Abstract:With an attempt to investigate the effect of gold impurity and tungsten oxide on the recombination and separation of electron-hole pairs, and disclose the effect of surface state on the photo-catalytic activity of TiO₂, an innovative photo-catalyst 3%WO₃/0.5%Au³⁺/TiO₂ was prepared by means of sol-gel method. The photo-oxidation efficiency of photo-catalyst was evaluated by conducting a set of experiments to photo-degrade methylene blue (MB) in aqueous solution. The surface state properties were examined by means of surface photo-voltage spectra (SPS) and electron-field-induced SPS (EFISPS). The experiments demonstrate that the strongest peak is attributed to electron excited from valence band to conduction band and the second strongest peak is attributed to electron excited from valence band to oxygen molecular for all samples. Electron is trapped by O₂ absorbed on the surface of TiO₂. And the surface state of O^-₂ forms. For(1%, 3%)Au³⁺/TiO₂ sample, two new peaks that significantly present at 414nm and 400nm respectively should be attributable to gold impurity energy level. And for tungsten oxides doping samples, 4 peaks that significantly present in the region of 500～800nm should be attributable to tungsten impurity energy level. The intensity of EFISPS decreases with increasing the content of gold ion or tungsten oxide when its content is no more than their optimal dosage. However, when the content of gold ion or tungsten oxide is more than their optimal dosage, impurity energy level becomes recombination center from separation center and the intensity of all peaks increases for them. 

Key words: surface state; titanium dioxide; tungsten oxide; surface photo-voltage spectra; methylene blue; gold ion