Reductive Degradation of Florfenicol by Electrogenerated Hydrated Electrons via the Electron Tunneling Effect

Degradation of fluorinated organic pollutants remains a challenge due to the strong electronegativity of fluorine and the high structural stability of C-F bonds. Advanced reduction processes (ARPs) based on strong reducibility of hydrated electrons (e_aq^-) are effective for destroying recalcitrant fluorinated organic pollutants. Ultraviolet (UV) photolysis is a frequently used method for producing e_aq^-, but it is limited by the need for chemical addition and light-shielding effects. This study reported the generation of e_aq^- via electron tunneling based on the n⁺Si/Al₂O₃ cathode with a metal-insulator-semiconductor (MIS) structure for the rapid reductive degradation of a halogenated emerging pollutant (florfenicol, FLO). The results demonstrate that the n⁺Si/Al₂O₃ cathode achieved 97.5% degradation (30 min), accounting for 92.3% defluorination and 97.0% dechlorination (120 min). The electrogenerated e_aq^- was responsible for the degradation and dehalogenation of FLO, as indicated by electron spin resonance (ESR) measurements, scavenger experiments, and electrochemiluminescence (ECL) tests. The theoretical calculations revealed the occurrence of electron tunneling on the thin Al₂O₃ film at the n⁺Si/Al₂O₃ cathode, where the tunneling electron jumped to the water to form e_aq^-. The ARPs based on electrogenerated e_aq^- also demonstrated efficient degradation of chloramphenicol (CAP), hydroxychloroquine (HCQ), and levofloxacin (LVF). This study not only provides a simple approach to e_aq^- generation via the electron tunneling effect but also suggests a possible strategy for developing ARPs to remove halogenated emerging organic pollutants in water.