The overlooked role of different Fe-N4Cx configuration in single atom catalyst for efficient peroxymonosulfate activation

The coordination environment between the metal center and ligands in single atom catalysts (SACs) is a curial factor influencing their catalytic activity. Herein, two types of Fe-centered SACs were synthesized for peroxymonosulfate (PMS) activation. The result showed that SACs enriched with pyrrolic ligands (Fe-N4C12) exhibited significantly higher PMS activation performance compared to those with pyridinic ligands (Fe-N4C10). Density functional theory (DFT) calculations revealed that electron delocalization in pyrrolic ligands is more effective, rendering a stronger reactivity of Fe in Fe-N4C12. The adsorption of PMS onto Fe-N4 sites regulated the ligand field surrounding Fe from a square planar to a pseudo-octahedral field, thereby significantly activating the delocalization orbital. Pyrrolic ligands further maintained a lower d‐band center of Fe in the Fe-N4C12 configuration than Fe-N4C10 by pyridinic ligand. This led to a higher electron occupancy in antibonding band of Fe-N4C12 when PMS was adsorbed, and consequently, for better oxidation performance.