CuMgFe-LDO as superior peroxymonosulfate activator for imidacloprid removal: Performance, mechanism and effect of pH

Recently, the pollution of neonicotinoid insecticides in aquatic environment has attracted attention. Due to its potential neurotoxicity, it is necessary to develop convenient and high-efficient methods to degrade neonicotinoid insecticides in water. In this study, a heterogeneous composite catalyst CuMgFe-LDO was prepared by precipitation-calcination method, and then used to activate peroxymonosulfate (PMS) to degrade a common neonicotinoid insecticide imidacloprid. The key parameters such as Cu:Mg:Fe ratio, catalyst dosage, PMS dosage and initial pH value were optimized. The results showed that CuMgFe-LDO/PMS system exhibited excellent catalytic performance, and imidacloprid could be completely degraded within 15 min under the optimum conditions ([CuMgFe-LDO] = 50 mg L−1, [PMS] = 0.2 mM and [imidacloprid]0 = 10 μM, initial pH = 4–9). Through quenching experiment, EPR test and characterization analysis, it was identified that the main active species in the system were Cu(III), SO4– and OH. In addition, pH had a great impact on the contribution of these active species. During the reaction, Cu and Fe may participated in valence circulation, and Mg was beneficial to the hydroxylation of catalyst surface and stabilization of copper ions. Finally, the main degradation pathways of imidacloprid were obtained by UPLC-MS/MS analysis, and the toxicity of the intermediate products was calculated with TEST program. In this paper, a high-efficient PMS activation strategy is proposed, which provided a reference for the further development of metal catalysts for advanced oxidation technology.