Photoelectrochemical Performance of S,N-Codoped TiO ₂ Films Supported on Ti and their Enhanced Photoelectrocatalytic Activity in the Generation of Hydroxyl Radicals

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-TiO ₂ ) 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-TiO ₂ were used for the materials characterization. While sulfur was found as S ⁴⁺ or S ⁶⁺ cations related to surface doping, nitrogen appears as N ³⁻ anion occupying substitutional positions in TiO ₂ . This caused an improvement in the photoelectrochemical response of TiO ₂ related to a decrease of up to 0.25 eV in the optical band gap and the alignments of the TiO ₂ band structure. S,N-TiO ₂ films exhibit significantly higher photoelectrocatalytic activity towards ^· OH generation under UV–vis light irradiation than the undoped TiO ₂ films. Using 2.5 at.% S,N-TiO ₂ film, an increase of 166% in current efficiency was obtained at 0.5 V vs Ag/AgCl, in regard to undoped TiO ₂ films, together with an enhance of 8.8 times in the initial ^· OH generation rate.