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, Li3PO4-Co3O4, 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 Li3PO4 and Co3O4, 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 Li3PO4 could increase the content of oxygen vacancy on the catalyst surface to enhance the activation performance, and the conversion between Co2+ and Co3+ 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 Li3PO4-Co3O4/S(IV) system were SO4•− and •OH, and the production and transformation mechanisms of SO4•− 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. [Display omitted] •An emerging catalytic material Li3PO4-Co3O4 was first synthesized.•The composite material has more oxygen vacancy content than Co3O4.•The conversion between Co2+ and Co3+ was the key factor for activating sulfite.•Li3PO4-Co3O4/S(IV) system can significantly reduce the ecological toxicity of MNZ.•SO4•−and •OH are the main ROS involved in the degradation process of MNZ.