Abstract: Li⁺-doped nano-TiO₂ photocatalysts were prepared by sol-gel route and by impregnation method, respectively. The catalysts were characterized by TEM and XRD techniques, and pH of zero charge (pH_pzc) of catalysts were measured by pH drift method. The results show that all catalysts prepared at 500℃ are anatase phase. Li⁺-doping restrains the growth of TiO₂ particles, improves the dispersivity of the catalyst. The pHpzc of catalysts is in the range 6.6—8.1, depending on the doping method and concentration of doped Li⁺. UV light and sunlight were used as light sources to investigate the photocatalytic activity of the catalysts for the degradation of malachite green and methyl orange, and the contents of CO₂ produced by the degradation of pollutants were determined by gas chromatography(GC). It has been found that , for the degradation malachite green, Li⁺-doping both by sol-gel route and by impregnation method can all enhance the catalytic activity of TiO₂, effectively, but the catalysts prepared by the impregnation method are more efficient than those prepared by sol-gel route,and the best photoactivity is obtained for 5%(mole fraction) Li⁺-doped TiO₂ prepared by impregnation technology and its photocatalytic efficiency is 6—8 times under UV light and 9—10 times under sunlight higher than that of pure TiO₂; for methyl orange degradation, Li⁺-doping reduces the catalytic activity of TiO₂ to some extent, except for 3%(mole fraction)Li⁺-doped TiO₂ which is slightly better prepared by sol-gel route. The contents of the final degradation products CO₂ increase with improving of the photocatalytic activity of the catalysts. The main reasons of reverse photocatalytic activity of Li⁺-doped TiO₂ in degrading different organic pollutants is that Li⁺-doping changes pHpzc and the state of the charge of TiO₂ surface.

Key words: lithium, titania, photocatalysis, malachite green, methyl orange