Effects of the spacer length of gemini surfactants on the ordered pore of silica

A family of designed gemini surfactants C14H29(CH3)(2)N+-(CH2)(S)-N+(CH3)(2)C14H29 center dot 2Br(-) (designated as C14-S-14, S = 4, 6, 8, 10) was utilized as structure-directing agent to prepare ordered porous MCM-41 silica. The samples were characterized by small angle X-ray diffraction, high-resolution transmission electron microscopy and N-2 adsorption/desorption analysis. The results showed that the obtained materials possessed 2D-hexagonal periodic structure (space group 2D-p6mm), but the pore diameter obviously decreased as the length of the spacer group of the gemini surfactants increased. Two types mesoporosity, that is, framework-confined mesoporosity (primary pores) and voids between particles (textural mesoporosity) existed in the samples. In addition, the self-assembly ability of C14-S-14 was stronger than that of tetradecyltrimethylammonium bromide (TTAB, which was regarded as the corresponding monomer of gemini surfactant C14-S-14) in controlling the orderly pore structure and pore size of the porous materials.