Study of Au/Au3+-TiO2 Photocatalysts toward Visible Photooxidation for Water and Wastewater Treatment

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Abstract
With an attempt to extend light absorption of TiO2-based photocatalyst toward the visible light range and eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalysts (Au/Au3+-TiO2) powder was prepared by a photoreduction/sol−gel process. The crystal phase composition, surface structure, and light absorption of the new photocatalysts were comprehensively examined by X-ray differential detection (XRD), UV−visible absorption spectra, X-ray photoelectron emission spectroscopy (XPS), and photoluminescence (PL) spectra. The photooxidation efficiencies of the photocatalysts were also evaluated in the photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation from a high-pressure sodium lamp (λ > 400 nm). The results of PL analyses 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−visible diffuse reflection spectra (DRS) and optical absorption spectra indicated that a new energy level below 3.2 eV generated in the Au/Au3+-TiO2 promoted the optical absorption in the visible region and made it possible to be excited by visible light (E < 3.2 eV). The experiment demonstrated that the photooxidation efficiency of MB using the Au/Au3+-TiO2 powder were significantly higher than that using conventional TiO2 powder and an optimum molar content of gold doping/deposition in the TiO2 was 0.5%. The development of such photocatalysts may be considered a breakthrough in large-scale utilization of solar energy to address environmental needs.