Sustainable activation of sulfite by oxygen vacancies-enriched spherical Li3PO4-Co3O4 composite catalyst for efficient degradation of metronidazole

The development of a new catalyst is of great significance for the potential application of advanced oxidation processes using sulfites as the sources of sulfate radical. In this study, a novel composite catalytic material, Li 3 PO 4 -Co 3 O 4 , was synthesized to activate sulfite to degrade metronidazole (MNZ) in water. Characterization techniques were used to characterize the prepared materials. The key factors affecting the degradation of MNZ, including molar ratio of Li 3 PO 4 and Co 3 O 4 , catalyst dosage, sulfite concentration, pollutant concentration and initial pH, were investigated. Under the optimal experimental conditions, the degradation rate of MNZ can reach 94% within 30 min. The effects of ions on the degradation of MNZ in water were investigated. The XPS test showed that Li 3 PO 4 could increase the content of oxygen vacancy on the catalyst surface to enhance the activation performance, and the conversion between Co 2+ and Co 3+ was the key factor for the activation of sulfite. By electron paramagnetic resonance detection and reactive oxygen species (ROS) clearance experiments, it was concluded that the main ROS in Li 3 PO 4 -Co 3 O 4 /S(IV) system were SO 4 •− and • OH, and the production and transformation mechanisms of SO 4 •− and • OH were fully revealed and demonstrated. MNZ is degraded into multiple intermediate products through two pathways, which are ultimately mineralized into inorganic small molecules. The toxicity analysis of the intermediate products indicate that the system has a strong detoxification effect on MNZ. In addition, the catalyst has good reusability and low metal ion leaching characteristics, indicating that the catalytic system has good practical application potential.