Keywords: 
• nitrogen-doped titania catalyst /
• sol-gel method /
• surface structure /
• visible-light sensitivity /
• 2,4-dichlorophenol

Abstract: In order to develop catalyst sensitive to visible light, nitrogen-doped titania oxides were prepared by a simple sol-gel method, with the elemental nitrogen derived from urea. Photocatalytic activity of the catalysts was tested through the degradation of aqueous 2,4dichlorophenol. XRD, BET, XPS and UV-Vis diffuse reflectance spectroscopy analysis showed that the crystallite size of the catalysts decreased and the specific surface area of ones increased with the increase of atomic ratio of nitrogen to titania(N/Ti). The transformation was restrained of anatase to rutile. Except that 0# sample consisted of anatase and rutile, other catalysts were only anatase. Nitrogen was doped into tiatnia crystal lattice, substituting lattice oxygen and siting lattice interstice. Both substitutional and interstitial nitrogendoped titania catalysts exhibited notable redshift of light-adsorbtion edge. Fluorescence spectroscopy analysis showed that the rate of ·OH forming in reactiong syetem was upgoing when N/Ti increased from 0 to 6, but was downgrade when N/Ti was upto 8. The similar rule did the effect of the N/Ti on photocatalytic activity follow. In conclusion, a certain amount of nitrogen doping can enhance the visiablelight photocatalytic activity of titania oxides. The modified catalysts can be used for organic pollutant photoderadation under sunlight.