羧基官能化SBA-15型介孔分子筛的小角X射线散射研究

Small-Angle X-Ray Scattering Studies of Carboxyl Functionalized SBA-15 Type Mesoporous Molecular Sieves

使用小角X射线散射(SAXS)技术对共缩聚法制备的羧基官能化SBA-15介孔分子筛进行了表征,利用相关函数理论和弦长分布理论获得了羧基化分子筛的孔结构、界面和周期性信息,辅以常规的氮气吸附-脱附测试,并将基于Barrett-Joyner-Halenda(BJH)模型计算的孔结构与弦长分布理论得到的结果进行比较.结果表明:除了羧基引入量高达50%(摩尔分数,相对无机硅源)的样品外,随着羧基引入量的增加所有羧基官能化SBA-15均能保持较高的有序结构且有序度变化不大.所有样品的Porod曲线均无明显偏离,羧基基团倾向于进入介孔的骨架结构而不仅仅是键合在表面的Si—OH上.利用弦长分布法,无需建立模型,可以得到独立的孔壁厚度分布和孔径分布,尤其是其它方法无法给出的孔壁厚度分布,对于进一步认识有序介观结构材料有很大帮助.

Carboxyl functionalized SBA-15 type mesoporous molecular sieves synthesized via co-condensation process were characterized by small-angle X-ray scattering （SAXS）. Correlation function and chord length distribution theory were used to analyze the pore structure, interface, and periodic information. The pore structure parameters calculated from chord length distribution theory were compared with the Barrett-Joyner-Halenda （BJH） model cal-culation results, which are based on conventional nitrogen adsorption-desorption tests. The results showed that the samples preserved the structure order of their mesostructures since no significant degradation occurred with an increase in carboxyl group loading, except for the samples with a high carboxyl loading of 50% （molar fraction, versus inorganic silica source）. There are no significant deviations in the porod curves of all of the samples. The carboxyl groups may become internally embedded within the framework walls of the mesostructure, as opposed to being externally linked to the pore channels via condensation on surface Si—OH sites. Individual pore size and pore wall thickness distribution data were obtained from the chord length distribution theory calculation without modeling. The pore wall thickness distribution data, which are inaccessible by other method, are very helpful for a further understanding of the mesostructure materials.