Insights into the degradation mechanisms and pathways of cephalexin during homogeneous and heterogeneous photo-Fenton processes.

The widespread occurrence of antibiotics in the environment poses a potential threat to human health. The photo-Fenton process has demonstrated better degradation performance compared with the conventional wastewater treatment processes. In this study, the degradation of cephalexin was evaluated comparatively by homogeneous (Fe/HO/UV) and heterogeneous (MoS@Fe/HO/UV) photo-Fenton processes. Key influencing factors affecting photo-Fenton performance were assessed, confirming the optimum Fe concentration at 0.2016 mg L and HO/Fe molar ratio at 6. Higher degradation efficiency (73.10%) and pseudo-first-order degradation rate constant (0.0078 min) were achieved with the assistance of MoS@Fe as the heterogeneous catalyst. Completely different degradation products were identified in the homogeneous and heterogeneous photo-Fenton processes, with main degradation pathways proposed as β-lactam ring-opening, sulfoxide formation, demethylation, N-dealkylation, decarbonylation, hydroxylation and deamination in the Fe/HO/UV system and β-lactam ring-opening, hydroxylation, dehydration, amide hydrolysis, and demethylation and ring contraction in the MoS@Fe/HO/UV system, respectively. The formation of newly identified products might root in the attack on cephalexin from active species (i.e., OH, h, e, O) photoinduced by the MoS@Fe catalyst. Results also indicated the importance of understanding the underlying mechanisms and pathways to eliminate the antimicrobial activities of antibiotics in the future.