Singlet oxygen-dominated dual-pathways catalytic ozonation of sulfamethoxazole over FeOx-N-BC/O3–MNBs system

Heterogeneous catalytic ozonation (HCO) is a promising technology for water purification but is often restricted by low ozone utilization and poor gas-liquid-solid mass transfer. In this work, a dual-enhanced catalytic ozonation system was developed by coupling a nitrogen-doped cotton-straw-derived biochar supported mixed-valent iron catalyst (FeO x -N-BC) with ozone micro-nanobubbles (O 3 -MNBs). The catalyst was synthesized via impregnation and two-step pyrolysis, enabling uniform dispersion of Fe active sites and electronic structure modulation through nitrogen doping. The O 3 -MNBs improved ozone dissolution and transfer efficiency at the interface. Under optimal conditions, the FeO x –N–BC/O 3 –MNBs system achieved an SMX removal efficiency of 83.3 % and a mineralization rate of 37.9 %, with a pseudo-first-order kinetic constant of 0.30 min −1 , significantly outperforming single ozonation. EPR and quenching experiments confirmed a radical-nonradical dual degradation pathway dominated by singlet oxygen ( 1 O 2 , 25.13 %). XPS revealed that C, N, and Fe species underwent synergistic valence state evolution, sustaining ROS generation and catalytic stability. The system maintained 51.1 % removal efficiency after five cycles with negligible anion interference. This study demonstrates a low-cost, efficient, and stable catalytic ozonation strategy, providing a practical route for antibiotic wastewater treatment and valorization of agricultural residues.