Non-ionic surfactant(C₁₃EO_mm=6, 12 and 18) for large pore mesoporous molecular sieves preparation

Polyoxyethylene tridecylether (C_13(EO)m, m = 6, 12 and 18) has been used as templating agent for synthesis of large pore mesoporous materials. The effect of surfactant/silicium molar ratio, heating time, and temperature, and the number of oxyethylene units on the mesoporous material syntheses has been studied in detail. Final compounds were characterized by different techniques such as SEM, TEM and nitrogen adsorption-desorption analysis. The present work shows that the surfactant/tetramethoxysilane molar ratio has a strong effect on the pore diameter for a given surfactant. It is evidenced that both TMOS and surfactant can play a role of swelling agent depending on the surfactant/TMOS molar ratio. It is also shown that the pore diameter depends strongly on the heating time and temperature, oxyethylene unit number and surfactant/TMOS molar ratio. All these factors can affect jointly or separately the pore diameter of obtained materials. It is revealed that the surfactant conformation can be changed with the heating temperature. At higher temperature, a more extended molecular conformation can be obtained, which leads to materials with larger pore size.