Selective degradation of parachlorophenol using Fe/Fe3O4@CPPy nanocomposites via the dual nonradical/radical peroxymonosulfate activation mechanisms

Metal-carbon composite materials have been regarded as emerging catalysts for peroxymonosulfate (PMS) activation by combining the advantages of both parties. Nevertheless, these novel catalysts usually face the side effect of the complex water matrix, and the PMS activation mechanism need to be further clarified. Herein, we rational synthesized the Fe/Fe3O4@CPPy nanocomposites, and the catalytic performance of PMS activation was evaluated by parachlorophenol (4-CP) degradation. The elevated catalytic activity was observed in the optimal Fe/Fe3O4@CPPy-4/PMS system over a wide temperature (10–45 °C) and pH range (3–9), in which the 4-CP removal rate could achieve up to 98.64% within 10 min, as well as the low leakage of iron (49.0 μg/L). Notably, the normal concentrations of coexisting irons and humic acid in surface water matrix could hardly affect the 4-CP removal efficiency, demonstrating the superior selective oxidation capacity of Fe/Fe3O4@CPPy nanocomposites. A positive correlation was displayed between k values and the content of electron-rich carbonyl group (CO), and the pyridinic N, graphitic N and Fe species also participated in the 4-CP removal, which synergistically resulted in the outstanding performance. Moreover, the O2−, 1O2 and direct electron transfer pathways played a primary role in 4-CP elimination, whereas the SO4−/OH displayed the secondary contribution. Therefore, a dual non-radical/radical PMS activation mechanism was unveiled in the Fe/Fe3O4@CPPy-4/PMS system. This work not only provides a high-activity and well-adjusted PMS catalyst for complicated water matrix, but also elucidates PMS activation mechanism in the metal–carbon composite materials.