WO3-TiO2 vs. TiO2 photocatalysts: effect of the W precursor and amount on the photocatalytic activity of mixed oxides

Aiming at producing TiO2-based photocatalytic materials with reduced charge carriers recombination, WO3-TiO2 mixed oxides were synthesized by a sol-gel method employing either an inorganic salt, Na2WO4, or an organic alkoxide, W(OC2H5)(6), as tungsten precursor, with different W/Ti ratios. The so-obtained materials were characterized by XRPD, BET, UV-vis reflectance, XPS and EDX analyses and their photoactivity was tested under UV-visible irradiation in both the mineralization of formic acid in aqueous suspension and the gas phase oxidation of acetaldehyde. Both photoactivity results and photocurrent measurements point to a superior performance of photocatalysts obtained from the organic precursor with an optimal tungsten content (3%). The formation of an intimately mixed oxide, as revealed by XRPD analysis, results in photoactivity higher than that of pure TiO2, and also of benchmark P25 TiO2, consequent to a better charge separation due to the migration of photoproduced holes from WO3 domains to TiO2 and of photopromoted electrons in the opposite direction. The persistence of pure anatase phase in W-containing photocatalysts also after calcination at 700 degrees C and their higher surface area with respect to pure TiO2 also contribute in increasing the photocatalytic activity of the WO3-TiO2 mixed oxides. (C) 2013 Elsevier B.V. All rights reserved.