in the form of hydrogen. However, the current photoconversion efficiency over nanostructured metal oxides is limited by a number of factors such as low surface area, limited light absorption, poor conductivity, poor electron mobility and high rate of electron-hole recombination. In this project, a number of strategies have been developed to overcome these difficulties. Firstly, optimizing the film morphology, density and thickness helps to increase the photoconversion efficiency. 1-D nanorods with relatively low densities offer high surface area with a large number of reaction sites to be in contact with the electrolyte. In addition, the small film thickness allows light to illuminate through the whole nanorods layer. This offers good electron conductivity through the rods, reducing the rate of electron-hole recombination. TiO2 nanorods (TNR) with optimised structures were prepared and the photoelectrochemical measurements revealed that a tilted TNR film at the density of 14 µm-2 and the thickness of 2.2 µm exhibited optimal photocatalytic performance. Secondly, the surface treatment over TNRs, through a reduction in hydrogen and re-oxidation in air, was demonstrated in order to improve electron mobility and inhibit the electron-hole recombination. The measurements revealed that a sequence of reduction and re-oxidation helps to achieve an enhancement in the photoelectrochemical water splitting efficiency. Thirdly, copper doped TiO2 nanorods were synthesized through one step hydrothermal synthesis for enhancing their photoelectrochemical (PEC) water splitting performance. The performance of the Cu doped TNRs was improved by at least a factor of 3 due to the improved light absorption, charge separation and transportation and appropriate nanorods morphology. Finally, a three dimensional photoanode was designed and fabricated for a PEC device in order to enhance the photocatalytic performance. Clear conductive glass rods decorated with a zinc oxide thin film were attached to a copper disc, forming a three dimensional photoanode. It was observed that, high photocurrent can be achieved by using this 3-D photoanode configuration. The efficiency of this electrode can be further enhanced by improving the conductivity of the ITO film and the light leakage from the side of the glass rods (with increased roughness of the glass surface). In addition, by adding organic compounds to the PEC system, the photocurrent density could also be further enhanced. Further effort was involved in the developing of perovskite copper titanate. Cubic shaped CuTiO3 crystals were successfully synthesised with molten salt synthesis. The reaction conditions have been investigated in order to achieve high purity CuTiO3. In summary, different strategies and nanomaterials have been developed and demonstrated in this thesis for specific applications.