Niobium oxide based material for visible light photocatalysis

The primary aim of the work presented in this thesis was to design and synthesise well-characterised material that would exploit visible light to promote photocatalysis, involving the degradation of organic compounds in water, or generation of hydrogen from the water splitting reaction. In doing so, both environmental concerns, such as the removal of pollutants in wastewater, and energy concerns, such as the generation of a clean and safe form of hydrogen for use as a renewable fuel could be addressed. The approach used was to employ existing methods to synthesise high surface area quasi-amorphous material that is active in UV light for photocatalysis, and then design and employ post synthetic modification to promote the material for visible light photocatalysis. Niobium (V) oxide was synthesised in a high surface area form, successfully scaling up the synthesis from 2 g to over 200 g quantities of as made material. This UV active photocatalyst was fully characterized by methods including X-ray diffraction and thermal gravimetric analysis. The material was used to degrade the model dye Methyl Orange and generate hydrogen from a methanol / water solution without further modification. By adding platinum group metals (PGMs) to the niobium (V) oxide, a greatly enhanced efficiency for hydrogen generation was realized. A survey of metals (platinum rhodium and palladium) and weight percentages of metal added (0.01 – 1%) was carried out, with the PGM added materials characterised for hydrogen generation using a methanol / water sacrificial reagent system, as well as PGM dispersion, TEM imaging, EDX and X-ray photoelectron spectroscopy for characterising the higher weight percentage material. Finally, chromium (III) oxide was added to the surface of the niobium (V) oxide in various weight percentages (1% - 5%). The optical properties of this composite material, in comparison with the starting materials were investigated, in particular the difference in diffuse reflectance of the starting materials and composite were highlighted to demonstrate charge transfer between the chromium (III) on the surface, and niobium (V), in the bulk of the material, with the oxidation states being confirmed by XPS. Furthermore, this material was found to degrade methyl orange under visible light. An action spectrum was carried out measuring the quantum efficiency of the reaction at different wavelengths, which proved it was the chromium – niobium charge transfer absorbance in isolation that was responsible for the methyl orange degradation