Spatiotemporal Magnetic Decoupling Directs Spin-Dependent Cascade ROS Evolution for Electro-Fenton Water Decontamination

Abstract

Heterogeneous electro-Fenton (HEF) systems hold great potential for decentralized water purification, yet concurrently achieving high catalytic activity, structural stability, and controlled reactive oxygen species (ROS) selectivity remains challenging. Herein, we propose a spatiotemporal magnetic decoupling strategy to concurrently address these design objectives. The carbon shell spatially separated exterior Fe⁰ satellites from the FeN_x core, eliminating deleterious short-range magnetic quenching and altering the local magnetic environment to modulate the internal Fe(III) spin state. The resulting low-spin Fe(III) sites suppressed electron back-donation into the H₂O₂ σ∗ antibonding orbital, favoring an additional ¹O₂ generation pathway. Spatial decoupling also enabled a gradient cascade activation of H₂O₂ across the Fe⁰ and FeN_x domains, synergistically boosting the evolution of both ^•OH and ¹O₂, with steady-state concentrations reaching 18.25 and 5.27 μM, respectively. Consequently, the FeN_x@C–Fe⁰-based HEF achieved complete naproxen degradation within 60 min with significantly suppressed Fe leaching (0.85 mg L^–1), outperforming all comparative systems. Comprehensive characterizations and density functional theory (DFT) calculations established a definitive relationship between topological engineering and spin-state dynamics. Furthermore, the system demonstrated proof-of-concept applicability in real hospital wastewater, highlighting the potential of spatiotemporal spin-state engineering for regulating ROS evolution in HEF systems.