La^(3+)掺杂对吸附相反应制备TiO_2复合催化剂的结晶过程及弱紫外光下活性的影响

Influence of La^(3+) doping on the crystallization of TiO_2 composite photocatalysts via adsorption phase synthesis and their performance under illuminted weak UV light

利用吸附相反应技术制备弱紫外光响应的高效催化剂,并通过XRD、XPS以及HRTEM探索了不同焙烧温度下La3+掺杂量对TiO2结晶过程的影响.结合弱紫外光下甲基橙的降解反应,深入研究催化剂结晶过程的变化对弱紫外光下催化剂活性的影响.结果表明,La3+掺杂会抑制TiO2的结晶过程.当焙烧温度或者掺杂量较低时,La3+不能进入TiO2的晶格结构但会轻微地抑制TiO2的结晶过程;未进入晶格结构的La3+存在会引入光生载流子的浅能级捕获中心,在弱光体系中极大提升了催化剂的活性.当La3+的掺杂量为0.05%(原子分数)时,经过900℃焙烧后催化剂降解能力最高,其活性超过商用P25的2倍多.在较高La3+掺杂量(超过0.20%)时,900℃焙烧后一定量La3+进入TiO2的晶格结构而大大抑制了TiO2结晶;这种强烈的抑制作用使得催化剂中存在大量无定形结构TiO2,无定形TiO2甚至多于700℃焙烧后的催化剂,反而大大抑制了弱光体系中催化剂活性.

Weak UV light-driven TiO2 composite photocatalysts were first prepared via adsorption phase synthesis. Then, XRD, XPS and HRTEM were employed to study the influence of La3＋ doping on the crystallization of TiO2 under different sintering temperatures. The degradation of methyl-orange illuminated under weak UV light was carried out to explore the effect of the crystallization of TiO2 on its catalytic activity. The results showed that La3＋ doping would inhibit the crystallization of TiO2. At low sintering temperature or low doping content, La3＋ could not enter the lattice structure of TiO2 and thus slightly restrained the crystallization of TiO2 after doping. This distribution of La3＋ would introduce the shallow capture center of the photo-carrier and greatly enhanced the photocatalytic activity. While the doping content of La3＋ was 0.05% （atomic ratio）, the catalyst sintered under 900 ℃ had the highest activity. The degradation efficiency of this catalyst was two times more than the commercial photocatalyst P25 illuminated under weak UV light. At high doping content, certain amount of La3＋ entered the TiO2 lattice structure and greatly inhibited the crystallization of TiO2 after sintering at 900 ℃. This strong restriction on the crystallization caused a large amount of amorphous TiO2 formed in the catalysts after sintering at 900 ℃. The amorphous TiO2 in the catalyst sintered at 900 ℃ was even more than that sintered at 700 ℃ under this condition. Hence, the photocatalytic activity of the catalyst sintered at 900 ℃ decreased more obviously than that sintered at 700 ℃.