Catalytic activity enhancement by P and S co-doping of a single-atom Fe catalyst for peroxymonosulfate-based oxidation

High-valent iron–oxo species (FeV=O) generated through peroxide activation by Fe-based catalysts can realize the selective and efficient degradation of organic pollutants in water treatment. However, the rapid and efficient generation of FeV=O for the selective degradation of pollutants over a wide pH range with high stability is challenging. In this study, a N, P, and S co-doped Fe-single atom (SA) catalyst (FeSA[email protected]) with FeN4 active center was synthesized as a highly efficient catalyst for the peroxymonosulfate (PMS)-based oxidation. The FeSA[email protected] catalyst exhibited an excellent catalytic performance at low dosages of both the catalyst and PMS for the degradation of pollutants over a wide pH range with high stability. For the degradation of ofloxacin (OFX), the rate constant pertaining to PMS with FeSA[email protected] was 1.68 min−1, considerably higher than those obtained using the N-doped and N and P co-doped Fe-SA catalysts. The degradation pathway of OFX revealed that the electrostatic effect was of significance in its degradation by FeVN4=O with FeVN4=O being the dominant reactive species. Density functional theory calculations revealed that the heteroatom doping effectively altered the electronic structure of the FeN4 site of FeSA[email protected], which strengthen its coordination with PMS, promote the electron transfer to PMS, and facilitate the interaction between FeVN4 = O and OFX, and thus significantly enhanced its catalytic activity. These findings provide new insights into the oxidation mechanism of FeV=O in heterogeneous systems and the catalytic ability enhancement through heteroatom doping.