Nitrogen-doped titanium dioxide (N-doped TiO_(2)) photocatalyst was synthesized from nanotube titanic acid (denoted as NTA; molecular formula H_(2)Ti_(2)O_(5) (centre dot) H_(2)O) precursor via a hydrothermal route in ammonia solution. As-synthesized N-doped TiO_(2) catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, diffuse reflectance spectrometry, X-ray photoelectron spectroscopy, electron spin resonance spectrometry and Fourier transform infrared spectrometry. It was found that nanotube ammonium titanate (NAT) was produced as an intermediate during the preparation of N-doped TiO_(2) from NTA, as evidenced by the Nls X-ray photoelectron spectroscopic peak of NH_(4)~(+) at 401.7 eV. The catalyst showed much higher activities to the degradation of methylene blue and p-chlorophenol under visible light irradiation than Degussa P25. This could be attributed to the enhanced absorption of N-doped TiO_(2) in visible light region associated with the formation of single-electron-trapped oxygen vacancies and the inhibition of recombination of photo-generated electron-hole pair by doped nitrogen.
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