Q. Li, M. Afeworki, D.C. Calabro, R.J. Colby, M. Kochersperger, B.K. Peterson, S.C. Weston
ExxonMobil Research and Engineering Company,
Keywords: hybrid organic-inorganic, sol-gel self-assembly, gelation
Summary:The advent of surfactant-templated mesoporous silicas more than 25 years ago introduced a novel methodology for creating controlled porosity solids. Subsequently, both hard and soft templating techniques have been applied broadly to the synthesis of catalyst supports, adsorbents, membranes, textured surfaces and low k dielectrics. The combination of controllable porosity with a typically high concentration of surface hydroxyls has also made these materials attractive as substrates for a diverse range of surface-grafted functional groups. We have recently reported the template-free synthesis of a family of mesoporous organosilicas based on a common cyclic organosilane precursor. These materials are found to have textural properties comparable to that of templated materials prepared from the same precursor. The high organic content of these organosilicas (Si:C=1:1) affords these materials superior hydrothermal stability compared to mesoporous silicas. The self-assembly of this precursor results purely from conventional hydrolysis/condensation sol-gel chemistry, free of any supplementary coulombic, H-bonding, or hydrophilic/hydrophobic organizing interactions. It will be shown that the textural properties of these materials can be altered over a wide range by the straightforward variation of synthesis conditions. This textural variability will be explained in terms of changes in the structure of the gel network produced by this building block during drying.