Insight on the heterogeneously activated H₂O₂ with goethite under visible light for cefradine degradation: pH...

The iron mineral-catalyzed degradation of cephalosporin antibiotics with H₂O₂ occurs ubiquitously in nature. Despite numerous studies, the effects of environmental conditions on reactive species production and degradation processes of cephalosporins remain unclear. Here, we report the iron mineral of goethite as the efficient and heterogenous catalyst for the degradation of cefradine (CRD) via H₂O₂ activation under different conditions involving pH and visible light irradiation. Results show that the CRD removal rate is highly dependent on pH and visible light irradiation. Interestingly, when the pH ranges from 4.0 to 7.0, the degradation intermediates of CRD under dark are the same as under visible light conditions in the goethite/H₂O₂ system. And, the ratio of CRD degradation rate constant (k_Light/k_Dark) reaches a maximum at pH 5.0, suggesting that CRD existing as zwitterion species is preferable for its removal with photoassistance. The mechanism investigation reveals that both •OH and ≡[Fe^IVO]²⁺ oxidants are generated during the reaction process, and •OH is the major oxidant at acidic pH, while ≡[Fe^IVO]²⁺ is more likely to be formed with photoassistance at near-neutral pH. According to UPLC-MS/MS analysis, CRD degradation likely happens via hydrogen atom abstraction from cyclohexadienyl by •OH, thioether and olefin oxidation by ≡[Fe^IVO]²⁺, and Fe^III-catalyzed hydrolytic cleavage of β-lactam ring. These findings highlight the vital roles of pH and photoassistance in the heterogeneously activated H₂O₂ with goethite for CRD degradation.