(521f) One Pot Synthesis of Ordered Biphasic Mesoporous Silica with 2d Hexagonal and Mesh Structure and Its Use for Controlled Deposition of Metal Oxides

Mixtures of certain hydrocarbon and fluorocarbon surfactants in dilute solution are known to form demixed micellar phases made up of coexisting hydrocarbon-rich and fluorocarbon-rich micelles. However, the practical application of the two distinct types of micelles in solution is not well explored. The surfactant-templated sol-gel process provides a simple but practical method to verify the demixing of micelles composed by fluorocarbon and hydrocarbon surfactants, to study the demixing process in highly concentrated mixtures, and potentially to synthesize mesoporous materials with interesting structure. In this study, highly organized mesoporous silica powders are prepared with mixed hydrocarbon surfactant hexadecyltrimethylammonium chloride (CTAC) and fluorocarbon surfactant N-(1,1,2,2-tetrahydroperfluorodecanyl) pyridinium chloride (HFDePC) as templates over a range of fluorocarbon:hydrocarbon ratios. For molar fractions of fluorinated surfactant equal to 0.5 and total surfactant concentrations above the highest CMC in the mixed system (2.7 mM), ordered biphasic mesoporous silica with coexisting 2D hexagonal and mesh phase structure can be prepared in the presence of large amount of ammonia. The results suggest that two domains of different mesostucture are formed due to micelle demixing. Based on the structures of materials prepared with each of the pure surfactants, we can associate the 2D hexagonal mesostructure with CTAC-rich micelles, and the mesh phase mesostructure with HFDePC-rich micelles. The intimate mixture of these two types of domains in the as-synthesized materials provides an opportunity to utilize the separate hydrocarbon and fluorocarbon domains for controlled deposition of two different transitional metal oxides into the two different types of ordered mesoporous channels. The incorporation of metals into the two domains using fluorinated and hydrogenated complexes during synthesis is studied, and allows the deposition of metal clusters that are interesting from a multifunctional catalysts perspective. The final materials are characterized by FTIR, X-ray diffraction, nitrogen adsorption, SEM, TEM, STEM and EDS.