Effect of WO3 coupling on the photocatalytic activity of TiO2

Many strategies have been employed in the last decade in order to minimize the fast and undesired recombination of photoproduced e-/h+ pairs on the TiO2 surface. In particular, apart from the well-established effects induced by noble metal (Au/Pt) nanoparticles surface deposition, the idea of coupling TiO2 with another metal oxide can be suggested as one of the most promising routes. In the present study the effect induced by modifying 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 photocatalytic process, i.e. in formic acid (FA) mineralization and in Cr(VI) reduction. A different photo-activity trend of TiO2-WO3 materials in the two investigated test reactions was observed. While the progressive increase of W/Ti content limited the surface properties of titanium dioxide 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) photo-catalytic reduction, pointing to an essential role of WO3 domains, acting as electron acceptors, in increasing the efficiency of photoproduced charge carriers separation and of photopromoted electron transfer to the substrate. The correlation between the local distribution of WO3 regions and the photocatalytic activity of our home-made mixed oxides is discussed in terms of their bulk (XRPD) and surface (BET, DRS, STEM) characterization.