常压干燥溶胶-凝胶法制备的TiO_2气凝胶织构和结构研究

Study of texture and structure of TiO_2 aerogel prepared by ambient pressure drying and sol-gel method

以廉价的四氯化钛为前驱体,环氧丙烷为促凝剂,甲酰胺为干燥控制化学添加剂,有机配体丙酸为水解降速剂,采用正交实验设计以常压干燥-溶胶-凝胶法制备TiO2气凝胶,并用BET和XRD对样品的织构和结构进行表征。结果表明,以n(四氯化钛)∶n(去离子水)∶n(甲酰胺)∶n(丙酸)∶n(环氧丙烷)=1∶14∶2∶0.5∶10制备的TiO2气凝胶,比表面积为632.87 m2·g-1,平均孔径7.87 nm,孔容1.24 cm3·g-1;当平均孔径小、孔容大时比表面积较高,反之,比表面积很低;随着焙烧温度升高,晶化度增强,但仍未出现金红石相衍射峰,表明具有较好的热稳定性。TiO2气凝胶孔容较大时,锐钛矿相结晶度差,反之,结晶度好;孔容居中的TiO2气凝胶出现游离的无定型SiO2,而较低的丙酸含量有利于提高焙烧后样品的晶化度。

Using inexpensive titanium tetrachloride as the precursor,epoxy propane as the gelation promoter, formamide as the drying control chemical additive and organic ligand propionic acid as the hydrolysis moderator,TiO2 aerogel was prepared by ambient pressure drying and sol-gel method. The texture and structure of TiO2 aerogel were characterized by BET and XRD. The results indicated that TiO2 aerogel was obtained under the optimal condition of n（titanium tetrachloride）∶ n（deionized water）∶ n（formamide）∶n（propionic acid）∶ n（propylene oxide）= 1 ∶ 14 ∶ 2 ∶ 0. 5 ∶ 10,and possessed the specific surface area of 632. 87 m^2 ·g ^- 1 ,average pore size of 7. 87 nm and the pore volume of 1. 24 cm^3 ·g ^- 1 . The smaller average pore size and bigger pore volume lead to the bigger specific surface area,and conversely the specific sur-face area was quite low. The crystallinity of TiO2 aerogel was enhanced with the increase of calcination temperatures. The characteristic diffraction peak of rutile did not appear,which demonstrated that TiO2 aerogel had excellent thermostability. TiO2 aerogel with bigger pore volume possessed worse crystallinity of anatase phase,and vice versa. The amorphous silica appeared in samples with medium pore volume. Lower amount of propionic acid was beneficial to improving the crystallinity of calcined samples.