Band structure and visible light photocatalytic activity of multi-type nitrogen doped TiO2 nanoparticles prepared by thermal decomposition

Multi-type nitrogen doped TiO2 nanoparticles were prepared by thermal decomposition of the mixture of titanium hydroxide and urea at 400 degrees C for 2 h. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS). UV-vis diffuse reflectance spectra (UV-vis DRS), and photoluminescence (PL). The results showed that the as-prepared samples exhibited strong visible light absorption due to multi-type nitrogen doped in the form of substitutional (N-Ti-O and Ti-O-N) and interstitial (pi* character NO) states, which were 0.14 and 0.73 eV above the top of the valence band, respectively. A physical model of band structure was established to clarify the visible light photocatalytic process over the as-prepared samples. The photocatalytic activity was evaluated for the photodegradation of gaseous toluene undervisible light irradiation. The activity of the sample prepared from wet titanium hydroxide and urea (TiO2-Nw, apparent reaction rate constant k = 0.045 min(-1)) was much higher than other samples including P25 (k = 0.0013 min(-1)). The high activity can be attributed to the results of the synergetic effects of strong visible light absorption, good crystallization, large surface hydroxyl groups, and enhanced separation of photoinduced carriers. (C) 2008 Elsevier B.V. All rights reserved.