Structuring and functionalisation of titania : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Palmerston North, New Zealand

Abstract

Grätzel cells are liquid-electrolyte photoelectrochemical cells that contain dyesensitised titania electrodes. The sensitiser is typically an organic species that absorbs visible light and increases the spectral region in which Grätzel cells may produce electricity. A key feature in the success of Grätzel cells is the high surface area of nanostructured titania electrodes. In this study, the nanostructuring of titania has been explored by two complementary methods: templation and self-assembly. The templation of silica colloidal crystals (opals) was chosen as an inverse opal of titania would display a porous, bicontinuous structure in addition to a photonic bandgap. A diverse variety of titania inverse opals was produced, ranging from ideal ‘honeycomb’ to non-ideal ‘grape-like’ morphologies. However, the fragility of the material and difficulties in reproduction meant that the testing of such electrodes within Grätzel cells was limited. Study towards the formation of a nanoparticle superlattice of titania via chemically assisted self-assembly involved the investigation of both nanostructured titania surfaces and dye adsorption. The mode of dye binding to titania and the stability of adsorbed dyes was studied to aid work toward the design of a self-assembled titania superlattice, as well as to assist in the analysis of dye performance in Grätzel cells. Crystalline, aggregated titania and amorphous, dispersible titania was produced for dye binding studies of small organic carboxylic acid dyes. It was found that while dyes are adsorbed and intimately associated with titania, the mode of dye binding is different on a dry electrode than upon dispersed and solvated titania. The dyes appear to be bound to titania in a carboxylate form in the dry state, but in a mode that closer resembles that of the native dye upon dispersed titania.