Synergistic Tuning of Heterovalent States and Oxygen-Vacancy Defect Engineering in Hydrophilic W-Doped Sb₂OS₂ for Enhanced Nitrogen Photoreduction to Ammonia

Nitrogen fixation reaction via photocatalysis offers a green and promising strategy for renewable NH₃ synthesis, and catalysts with high-efficiency photocatalytic properties are essential to the process. Herein, we demonstrate a W-doped Sb₂OS₂ bimetal oxysulfide catalyst (labeled as SbWOS) with abundant oxygen vacancies, heterovalent metal states, and hydrophilic surfaces for nitrogen photoreduction to ammonia. The SbWOS-3 with suitable W-doping exhibited excellent nitrogen fixation activity of 408.08 μmol·g^-1·h^-1 and an apparent quantum efficiency (AQE) of 1.88% at 420 nm and a solar-to-ammonia (STA) conversion efficiency of 0.082% in pure water under AM1.5G light irradiation. The W-doping not only transforms hydrophobic Sb₂OS₂ into a hydrophilic catalyst, making it easier for H₂O molecules adsorbed on the SbWOS surface and catalyzed into protons, but also endows the SbWOS catalyst with rich oxygen vacancies, acting as the active sites for trapping and activating the N₂ molecule, and for trapping and activating H₂O to produce the protons for the N₂ photocatalytic reduction reaction. The hydrazine drives the SbWOS catalyst with the heterovalent metal states, which acts as the photogenerate electrons quickly hopping between W⁵⁺ and W⁶⁺ to transfer for the N₂ reduction reaction. This study provides a feasible scheme for applying oxygen vacancy defects, heterovalent metal states, and surface hydrophobic-to-hydrophilic wetting engineering in bimetal oxysulfide for N₂ photoreduction to ammonia.