Layered-confinement steering of single-atom Fe-N3O1 sites in carbon nitride for peroxymonosulfate activation: Tuning coordination geometry toward 1O2/•O2− selective generation

Modulating the coordination environment of single-atom catalysts (SACs) and designing architectures to maximize the exposure of active sites are pivotal strategies for enhancing peroxymonosulfate (PMS) activation. The fabrication of single-atom‑iron catalysts on support with particular coordination is essential but still remains challenge. Herein, we proposed the construction of single-atom‑iron embedded in graphitic carbon nitride nanosheets (SA-Fe@C 3 N 4 ) catalyst. The layer-confined synthesis strategy realized the loading of single-atom irons and ultrathin C 3 N 4 nanosheet formation in the interlayer of layered template RUB-15. XANES analysis corroborated that the isolated iron atoms are coordinated with three nitrogen and one oxygen atoms (Fe-N 3 O 1 ). Notably, the single iron atoms within the SA-Fe@C 3 N 4 matrix serve as the predominant active sites for PMS activation. The catalyst exhibited exceptional activity for the degradation of sulfamethoxazole (SMX), achieving a mass-normalized rate constant ( k Fe ) of 1.54 × 10 5  min −1  mol −1 with high selectivity toward 1 O 2 /•O 2 − .Theoretical calculations revealed that the Fe-N 3 O 1 moiety accelerated the PMS adsorption and reduced energy barriers for the activation of PMS, thus produce key *O intermediate SO 5 •- and form 1 O 2 /•O 2 − with nearly 100% selectivity. This study supplied a simple avenue to fabricate single-atom‑iron on C 3 N 4 with regulated coordination for wastewater treatment.