Surface characteristics and photocatalytic properties of TiO2–In2O3 composite powders by using the sol–gel method: effects of preparation conditions

Abstract

TiO2–In2O3 composites were synthesized with various Ti/In molar ratios (13.5, 27 and 54), calcination temperatures (300, 450 and 600 °C) and durations (1, 2 and 4 h) by the sol–gel method. The surface properties of the prepared powders were analyzed by X-ray diffraction, UV–Vis spectrophotometry, scanning electron microscopy, transmission electron microscopy, BET surface area analysis, surface charge analysis and X-ray photoelectron spectroscopy. The C.I. Reactive Red (RR2) removal efficiency of the TiO2–In2O3 composites with or without UV irradiation was determined. Analytical results reveal that at a Ti/In molar ratio of 54 and a calcination temperature of 450 °C for 2 h, the average diameter, BET surface area, pore volume and band gap of the prepared TiO2–In2O3 composite were 57 nm, 35.7 m2/g, 0.17 cm3/g and 2.97 eV. The removal rate constants of RR2 in the UV/TiO2–In2O3 composite systems fit pseudo-first order kinetics. The RR2 removal efficiency of the TiO2–In2O3 composite exceeded that of TiO2 or In2O3 alone, possibly owing to its greater BET surface area, hydrophilicity and separation of photogenerated electron–hole pairs. Although inversely related to the RR2 concentration, the RR2 decolorization rate constant was directly proportional to the amount of the TiO2–In2O3 composite, according to the pseudo-first order kinetics.