Construction of Fe3S4/PDA/HA composites with enhanced interfacial effect for photo-Fenton degradation of tetracycline: Mechanism and toxicity assessment

Antibiotic pollution in aquatic environments poses critical ecological and health risks worldwide. In this study, a novel Fe 3 S 4 /PDA/HA (FPA) composite was designed as a heterogeneous photo-Fenton catalyst for peroxymonosulfate (PMS) activation to degrade tetracycline hydrochloride (TCH). The FPA catalyst was synthesized through a solvothermal route combined with polydopamine (PDA) coating and humic acid (HA) functionalization. Characterizations revealed that PDA and HA modification effectively suppressed nanoparticle agglomeration, reduced iron leaching, broadened the visible-light response, and accelerated Fe 2 + /Fe 3+ redox cycling. Under visible-light irradiation, the FPA/PMS system attained 86.8% TCH removal and 45.6% total organic carbon mineralization within 60 min, with a pseudo-first-order rate constant (0.06658 min −1 ) 2.72-fold higher than that of pure Fe 3 S 4 . The catalyst maintained excellent catalytic activity over a wide pH range (2–10) and showed strong resistance to common coexisting anions. After five cycles, TCH degradation efficiency remained above 87%, confirming excellent reusability. Quenching tests and electron paramagnetic resonance demonstrated that •OH, •O 2 ⁻, SO 4 •⁻, and 1 O 2 were generated, with 1 O 2 acting as the predominant reactive oxygen species. Liquid chromatography–mass spectrometry revealed three TCH degradation pathways, and ECOSAR toxicity analysis verified that most intermediates exhibited lower toxicity than the parent compound. This work provides a promising and stable photo-Fenton catalyst for efficient degradation of antibiotic pollutants and offers new insights into advanced oxidation processes for wastewater remediation.