[Influential factors and degradation pathway of imidacloprid by homogeneous Co/PMS system]

Cobaltous-mediated decomposition of peroxymonosulfate (Co/PMS) system is one of novel advanced oxidation technologies (AOTs), which leads to the formation of very strong oxidizing species in aqueous phase. Effects of PMS concentrations, Co2+ concentrations and various inorganic anions (H2PO4-, HCO3-, NO3-, Cl-) on the degradation of Imidacloprid induced by Co/PMS system was investigated as emphasis. The degradation kinetics of imidacloprid followed pseudo first-order kinetics and reaction rates related to PMS and Co2+, concentrations. The reaction rates increased with increasing [PMS] and [Co2+] when the other parameters were constant. However, the decrease of degradation rates was found when the molar ratio of PMS versus imidacloprid was over 20. The effects of H2PO4- had positive effect on the degradation of Imidacloprid, low concentration HCO3- had positive effect and high concentration HCO3- had negative effect, Cl- had negative effect, while NO3- had little effect. Based on the results of GC/MS, two main intermediates were identified, 6-chloronicotinic acid and 6-chloronicotinamide, and the reaction pathway for SO4*- induced by homogeneous Co/PMS was proposed accordingly.