Sustainable antibiotic degradation in a pH-adaptable heterogeneous electro-Fenton system: insights into cross-scale mechanism validation

Fenton-based advanced oxidation processes had shown significant potential for antibiotics remediation, yet their application remained constrained by challenges including the dependence on continuous H 2 O 2 supplementation, limited catalyst reusability, and insufficient mechanistic understanding of antibiotic degradation. This study developed a pH-universal heterogeneous electro-Fenton system using an in-situ synthesized Fe@Fe 2 O 3 /active carbon fiber (ACF) composite cathode for sulfadiazine (SDZ) removal from wastewater. Under optimal conditions (pH of 2-3, current density of 20 mA/cm 2 , aeration rate of 0.6 L/min, and electrolyte concentration of 0.05 mol/L Na 2 SO 4 ), the removal efficiency of SDZ achieved 90.0 % ± 0.6 % and the corresponding removal rate was as high as 22.4 ± 0.1 g/(m 3 ·h). Notably, the Fe@Fe 2 O 3 /ACF composite cathode demonstrated exceptional stability with minimal iron leaching of 18.2 ± 0.6 μg/L in each cycle. Cross-scale mechanism validation, which integrated radical scavenging experiments, electron spin resonance spectroscopy, density functional theory, and intermediates analysis, revealed that hydroxyl radicals (·OH) was the exclusive reactive species driving SDZ degradation and that the preferential substitution of the free amino group and cleavage of the pyrimidine ring were critical steps in intermediate formation. This work advanced the mechanistic understanding of Fenton-based antibiotic degradation while providing a sustainable strategy for stable catalytic system design.