Monoatomic Fe-N₂O₂ sites and carboxyl groups in biochar synergistically driving HV-Fe(IV) dominated peroxymonosulfate activation for anilines degradation

High-valent ferric oxide species (HV-Fe(IV)) has been increasingly explored to selectively and efficiently remove pollutants from wastewater owing to its high reduction potential, long lifetime, and valuable resistance to anions. However, the directional production of HV-Fe(IV) and its mechanism remain challenging. Herein, a biochar-based catalyst with monoatomic Fe-trans-N₂O₂ configuration and rich COOH group (SAFe-NKBC) was rationally constructed via KOH and supramolecular organic framework co-pyrolysis. As a result, the SAFe-NKBC/PMS system exhibited exceptional catalytic performance, achieving rapid sulfamethoxazole degradation (97.4% within 10 min) and TOC removal (73.1%). Mechanistic investigations revealed the cooperative catalytic role of single-atom Fe-trans-N₂O₂ and COOH in biochar support via surface-confinement effect in boosting peroxymonosulfate activation and directional HV-Fe(IV) generation, mediating spatially coupled electron transfer and promoting selective oxidation pathways. Furthermore, a structure–activity relationship for various para-substituted anilines was systematically established via quantitative structure–activity relationship modeling based on different adsorption and oxidation descriptors. The valid descriptors were confirmed to predict reactivity, offering a molecular-level framework for water purification. Meanwhile, the catalyst demonstrated excellent resistance to matrix interference, long-term stability in flow-through systems, and significantly reduced toxicity of degradation byproducts, underscoring its potential in sustainable and precision-oriented water remediation. This work offered new insights into rational SAC design and reactivity prediction for sustainable water remediation.