Synthesis of large pore disordered MSU-type mesoporous silicas through the assembly of C16(EO)10 surfactant and TMOS silica source: Effect of the hydrothermal treatment and thermal stability of materials

Decaoxyethylene cetyl ether [C 16(EO) 10] has been employed as templating agent for large pore disordered MSU-type mesoporous silicas synthesis. The effect of the hydrothermal treatment (heating time and temperature) on the textural properties, in particular, pore diameter of materials has been investigated. The obtained materials have been characterized by different techniques such as X-ray diffraction, scanning and transmission electron microscopy and nitrogen adsorption-desorption analysis. The thermal stability of the compounds is also evaluated. Our results show that the pore diameter depends strongly on the heating time and temperature. This is the result of a competition between the stretching of the surfactant chains, which can lead to the breakdown of the walls separating adjacent pores, and the reorganization of micelles with heating time and temperature. At higher temperature or for longer durations, a more extended surfactant molecular conformation can be obtained, which leads to materials with larger pore sizes. A reorganization of the micellar solution during the hydrothermal treatment in autoclave can also simultaneously occur to give materials with smaller pore diameter. It is found that compounds prepared with the nonionic surfactant exhibit an enhanced thermal stability compared to those synthesized with cetyltrimethylammonium bromide (CTMABr) as templating agent. This higher stability is related to the synthesis pathway and the structure of materials.