Mechanism insights into the degradation of thiamethoxam based on partial Fe-substituted Co3S4 for effective activation of PMS: Experimental and theoretical calculations

Thiamethoxam (THX), a neonicotinoid pesticide, exhibits potential ecotoxicity in aquatic environments. In this study, a combined experimental and density functional theory (DFT) approach was applied to investigate partial Fe-substituted Co 3 S 4 (Fe x Co, x = 0.01, 0.03, 0.05, 0.07, 0.09, and FeCo 2 S 4 ) for the effective activation of PMS and the degradation of THX. Fe doping elongated Co S bonds on the catalyst to promote the formation of sulfur vacancies, which enhance the adsorption and charge transfer capability of PMS. Due to the fastest degradation rate (0.511 min −1 ), the optimal PMS adsorption stability (1.11 eV), more electron transfer (0.72 e − ), and longer O O bond (1.468 Å), Fe 0.03 Co catalyst can preferably activate PMS to generate SO 4 •- and 1 O 2 , which was the most significant ROS for degrading THX. The initiation reaction of SO 4 •- -addition was superior to 1 O 2 , and the optimal active site was the C2 sites. Proposed degradation pathways and ecotoxicity evaluation highlighted the critical role of denitrification and hydroxylation in toxicity attenuation. In addition, Fe 0.03 Co/PMS catalyst had certain catalytic stability and reusability, and its degradation efficiency in farmland irrigation water can reach 80 %. This work not only elucidated the performance enhancement mechanism of Fe-substituted Co 3 S 4 catalyst, but also provided support for the application of sulfide-metals on advanced oxidation treatment of pesticide wastewater.