TiO2-In2O3 photocatalysts: preparation, characterisations and activity for 2-chlorophenol degradation in water

Nanocrystalline bicomponent TiO2–In2O3 powders with various Ti/In ratio have been prepared by the sol–gel technique and calcined at 473 and 723 K. Their crystalline structure, surface area, surface acidity, sorption properties with respect to 2-chlorophenol, and optical absorption were determined by appropriate techniques (XRD, BET, FTIR, and UV-Vis spectroscopies), while their photocatalytic activity (PCA) was tested in the case of the degradation of 2-chlorophenol in water. For both calcination temperatures, PCA increased with decreasing In2O3 contents reaching a maximum at ca. 10 wt.% of In2O3. For this latter sample and the one containing 20 wt.% In2O3, PCA was greatly enhanced with respect to TiO2 especially for the samples pretreated at 473 K. The concentration of the main aromatic intermediate products (chlorohydroquinone and catechol) was considerably lower for TiO2-In2O3 photocatalysts than for pure TiO2. On the basis of various characterisations of the photocatalysts, the reasons invoked to explain the PCA enhancement due to In2O3 include a better separation of photogenerated charge carriers, an improved oxygen reduction and an increased surface acidity inducing a higher extent of adsorption of the aromatics.