Asymmetric Coordination-Engineered High-Spin Iron Single-Atom Catalysts Facilitating 3d-2p Orbital Hybridization for Superior Persulfate Activation

Here, we present a single-atom iron catalyst embedded in a crystalline carbon nitride framework (Fe-CCN-H) that demonstrates exceptional efficiency in activating persulfate (PDS) to degrade recalcitrant emerging contaminants. Such high activity is due to the strong interactions between the 3d-orbitals of the asymmetric low-coordination Fe and the σ*2p orbitals of PDS.

In situ electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), Raman spectroscopy, and density functional theory (DFT) calculations reveal that Fe 3dyz orbitals interact with σ* orbitals of S=O bonds in PDS to enhance PDS adsorption, while Fe 3dxz orbitals effectively drive PDS conversion to ·SO4−. Concurrently, electron transfer from adsorbed water molecules through the carbon nitride lattice to Fe 3dx2−y2 orbitals generates hydroxyl radicals (·OH), enabling synergistic oxidation by ·SO4− and ·OH.