Hydrazine-driven cation valence regulation and oxygen defect engineering in sulfur-doped CoMoO4·0.9H2O for highly efficient reduction of toxic organics and hexavalent chromium under dark

CoMoO 4 ·0.9H 2 O-based S–CoMoO bimetallic oxysulfide catalyst performed high catalytic activity after being synthesized by a facile method. Hydrazine used in synthesis drives the reduction of Mo 6+ cations to Mo 4+ , while sulfur ion is introduced to balance the valence-charge deviations from electrical neutrality induced by high Mo 4+ concentrations. Moreover, sulfur doping induces lattice strain to facilitate the creation of oxygen vacancies (Vo). Vo acts as an electron accommodation site and reaction active site for pollutant adsorption by promoting electron transfer and reacting with adsorbed pollutants. Additionally, electron hopping between Mo 6+ and Mo 4+ effectively facilitates the reaction rate. The S–CoMoO-3 with a suitable Mo 4+ /(Mo 6+ +Mo 4+ ) ratio of 0.46 exhibited remarkable performance, achieving a complete reduction of 100 ml 20 ppm 4-NP and 100 ml 50 ppm solutions of RhB and MO in 4 min, and 100 ml 20 ppm MB fully reducte it within 2 min. The Cr 6+ reduction was achieved in 8 min with a kinetic rate constant of 28.33 min −1 ·g −1 for a pseudo-first-order reaction. After six rounds of repeated experiments, the catalyst still achieved a 98.67% reduction of Cr 6+ within 8 min, demonstrating its excellent stability and durability and making it a promising candidate for reducing pollution in various industrial processes.