Template-Free Self-Assembly of Mesoporous Organosilicas,Chemistry of Materials

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Template-Free Self-Assembly of Mesoporous Organosilicas
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-03-09 00:00:00 , DOI: 10.1021/acs.chemmater.7b04480
Quanchang Li ₁ , Mobae Afeworki ₁ , Nicole M. Callen ₁ , Robert J. Colby ₁ , Manesh Gopinadhan ₁ , Meghan L. Nines Kochersperger ₁ , Brian K. Peterson ₁ , Michael Sansone ₁ , Simon C. Weston ₁ , David C. Calabro ₁

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Using a known organosilane building block (1,1,3,3,5,5-hexaethoxy-1,3,5-trisilacyclohexane), materials with unexpectedly high surface area (>1200 m²/g) and porosity with narrow pore-size distributions were synthesized in the total absence of pore-templating agents. The properties of these mesoporous organosilicas (MOS), closely resembling those of surfactant-templated mesoporous silicas, are found to vary over a wide range depending on synthesis gel pH and gelation temperature and time. Considerable microporosity is observed at short 90 °C gelation times at pH 12.5, which diminishes to a very minor component of the porosity at times > 23 h. Under the gelation conditions used here (90 °C, pH 12.5), pore volume and pore diameter rise sharply with time, ultimately leveling off at 1.2 cm³/g and 70 Å at times > 70 h. This building block is shown to be stable in acidic gels but undergoes gradual ring opening at gelation temperatures and times in excess of “standard” conditions employed for alkaline gels.The synthesis and properties of these materials, called EMA-2, are compared with materials made from the same precursor in a templated synthesis and from other organosilane precursors in nontemplated syntheses. Comparative TEM and SAXS analysis of products from identical preparations using tetraethylorthosilicate and the 1,1,3,3,5,5-hexaethoxy-1,3,5-trisilacyclohexane precursors indicates that the latter forms a highly interconnected network gel lacking discrete particle aggregates.

中文翻译：

介孔有机硅的无模板自组装

使用已知的有机硅烷结构单元（1,1,3,3,5,5-六乙氧基-1,3,5-三硅环己烷），具有出乎意料的高表面积（> 1200 m ² / g）和孔隙率窄的材料，在完全没有孔模板剂的情况下合成了尺寸分布。发现这些介孔有机二氧化硅（MOS）的性质与表面活性剂模板介孔二氧化硅的性质极为相似，取决于合成凝胶的pH值，胶凝温度和时间，它们的变化范围很广。在pH值为12.5的短时间90°C胶凝时间观察到相当大的微孔率，在> 23 h的时间里，它会减小至很小的孔隙率。在此处使用的胶凝条件下（90°C，pH 12.5），孔体积和孔径随时间急剧增加，最终在1.2 cm ³处趋于平稳/ g和70Å，时间> 70小时。该结构单元在酸性凝胶中稳定，但在凝胶化温度和超过碱性凝胶“标准”条件的时间下会逐渐开环。将这些材料的合成和性能（称为EMA-2）与材料进行了比较。由模板合成中的相同前体和非模板合成中的其他有机硅烷前体制成。使用原硅酸四乙酯和1,1,3,3,5,5-六乙氧基-1,3,5-三硅杂环己烷前体对相同制剂的产品进行TEM和SAXS对比分析，结果表明后者形成了高度互连的网络凝胶，没有离散的颗粒聚集体。

更新日期：2018-03-09

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