Preparation of high-quality MCM-48 mesoporous silica and the mode of action of the template

Ultrastable MCM-48 silica with Ia3d cubic structure was synthesized by using only the surfactant cetyltrimethylammonium tosylate (CTATos) as template at extremely low surfactant concentration (CTATos/SiO₂ = 0.068). Characterization by small-angle X-ray diffraction (XRD), nitrogen adsorption, and high-resolution transmission electron microscopy (HRTEM) clearly shows that the obtained MCM-48 silica has a highly ordered structure and large surface area (ca. 1281 m²/g) and pore volume (ca. 1.07 cm³/g). The regular cubic arrays were well retained even after this material was calcined at a high temperature of 900 °C for 3 h or heated at reflux in boiling water for 12 h. The Fourier transform infrared (FTIR) spectrum, thermogravimetric analysis (TG), and chemical analysis provide strong evidence that the formation of MCM-48 is attributed to the retention of tosylate (Tos^-) counteranions of the surfactant in the interface between surfactant and silicate. The current synthetic strategy is suitable for routine and large-scale preparations of mesoporous silica with different topological structures.