Synthesis of novel L-cysteine-modified TiO2–In2O3 composites by the sol–gel method: evaluating surface characteristics and photocatalytic activity

Abstract

This study applied the sol–gel method to generate TiO2–In2O3 composites (Ti–In), and this prepared Ti–In was further modified with l-cysteine to form S–N co-doped Ti–In (Ti–In–SN). Surface properties of the Ti–In–SN were analyzed by X-ray diffraction, UV–vis spectrophotometry, scanning electron microscopy, transmission electron microscopy, surface area analysis, and X-ray photoelectron spectroscopy. The dye C.I. reactive red 2 (RR2) was utilized as the model compound subjected to Ti–In and Ti–In–SN and measured for removal by adsorption and photocatalytic degradation. The Ti–In–SN had an average diameter of 13 nm, surface area of 48.6 m2/g, and band gap energy of 2.75 eV. Removal rate constants for RR2 in the UV/Ti–In and UV/Ti–In–SN systems fitted pseudo-first-order kinetics and were 0.43 and 0.68 h−1, respectively. Co-doping S–N in Ti–In via l-cysteine formed Ti–N–O, Ti–O–N, and Ti–O–S bonds; hence, crystalline size and band gap energy were decreased. Accordingly, adsorption ability and photocatalytic activity of Ti–In–SN for RR2 decolorization was improved.