Kinetic Influence of Siliceous Reactions on Structure Formation of Mesoporous Silica Formed via the Co-Structure Directing Agent Route

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• 作者：Ruiyu Lin ; Göran Carlström ; Quoc Dat Pham ; Michael W. Anderson ; Daniel Topgaard ; Karen J. Edler ; Viveka Alfredsson
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：February 25, 2016
• 年：2016
• 卷：120
• 期：7
• 页码：3814-3821
• 全文大小：398K
• ISSN：1932-7455

文摘

We investigate the mechanism responsible for the formation of mesoporous silica formed with the so-called costructure directing agent (CSDA) route. The synthesis relies on the interaction between silica source (tetraethylorthosilicate), cationic surfactant (C₁₈H₃₇N⁺(CH₃)₂(CH₂)₃N⁺(CH₃)₃Br₂), and CSDA (carboxyethylsilanetriol), which results in a material functionalized with carboxylic groups. Depending on the concentration of HCl in the synthesis, the structure is defined by Fm3̅m (at high pH) and by Fd3̅m (at low pH), with a gradual transition in the intermediate pH range. Here, we aim at finding the origin for the structural change triggered by pH and investigate the effects of the hydrolysis of the silica source on the overall kinetics of the synthesis. A fast process results in Fm3̅m, regardless of pH, and a slow process results in Fd3̅m. The hydrolysis step is the important structural control parameter. We studied the cross-linking of silica and CSDA using ²⁹Si NMR. The cross-linking is similar for the two structures, and possibly the Fd3̅m structure contains slightly more CSDA. ¹³C PT ssNMR was used to investigate the surfactant mobility/rigidity during the synthesis. The rigidity of the Fm3̅m is established much faster than that of the Fd3̅m.