Mixed Surfactant Assemblies in the Synthesis of Mesoporous Silicas

MCM-41 type mesoporous silica material is synthesized, under mild conditions, in the presence of cetylpyridinium chloride as the templating species. Seven reflections become observable in the powder X-ray diffraction pattern of this material that can be indexed on the basis of a hexagonal close-packed unit cell with a o = 47.62 Å. Synthesis of mesoporous silica materials is also demonstrated using self-assembling micellar aggregates of a mixture of two surfactants: cetylpyridinium chloride (CPCl) and cetyltrimethylammonium chloride (CTACl). As the CPCl:CTACl molar ratio between the two amphiphilic molecules decreases, a gradual increase in the d 100-spacing is observed starting at ca. 41 Å and in subangstrom increments reaching to that of ca. 43 Å. The materials were also characterized by DTGA, TEM, and Ar adsorption studies. A model is presented that simultaneously accounts for the higher degree of structural order of the mesoporous silica templated with CPCl and the ability to fine-tune d spacings on a subangstrom length scale using CPCl/CTACl mixtures.