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 °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 (π* 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 under visible 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.