Effect of Surfactant/Silica Molar Ratios on the Formation of Mesoporous Molecular Sieves: Inorganic Mimicry of Surfactant Liquid-Crystal Phases and Mechanistic Implications

Abstract

The influence of surfactanthilica molar ratio (Sur/Si) in the synthesis of the mesoporous molecular sieve materials (M41S) was studied in a simple ternary synthesis system containing tetraethylorthosilicate (TEOS), water, and the cetyltrimethylammonium (CTMA) cation at 100 "C. The resulting silicate materials were characterized by X-ray diffraction, 29Si NMR, and FTIR. As the Sur/Si molar ratio increased from 0.5 to 2, the siliceous products obtained could be classified into four separate groups: MCM-41 (hexagonal), MCM-48 (cubic), thermally unstable M41S, and a molecular species, the cubic octamer [(CTMA)SiO2.5]8. One of the thermally unstable structures has been identified as a lamellar phase. These results are consistent with known micellar phase transformations that occur a t various surfactant concentrations and reinforce the concept that liquid-crystal structures serve as templating agents for the formation of M41S type materials.

Mesoporous Silica Nanoparticles: A Review

“…The 2D hexagonal p6m (MCM-41), the 3D cubic Ia3d (MCM-48) and the lamellar p2 (MCM-50) are the common mesophases in silicas with pore sizes between 2 and 5 nm [31]. Similarly, 2D hexagonal p6m is reported in MSNs with large pore size 6-20 nm [33].…”

Preparation and characterisation of a Ni2+/Co2+-cyclam modified mesoporous cellular foam for the specific immobilisation of His6-alanine racemase

“…The general pattern for the formation of mesoporous silicates is shown in and their hydrophilic head groups orientating outside to provide protection from water molecules. In order to form the micelles, the critical micelle concentration at a set temperature must be exceeded 54 . These organized micellar liquid crystal structures act as templates so that the inorganic substances can attach around them.…”

An Overview of Zeolite, Zeotype and Mesoporous Solids Chemistry: Design, Synthesis and Catalytic Properties

“…It was reported that the surfactant to silica ratio was the crucial parameter in determining the shape of the micelle aggregates. [35] More recently, n-alkanes of different chain lengths were used as swelling agents for the mesoporous products. [36] The pore diameters of the products increased proportionally with the length of the n-alkanes, containing up to 15 carbon atoms.…”