Titanium Dioxide photocatalysis is now being used in practical applications such as self-cleaning, sterilization, deodorizing and air-cleaning. It is chemically and photochemically stable, but is only excited by ultraviolet light so that the light utilization efficiency to solar irradiation and a fluorescent lamp is very low. Therefore, attempts were made to extend the adsorption rang of titanium dioxide into the visible-light region by different methods. We prepared N-doped TiO₂ powders that respond to visible-light by high temperature reaction of TiO₂.nH₂O, prepared by the hydrolysis of Tetraisopropylorthotitanate with urea. We studied the effect of time and temperature and different weight ratios of urea/TiO₂.nH₂O and we found that our best sample was the one with 500°C heat treatment for 2h and in this sample the weight ratio of urea/TiO₂.nH₂O was 1. The absorption edge of the samples shifts toward a longer wavelength (about 550 nm). The nanoparticles had a relative specific surface area of about 51m²g^-1. The prepared N-doped TiO₂ nanopowders that respond to visible light (400nm<λ<550nm) showing better photocatalytic activity to that prepared by reaction of TiO₂ (P25-Degussa) with urea. We used Diffused Reflectance, XPS, XRD, SEM, FT-IR, CHN analyzer, TEM and EDS for characterization and we evaluated their photocatalytic activity.

Fig. 1 Light absorption spectra of samples prepared without urea as a reference (green curve) and with the weight ratio of urea/ TiO₂.nH₂O of 1 and 2h annealing time in different temperatures.

Fig. 2 Photocatalytic decomposition of Methylene Blue under visible light. Blue under visible light)

Reference : “Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides”, R. Asahi, T. Ohkawa, K. Aoki, Y. Taga, Science, 293, 269(2001).)

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