Degradation of neonicotinoids with different molecular structures in heterogeneous peroxymonosulfate activation system through different oxidation pathways

Abstract

The elimination of neonicotinoids (NEOs) from water has been a research priority due to their threats to human health and ecosystems. In this study, we established the heterogeneous peroxymonosulfate (PMS) activation system using manganese catalyst (Mn NC) and cobalt catalyst (Co NC) to trigger the nonradical oxidation and synergistic oxidation pathway, respectively to remove NEOs. The results showed that the nonradical oxidation system exhibited superior NEOs degradation capability. The composition of organic pollutants in wastewater significantly impacted subsequent degradation processes. The charge distribution and reaction sites of various NEOs were analyzed using density functional theory (DFT) calculations, and it demonstrated the electron distribution and activity of NEOs were significantly influenced by the type and number of substituents. Nitro group (–NO2) and cyanide group (–CN) were identified as strong electron-withdrawing groups and prone to be attacked by negatively charged radicals. The transformation of NEOs was analyzed, and result showed that the C and N sites adjacent to the nitro group and cyanide group were more susceptible to oxidation attacks. S and N atoms, which possess strong electronegativity and high electron cloud density, were identified as key active sites in the degradation pathway. The outcomes of this study provide valuable guidance for the oriented regulation of oxidation pathways towards efficient removal of NEOs in water.