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

Abstract

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 lightshielding effects. This study reported the generation of e aq − via electron tunneling based on the n + Si/Al 2 O 3 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/ Al 2 O 3 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 Al 2 O 3 film at the n + Si/Al 2 O 3 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.