Mechanisms of Pore Size Control in MSU-X Mesoporous Silica

Abstract

Mesoporous silicas of the MSU-X type, made with nonionic polyethylenoxide-based (PEO) surfactants, were synthesized according to a two-step process that gives intermediary stable hybrid micelles. The influence of the various synthesis parameters, such as the silica concentration, the addition of a swelling agent (TMB: trimethyl-1,3,5 benzene), the condensation catalyst (NaF), and the temperature of silica condensation, was systematically explored, especially their influence on the material pore size. Surprisingly, changing the silica over surfactant ratio does not modify the silica wall thickness but the other parameters have a strong effect on the final pore size. Considering the model of hybrid micelles that was previously reported (Boissière et al. Chem. Mater. 2001, 13, 3580), we explained the effect of the different parameters by a classical swelling effect of the hydrophobic micelle core for TMB, whereas the modulation of the hydrophilicity of the PEO chains (for temperature) or that of the silica oligomers (for NaF) describes correctly the variations observed. Finally, the cumulative effect of these parameters is demonstrated and we show that materials with narrow pore size distributions tuned between 2.5 and 5 nm can be obtained without changing the surfactant nor adding any swelling agent, by varying only the synthesis parameters.

Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films

“…It is well known that fluoride ions act as a nucleophilic catalyst and accelerates the hydrolysis and condensation rates of TEOS [116][117][118][119][120]. The increased hydrolysis comes from a nucleophilic attack, where the fluoride ion assists with the removal of an alcohol chain.…”

Synthesis of wormhole mesoporous silica by compressed carbon dioxide and application in catalytic hydrogenation

“…The conventional routes are N o I o or S o I o (N o neutral amines, S o nonionic surfactants, I o hydrated silicate oligomers from TEOS) assembly pathways. The wormhole like framework structures such as HMS [9] and MSU-X silicas [12][13][14] were usually obtained by hydrogen-bonding interaction mechanisms. Both of these silicas only show one broad X-ray diffraction peak, as a result of the disordered mesostructure in long range.…”

Post-treatment of mesoporous material with high temperature for synthesis super-microporous materials with enhanced hydrothermal stability

“…Up to now, a variety of mesoporous materials have been successfully synthesized [3][4][5][6][7][8][9][10][11]. The M41S family of mesoporous molecular sieves, especially MCM-41 and MCM-48 has been attracting considerable attention for their high surface area, ordered mesoporous pore size distribution and larger pore volume.…”