Design of mesoporous silica at low acid concentrations in triblock copolymer-butanol-water systems

Abstract

Assembly of hybrid mesophases through the combination of amphiphilic block copolymers, acting as structure-directing agents, and silicon sources using low acid catalyst concentration regimes is a versatile strategy to produce large quantities of high-quality ordered large-pore mesoporous silicas in a very reproducible manner. Controlling structural and textural properties is proven to be straightforward at low HCl concentrations with the adjustment of synthesis gel composition and the option of adding co-structure-directing molecules. In this account, we illustrate how various types of large-pore mesoporous silica can easily be prepared in high phase purity with tailored pore dimensions and tailored level of framework interconnectivity. Silica mesophases with two-dimensional hexagonal (p6mm) and three-dimensional cubic (Fm (3) over barm, Im (3) over barm and la (3) over bard) symmetries are generated in aqueous solution by employing HCl concentrations in the range of 0.1-0.5 M and polyalkylene oxide-based triblock copolymers such as Pluronic P123 (EO20-PO70-EO20) and Pluronic F127 (EO106-PO70EO106). Characterizations by powder X-ray diffraction, nitrogen physisorption, and transmission electron microscopy show that the mesoporous materials all possess high specific surface areas, high pore volumes and readily tunable pore diameters in narrow distribution of sizes ranging from 4 to 12 nm. Furthermore, we discuss our recent advances achieved in order to extend widely the phase domains in which single mesostructures are formed. Emphasis is put on the first synthetic product phase diagrams obtained in SiO2-triblock copolymerBuOH-H2O systems, with tuning amounts of butanol and silica source correspondingly. It is expected that the extended phase domains will allow designed synthesis of mesoporous silicas with targeted characteristics, offering vast prospects for future applications.