Synthesis of mesoporous silica with cationic-anionic surfactants

Ordered mesoporous silica was successfully synthesized by using mixed surfactants, cetyltrimethylammonium bromide and sodium dodecylsulfate, proceeded with the hydrolysis and condensation of tetraethyl orthosilicate in a mixture of TritonX-100 as a cosolvent. The synthesized products were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen sorption analysis. It was found with increasing the anionic surfactant sodium dodecylsulfate to cetyltrimethylammonium bromide molar ratio, the morphologies of mesoporous silica changed from spherical shape to ellipsoidal shape, at last became rod-like and lamellar shape. Correspondingly the pore diameter and surface area of mesoporous silica all decreased according to nitrogen sorption analysis. The TEM analysis illustrated the product with ordered hexagon mesostructure and homogeneous pore arranged can be obtained, when the molar ratio of cetyltrimethylammonium bromide/sodium dodecylsulfate is 15: 1. It also demonstrated the less the molar ratio of sodium dodecylsulfate was used, the more ordered pore structure the products exhibited. Furthermore, prolonging the crystal time was beneficial to improve the stability of the product.