Synergistic Fe-N₃ and Fe₂O₃ structures for high-valent metal-oxo species generation and enhanced tetracycline...

Fe-N-C catalysts enable efficient peroxymonosulfate (PMS) activation for tetracycline (TC) removal through high-valent metal-oxo species (HVMO), which act as key non-radical oxidants to achieve selective contaminant degradation with minimal interference. However, precisely modulating active sites in Fe-N-C/PMS systems to generate HVMO remains challenging. Herein, controlled nitrogen doping is shown to construct Fe-N₃/Fe₂O₃ coexistence structures, driving a mechanistic transition toward HVMO pathways. Research reveals that increased nitrogen content promotes higher Fe-N_x coordination numbers while suppressing Fe₂O₃ formation. Surprisingly, at a critical nitrogen loading of 0.34 wt%, a complete mechanistic shift occurs from electron transfer process to HVMO pathway. Theoretical calculations further verify that the unique coexistence of Fe-N₃ and Fe₂O₃ structures in this catalyst exhibits stronger reactivity toward PMS and facilitates dual-site adsorption, inducing remarkable O-O bond elongation that favors HVMO generation. This atomic-level modulation ultimately translates to exceptional catalytic efficiency, achieving 86.6 % TC removal within 5 min. Moreover, the Fe-N-C/PMS system exhibits effective detoxification capability, preferential selectivity for electron-rich pollutants, strong anti-interference ability, and excellent stability, underscoring its application potential. This study identifies a turning point for mechanistic switching based on the synergistic Fe-N₃/Fe₂O₃ structures, which provides new inspiration for the design of HVMO-dominated catalysts.