Photoelectrochemical Performance of S,N-Codoped TiO2 Films Supported on Ti and their Enhanced Photoelectrocatalytic Activity in the Generation of Hydroxyl Radicals

Abstract

New photoanodes for recalcitrant pollutant degradation should harvest photons from a wide region of the solar spectrum and promote a direct water oxidation reaction towards the hydroxyl radical generation. For this purpose, sulfur, nitrogen-codoped titanium dioxide (S,N-TiO2) films were prepared with different sulfur percentages (1.0, 2.5 and 5.0 at.%) on Ti expanded meshes by sol-gel dip-coating followed by thermal treatment at 400 °C. The morphology, composition, oxidation states of dopants, structural features, optical and semiconducting properties of S,N-TiO2 were used for the materials characterization. While sulfur was found as S4+ or S6+ cations related to surface doping, nitrogen appears as N3− anion occupying substitutional positions in TiO2. This caused an improvement in the photoelectrochemical response of TiO2 related to a decrease of up to 0.25 eV in the optical band gap and the alignments of the TiO2 band structure. S,N-TiO2 films exhibit significantly higher photoelectrocatalytic activity towards ·OH generation under UV–vis light irradiation than the undoped TiO2 films. Using 2.5 at.% S,N-TiO2 film, an increase of 166% in current efficiency was obtained at 0.5 V vs Ag/AgCl, in regard to undoped TiO2 films, together with an enhance of 8.8 times in the initial ·OH generation rate.