Optimizing FeS crystallinity of sulfidated nZVI to enhance electron transport capacity for clothianidin efficient degradation：Regulation of biochar pyrolysis temperature

Abstract

Clothianidin (CTD), a higher water-soluble neonicotinoid insecticide, easily enters water through runoff. Developing eco-friendly materials to degrade CTD is essential. Nano zero valent iron (nZVI) is effective for contaminant removal, but it deactivates due to agglomeration. Biochar supported sulfidated nano zero valent iron (S-nZVI-BC) can effectively mitigate nZVI aggregation while enhancing anti-passivation and electron transfer. However, the regulation of BC preparation conditions on S-nZVI-BC performance and contaminant degradation mechanism remains elusive. This work systematically investigated the effects of BC pyrolysis temperature on FeS formation in S-nZVI-BC and CTD degradation mechanism. BC enhanced FeS crystallinity and increased Fe⁰ lattice constants, facilitating electron transfer. Compared to S-ZVI, the CTD removal kinetics constants of S-nZVI-BC was 2.30 folds higher. Competitive dynamics model revealed BC pyrolysis temperature and S modulated the competition between O₂ and CTD, enhancing electron utilization efficiency and improving nZVI anti-passivation under oxic conditions. Quenching experiment and electrochemical tests indicated S incorporation and changes in BC pyrolysis temperature modulated nZVI active reduced species (H^⁎) production and contribution to CTD degradation. Additionally, increasing FeS crystallinity by adjusting BC pyrolysis temperature improved the electron transfer efficiency of S-nZVI-BC, enabling efficient CTD degradation. Density functional theory (DFT) calculations revealed CTD preferentially undergoes nitro-reduction over dechlorination. All these findings can provide guidance for the application of S-nZVI-BC.