Enhanced visible photocatalytic activity of titania–silica photocatalysts: effect of carbon and silver doping

Abstract

To utilize efficiently visible light in photocatalytic reactions, a series of doped TiO₂ photocatalysts were synthesized via a facile solvothermal method. The photocatalysts were characterized with various techniques. The results indicated that all the photocatalysts were of an anatase phase, the Ag_0.010C_2.0–TS_0.20 sample possessed the largest surface area (306.0 m² g⁻¹) and pore volume (2.05 cm³ g⁻¹). The carbon dopant existed in the surface layer of the TiO₂–SiO₂ composite and narrowed the energy band gap, which induced visible light absorption. Silver existed on the particle surface and in two forms, Ag⁺ and Ag⁰, which acted together to inhibit the recombination of photogenerated electrons and holes. The photoactivities were evaluated by decomposition of RhB under visible irradiation. It was found that the Ag–C/TS photocatalyst exhibited the highest visible photoactivity, with the molar ratios of Ag–Ti, and C–Ti of 0.005, and 2.0, respectively, corresponding to the reaction rate constant 2.09 h⁻¹. The reaction rate was 52.3, 11.2 and 2.33 times higher than that of TiO₂ (0.04 h⁻¹), Ag_0.005–TiO₂ (0.186 h⁻¹) and C_2.0–TiO₂ (0.897 h⁻¹), respectively. The enhanced visible photocatalytic activity can be attributed to the synergetic effects of silver and carbon doping, as well as silicon introduction. The photocatalytic reaction mechanism was verified with ESR technique; furthermore, both the hydroxyl radical and superoxide radical played a critical role on the photocatalytic reaction, in addition, DMPO–˙H was found in the ESR experiments.