Methylene Blue (MB) undergoes rapid mineralization in aqueous TiO2 dispersions with or without doping with gold ion upon radiation with visible light (high-pressure sodium lamp). UV-visible absorption and TOC measurement were employed to disclose details of decolorization and mineralization. The presence of gold ion in TiO2 greatly enhaniced their photo-activity. The optimum molar content of gold ion doping was 0.5%. Investigation of crystal structure, chemical components, optical absorption properties, photoluminescence emission spectra and photo-voltage properties disclosed the mechanism of gold ion doping. UV-visible absorption spectra showed that the optical absorption increased in the visible region. Owing to gold impurity energy level, it is possible for gold ion doped TiO2 to be excited by visible light (E<3.2 eV). Gold impurities also lead to decrease photoluminescence (PL) emission and electron-field-induced surface photo-voltage spectra (EFISPS) and hinder the recombination of electron/hole. The order of EFISPS intensity and PL intensity (from weak to strong) had a good agreement with that of photo-activity (from strong to weak).

Key words: GOLD ION, DOPE, VISIBLE LIGHT, CATALYTIC ACTIVITY, ORGANIC POLLUTANTS, DEGRADATION, METHYLENUM CAERULEUM, TITANIUM DIOXIDE, PHOTOCATALYSIS