Photocatalytic performance of particulate semiconductors under natural sunshine—Oxidation of carboxylic acids

With natural sunlight, particulate TiO2 (anatase), CuO, ZnO, Pb2O3, PbO2 and Bi2O3 photomineralize oxalic acid and the mineralization depends linearly on the acid concentration and the surface area of the catalyst bed. Oxygen is essential for mineralization and the metal oxides show sustainable photocatalysis. While oxalic acid is effectively mineralized, the oxalate ion is not so. Pre-sonication fails to enhance the photocatalytic efficiencies and the system does not respond to application of a potential bias for enhancement of photocatalysis. The photocatalytic performance is of the order ZnO>CuOTiO2Bi2O3Pb2O3>PbO2 and the ease of degradation is formic acid>oxalic acid>acetic acid>citric acid.