Enhancement of the photo catalytic performance of TiO 2 catalysts via transition metal modification

Abstract

The physicochemical properties and photo catalytic activity of transition metal-loaded TiO 2 catalysts were studied. The transition metal was deposited on TiO 2 via post-hydrothermal synthesis and photo-assisted reduction/impregnation. The structure of TiO 2 is preserved upon adding Pd, Cr, and Ag into it. Nevertheless, the structure of TiO 2 was destroyed when reacted with silicotungstic acid (Si-W). As a consequence, under the irradiation of visible light, the Pd and Cr loaded TiO 2 showed higher photo catalytic activity compared to pristine TiO 2 and Si-W loaded TiO 2 has no catalytic activity, although the threshold absorptions of all metal loaded TiO 2 is similar to that of pure TiO 2. Transition metal was homogeneously coated on the TiO 2 particles and there is no phase separation between metal salts and TiO 2 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 TiO 2 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 TiO 2. These results suggested that the crystallinity was important for the photo catalytic activity of TiO 2 based catalysts and the function of transition metal is to increase the electron-hole recombination time, therefore increase the catalytic activity.