Activation of peroxymonosulfate by single-atom Fe-g-C3N4 catalysts for high efficiency degradation of tetracycline via nonradical pathways: Role of high-valent iron-oxo species and Fe–Nx sites

A Fenton-like catalyst was prepared based on isolated Fe single-atom and Fe clusters anchored onto a g-C3N4 framework. It exhibited high activity and stability in the heterogeneous activation of peroxymonosulfate (PMS) for tetracycline (TC) degradation. Both experimental and density functional theory calculation results demonstrated that the unique N-coordinated single Fe atom (Fe–N4) served as active sites with optimal binding energy for PMS activation. The experimental analysis indicated that the single Fe atoms displayed superior catalytic activity to Fe clusters. Furthermore, both high-valent iron-oxo species and single oxygen-dominated nonradical processes caused TC degradation. Among them, single Fe atoms anchored onto Fe-g-C3N4 served as Fe–N4 reactive sites can directly activate PMS to produce high-valent iron-oxo species, which was the key active nonradical species causing TC degradation.