Synthesis of Fe-Nx site-based iron-nitrogen co-doped biochar catalysts for efficient removal of sulfamethoxazole from water by activation of persulfate: Electron transfer mechanism of non-free radical degradation

Fe-N co-doped carbon materials (Fe-NC) have drawn increasing attention in advanced oxidation due to their unique structure and significant promise in heterogeneous catalysis. Herein, a Fe-N co-doped biochar catalyst was prepared by a simple pyrolysis method and was applicated to activate persulfate (PS) for the degradation of sulfamethoxazole (SMX) in wastewater. The catalytic performance of Fe-NBC was proportional to the pyrolysis temperature, and Fe-NBC-800 exhibited excellent PS activation performance with larger specific surface area (254.3 m2/g), higher defect (ID/IG = 1.04). Fe-NBC-800 exhibits high stability and reusability over multiple cycles, high catalytic activity over a wide pH range of 3–9 and good tolerance to inorganic anions. The introduction of nitrogen and iron into the carbon lattice leads to a redistribution of charge density in graphitic carbon, enhancing the interaction of PS with Fe-NBC-800 surface to form surface complexes and promoting charge transfer. Five major SMX degradation pathways are proposed, including the oxidation of nitro on the aniline ring, the breakage of S-N bond and the ring opening of isoxazole ring. This study provides new ideas for the design of Fe-NC catalysts in the field of advanced oxidation.