Synthesis of High-Quality MCM-48 Mesoporous Silica Using Gemini Surfactant Dimethylene-1,2-bis(dodecyldimethylammonium bromide)

Abstract

Using the Gemini surfactant [C12H25N+(CH3)2-(CH2)2-N+(CH3)2-C12H25]·2Br- (abbreviated as C12-2-12) with the short spacer group (s = 2) as structure-directing agent and sodium silicate as precursor, high-quality ordered cubic mesoporous silica (space group Ia3d) was prepared through the S+I- route (S denotes surfactant, I precursor). The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption−desorption techniques. Results showed that the pore structure of the resulting mesoporous silica belonged to the cubic structure (space group Ia3d). The high-quality cubic mesoporous structure was formed at 1:0.33 (molar ratio of sodium silicate to C12-2-12), 2:1 (ethyl acetate to sodium silicate), and at 30 °C. The formation conditions of MCM-48 with C12-2-12 were milder than those with the corresponding monovalent surfactants, such as alkyltrimethylammonium bromide. N2 adsorption−desorption curves revealed type IV isotherms and H1 hysteresis loops; Brunauer−Emmet−Teller (BET) surface areas increased with the decrease of the molar ratio of sodium silicate to C12-2-12 and of ethyl acetate to sodium silicate as well as of the hydrothermal temperatures.