Preparation of Ag-doped TiO2 nanoparticles by a miniemulsion method and their photoactivity in visible light illuminations

Visible-light-driven photocatalysts based on silver-doped TiO2 (Ag-TiO2) nanoparticles were successfully synthesized by a miniemulsion method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analysis and UV-vis diffuse reflectance spectroscopy (DRS). Degradation of methylene blue (MB) was applied to evaluate photocatalytic activity of samples. The results show that Ag doping showed a controlling effect on the transformation of titania from anatase to rutile. A red shift occurred in the absorption edge of titania with the certain Ag-doped amount. Moreover, the addition of Ag resulted in a higher Brunauer-Emmett-Teller (BET) surface area as well as a larger average pore size of TiO2 nanoparticles. The specific surface area increased with the Ag-doped amount to reach a maximum (86.3 m(2) g(-1)) at Ag/Ti molar ratio of 0.8% and then decreased with further increase of the Ag-doped amount. The Ag-TiO2 nanoparticles could effectively photodegrade MB under visible light irradiation and the obtained maximum reaction constant (k(app) = 0.007 min(-1)) was three times higher than that of pure TiO2 (k(app) = 0.002 min(-1)) when the Ag-doped amount was 0.8%. The commendable visible photoactivities of Ag-TiO2 photocatalysts are predominantly attributable to simultaneous effects of Ag deposits by the acting as electron traps, enhancing the MB adsorption on the Ag-TiO2 surface, occurring red shift of the absorption edge and decreasing band gap. (C) 2011 Elsevier B.V. All rights reserved.