Effective degradation of 2,4,4′-trichlorodiphenyl by Fe3C@Fe-800 activated peroxymonosulfate: Superoxide radical and singlet oxygen-dominated advanced oxidation process

Polychlorinated biphenyls (PCBs) degradation by peroxymonosulfate (PMS) activation through •OH and SO4•- radical oxidation process was the effective technology in the last decades; however, there were few research focusing on removing PCBs by O2•- and 1O2 induced by PMS activation. In this work, 90.86% of 2,4,4-trichlorodiphenyl (PCB 28) was degraded by 0.3 g/L Fe3C@Fe-800 activated 0.5 mM PMS system under the synergistic action of O2•- and 1O2. The structures of Fe3C@Fe-800 were identified by Scanning electron microscope (SEM), High resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), Raman spectra and Fourier transform infrared (FT-IR) spectra. Electron paramagnetic resonance (EPR) measurements and quenching tests verified that O2•- and 1O2 were the primary reactive species in Fe3C@Fe-800/PMS/PCB 28 ternary reaction system. Density functional theory (DFT), Linear sweep voltammetry (LSV), and chronoamperometry test revealed that electron-deficient Fe atoms on Fe3C were the main active sites in Fe3C@Fe-800 for PMS activation to generate 1O2. Unlike the reported •OH and SO4•- mediated degradation induced by the iron-based catalyst, both O2•- and 1O2 contributed to PCB 28 degradation： nucleophilic dichlorination reaction by O2•- and then ring-open oxidation process by 1O2. Fe3C@Fe-800/PMS system had excellent catalytic performance under different reaction conditions and possessed desirable inorganic salt and natural organic matter resistance. This work elucidated the important role of Fe3C in PMS activation to generate O2•- and 1O2 for PCB 28 decontamination by nonradical way and provided a clue to design rationally catalysts in polychlorinated biphenyl pollution remediation.