Catalytic ozonation of penicillin G using cerium-loaded natural zeolite (CZ): Efficacy, mechanisms, pathways and toxicity assessment

A cerium-loaded natural zeolite (CZ) was synthesized for catalytic ozonation of penicillin G (PG) in this work. The effects of key factors including Ce loading mass, the initial solution pH, catalyst dosage and ozone dosage were elucidated. Under the optimal conditions: Ce loading mass = 4%, CZ dosage = 2 g/L, ozone dosage = 6 mg/min and the initial solution pH = 4.5, the removal efficiency of PG (50 mg/L in 1 L reactor) reached 99.5% after 15 min, and the total organic carbon (TOC) removal of PG solution reached 21.2% after 2 h. Meanwhile, the results of control experiments indicated that the PG degradation efficiency of CZ/O-3 system was higher than that of O-3 alone system. The CZ catalyst was characterized by TEM, SEM-EDS, XRD, BET and XPS. The results showed that the CZ catalyst retained the high mesopore framework of natural zeolite. Cerium oxide was successfully supported on the zeolite. Then, radical scavenging tests revealed that hydroxyl radical ((OH)-O-center dot) and superoxide radical (O-center dot(2)-) were the dominant reactive oxygen species (ROS) for PG degradation. Furthermore, fifteen species of PG degradation intermediates were found by ultra-high performance liquid chromatography coupled with hybrid quadrupole-orbitrap mass spectrometry (UHPLC/orbitrap-MS) and ion chromatography (IC). Also, two possible PG degradation pathways in the heterogeneous catalytic ozonation systems were proposed and the catalytic mechanism of CZ/O-3 system was analyzed in detail. Finally, the potential toxicity of the intermediates formed during the catalytic ozonation was examined, the toxicity decreased after 60 min. In brief, this study would provide a low-cost and efficient method for removing high concentration PG in solution.