Co-removal of thiamethoxam and piperonyl butoxide in an Fe3S4-activated H2O2 system: Enhanced Fe3 + /Fe2+ cycle

While the co-exposure toxicity of neonicotinoids (NENIs) and their synergists has attracted attention, it is of high demand to establish effective methods for achieving their co-removal under real environmental conditions. In this study, a magnetically recoverable Fe 3 S 4 catalyst was synthesized via a facile hydrothermal route and employed to activate H 2 O 2 for the simultaneous removal of thiamethoxam (THM) and piperonyl butoxide (PBO). The system demonstrated high co-removal efficiency of THM and PBO under optimized conditions. Although co-existence of PBO significantly suppressed THM removal in comparison to single system, complete removal of THM (in 5 h) and PBO (in 1 h) was still achieved. Notably, co-existence of humic acid and inorganic anions, and change in water matrix displayed negligible influence on the reaction process, with removal efficiencies remaining above 80 %. Mechanism investigations through quenching tests and electron paramagnetic resonance (EPR) verified that hydroxyl radicals (•OH) served as the primary reactive species, contributing almost 100 % to THM degradation. In contrast, PBO removal occurred via a dual pathway involving •OH oxidation and surface adsorption. X-ray photoelectron spectroscopy (XPS) analysis of Fe 3 S 4 before and after reaction further revealed the pivotal role of surface sulfur species in accelerating Fe 3+ /Fe 2+ cycle and facilitating sustained H 2 O 2 activation. •OH oxidized THM and PBO via four routes: denitration, cleavage C-C or C-N bond, ring opening, and hydroxylation. These findings provide remarkable insights for the remediation of water containing mixed pesticide pollutants.