Anchoring Iron Single Atoms into Ordered Mesoporous C3N4@N-C Hybrids for Efficient Peroxymonosulfate Activation: Simultaneous Substrate and Pore Structure Modulation.

Carbon nitride-supported single-atom catalysts have shown considerable promise in activating peroxymonosulfate (PMS) for pollutant removal. However, constructing an ordered mesoporous structure to increase the accessible surface area and maximize the utilization of reactive species remains a challenge. In this study, a single-atom Fe catalyst confined in a mesoporous C3N4@N-C hybrid support (denoted as Fe-C3N4@N-C) was synthesized via a facile solvent-free nanocasting strategy. The catalyst comprises atomically dispersed Fe-N4 sites in C3N4@N-C hybrids with enhanced interfacial electron transfer. Faithful replication of the silica template imparted ordered mesoporous architecture with a high surface area (∼462 m2/g) and a large pore volume (0.46 cm3/g). The optimized catalyst exhibited superior performance in degrading bisphenol A (BPA), achieving nearly complete removal (>99%) within 20 min and a mineralization rate of ∼77% within 60 min. The degradation rate constant was 1 order of magnitude greater than that of the mesoporous Fe-C3N4 (prepared using Dicyandiamide as a precursor) and 2 orders of magnitude higher than that of a nonporous reference sample. Mechanistic studies revealed a nonradical degradation pathway dominated by singlet oxygen (1O2) and electron transfer, which conferred strong anti-interference capability, broad pH adaptability and excellent stability under continuous-flow conditions. Density functional theory calculation reveals that the Fe-N4 sites within the cavity of C3N4 serve as dominant active sites for PMS activation and the ordered mesoporous structure facilitates their accessibility.