V-/O-Doping to Endow Ag2S-based Bimetal Oxysulfide with Sulfur Vacancies and Heterovalent States for Rapid Reduction of Organic and Cr(VI) Pollutants in the Dark

Abstract

A novel AgVOS oxysulfide catalyst for rapid catalytic reduction of toxic organic substances and Cr(VI) under dark is synthesized by a facile method. With the V/O co-doping, the doped Ag₂S catalyst has the effectively regulated electron transfer performance, the hydrazine-driven V⁵⁺-to-V⁴⁺ reduction to disturb charge equilibrium, and the formed sulfur vacancy balanced by oxygen doping to maintain charge equilibrium. The formed sulfur vacancy acts as the active site for electrophilic nucleophilic reaction, while the orbital hybridization of O_2p and S_3p stabilizes the valence state of S²⁻. A suitable ratio of n(V⁴⁺/V⁵⁺) is regulated during the hydrazine-driven synthesis to facilitate the electron transfer and enhance the V⁵⁺-to-V⁴⁺ reduction reaction. V/O co-doped AgVOS-3 prepared by a suitable hydrazine content exhibits super catalytic reduction performance of organic 4-NP (4-nitrophenol), MB (methyl blue), MO (methyl orange), and RhB (Rhodamine B, 20 ppm, 100 mL) dyes, which are completely reduced within 8, 8, 10, and 8 min, respectively. In comparison, Cr⁶⁺ (50 ppm, 100 mL) is also completely reduced within 6 min by AgVOS-3, indicating its good catalytic reduction activity for organic and inorganic mixture pollutants. Furthermore, AgVOS-3 has good stability after cyclic tests to maintain a reduction efficiency of 96.5%. Therefore, the AgVOS catalyst shows a promising application for industrial wastewater treatment.