Regulating peroxymonosulfate activation by biochar-supported single-atom Fe toward selective polymerization of sulfonamide antibiotics

Catalytic polymerization represents a promising approach for the removal of sulfonamide antibiotics (SAs) with minimal oxidant demand. Here, we developed a biochar-supported Fe single-atom catalyst (Fe 1 /DNBC) featuring Fe-C x coordination anchored at carbon defects, enabling selective peroxymonosulfate (PMS) activation toward polymerization of SAs. Fe 1 /DNBC achieved 93.4% sulfamethoxazole (SMX) removal and 73.5% total organic carbon (TOC) reduction within 10 min at a low PMS dosage (0.06 mM), corresponding to an approximately 90% reduction in oxidant demand relative to the theoretical requirement for complete mineralization. Mechanistic studies revealed that Fe-C x sites created electron-deficient microenvironments that promoted PMS chemisorption and the formation of surface-bound PMS complex (PMS*) as the dominant reactive species. The shortened O β -O γ and S-O β bonds in PMS* suppressed radical formation and oxygen-transfer pathways, thereby favoring a selective electron-transfer-driven polymerization pathway. Electrochemical analysis demonstrated that the oxidation potential of PMS* could be tuned by PMS concentration, regulating the balance between polymerization and mineralization. This system exhibited robust performance across complex water matrices and continuous-flow conditions. More importantly, Fe 1 /DNBC/PMS treatment effectively eliminated the phytotoxicity of SMX-contaminated water, shifting wheat shoot and root responses from 49.7% and 72.3% inhibition to 19.8% and 17.0% promotion, respectively. This work establishes a Fe-C x coordination engineering strategy to regulate PMS activation pathways, enabling efficient and selective removal of SAs with reduced oxidant consumption and mitigated environmental risks.