N-doped Carbon Nanosheets Supported-single Fe Atom For P-nitrophenol Degradation Via Peroxymonosulfate Activation

Fenton-like reactions with persulfates as the oxidants have attracted increasing attentions for the remediation of emerging phenolic organic pollutions.Among them,peroxymonosulfate（PMS） activation is one of the most effective advanced oxidation processes owing to the generated reactive oxygen species（ROS）with high oxidation capacity,such as hydroxyl radicals （·OH）,sulfate radicals （SO4·-）,superoxide radical （O2·-） and singlet oxygen （¹O₂）.In recent years,single-atom catalysts （SAC）,with active metal sites dispersed in the single-atom state,shows excellent structural stability and catalytic activity has attracted wide interest for environmental remediationcatalytic reactions.Especially single Fe atom catalysts with a high density of Fe Nx active site,have attracted the researchers’ attention due to their high atomic utilization,local coordination active sites,low metal leaching and good catalytic performance.Therefore,the design of highly active,stable,and cost-effective catalysts for environmental applications is critical for sustainable development.In this study,Single Fe atoms dispersed on N-doped carbon nanosheets（NC） was synthesized and employed as efficient catalyst to degrade PNP via PMS activation.The surface morphology and crystal structure of the FeSA samples were characterised by scanning electron microscopy（SEM）,transmission electron microscope（TEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.High-angle annular dark-field scanning transmission electron microscopy（HAADF-STEM）results show that Fe species in FeSA are mainly single atom Fe.Compared with traditional iron nanoparticle catalysis（Fe NP）,the FeSA catalyst exhibits high activity and stability in the heterogeneous activation of PMS for organic pollutant degradation,showing an outstanding turnover frequency of greater than 6.04? min-1,99% degradation within 5 min and 71.12% TOC removal efficiency.X-ray absorption near-edge structure（XANES） and density functional theory（DFT）calculations suggest that the unique N-coordinated single Fe atom（Fe N4） serves as a highly catalytically active site for PMS activation.The results of our degradation experiments indicated that FeSA exhibited remarkable catalytic activity for the PNP degradation in complex water bodies containing different anions and humic acids and over a wide pH range.Quench tests and electron paramagnetic resonance（EPR）spectroscopy indicated that O2·- and ¹O₂ were the main oxidative active species in the FeSA/PMS system for PNP degradation.The degradation products of the reaction were analysed by High Performance Liquid Chromatography-Mass Spectrometry（HPLC-MS）,and possible degradation pathways for the PNP degradation were proposed.In addition,DFT was used to analyze the degradation mechanism of PNP in Fe SA/PMS system,charge transfer existed between Fe N4 sites on the main Fe SA surface and PMS,the charge transfer between Fe N4 sites on the main Fe SA surface and PMS accelerated the degradation of PNP into small molecule compounds and then further mineralized into CO2 and H2 O.Moreover,the iron leaching rate is only4%,which is difficult to cause secondary pollution to the waterbodies.