Rational synthesis of Na and S co-catalyst TiO-based nanofibers: Presence of surface-layered TiS shell grains and sulfur-induced defects for efficient visible-light driven photocatalysis

Surface-modified TiO nanofibers (NFs) with tunable visible-light photoactive catalysts were synthesised through electrospinning, followed by a sulfidation process. The utilization of sodium-based sulfidation precursors effectively led to the diffusion and integration of sulfur impurities into TiO, modifying its band function. The optical band function of the sulfur-modified TiO NFs can be easily manipulated from 3.17 eV to 2.28 eV through surface modification, due to the creation of oxygen vacancies through the sulfidation process. Sulfidating TiO NFs introduces Ti-S-based nanograins and oxygen vacancies on the surface that favor the TiO-TiS core-shell interface. These defect states extend the photocatalytic activity of the TiO NFs under visible irradiation and improve effective carrier separation and the production of reactive oxygen species. The surface oxygen vacancies and the Ti-S-based surface nanograins serve as charge traps and act as adsorption sites, improving the carrier mobility and avoiding charge recombination. The diffused S-modified TiO NFs exhibit a degradation rate of 0.0365 cm for RhB dye solution, which is 4.8 times higher than that of pristine TiO NFs under visible irradiation. By benefiting from the sulfur states and oxygen vacancies, with a narrowed band gap of 2.3 eV, these nanofibers serve as suitable localized states for effective carrier separation.