Gallium- and iodine-co-doped titanium dioxide for photocatalytic degradation of 2-chlorophenol in aqueous solution: Role of gallium

Visible-light-driven TiO2-based catalysts for the degradation of pollutants have become the focus of attention. In the present work, iodine-doped titania photocatalysts (I-TiO2) were improved by doping with gallium (Ga,I-TiO2) and the resulting physicochemical properties and photocatalytic activity were investigated. The structural properties of the catalysts were determined by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis and transmission electron microscopy. We found that Ga probably enters the TiO2 framework for doping levels <0.5 mol%. A further increase in Ga content probably leads to dispersal of excess Ga on the TiO2 surface. The photocatalytic activity of Ga,I-TiO2 catalysts was evaluated using 2-chlorophenol (2-CP) as a model compound under visible and UV-vis light irradiation. The results indicate that 0.5 mol% Ga loading and calcination at 400 °C represent optimal conditions in the calcining temperature range 400-600 °C and with doping levels from 0.1% to 1 mol%. The effective enhancement of 2-CP degradation might be attributed to the formation of oxygen vacancies by Ga doping, which could decrease the recombination of electron-hole pairs.

Research highlights▶ Iodine-doped titanium dioxide photocatalysts are improved by doping with gallium. ▶ Catalysts for degradation of 2-chlorophenol. > 0.5 mol% Ga loading and calcination at 400 oC are optimal preparation conditions. ▶ Ga addition retards the anatase-rutile phase transformation. ▶ Oxygen vacancies may be formed by Ga doping.