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

The iron mineral-catalyzed degradation of cephalosporin antibiotics with H 2 O 2 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 H 2 O 2 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/H 2 O 2 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 ≡[FeIVO]2+ oxidants are generated during the reaction process, and •OH is the major oxidant at acidic pH, while ≡[FeIVO]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 ≡[FeIVO]2+, and FeIII-catalyzed hydrolytic cleavage of β-lactam ring. These findings highlight the vital roles of pH and photoassistance in the heterogeneously activated H 2 O 2 with goethite for CRD degradation. [Display omitted] • The degradation rate of cefradine by goethite/H 2 O 2 system highly depends on pH and visible light irradiation. • Cefradine degradation intermediates under dark are the same as under visible light in goethite/H 2 O 2 system at pH 4.0–7.0. • Photo-assisted effect reaches a maximum when cefradine exists as zwitterions at pH 5.0 in goethite/H 2 O 2 system. • Both •OH and ≡[FeIVO]2+ are the oxidants under dark and visible light conditions in goethite/H 2 O 2 system at pH 4.0–7.0. • Three degradation pathways of cefradine in goethite/H 2 O 2 system were found, i.e. H abstraction, oxidation, and hydrolysis. [ABSTRACT FROM AUTHOR]