Performance and mechanism of carbamazepine removal by FeS-S2O82− process: experimental investigation and DFT calculations

As persulfate (S 2 O 8 2− ) is being increasingly used as an alternative oxidizing agent, developing low-cost and eco-friendly catalysts for efficient S 2 O 8 2− activation is potentially useful for the treatment of wastewater containing refractory organic pollutant. In this study, the degradative features and mechanisms of carbamazepine (CBZ) were systematically investigated in a novel FeS- S 2 O 8 2− process under near-neutral conditions. The results exhibited that CBZ can be effectively eliminated by the FeS-S 2 O 8 2− process and the optimal conditions were: 250 mg/L FeS, 0.5 mmol/L S 2 O 8 2− , and pH = 6.0. The existence of Cl − (1 and 50 mmol/L) has little influence on the CBZ elimination, while both HCO 3 − and HPO 4 2− (1 and 50 mmol/L) significantly suppressed the CBZ removal in the FeS-S 2 O 8 2− process. CBZ could be degraded via a radical mechanism in the FeS-S 2 O 8 2− process, the working radical species (i.e., SO 4 •− and •OH) were efficiently formed via the promoted decomposition of S 2 O 8 2− by the surface Fe 2+ on the FeS and the dissolved ferrous ions in solution. Based on the identified oxidized products and Fukui index calculations, a possible degradation pathway of CBZ was speculated. More importantly, a two-stage oxidation mechanism of CBZ elimination was speculated in the FeS-S 2 O 8 2− process, the activation of S 2 O 8 2− by the surface-active Fe (II) of FeS dominated in the initial 5 min, while homogeneous oxidation reactions played more essential parts than others in the following reaction stage (5–60 min). Overall, this study demonstrated that the FeS-S 2 O 8 2− process is capable of removing CBZ from water efficiently.