Study of Au/Au3+-TiO2 photocatalysts toward visible photooxidation for water and wastewater treatment

With an attempt to extend light absorption of TiO2-based photocatalyst towa rd the visible right range and eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalysts (Au/AU( 3+)-TiO2) powder was prepared by a photoreduction/sol-gel process. The crys tal phase composition, surface structure, and light absorption of the new p hotocatalysts were comprehensively examined by X-ray differential detection (XRD), UV-visible absorption spectra,-X-ray photoelectron emission spectro scopy (XPS), and photoluminescence (PL) spectra. The photooxidation efficie ncies of the photocatalysts were also evaluated in the photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation fr om a high-pressure sodium lamp (lambda > 400 nm). The results of PL analyse s in this study indicated that the gold/ gold ion-doping on the surface of TiO2 could eliminate the electron/holes recombination and also increase the light absorption in the visible range. The analytical results of UV-visibl e diffuse reflection spectra (DRS) and optical absorption spectra indicated that a new energy level below 3.2 eV generated in the Au/Au3+-TiO2 promote d the optical absorption in the visible region and made it possible to be e xcited by visible light(E < 3.2 eV). The experiment demonstrated that the p hotooxidation efficiency of MB using the Au/Au3+-TiO2 powder were significa ntly higher than that using conventional TiO2 powder and an optimum molar c ontent of gold doping/deposition in the TiO2 was 0.5%. The development of s uch photocatalysts may be considered a breakthrough in large-scale utilizat ion of solar energy to address environmental needs.