Elucidation of the mechanistic origin of spin-state-dependent P-doped Fe single-atom catalysts for the oxidation of organic pollutants through peroxymonosulfate activation

In this study, the Fe single-atom catalyst (Fe-NC) was decorated via electronic structure modulation strategy and P was introduced into the second shell layer to improve the ability for peroxymonosulfate (PMS) activation. The Fe-PNC exhibits outstanding activity for bisphenol A (BPA) oxidation ascribed to its unique coordination environment (Fe-N4P2) and high spin state in comparison with Fe-NC (Fe-N4, low spin state) supported by the experimental data and density functional theory (DFT) calculations. We demonstrate that the higher energy of Fe 3d orbitals could better overlap with the O 2p orbitals of PMS, facilitating the electron transfer from Fe sites to PMS. In addition, P doping lowered the splitting field energy of the ligand and the energy gap between the contaminant and the catalyst, accelerating the transfer electrons from the adsorbed contaminant to the Fe site, thus maintaining the high spin state of Fe site and improving the stability of catalysis.