Preparation of Fe-N Co-doped biochar from cotton stalk for peroxymonosulfate activation and efficient tetracycline degradation

The development of cost-effective alternatives to precious carbon nanomaterials (e.g., carbon nanotubes, graphene) for advanced oxidation processes (AOPs) remains a critical challenge in water remediation. In this study, a sustainable Fe, N co-doped biochar-based catalyst (Fe-N-BC) was synthesized from cotton stalk biomass via a facile pyrolysis strategy. The catalytic performance and mechanism of Fe-N-BC in peroxymonosulfate (PMS) activation for tetracycline (TC) degradation were systematically investigated. The results showed the successful anchoring of Fe-Nx sites within a hierarchically porous carbon matrix, which exhibited a 6.7-fold increase in specific surface area compared to pristine biochar. Under optimized conditions (100 mg/L catalyst, 1 mM PMS, pH 11), the Fe-N-BC/PMS system achieved 94 % TC removal within 18 min, outperforming conventional carbon-based catalysts. Remarkably, the catalyst retained 88.5 % degradation efficiency after five consecutive cycles, demonstrating exceptional structural stability. Mechanistic studies, including quenching experiments and spectroscopic analysis, revealed that singlet oxygen (¹O₂) played a dominant role in the oxidative degradation pathway. This work not only provides fundamental insights into the structure-activity relationship of biomass-derived biochar catalysts but also offers a practical and sustainable solution for wastewater treatment, bridging the gap between economic feasibility and high catalytic performance in environmental applications. • An Fe-N-BC catalyst for PMS activation and TC degradation was prepared from cotton stalk. • The Fe-N-BC/PMS system achieved 94 % TC removal within 18 min under optimal condition. • Singlet oxygen was identified as the primary reactive species in TC degradation. • The Fe-N-BC/PMS system retained high stability and removal efficiency after 5 cycles.