Electronic and Structural Evolution of Cationic S(IV)/S(VI)-Doped TiO ₂ Synthesized by Single-Step Aerosol Pyrolysis: A Combined Experimental and Computational Study

High Resolution Image Download MS PowerPoint Slide This work investigates the electronic properties of S-doped TiO 2 prepared by a single-step flame spray pyrolysis method developed for the synthesis of sulfur-doped TiO 2 nanoparticles with a controlled sulfur content. This scalable approach enables facile incorporation of sulfur in cationic forms, with S(IV) substituting at Ti lattice sites and S(VI) occupying interstitial sites, as corroborated by a detailed structural and spectroscopic characterization. Complementary computational investigations by using density functional theory (DFT) have been carried out on multiple models of cationic S(IV) and S(VI) doping to understand the evolution of sulfur-doping sites with increasing dopant concentration. A comprehensive analysis of the electronic properties and frontier molecular orbitals reveals that sulfur-doping predominantly influences the valence band region of TiO 2, as demonstrated by the projected density of states (PDOS), which shows increasingly pronounced localized S 3p states near the Fermi level with higher sulfur loadings. This valence band modulation leads to a gradual reduction in the electron excitation energy and band gap narrowing, while the conduction band remains largely unaltered. The selective tuning of the valence band renders this flame spray synthesis method particularly effective for band gap modulation, enhancing the reactant adsorption and activation, overall photocatalytic activity, and selectivity. The novelty of this work lies in the combination of a facile and scalable synthesis route with an in-depth theoretical and experimental elucidation of the distinct roles of S(IV) and S(VI) dopants in modulating the electronic structure of TiO 2, thus providing valuable insights into the rational design of sulfur-doped photocatalysts.