Generation of Fe IV =O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst.

Generating Fe IV =O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the Fe IV =O generation pathway and oxidation behavior remain obscure. Employing an Fe-N-C catalyst with a typical Fe-N 4 moiety to activate peroxymonosulfate (PMS), we demonstrate that generating Fe IV =O is mediated by an Fe-N-C-PMS* complex-a well-recognized nonradical species for induction of electron-transfer oxidation-and we determined that adjacent Fe sites with a specific Fe 1 -Fe 1 distance are required. After the Fe atoms with an Fe 1 -Fe 1 distance <4 Å are PMS-saturated, Fe-N-C-PMS* formed on Fe sites with an Fe 1 -Fe 1 distance of 4-5 Å can coordinate with the adjacent Fe II -N 4 , forming an inter-complex with enhanced charge transfer to produce Fe IV =O. Fe IV =O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential.