A magnetic biochar catalyst with dual active sites of Fe₃C and Fe₄N derived from floc: The activation mechanism for persulfate on degrading organic pollutant

This study, a magnetic biochar catalyst (Fe-N@MFC) with Fe₃C and Fe₄N was synthesized via one-step pyrolysis using waste floc as a raw material. Fe-N@MFC shows an efficient catalysis in activating peroxydisulfate (PDS) to degrade tetracycline (TC). 90.5 % of TC (5 mg/L) is removed within 60 min in the Fe-N@MFC/PDS (0.5 g/L and 1.8 mM) system with a degradation rate constant of 0.33043 min⁻¹. Reactive oxygen species (·OH, SO₄^·−, ¹O₂, and ·O₂⁻) and electron transfer are generated in the reaction system. ·OH and SO₄^·− radicals make a major contribution to TC degradation. Variation in material structure and DFT calculations prove that the existence of Fe₃C and Fe₄N enhances the adsorption energy of PDS and promotes the redox reaction between PDS and Fe species (Fe⁰ and Fe-N). Based on iron ion leaching, recycling experiment and application in real water, the Fe-N@MFC catalyst is found to exhibit promising potential. This work represents a progress compared to the traditional technology used for preparing Fe[sbnd]N[sbnd]C biochar catalysts and provides significant guidance for the further development of biochar in the future.