Alkanes-assisted low temperature formation of highly ordered SBA-15 with large cylindrical mesopores

Abstract

Highly ordered SBA-15 silicas with large cylindrical mesopores (y15 nm) are successfully obtained with the help of NH 4 F by controlling the initial reaction temperatures in the presence of excess amounts of alkanes.With the discovery of M41s, 1 great efforts have been made on the construction of texture controllable mesoporous materials. Among them, tailoring the pore size of the mesoporous materials has been one of the hot issues for the purpose of providing a good performance for specific applications, such as the adsorption/ separation of bulky molecules, the immobilization of enzymes as well as the catalytic transformation reactions of macromolecules, etc. Methods to modify the pore size of the mesoporous materials include the post synthesis treatment, 2 using different surfactant molecules (template) with different chain lengths 3 and employing organic solvents as swelling agents. 4 The addition of swelling agents, such as TMB, alkanes, 5,6 has been proved to be the most effective way in expanding the pore size of MCM-41 silicas (2-10 nm). Recently, the nonionic triblock copolymers templated SBA-15 silicas have attracted great interests due to their larger pores, thicker pore walls and therefore higher hydrothermal stabilities. 7 Meanwhile, the pore size of SBA-15 could be tuned in the range of 7-30 nm by using TMB as expander. However, extensive studies show that a phase transition from highly ordered SBA-15 (7-12 nm) to mesoporous cellular foams (MCF) with large nodded pore structures (y22-42 nm) occurred with increasing amounts of TMB. 8 Therefore, it is still essential to find other methods of tuning the pore size of highly ordered mesoporous materials. In other works, organic auxiliary chemicals (e.g., DMF, 9 alkanes 10,11 ) have also been investigated. Unfortunately, the maximum pore size of the highly ordered SBA-15 is only ca. 12 nm (with decane). Furthermore, when alkanes with shorter chain length (such as nonane, octane, etc.) were employed, disordered MCF silicas were produced under the temporal reaction conditions. 10 Up to now, to our knowledge, the synthesis of highly ordered SBA-15 silicas with cylindrical pore sizes larger than 12 nm has rarely been reported. Herein, it is demonstrated for the first time that the pore size of highly ordered SBA-15 could be continuously expanded to y15 nm by carefully controlling the initial reaction temperatures with excess amounts of alkanes (from nonane to hexane). To our knowledge, it is the largest cylindrical mesopore diameter with regard to highly ordered SBA-15 silicas.As a typical synthesis procedure, 2.4 g of EO 20 PO 70 EO 20 (P123) was dissolved in 84 ml HCl solution (1.30 M), followed by the addition of 0.027 g of NH 4 F. The mixture was then stirred at 288 K to yield a clear solution. Different alkanes (with a constant alkane/P123 molar ratio of y240) and 5.5 ml TEOS were premixed and then introduced into the solution under stirring. The above mixture was stirred at a given temperature for 20 h, and then transferred into an autoclave for furthe...

Expanding mesoporosity of triblock-copolymer-templated silica under weak synthesis acidity

“…The big pore size and large pore volume is considered as desirable characteristic in the adsorption or catalysis applications especially when organics with bulky molecules are involved as adsorbates or reactants owing to facilitated mass transfer [3]. In recent years, much effort has been devoted to further expanding the porosity of SBA-15, and the general method was the utilization of swelling agents such as aromatics [1,[4][5][6] or alkanes [7][8][9][10], which could dissolve in the hydrophobic core of template micelles to make enlarged hydrophobic volume, leading to bigger pore size and larger pore volume. Large pore volume of up to 2.2 cm 3 /g was achieved with the use of mesitylene as swelling agent [1].…”

Solubilization of decane into gemini surfactant with a modified Jeffamine backbone: Design of hierarchical porous silica

“…It should be noted that a small uptake in the mesopore size was also observed for SBA-15 when alkanes are used as expanders. It is reported for SBA-15, prepared from P123 surfactant that the pore size increases when the chain length of alkane decreases in a series from decane to pentane [37,38]. One way to modify the value of the pore diameter consists in changing the conditions of the hydrothermal treatment [39][40][41][42][43].…”

Advances in Mesoporous Metal Phosphonate Hybrid Materials

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