Synthesis of large mesoporous silicas and polymer/silica composite frameworks

Abstract

The hexagonally ordered mesoporous silica denoted as SBA-15 was reported by Zhao et al. in 1998. The silica materials exhibit large surface area (700-900 $m^2 g^{-1}$) , extended pore size (5 - 15 nm) and thick walls (2 - 4 nm). Due to its appealing textural properties and appreciable thermal and hydrothermal stability, SBA-15 has recently attracted much research attention for potential applications in catalysis or separation processes. Along the way, the precise character of the 1-dimensional channel or 3-dimensional interconnection of the pore systems has been a matter of debate for the past few years and direct control of the interconnecting porosity during synthesis still remains as a challenge. Such control is particularly desirable for applications involving host-guest interactions, adsorption or diffusion processes, and template synthesis for other nano-structured materials. Another important aspect of SBA-15 materials is linked to the commercial requirements for their synthesis. There is a strong demand for low cost processes, the possibility of scaling-up the batch size, high yields and synthesis efficiency. Here, a simple synthetic approach allowing an easy and highly reproducible control of the network connectivity and wall thickness of SBA-15 is proposed, by adjusting the $SiO_2$: P123 ratio and decreasing substantially the HCl concentration compared with the original system. In addition, the present synthesis conditions, with stirring at decreasing acid concentration, are suitable for the production of high-quality SBA-15 materials, irrespective of the synthesis batch size and the different silica precursors. In contrast to ordinary mesoporous silicas, the SBA-15 type large mesoporous silicas exhibit sufficiently high affinity toward organic species, allowing the systematic incorporation of polymers without blocking the mesopores. The resultant mesoporous polymer/silica composite materials have advantages due to their synergistically enhanced prope...