Influence of In3+-doping and Ag0-depositing on the visible-light-induced photocatalytic activity of TiO2

In3+-doped and Ag0-deposited TiO2 (Ag0/In3+/TiO2), In3+-doped TiO2 (In3+/TiO2), Ag0-deposited TiO2 (Ag0/TiO2), and pure TiO2 were synthesized via sol-gel and photocatalytic reduction route. The as-prepared samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), X-ray photoelectron spectroscope (XPS), UV-visible absorption spectra techniques and photoluminescence (PL) emission spectra, and their visible-light-induced photocatalytic activity was evaluated by the decomposition of methylene blue (MB). Modifying of TiO2 by making Ag0 deposit on its surface extended the absorption limit of TiO2 from 390 to 464 nm due to the broadening of surface plasmon absorption, and promoted charge separation of photoinduced electrons (e-) and holes (h+) because of the Schottky barrier at Ag0-TiO2 interface. Modifying of TiO2 by making In3+ (r = 81 pm) to take the place of Ti4+ (r = 68 pm) in its lattice extended the absorption limit of TiO2 from 390 to 602 nm by the donor-doped energy level (2.06 eV) formed in the forbidden band of TiO2 (3.18 eV), and promoted charge separation of photoinduced e-/h+ by the decrease of crystallite size, increase of anatase content and formation of point defects (oxygen vacancy and titanium interstitial) resulting from the local expansive lattice distortion of TiO2. Because of their synergistic effects, co-modifying of TiO2 by making both In3+ take the place of Ti4+ in its lattice and Ag0 deposit on its surface extended the absorption limit of TiO2 from 390 to 670 nm, and promoted the charge separation of photoinduced e-/h+ more efficiently. The co-modifying's synergistic effects made Ag0/In3+/TiO2 exhibit distinctly higher visible-light-induced photocatalytic activity than either pure or single-modified one. The degradation rate of MB in aqueous solution (8 mg/L) reached 90% after 7 h visible light irradiation over Ag0/In3+/TiO2 (5 g/L), while pure TiO2 showed only 40% under the same conditions.