Preparation of N-doped TiO2: characterization and photocatalytic performance under UV and visible light

Nanocrystalline N-doped TiO2 samples were prepared by using TiCl4 or TiOSO4 as precursors. The powders were characterized by X-ray diffraction, BET specific surface area measurements, scanning electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested using the photodegradation of 4-nitrophenol under UV and visible light. Some samples were more active than commercial Degussa P25. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed in the samples obtained from TiCl4. Two absorption edges were observed in the samples derived from TiOSO4 and calcined at 400 degrees C: the main edge due to TiO2 and the second one due to the presence of a localised midgap band that induces the visible light activity.