Oxygen-Vacancies-Bridged Cu2O/Cu Heterojunction Enables Closed-Loop Electron Cycling for Bidirectional Peracetic Acid Activation in Fenton-like Reactions

Integrating the strong oxidative capacity of radicals with the high selectivity of nonradicals is crucial for efficient pollutant degradation under complex aqueous conditions. However, conventional peroxide activation relies on unidirectional electron utilization, where a single oxidant molecule typically generates only one reactive species, thereby limiting oxidant utilization and electron recycling. Herein, we employ oxygen vacancies (Vo) to bridge asymmetric electronic sites at the Cu2O/Cu heterojunction, achieving bidirectional activation of a single peracetic acid (PAA) within a "closed-loop electron cycle" to simultaneously generate •OH and nonradical active species (NRS). Vo-induced electron delocalization forms continuous electronic levels that facilitate Cu2O→Cu electron transfer, leading to electron enrichment at Cu sites and depletion at Cu2O sites. This electronic asymmetry, coupled with the unoccupied orbitals inherent to Vo, enables a thermodynamically favorable dual-coordination (Cu-(C═Oα) and Cu2O-(Oβ-Oγ), Eads = -3.74 vs -0.79 eV) of a single PAA (CH3-C(Oα)-Oβ-Oγ-H) with Vo-Cu2O/Cu. Driven by the electron-inductive effect, electrons are transferred from Cu to Oβ-Oγ via C═Oα, triggering Oβ-Oγ homolysis to generate •OH and a metastable NRS. The latter extracts electrons from organics via Cu2O to initiate the direct electron-transfer pathway (ETP, ∼46.90%, ΔE = -1.314 eV), thereby achieving a "closed-loop electron cycle". Unlike conventional unidirectional catalytic pathways, bidirectional activation within a single PAA molecule boosts synchronous enhancement in oxidation-mineralization synergy (∼33-fold increase in k2,O and ∼1.5-fold increase in TOC removal), PAA utilization efficiency (∼1.5-fold increase), and superior resistance to water matrix interference. This previously unrecognized oxidant activation mechanism offers new insights into coupling radical and nonradical pathways via interfacial electron-flow regulation for efficient and energy-saving water remediation.