Efficient degradation of thiamethoxam pesticide in water by iron and manganese oxide composite biochar activated persulfate

Neonicotinoid pesticides in aquatic environments pose a risk to the sustainability of ecosystems and human health. However, there is limited research on the removal of these pesticides from aquatic systems. In this study, biochar doped with different Fe/Mn ratios (FeMn­BC) were prepared at various pyrolysis temperatures and used for the degradation of a typical neonicotinoid pesticide, thiamethoxam (TMX), by activated persulfate (PS). From the experimental results, it is known that the biochar with a Fe/Mn ratio of 3/1 prepared at 600 °C has the most excellent removal efficiency. Optimal degradation conditions were investigated, and under these conditions, TMX removal rates of up to 99.0 % in 90 min were achieved. The applicability of this system in natural surroundings were tested by investigating the effects of inorganic anions and humic acid and in real water samples on TMX removal. In addition, the TMX removal remainly reach to 90.0 % by FeMn-BC activated PS and basically no change after five reuse cycles. Free radical quenching experiments and electron paramagnetic resonance analysis revealed that SO4− and OH radicals on the catalyst surface were the main radicals promoting TMX degradation. Combining the catalyst characterization and experimental results, the possible mechanisms were proposed: the interaction of iron and manganese ions and the oxygen-containing functional groups on the catalyst surface together promote the generation of reactive radicals. This study provides a novel approach for removing neonicotinoid pesticides using modified biochar.