Enhancement of photocatalytic oxidation of oxalic acid by gold modified WO 3/TiO 2 photocatalysts under UV and visible light irradiation

Abstract

The photooxidation of oxalic acid, catalyzed by nanosized TiO 2 or WO 3 and composite photocatalysts: Au/TiO 2, Au/WO 3, WO 3/TiO 2, Au/WO 3/TiO 2 was studied under irradiation with UV, visible and combined UV–visible light. The catalysts were characterized by the XRD, XPS, SEM and TEM methods. The photocatalytic mineralization of oxalic acid, catalyzed by WO 3/TiO 2 or Au/WO 3/TiO 2, proceeded at a significantly higher rate under UV-A irradiation than that under visible light. This is due to the lower specific surface area of the WO 3 and its small amount in the composite catalyst. Doping of the semiconductor materials with gold nanoparticles more than doubles the rates of mineralization of oxalic acid, compared to the un-doped samples, and more significantly in the case of Au/WO 3/TiO 2. The higher rate constants of oxalic acid decomposition under UV, visible or UV–visible light irradiation with the WO 3/TiO 2 and Au/WO 3/TiO 2 catalysts, compared with those measured with the individual oxide photocatalysts, are due to the more efficient separation of the electron–hole charges generated upon irradiation. Especially efficient is the charge separation in the case of the Au/WO 3/TiO 2 photocatalyst under irradiation with UV or combined UV–visible light, when the rate constants of oxalic acid destruction are approximately 1.7 times higher than that of the process catalyzed by Au/TiO 2 and 3 times higher than that catalyzed by pure TiO 2.