Enhancement of the photo catalytic performance of TiO2 catalysts via transition metal modification

The physicochemical properties and photo catalytic activity of transition metal-loaded TiO2 catalysts were studied. The transition metal was deposited on TiO2 via post-hydrothermal synthesis and photo-assisted reduction/impregnation. The structure of TiO2 is preserved upon adding Pd, Cr, and Ag into it. Nevertheless, the structure of TiO2 was destroyed when reacted with silicotungstic acid (Si-W). As a consequence, under the irradiation of visible light, the Pd and Cr loaded TiO2 showed higher photo catalytic activity compared to pristine TiO2 and Si-W loaded TiO2 has no catalytic activity, although the threshold absorptions of all metal loaded TiO2 is similar to that of pure TiO2. Transition metal was homogeneously coated on the TiO2 particles and there is no phase separation between metal salts and TiO2 as revealed with scanning electron micrographs (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) data. X-ray photoelectron spectroscopy (XPS) spectra showed that all metals in metal loaded TiO2 presented as an ionic state with slightly reduction compared to the metal in metal salt used in the reaction, probably due to the interaction with TiO2. These results suggested that the crystallinity was important for the photo catalytic activity of TiO2 based catalysts and the function of transition metal is to increase the electron-hole recombination time, therefore increase the catalytic activity. (C) 2004 Elsevier B.V. All rights reserved.