Oxygen Vacancy-Dependent Reactive Oxygen Species Generation over Defect-Engineered Bi ₂ O ₃ for Efficient Visible Light-Driven NO Deep Oxidation

Oxygen-vacancy engineering was exploited to create vacancy-rich Bi2O3 nanosheets (denoted Defect-BO) by in situ pyrolysis under an inert atmosphere, alongside vacancy-free Bi2O3 (denoted BO) calcined in air. Defect-BO achieved a high NO removal rate of 38% and long stability under visible-light (λ ≥420 nm) irradiation while strongly suppressing toxic NO2 formation and retaining activity over repeated cycles. Besides, the surface oxygen vacancies serve both as low-energy adsorption-activation sites (stabilizing an NO+ intermediate) and as localized defect states that lower the excitation energy, favor triplet-exciton formation, and enable efficient energy transfer to adsorbed O2, thereby generating singlet oxygen (1O2). The simultaneous production of 1O2 and hydroxyl radicals (•OH) drives a synergistic pathway in which NO is rapidly oxidized to nitrate, avoiding NO2 accumulation. Electron-paramagnetic-resonance and O2-TPD experiments confirm fast, vacancy-mediated O2 activation, whereas in situ DRIFTS tracks the evolution of NO+, NO2–, and NO3– surface species, validating the proposed mechanism. Continuous regeneration of 1O2 sustains reactive oxygen species (ROS) levels, accounting for the catalyst’s durability. This work discloses a previously unrecognized oxygen-activation route and furnishes a design principle for highly efficient, selective photocatalysts for gaseous pollutant abatement.