块状TiO2/SiO2气凝胶的非超临界干燥法制备及其表征

分别通过TiO2和SiO2的单独溶胶和TiO2/SiO2复合凝胶,并添加干燥控制化学添加剂甲酰胺,形成比较完善的凝胶网络结构,同时通过正硅酸乙酯的乙醇溶液浸泡,低表面张力溶剂替换和分级陈化以及干燥等步骤,实现了块状TiO2/SiO2复合气凝胶的非超临界干燥制备.所得TiO2/SiO2气凝胶为无色或乳白色轻质块状多孔固体,表观密度约0.4～0.9g/cm3,孔隙率约80%～95%.它由直径约10nm的TiO2和SiO2微粒相互分散复合而成,孔洞直径约几十纳米.其相态SiO2为无定形,TiO2为锐钛矿晶型.随着焙烧温度的升高,直到800℃不发生相变化.

Preparation and Characterization of Monolithic TiO2/SiO2 Aerogels Obtained by Non-supercritical Drying Method

TiO2/SiO2 aerogels, a special kind of mesoporous materials, is comprised of linked nano-sized pores which possess a high photocatalytic activity. In our work, sols of TiO2 and SiO2 were prepared separately and mixed to prepare TiO2/SiO2 gels. Formamide as the drying control chemical additive(DCCA) was added to stiffen the microstructure of TiO2/SiO2 gels. TiO2/SiO2 gels were immersed in the tetraethoxysilane/ethanol solutions, exchanged pore fluid with low surface tension solvent, aged and then dried in different stages to realize the preparation of TiO2/SiO2 aerogels by non-supercritical drying. The resultant aerogels were transparent or translucent, highly porous and low density foams with bulk densities in the range of 0.4—0.9 g/cm3 and porosity about 80%—95%. The TiO2/SiO2 aerogels were comprised of dispersed TiO2 and SiO2 particles. The average particle diameter is about 10 nm, and average pore diameter is tens of nanometers. The phase of SiO2 is amorphous and TiO2 remains anatase microcrystal until 800 ℃. The effects of molar ratio of TiO2 to SiO2 and amount of formamide on sol-gel process and aerogel properties were also discussed.