Linking Mo/Fe ion conversion to green treatment of sulfonylurea pesticides in farmland drainage: Role of directed electron transfer and self-produced hydrogen peroxide

Harmless Resource Utilization of Iron Sludge. • Green Water Restoration Technology. • A study of continuous flow applications in agricultural drainage systems. • Full-link environmental safety assessment of microorganisms, plants, and human cells. The generation of iron sludge remains a key bottleneck in Fenton wastewater treatment technology. This study proposes a waste-to-treasure strategy, utilizing a simple calcination-hydrothermal process to prepare the S-scheme heterojunction photocatalyst iron-sludge-derived oxide/MoS 2 composite (FMx). FMx exhibited excellent photo-self-Fenton activity in degrading refractory sulfonylurea herbicides. Kelvin probe force microscopy and density functional theory calculations provide evidence for the formation of an internal electric field, unequivocally confirming the S-scheme charge transfer pathway. This configuration, coupled with the Mo-O-Fe interface, coordinates efficient space charge separation and drives a sustainable Mo 4+ /Mo 6+ co-catalytic redox cycle, thus accelerating Fe 3+ /Fe 2+ conversion and in situ H 2 O 2 generation. Therefore, the reaction rate constant of the FM4 (4% iron-sludge-derived oxide) system is 74.6 times higher than that of pristine MoS 2 . To bridge the gap with practical applications, a continuous flow reactor was constructed, demonstrating strong remediation efficacy in real agricultural runoff. Furthermore, a comprehensive multi-trophic ecotoxicological assessment covering microbial communities, plants, and human cell lines validated the biosafety and ecological compatibility of treated wastewater. This work not only proposes a cost-effective solid waste recycling value-added scheme (< 0.5 RMB L −1 ) but also clarifies the mechanism for controlling advanced self-photo-self-Fenton systems.