Synergistic oxidative–reductive degradation of florfenicol by active sulfur sites on Cu-doped zero-valent iron: mechanistic insights into redox synergy

The complete dehalogenation and mineralization of halogenated organic pollutants have consistently posed a significant technical challenge in detoxification processes. The redox synergistic system effectively reduces the production of highly toxic, small molecular halogenated hydrocarbons during mineralization. The synergistic activation of sulfites by zero-valent iron‑copper materials enables rapid removal of efficiently eliminate florfenicol (FF), however, a comprehensive understanding of the mechanism is lacking. Here, we employed experimental data and density functional theory calculations to demonstrate that the synergistic degradation of FF is an interdependent and interconnected process. Specifically, the reduction process primarily follows the sequence of chlorine removal followed by fluorine removal, while the oxidation process primarily involves three key reaction sites at C11, C17, and C20, where hydroxyl substitution reactions occur. Notably, the dehalogenation process reduces the activation energy required for oxidation. The activation energy for the oxidation reaction at the C17 position is 6.34 kcal/mol, whereas after dehalogenation, it decreases to 5.84 kcal/mol at the same site. Oxidation also affects the distribution of internal charge density within the molecule, thereby influencing the dehalogenation reaction. Furthermore, both toxicity predictions and experimental results indicate that the substances produced by synergistic degradation exhibit significantly lower toxicity than those generated by oxidation alone. The degradation mechanism of FF by the redox synergistic system provides valuable insights into the detoxification of halogenated organic compounds.