Preparation and spectroscopic characterisation of nitrogen doped titanium dioxide

Photocatalytic oxidation constitutes one of the most promising methods for indoor and outdoor air purification. Solar energy contains only about 5% UV light and much of the rest is visible light. In order to utilize solar energy efficiently in photocatalytic reactions, it is necessary to develop a visible light reactive photocatalyst having smaller band gaps than TiO2 rutile and anatase. In 1986 Sato reported that calcinations of NH4Cl containing titanium hydroxide caused the photocatalytic sensitization of TiO2, into the visible light region. The author proposed that the powder prepared according to the described method are actually NOx-doped TiO2 and that the sensitization of these materials is due to the presence of NOx impurity. Several years after it has been reported that nitrogen-doped titania with a particularly high visible light photocatalytic activity had been prepared. The aim of the present work was to synthesize and characterize new materials based on N-doped TiO2. The materials N/TiO2 were prepared via sol-gel technique using solutions containing various kind of nitrogen compounds. UV-Vis diffuse reflectance spectroscopy and Electron Paramagnetic Resonance were the main experimental techniques used to characterized the materials. The latter technique was adopted to verify the presence of paramagnetic entities formed during the synthesis. In most cases the samples prepared via sol-gel reaction exhibit a pale yellow color.