Optimal Oxophilicity at the Fe-N_x Interface Enhances the Generation of Singlet Oxygen for Efficient Fenton-Like Catalysis

In the pursuit of efficient singlet oxygen generation in Fenton-like catalysis, the utilization of single-atom catalysts (SACs) emerges as a highly desired strategy. Here, a discovery is reported that the single-atom Fe coordinated with five N-atoms on N-doped porous carbon, denoted as Fe-N₅/NC, outperform its counterparts, those coordinated with four (Fe-N₄/NC) or six N-atoms (Fe-N₆/NC), as well as state-of-the-art SACs comprising other transition metals. Thus, Fe-N₅/NC exhibits exceptional efficacy in activating peroxymonosulfate for the degradation of organic pollutants. The coordination number of N-atoms can be readily adjusted by pyrolysis of pre-assembly structures consisting of Fe³⁺ and various isomers of phenylenediamine. Fe-N₅/NC displayed outstanding tolerance to environmental disturbances and minimal iron leaching when incorporated into a membrane reactor. A mechanistic study reveals that the axial ligand N reduces the contribution of Fe-3d orbitals in LUMO and increases the LUMO energy of Fe-N₅/NC. This, in turn, reduces the oxophilicity of the Fe center, promoting the reactivity of *OO intermediate—a pivotal step for yielding singlet oxygen and the rate-determining step. These findings unveil the significance of manipulating the oxophilicity of metal atoms in single-atom catalysis and highlight the potential to augment Fenton-like catalysis performance using Fe-SACs.