Natural hematite and oxalic acid co−enhance electrochemical system for degradation of sulfamethoxazole: role of oxalic acid and ROS generation

The performance of Fe-catalyzed electrochemical advanced oxidation in antibiotic degradation was typically hampered by poor reduction efficiency of Fe 3+ to Fe 2+ and a narrow pH working range. This work employed natural hematite (HM) as iron source and oxalic acid (OA) as complexing agent in conjunction with electrolysis (EC) to address these concerns. Results showed that the EC/HM/OA system can achieve a 99.77 % degradation efficiency of sulfamethoxazole (SMX) under the optimized reaction conditions. The SMX degradation rate constant in EC/HM/OA system was 2.53-fold higher than in EC/HM system, following pseudo first-order kinetics. The OA addition promoted the Fe 3+ reduction by complexing with HM in electrochemical system, as well as extended the pH application range of EC/HM system to 3 − 11. The ATR−FTIR test and DFT calculation demonstrated that the adsorption of OA on the HM surface occurred in a deprotonated bidentate mononuclear configuration. Radical quenching experiments and EPR analysis confirmed that the crucial reactive oxygen species for SMX degradation in EC/HM/OA system were the ·OH and ·O 2 - radicals. Five potential degradation pathways of SMX were proposed. ECOSAR model and Daphnia magna toxicity tests demonstrated attenuated toxicity of SMX after degradation. The EC/HM/OA system exhibited robust resistance to common anions (Cl⁻ and NO₃⁻), and achieved high SMX degradation (86.82 %–99.67 %) across different water matrices. The combination of natural HM with OA significantly improved the degradation performance of electrochemical process for persistent antibiotics.