Enhanced peroxymonosulfate activation process based on homogenously dispersed iron and nitrogen active sites on a three-dimensional porous carbon framework

Developing transition metal/nitrogen/carbon catalysts with maximizing the dispersion degree of the active sites presented an enticing prospect for environmental remediation. In this study, we have designed the novel three-dimensional porous carbon aerogel (CA) supported iron and nitrogen co-doped carbon (FeNC-CA) catalysts via facile pyrolysis of iron phthalocyanine (FePc) confined within CA precursor by the double fixed-protection strategy. The synergistic enhancement effect between CA and well-dispersed FeNC in FeNC-CA-500 (pyrolysis at 500 °C) was conducive to the rapid removal of 4-chlorophenol (4-CP) via peroxymonosulfate activation, which achieved almost 100% removal efficiency and 66.8% mineralization rate in 18 min with ultralow catalyst dosage and iron ions leaching of 0.019 ppm, and the reaction rate constant was about 11.3, 9.3 and 6.6 times higher than that of the homologous FeNC-500, CA-500 and Fe-CA-500 catalysts, respectively. Based on the electrons spin resonance (ESR) and radical quenching experiments, the FeNC-CA-500/PMS system with selective removal ability of several aromatic compounds containing different substituents and strong flexibility in actual wastewater involving competing inorganic ions and natural organic matter confirmed that the nonradical pathway was dominant in 4-CP removal while the generated reactive oxygen species (ROS) played a relatively small roles. Further investigations by X-ray photoelectrons spectroscopy (XPS) and control experiments verified that the evenly dispersed iron active sites were essential in accelerating the catalytic reaction, and the carbon matrix and surface nitrogen sites were mainly responsible for the removal rate of 4-CP via nonradical pathway. These findings provided new insights for synthesis of a more promising iron-based catalyst for practical wastewater treatment.