Oxygen vacancies enhance the photocatalytic deep oxidation of NO over an N-doped KNbO3 catalyst

Abstract

N-Doped KNbO₃ (N-KNbO₃) was prepared through mechanical mixing, grinding and calcination of urea and KNbO₃. The photocatalytic NO oxidation performance was evaluated at room temperature and under visible light irradiation. Compared with the pristine KNbO₃, N-KNbO₃ not only has a better NO oxidation performance but also can effectively inhibit the formation of NO₂ (electron paramagnetic resonance). EPR tests showed that the doping of non-metallic element N created oxygen vacancies (OVs) on the surface of KNbO₃, which was beneficial to the formation of impurity energy levels to reduce the band gap. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that NO acquired electrons around OVs to form N₂O₂⁻ intermediates, which were then oxidized by reactive oxygen species (˙OH, ˙O₂⁻ and ¹O₂). Moreover, visible light can promote the activation of NO and O₂ and also the formation of OVs. This work provided a new idea for the design and preparation of N-doped photocatalysts for NO photocatalytic oxidation.