Development of Fe-doped g-C3N4/graphite mediated peroxymonosulfate activation for degradation of aromatic pollutants via nonradical pathway

A new composite catalyst, i.e., Fe doped g-C3N4/graphite (Fe-CN/G), was successfully constructed to activate peroxymonosulfate (PMS) for efficient phenolic compounds (i.e., p-chlorophenol, 4-CP) degradation in the pH range of 3-10. The optimized Fe-CN/G, i.e., Fe3.75-CN/G5.0, was fabricated at the dosage of 3.75 mmol FeCl3·6H2O, 5.0 g dicyandiamide, and 5.0 mmol glucose. Fe complexed in the nitrogen pots of Fe3.75-CN/G5.0 was demonstrated to be the primary active site for PMS activation, and the introduction of graphite favored the exposure of more accessible active sites in Fe3.75-CN/G5.0, suggesting a synergistic effect between the Fe and graphite of Fe3.75-CN/G5.0 on 4-CP degradation. Multiple experiments confirmed that sulfate radical (SO4-), hydroxyl radical (HO), singlet oxygen (1O2) and superoxide radical (O2-) exerted negligible contribution on 4-CP degradation. The in-situ Fe K-edge X-ray absorption near-edge structure (XANEX) analysis revealed a redox cycle of Fe in PMS/Fe3.75-CN/G5.0, suggesting the formation of high-valent iron-oxo species (FeIVO) was responsible for 4-CP degradation. In addition, PMS/Fe3.75-CN/G5.0 exhibited acceptable degradation of 4-CP in the presence of coexisting anions and natural organic matters (NOM). We believe this study provides new insights into the design and development of Fe-based heterogeneous catalysts for PMS-based wastewater treatment.