Controlling the crystal morphology of mesoporous silica SBA-1

The SBA-1 mesoporous silica of Pm3¯n symmetry with different pore sizes have been conveniently prepared from a dilute aqueous solution of CnTMAX (n = 14-18, X = Br, Cl) and sodium silicate at pH value of 2.0. A mesophase transformation from cubic Pm3¯n to hexagonal p6mm occurs at relatively high surfactant concentration of about 6.0 × 10−2 M. Moreover, a slow self-assembling reaction in a dilute solution leads to the formation of the mesostructural SBA-1 crystals. The SBA-1 crystal shape also changes with the chain length of the surfactant. Basically, crystallization processes are thermodynamically and kinetically controlled. Many synthetic factors (such as pH value, silica/surfactant ratio, concentration of the surfactant and temperature) which can influence the silica condensation rate, surfactant micellization and surface free energy of the crystal have apparent effects on the crystal morphology of the SBA-1 mesoporous silica. The organic silica source (tetraethyl orthosilicate, TEOS) can serve as an alternative silica source to obtain the SBA-1 mesoporous silica crystals, but a longer aging time is needed than that of acidified sodium silicate.