Bifunctional Catalyst ZVI@PDA Mediated the Reduction Coupling Oxidation Reaction of Triclosan to Achieve a High Mineralization Rate

Zerovalent iron (ZVI)-based advanced oxidation processes for dechlorination degradation of chlorophenol pollutants are limited due to the existence of highly electronegative chlorine atoms on benzene. This study developed a polydopamine (PDA)-coated ZVI bifunctional catalyst (ZVI@PDA) to undergo a sequential reduction–oxidation reaction for the degradation of triclosan (TCS). Results showed that the solution TOC decreased by 17.89 and 24.09% after the separate reduction and oxidation process of TCS, while the solution TOC decreased by 76.90% through the sequential reduction–oxidation process. Mechanism exploration showed that the only oxidation process was not conducive to the dechlorination and mineralization of TCS, and the oxidation products of TCS were mainly 3-Cl and 2-Cl products. The predechlorination of TCS catalyzed by ZVI@PDA via a hydrogen atom (H•) could form 2-Cl and 1-Cl products, which were more easily oxidized and mineralized into lower-molecular-weight products during the oxidation process. Density functional theory calculations also showed that the 2-Cl and 1-Cl products of TCS reduction were more prone to be oxidized to lower-molecular-weight products. Overall, these findings proposed a sequential reduction–oxidation strategy that could efficiently and harmlessly eliminate chlorinated organic chemicals in aquatic ecosystems.