Photoactive centers responsible for visible-light photoactivity of N-doped TiO2

Abstract

N-doped TiO 2 (anatase) with high visible light photoactivity was obtained by the thermal treatment of nanotube titanic acid (denoted as NTA) in an NH 3 flow and investigated by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and photoluminescence (PL). With increasing NH 3 treatment temperature at T = 400 to 600 1C, the anatase crystallinity of the N-NTA(400-600) samples was gradually enhanced, while at 700 1C a new phase, TiN, appeared in the N-NTA(700) sample. XPS results show that the doped N atoms incorporated into anatase TiO 2 exist in the form of NO. A revised explanation for the triplet ESR signals obtained from the N-NTA(500-700) samples was put forward, i.e. the g = 2.004 main peak is contributed by single-electron-trapped oxygen vacancies (denoted as V o ), while two weak peaks (g = 2.023, 1.987) are contributed by chemisorbed NO in well-crystallized anatase TiO 2 .The visible light photoactivity is proportional to the height of the g = 2.004 main peak, which suggests that the photoactive centers are V o -NO-Ti. The adsorbed NO molecule can effectively suppress the photoluminescence of V o defects, which facilitates photogenerated charge transfer to the surface reactive centers to conduct redox reactions. The higher the V o -NO-Ti concentration, the better the visible light photoactivity. The highest photoactivity was obtained for the catalyst, NH 3 -treated at 600 1C. But the formation of TiN at T = 700 1C can readily destruct V o -NO-Ti photoactive centers, and thus readily decreases photoactivity efficiency.

Synthesis, Characterization, and Photocatalytic Activities of Nanoparticulate N, S-Codoped TiO2 Having Different Surface-to-Volume Ratios

“…This signal has often been assigned to a single electron trapped in an oxygen vacancy (V o ). [40][41][42][43][44][45] Annealing of undoped powders was unable to generate V o . Livraghi et al recently demonstrated that N-doping of TiO 2 could induced the formation of oxygen vacancies.…”

Enhanced visible-light-driven photocatalytic activity of mesoporous TiO2−xNx derived from the ethylenediamine-based complex

“…16,39 The principal rhombic ESR signals (Fig. 6) of SE-meso-TON and SG-meso-TON are very similar, and their characteristic g tensors at approximately 2.0034 can be assigned to the single-electron-trapped oxygen vacancies ðV In comparison to the major ESR signals in Fig.…”

The Comparison of Property and Visible Light Activity between Bulk and Surface Doped N-TiO2Prepared by Sol-gel and N2-plasma Treatment

“…Secondly, compared with N1-TiO 2 , much more doping N in N2-TiO 2 existed on the surface layer (Table 1). Feng et al 22 prepared N-doped TiO 2 by heating TiO 2 powders in NH 3 at elevated temperatures, and concluded that the oxygen vacancy (V o • ) accompanied with doping N in the surface layer was the surface active site for the visible light photoactivity. In this investigation, the doping N content in the surface layer and oxygen vacancy content of N2-TiO 2 were much higher than that of N1-TiO 2 .…”