Nanostructured promoted titania photocatalysts

Abstract

Concern over the economics of accessing fossil fuel and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change is driving academic and commercial research into new routes to sustainable fuels, to meet the demands of a rapidly rising global population and reduce an impact on the environment. The titania oxide semiconductor has attracted a great interest as a photocatalyst for wide-ranging applications including wastewater depollution, solar fuels via both H2 production and CO2 reduction. Tailoring the physicochemical properties of titania photocatalysts, and their resulting reactivity, in a predictable fashion remains challenging. The thesis explores the impact of thermal processing, macroporosity and metal deposition on the surfactant-templated mesoporous TiO2 and dual soft-hard templated macro-mesoporous TiO2 series and resulting activity in aqueous phase photocatalytic dye degradation, H2 production and CO2 reduction reactions. Control over the structural and photophysical properties of mesoporous titania enables systematic tuning of Methyl Orange photocatalytic depollution and H2 evolution. Hierarchical macro-mesoporous titanias exhibit uniform mesopores with macropore diameters that can be systematically tuned between 140-310 nm, resulting in a close-packed, ordered macropore framework. Hierarchically-structured TiO2 display two fold increase in photoactivity relative to mesoporous counterparts in the H2 production. Ultra-low concentrations (0.02-0.1 wt%) of copper introduced into the mesoporous and macro-mesoporous titania surfaces by wet-impregnation enhance activity for dye degradation by six fold, and for H2 production four fold, through the genesis of isolated Cu (I) species which suppress charge recombination. Furthermore, promotion with Pt increases photocatalytic activity in Methyl Orange degradation by eleven fold, H2 production 16-26 times and are the only series which display activity in the CO2 reduction reaction. Moreover, the impact of the macropore diameter on the activity of the Methyl Orange degradation is observed for Cu and Pt promoted macro-mesoporous TiO2 series. Nanostructured promoted titanias offer an insight into the relative importance of physicochemical and electronic properties upon their associated activity together with significantly enhanced photocatalytic performance.