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 m2 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 (kapp = 0.007 min−1) was three times higher than that of pure TiO2 (kapp = 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.