Rational synthesis of Na and S co-catalyst TiO2-based nanofibers: presence of surface-layered TiS3 shell grains and sulfur-induced defects for efficient visible-light driven photocatalysis

Abstract

Surface-modified TiO₂ 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 TiO₂, modifying its band function. The optical band function of the sulfur-modified TiO₂ 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 TiO₂ NFs introduces Ti–S-based nanograins and oxygen vacancies on the surface that favor the TiO₂–TiS₃ core–shell interface. These defect states extend the photocatalytic activity of the TiO₂ 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 TiO₂ NFs exhibit a degradation rate of 0.0365 cm⁻¹ for RhB dye solution, which is 4.8 times higher than that of pristine TiO₂ 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.