Ultrafast degradation of oxytetracycline in a defect-rich MoS₂/PMS system: dual radical–non-radical pathways, toxicity mitigation, and explainable machine learning

Oxytetracycline (OTC), a persistent and poorly biodegradable antibiotic, is increasingly detected in aquatic environments, posing ecological and health risks. Herein, a defect-rich, Co-free MoS₂/PMS system enables ultrafast OTC removal, achieving >99% elimination within 5   min (k obs = 0.791   min⁻¹). The process remained highly efficient across pH 2–10 and in real waters containing natural organic matter and common inorganic ions, demonstrating strong robustness under complex water matrices. Radical-quenching and electron paramagnetic resonance (EPR) analyses confirmed that •OH was the dominant reactive oxygen species (ROS), accompanied by SO₄•⁻ and ¹O₂. X-ray photoelectron spectroscopy (XPS) evidenced Mo⁴⁺/Mo⁶⁺ redox cycling and the participation of surface sulfur species and lattice oxygen, which jointly facilitated PMS activation and ROS generation, thereby establishing a coupled radical-non-radical degradation mechanism. Liquid chromatography–mass spectrometry (LC–MS) identified sequential demethylation, deamination, and ring-opening intermediates, while QSAR-based ecotoxicity assessment indicated an overall decrease in predicted toxicity for most transformation products relative to OTC. Machine-learning analysis (XGBoost with SHAP interpretation) highlighted reaction time, PMS dose, and natural organic matter as the primary determinants of degradation efficiency. Overall, this work integrates a Co-free, light-independent MoS₂/PMS system, refined dual radical–non-radical mechanistic elucidation, comprehensive toxicity mitigation assessment and explainable machine learning, offering both mechanistic and engineering guidance for the sustainable treatment of antibiotic-contaminated wastewater.