Spin‐Dependent Generation of Surface‐Bound Radicals Toward Selective and Long‐Lasting Water Purification

ABSTRACT To address the self‐quenching and poor anti‐interference limitations of conventional free radical oxidation processes, this study develops an atomic engineering strategy to fine‐tune the spin state of α‐Fe 2 O 3 catalysts to modulate peroxymonosulfate (PMS) activation and selectively yield surface‐bound radicals. Specifically, Cu 2+ (3d 9 ) doping triggers Jahn‐Teller distortion, intensifying crystal field splitting and transitioning Fe spin state from high‐spin (e g = 2) to medium‐spin (e g = 1.38). The decreased electron density in the Fe‐e g orbital reduces σ* anti‐bonding interactions between Fe 3d and O 2p, thus strengthening adsorption and inducing moderate electron transfer to PMS. With electron co‐injection from Cu, the O‐O cleavage generates the surface‐bound SO 4 •− on Cu sites. While the 3d 10 of Zn 2+ has minimal impact on the crystal field, ensuring α‐Zn 0.1 Fe 1.9 O 3 in a relatively high‐spin (e g = 1.81), which promotes intense electron transfer to PMS to generate free SO 4 •− . Additionally, surface‐bound radicals endow the α‐Cu 0.1 Fe 1.9 O 3 /PMS 1.4‐fold higher aceclofenac removal k obs than α‐Zn 0.1 Fe 1.9 O 3 /PMS and superior anti‐interference capacity to water background factors, due to the extended lifespan, surface confined environment, and moderate oxidation potential of surface‐bound SO 4 •− . This study provides insights into the advanced design of spin‐regulated catalysts for surface‐bound radicals generation to secure both high oxidation and anti‐interference capacity in water purification processes.