Strong enhancement on electron transfer pathway of peroxymonosulfate activation for rapid organic pollutant degradation in wastewater by iron encapsulated into nitrogen-doped carbon: Iron-cores as electron supply stations

Developing high-performance non-radical degradation systems is a valuable strategy to solve the inefficiency of free radical systems in complex aqueous conditions. In this paper, nitrogen-doped carbon materials encapsulating iron-based nanoparticles (Fe@CPAnPyX) were prepared by carbonizing polyaniline-polypyrrole copolymer precursors. Fe@CPAnPyX exhibited outstanding peroxymonosulfate (PMS) catalytic activity and could rapidly degrade 97.40 % of 2,4-dicholophenol (100 mg/L) within 6 min, with kinetic constant reaching 17.2 times than that of CPAnPyX without iron. Adequate reaction pathway investigations showed that, unlike most reported Fe-carbon composites, the Fe@CPAnPyX/PMS system is dominated by electron transfer pathway (97.60 %) after encapsulation of iron-based nanoparticles. The antitheses analysis, structure–activity relationship analysis and density functional theory calculations validated that the N-doped carbon shell, rich in defect and graphitic nitrogen, is the direct component involved in the reaction, while the internal iron core mainly acts as an auxiliary component significantly facilitating the electron transfer pathway by enhancing the overall conductivity and coulomb field of the material and serving as “electron resupply stations” for the external carbon shell. Benefiting from the enhanced non-radical pathway, the Fe@CPAnPyX/PMS system exhibits wide pH applicability (pH = 3.00–11.00), strong resistance to water matrixes, significant electron-rich pollutants selectivity and good reusability (92.58 % degradation efficiency was maintained in the seventh cycle). A custom-made catalytic membrane device exhibited good sustained operational stability, showing a good practical application prospect. This study provides an effective strategy to significantly enhance the non-free radical pathway of carbon-based materials, which promotes the application of non-free radical systems in complex wastewater.