H₂O₂-independent oxygen activation via proton-coupled electron transfer for selective hydroxyl radical generation

Ambient activation of molecular oxygen (O₂) into hydroxyl radicals (•OH) constitutes an elementary stage in green oxidation chemistry. However, conventional strategies that heavily rely on H₂O₂ represent great bottlenecks in sluggish O-O bond cleavage and poor •OH selectivity. Herein, we report an H₂O₂-independent O₂ activation pathway for robust •OH formation, though a transient iron-peroxo intermediate (surface-bound Fe-•OOH) on zero-valent iron (ZVI). This critical Fe-•OOH intermediate is formed from the oxalic acid (OA)-mediated proton-coupled electron transfer (PCET) of O₂, where OA, dual-functioning as electron acceptor and proton donor, can alter O₂ adsorption on Fe sites from a bridging mode into an end-on one, facilitating its direct mono-hydrogenation into Fe-•OOH. The asymmetric Fe-•OOH then undergoes facile O-O bond heterolysis, generating •OH with a high yield rate of 155.3 µmol L⁻¹ h⁻¹ and selectivity of 85.6%. In a structure-activity relationship investigation, the surface-coordinated organic carboxylic acids with available α-hydrogen atoms are determined as ideal reagents to initiate PCET for Fe-•OOH formation. This work provides a proof-of-concept scenario for efficient H₂O₂-independent O₂ activation and offers a sustainable alternative for green oxidation.