Kinetics of photocatalytic degradation of trichloroethylene in aqueous colloidal solutions of TiO2 and WO3 nanoparticles

Kinetic studies on the photocatalytic degradation of trichloroethylene (TCE) were performed in TiO2 or WO3 aqueous sol which consisted of anatase nanocrystalline TiO2 of ca. 3.9 nm or WO3 spherical particles of ca. 17.6 nm. Photocatalytic activity of TiO2 colloid is higher than that of WO3 by a factor of 2.1. Kinetic analyses for both sols give a similar rate law containing γ value which represents a ratio of the reaction rate of the photogenerated electrons with O2 against the total disappearance rate of the photogenerated electrons. Reaction temperature did not affect the TiO2 photocatalysis whereas higher temperature increased the oxidation rate of TCE in the WO3 sol. Such a difference in the temperature effect was explained in terms of the γ values. The photocatalytic degradation of TCE was enhanced by mixing the WO3 and the TiO2 sol and the best performance was obtained by using the mixed sol with WO3:TiO2 molar ratio of 1:2. In the mixed sol, the similar temperature dependence as in the WO3 sol was obtained. Reaction mechanism and the rate law are proposed to account for the obtained kinetic data.