Mechanism of the Doping Species Controlling the UV Photocatalytic Activity of Nitrogen Doped TiO2

Nitrogena2doped and pure TiO2 photocatalysts were synthesized by precipitation method using TiCl4 as titanium precursor. Both X-ray diffraction (XRD) and N2 adsorptiona2desorption isotherms show that the asa2prepared samples consis of anatase phase except for trace brookite phase with mesoporous structure. X-ray photoelectron spectroscopy(XPS) confirms that the incorporated nitrogen element exists as the chemical state of NOx. The UV-Vis diffuse reflection absorption spectra (UV-Vis) reveal that the nitrogena2doped TiO2 shows a new absorption region at 400-550nm. The photocatalytic activities of the nitrogena2doped TiO2 utilized for the photodegradation of 4-chlorophenol (4-CP) are higher than those of the pure TiO2 under UV and visible light irradiation. The improved photocatalytic activities under UV light irradiation of the nitrogena2doped TiO2 are attributed to the presence of NOx. With no influence on the energy gap of TiO2, NOx can extend the optical response of TiO2, excite more photoinduced electronsa2holes for photocatalysis and reduce the recombination probabilities of carriers.