Superexchange-Assisted Fe(IV)=O Chain Formation on Scalable Iron Single-Atom Catalysts for Low-Chemical Water Purification in Flow.

Abstract

Polymerization-based wastewater treatment can couple decontamination with resource recovery at low energy input by transforming dilute organics into separable products. However, it requires selective oxidant activation, and iron, although abundant and industrially relevant, often forms metastable over-oxidizing adducts that suppress polymerization selectivity. Here, we design and synthesize a distance-tailored iron single-atom catalyst (Fe-SAC) featuring a coupled Fe₁-Fe₂ pair that enables sequential generation of reactive Fe(IV)═O species from peroxymonosulfate. Theory and experiments reveal that formation of the first Fe₁(IV)═O triggers a spin-state transition of the adjacent Fe₂ site to a high-spin configuration, while the finely tuned Fe₁─Fe₂ separation geometrically matches the O─O bond in the oxidant. This spin reconfiguration strengthens Fe─O covalency and promotes a superexchange-assisted pathway, leading to chain formation of Fe₂(IV)═O through bidentate axial bonding and site-to-site electronic coupling. In a continuous-flow reactor, the scalable Fe-SAC increases polymerization selectivity from 29.9% to 73.3% and boosts electron utilization from 156.8% to 443.8%. Life-cycle and techno-economic analyses further indicate ∼88% and ∼79% reductions in environmental impacts for catalyst synthesis and operation, respectively, together with an estimated ∼90% decrease in pollutant removal cost. This work establishes a design principle to unlock selective Fe(IV)═O chemistry for low-chemical, polymerization-based water purification with engineering viability.