MSU-Type Mesoporous Silicas with Well-Tailored Pore Sizes Synthesized via an Assembly of Deca(ethylene oxide) Oleyl Ether Surfactant and Tetramethoxysilane Silica Precursor

Abstract

Deca(ethylene oxide) oleyl ether surfactant has been used as templating agent in the synthesis of MSU-type mesoporous materials with variable pore sizes. The syntheses were carried out at two different pH values (2 and 10) with tetramethoxysilane (TMOS). The effects of stirring time, hydrothermal treatment temperature, and time have been studied. The obtained materials have been characterized by N2 adsorption, X-ray diffraction, and transmission electron microscopy techniques. A correlation between the synthesis conditions and the structural and textural properties of materials has been established. The synthesis mechanism of MSU-type materials from an assembly of deca(ethylene oxide) oleyl ether surfactant and TMOS silica precursor has been postulated. It is found that with TMOS as inorganic source, both in basic and in acidic conditions, MSU-type mesoporous silicas can be obtained. The structural and textural properties of materials are strongly dependent on the synthesis conditions. For a given stirring time, the increase of both hydrothermal treatment temperature and time can expand the pore size of the obtained materials. However, it should be noted that too long a heating time or too high a heating temperature can lead to a destruction of the structured MSU materials. For the given heating temperature and time, increasing stirring time leads to the formation of materials with smaller pore size. A change of the surfactant conformation under different synthesis conditions has been shown which determines the pore size and the quality of the materials. Syntheses using sodium silicate solution as silica source were also performed at pH = 12. However only amorphous phases were obtained.