Thioether-bridged mesoporous organosilicas: Mesophase transformations induced by the bridged organosilane precursor

The achievement of structural control over thioether-bridged mesoporous organosilicas is reported. The mesoporous materials have been synthesized by co-condensation of bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPTS) and tetramethoxysilane (TMOS) in acetic acid/sodium acetate buffer solution (HAc-NaAc, pH 4.4), using the nonionic surfactant P123 as a template. The mesostructure of the material is mainly controlled by the molar ratio of TESPTS/TMOS in the initial gel mixture. A mesophase transformation, progressing from a highly ordered 2D hexagonal structure via a vesiclelike structure to a mesostructured cellular foam, can be clearly observed when the molar ratio of TESPTS/TMOS is increased in increments. Solid-state NMR results show that TESPTS is not completely hydrolyzed and condensed at the applied buffer conditions. At low concentrations, the unhydrolyzed TESPTS can penetrate into the core of the surfactant micelles and change the packing parameter of the P123 surfactant. Above a certain concentration, the TESPTS can form a microemulsion with P123 surfactant molecules. Therefore, the vesiclelike structure or cellular foam structure can be synthesized by simply controlling the molar ratio of TESPTS/TMOS. This approach provides a novel method for the facile synthesis of organic-inorganic hybrid materials with a controllable mesostructure under mild synthetic conditions.