Novel zero-valent Co-Fe encapsulated in nitrogen-doped porous carbon nanocomposites derived from CoFe2O4@ZIF-67 for boosting 4-chlorophenol removal via coupling peroxymonosulfate.

Environment-friendly treatment process relies on the robustness, durability, and performance of catalysts to drive the development of cutting-edge sustainable technologies for the elimination of refractory contaminants. Herein, nanocomposites prepared from zero-valent Co-Fe encapsulated in nitrogen-containing carbon (NC) nanoparticles (CFNC-30 NPs) derived from CoFe2O4@zeolitic imidazolate frameworks-67 were successfully prepared through pyrolysis integrated with self-reduction, and further utilized as the novel catalysts to degrade 4-chlorophenol (4-CP) by coupling with peroxymonosulfate (PMS). Three optimized parameters (CFNC-30 NPs dosage of 0.089 g L-1, PMS concentration of 1.1 g L-1, and initial pH of 6.6) were obtained via response surface methodology by using the Box-Behnken design model. Benefiting from the larger specific surface area, pore-volume, and existence of abundant hydroxyl groups, CFNC-30 NPs with more available active sites exhibited an excellent efficiency of 99.1% toward catalytic degradation of 4-CP within 30 min under the optimal conditions. Moreover, CFNC-30 NPs demonstrated durability and long-term stability even during the five consecutive cycle tests without a significant drop in its catalytic performance. The scavenging experiments and electron paramagnetic resonance technologies revealed that non-radical singlet oxygen (1O2), sulfate radicals (SO4-), and hydroxyl radicals (HO) were involved as active species in the CFNC-30/PMS system, contributing 46.8, 35.6, and 17.6% efficiency toward 4-CP degradation, respectively. Besides, the reaction mechanism on the CFNC-30 NPs and degradation pathways toward 4-CP were speculated under PMS activation. The results indicated that the synergistic effects between zero-valent Co-Fe and NC structures not only significantly boosted the removal efficiency and long-term stability of CFNC-30 NPs, but also facilitated the redox cycles of Co3+/Co2+ and Fe3+/Fe2+. This proof-of-concept approach to develop such high-efficient zero-valent Co-Fe encapsulated in NC structures opens up novel avenues for wastewater decontamination via PMS activation.