Effect of alkaline-doped TiO2 on photocatalytic efficiency

Alkaline (Li, Na, K) modified titanium dioxide nanoparticles were prepared by sol-gel route and by impregnation technology. XRD analysis showed that the crystallinity level of catalysts is largely dependent on both the nature and the concentration of alkaline. Indeed, the best crystallinity is obtained for Li-doped TiO2 and is lowest for K-doped TiO2. In general, it was found that the anatase phase is stabilised by the alkaline. pH of zero charge has been found to be in the range 6.6-7.9. Depending on the alkaline concentration, the charge compensation may occur at the surface of the catalyst in acidic and basic environment. For photocatalyfic test, Malachite green oxalate, 4-hydroxybenzoic acid and benzamide were used as representative organic pollutants. The catalysts prepared by the impregnation technique were found more efficient than those prepared by sol-gel route, for a given alkaline concentration. When applied to the Malachite green degradation, the best results were obtained for 5% Li-doped TiO2 prepared by impregnation technique. Whatever the alkaline used, and at low concentration, our results show that the efficiency of the catalysts, when prepared by impregnation technique, is better than that of TiO2-P25. Therefore, at low concentration, alkaline doped-TiO2 can be considered as promising materials for organic pollutants degradation. (C) 2003 Elsevier B.V. All rights reserved.