Oxygen vacancies enhanced photocatalytic removal of NO over N-doped TiO2 catalyst

In this study, non-metallic N doped TiO2 photocatalyst (N-TiO2) fabricated by a facile co-deposition methods with the use of the titanium isopropoxide (Ti(OC3H7)4) and ammonia as precursors exhibited a superior photocatalytic activity and selectivity to pure TiO2 on the degradation of NO under visible light irradiation at room temperature. The results of in-situ diffuse reflectance infrared Fourier transform spectra (in-situ DRIFTS) suggested that the NO was mainly adsorbed at Ti4+ sites and then formed the NO+ active intermediates under visible light illumination. The co-adsorption of NO and molecule oxygen results indicated that the generation of NO3- product over N-TiO2 was mainly attributed to the interaction between NO species adsorbed on catalyst surface and active oxygen (O-) rather than surface hydroxyl. Moreover, The UV-vis diffuse reflectance spectra (DRS), the Photoluminescence (PL) and the photocurrent and Electron paramagnetic resonance (EPR) results showed that TiO2 doped with N atoms not only enhanced the utilization efficiency of photo-generated charge carriers, but also promoted the formation of surface defects (e.g. oxygen vacancies) under visible light irradiation . Combined with this X-ray photo-electron spectroscopy (XPS) and the O2 temperature-programmed desorption (O2-TPD) measurements analysts, it was found that oxygen vacancies not only facilitated the absorption and activation of molecule oxygen but also acted as a bridge between molecule oxygen and lattice oxygen in catalyst (Ti4+↔Ti3+), which resulted in an outstanding oxygen circulation between Ti4+ and Ti3+ sites during NO oxidation process under visible light irradiation. Thus, an enhanced NO removal efficiency and photocatalytic stability for NO oxidation occurred on N-TiO2.