Roles of graphitic N and Fe-Nx sites on persulfate non-radical activation for 2,4-dichlorophenol degradation by porous magnetic Fe–N–C catalyst

Abstract

Fe-N-C catalysts with magnetism were successfully synthesized through one-step heat treatment of ferrosoferric oxide and covalent organic frameworks composite (Fe3O4@COF) as heterogeneous catalysts for persulfate (PS) activation and 2,4-dichlorophenol (2,4-DCP) degradation. The morphologies, compositions and active sites were adjusted by changing the pyrolysis temperature. The catalyst prepared at 900 °C showed excellent activity with 2,4-DCP removal of 90% in 60 min, recycling convenience and regeneration stability. Large surface area (342 m2 g−1) and hierarchical porous structure benefited PS activation. It was proved that the radical and non-radical mechanisms coexisted in Fe-N-C-900/PS system with the results of quenching and electrochemical experiments. Roles of graphitic N and Fe-NX were distinguished. Graphitic N and Fe-NX sites palyed an prominent part in the non-radical activation process, in which Fe-NX was closely related to the electron transfer activation mechanism. Density functional theory (DFT) calculation further verified that the FeN2 was the key site for PS activation. 2,4-DCP degradation was proved to be a toxicity-attenuation process according to the biotoxicity analysis. The effects of several operating parameters and degradation of different model pollutants were also systematically evaluated, and possible activation mechanism was proposed.