Li+掺杂纳米TiO2的制备及其光催化性能研究

采用溶胶-凝胶法和浸渍法制备了Li⁺掺杂纳米TiO₂光催化剂,并用XRD和TEM等技术进行了表征;用pH值漂移法测量了催化剂的零电位pH值(pHpzc).结果表明,500℃煅烧制得的催化剂均为锐钛矿相;Li⁺的掺杂抑制了TiO₂粒子的生长,提高了催化剂的分散性;催化剂的零电位pH值为6.6—8.1,其值取决于Li⁺的浓度和掺杂方式.分别以紫外光和太阳光为光源,孔雀石绿和甲基橙为降解物评价了催化剂的光催化活性;并用气相色谱测试了污染物降解产生的CO₂的含量.结果显示,对孔雀石绿的降解,浸渍法和溶胶-凝胶法掺Li⁺都能有效提高TiO₂的光催化活性,但浸渍法比溶胶-凝胶法效果更好,催化活性最高的为浸渍法制备的5%(摩尔分数)Li⁺掺杂TiO₂,其在紫外光和太阳光下的光催化活性分别比纯TiO₂提高了6—8倍和9—10倍;对甲基橙的降解,除溶胶-凝胶法制备的3%(摩尔分数)Li⁺掺杂TiO₂能稍提高光催化活性外,其它Li⁺的掺杂都不同程度降低了TiO₂的光催化活性;随污染物降解率的增加,最终降解产物CO₂的含量增加.实验结果表明,Li⁺掺杂改变了催化剂表面的电荷状态从而改变了催化剂的零电位pH值是造成催化剂降解不同污染物具有不同催化活性的主要原因.

Preparation and Photocatalytic Performance of Li+-Doped Nano-TiO2

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 (pHpzc) 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.