Giessler S, da Costa J C, Lu G Q
Nanomaterials Centre, Department of Chemical Engineering, University of Queensland, Brisbane, Queensland, 4072, Australia.
J Nanosci Nanotechnol. 2001 Sep;1(3):331-6. doi: 10.1166/jnn.2001.037.
Silica xerogels were prepared by a sol-gel process catalyzed by acid with tetraethylorthosilicate, and using an organic covalent ligand template (methyltriethoxysilane) or a noncovalent template C6 surfactant (triethylhexylammonium bromide). The influence of hydrotreatment on the structure of templated xerogels is examined in terms of surface area, micropore volume, average pore size, and pore size distribution, and compared against a blank xerogel (nontemplated). The role of surface functional groups was evaluated using 29Si nuclear magnetic resonance. The structural integrity of the xerogel was maintained to a large extent in samples that had a high contribution of Q4 species (siloxane groups). Xerogel matrix densification occurred when there was a large concentration of Q3 and Q2 species (silanol groups), which also were responsible for increased hydrophilicity. The templated xerogels resulted in up to a 25% concentration of methyl functional groups (T3 and T2 species), leading to hydrophobic xerogels. The best results in terms of structural integrity and hydrophobicity were obtained with templated xerogels prepared with the C6 surfactant. The results in this study suggest that surfactant-enhanced condensation reactions lead to structures with a high contribution of Q4 groups, which are not susceptible to water attack, but are strong enough to oppose matrix densification during rehydration.
通过溶胶 - 凝胶法，以正硅酸乙酯为原料，在酸催化下，使用有机共价配体模板（甲基三乙氧基硅烷）或非共价模板C6表面活性剂（三乙基己基溴化铵）制备二氧化硅干凝胶。从比表面积、微孔体积、平均孔径和孔径分布方面研究了加氢处理对模板化干凝胶结构的影响，并与空白干凝胶（非模板化）进行比较。使用29Si核磁共振评估表面官能团的作用。在具有高Q4物种（硅氧烷基团）贡献的样品中，干凝胶的结构完整性在很大程度上得以保持。当存在大量Q3和Q2物种（硅醇基团）时，会发生干凝胶基质致密化，这些物种也导致亲水性增加。模板化干凝胶导致甲基官能团（T3和T2物种）浓度高达25%，从而形成疏水性干凝胶。使用C6表面活性剂制备的模板化干凝胶在结构完整性和疏水性方面取得了最佳结果。本研究结果表明，表面活性剂增强的缩合反应导致具有高Q4基团贡献的结构，这些结构不易受到水的侵蚀，并且在再水化过程中足以抵抗基质致密化。
