Nitrogen-doped titanium dioxide powders were prepared by wet method, that is, the hydrolysis of acidic tetra-butyl titanate using aqueous ammonia solution, followed by calcination at temperatures about 350 degrees C. The catalysts exhibited photocatalytic activity in the visible light region owing to N-doping. The light absorption onset of TiO2-xNx was shifted to the visible region at 459 nm compared to 330 nm of pure TiO2. An obvious decrease in the band gap was observed by the optical absorption spectroscopy, which resulted from N2p localized states above the valence band of TiO2-xNx (compared to TiO2). The TiO2-xNx catalyst was characterized to be anatase with oxygen-deficient stoichiometry by X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS) and X-ray photoelectron spectroscopy (XPS). The binding energy of Nls measured by XPS characterization was 396.6 eV (Ti-N bonds, beta-N) and 400.9 eV (N-N bonds, gamma-NA respectively. The photocatalytic activity of TiO2-xNx under visible light was induced by the formation of beta-N in the structure. Photocatalytic decomposition of benzoic acid solutions was carried out in the ultraviolet and visible (UV-vis) light region, and the TiO2-xNx catalyst showed higher activity than pure Ti02. (C) 2006 Elsevier B.V. All rights reserved.