Transformation and removal of imidacloprid mediated by silver ferrite nanoparticle facilitated peroxymonosulfate activation in water: Reaction rates, products, and pathways.

Imidacloprid (IMI) is one of the most extensively used chlorinated organic pesticides and its widespread occurrence makes it attract increased public concern and scientific interest. Peroxymonosulfate (PMS) activation has been widely studied for the elimination of organic pollutants from water. But few studies are focused on their heterogeneous catalytic performance towards imidacloprid especially with the presence of silver ferrite nanoparticles (nAgFeO2)-based catalysts. Herein, the catalyst, nAgFeO2, was prepared via a co-precipitation method, and further applied to activate PMS for the removal of imidacloprid (IMI). Our results demonstrated that the prepared nAgFeO2 significantly promoted the activation of PMS for removing IMI, and the removal of IMI followed a pseudo first-order kinetics model with the corresponding nAgFeO2 dosage. Electron paramagnetic resonance (EPR) and quenching tests revealed the singlet oxygen (1O2)-mediated nonradical pathway, instead of hydroxyl radical (•OH) or sulfate radical (SO4•-), played the dominant role in the degradation of IMI. Eight products were identified and the degradation pathways of IMI were proposed. It is postulated that the primary site at the C-1 position of IMI was more easily attacked by the •OH yielding (6-chloropyridin-3-yl) methanol). While the site at the amidine nitrogen (2) of IMI was more likely attacked by the 1O2, and then reacted with •OH to produce 5-hydroxy imidacloprid. Overall, this study provides insights into the mechanisms of nonradical oxidation processes based on PMS for the elimination of pesticides from water, broadening the application of silver ferrite nanoparticles in wastewater treatment.