Nonionic block copolymer and anionic mixed surfactants directed synthesis of highly ordered mesoporous silica with bicontinuous cubic structure

Mesoporous silica with Ia3̄d structure has been successfully prepared by using mixed surfactants of commercially available nonionic block copolymer P123 (EC₂₀PO₇₀EO₂₀) and anionic sodium dodecyl sulfate (SDS) as structure-directing agents through an acid-catalyzed silica sol-gel process. XRD, TEM, and N₂ sorption measurements show that the products have highly ordered bicontinuous cubic mesostructure with high surface area (∼770 m²/g), large pore volume (∼1.5 cm³/g), and uniform pore size (∼10 nm). Effects of preparation parameters on the formation of the mesostructure have been extensively investigated. It is found that the molar ratios of SDS/P123 between 2.1 and 2.5 and that of silicic species to P123 in the range from 40 to 75 are favorable for the formation of highly ordered Ia3̄d mesostructure. Prolonging hydrothermal treatment time leads to almost unchanged cell parameters of the products, whereas there is obvious increase of the pore sizes and pore volume. The results show that resultant template-free mesoporous silica products have excellent thermal stability, and they are more stable in N₂ atmosphere than in air. Morphologies of the resultant materials can be further controlled by adding inorganic salt (such as Na₂SO₄) into the mixed surfactants system. Coral- and petaline-like mesoporous silica with continuous skeletons can be obtained. Understanding this synthesis system might be useful for economical and large-scale production of mesoporous materials with controllable structures.