Comparison of the photocatalytic activityof TiO2-WO3 materials in oxidation and reduction reactions

In order to minimize the rate of the fast and undesired recombination of photoproduced e-/h+ pairs on the TiO2 surface, the effect induced by coupling TiO2 with different amounts of WO3, according to an alkaline-catalyzed sol-gel method followed by an incipient wetting procedure, has been investigated in both an oxidation and a reduction process, i.e. in formic acid (FA) mineralization and in Cr(VI) reduction in aqueous suspensions at pH 3.7 under UV-vis irradiation. A different photoactivity trend of TiO2-WO3 materials in the two investigated test reactions was clearly observed. While the progressive increase of W/Ti content limited the surface properties of titania in FA oxidation, the coupling of TiO2 with relatively small amounts of WO3 (0.2-1.0 mol.%) was beneficial in increasing the rate of Cr(VI) photoreduction, pointing to an essential role of WO3 domains in photopromoted electron transfer efficiency.