Synthesis And Characterization Of Mesoporous Materials With Highly Catalytic Centers

There is a rapid growth in research and development of mesoporous materials. Mesoporous materials as an important class of nanostructured materials possess highly specific surface area, large pore volume, uniform pore size, and rich surface chemistry. These materials present great promises and opportunities for a new generation of functional materials with improved and tailorable properties for applications in adsorption, membranes, sensors, energy storage, catalysis, and biotechnology, etc. Scientists did a lot of work on the research of functional mesoporous materials in recent years. But these materials show poor hydrothermal stability with amorphous wall, which seriously limit their extensive uses.Recently, mesoporous silica materials containing organic sulfonic groups have been paid much attention because of their potential use as solid acidic catalysts for chemical conversion of large molecules. Generally, the organic sulfonic groups are transformed from the oxidation of mercapto groups in mesoporous silica materials by H2O2. Although there are a lot of successful examples for catalysis by solid mesoporous silica materials with organic sulfonic groups, their activities are still much lower than those of liquid concentrated sulfuric acid, which severely hinder their practical applications in catalytic reactions. The relatively low activities over mesoporous silicas with organic sulfonic groups, compared to liquid concentrated sulfuric acid, can be attributed to the low concentration of organic sulfonic groups in the samples. The increase of mercapto groups in the synthesis of mesoporous silica materials will significantly reduce the degree of crosslinking of silica condensation in the mesoporous walls to a level at which a stable ordered silica-based mesostructure cannot be formed. Therefore, mesoporous silica materials with an extremely high content of organic mercapto groups are greatly desirable.We have demonstrated a simple and general route for the synthesis of ordered mesoporous silica-based materials containing an extremely high content of mercaptopropyl groups using a surfactant mixture of fluorocarbon surfactant (FC-4) and block copolymer (P123). After the treatment with hydrogen peroxide, the ordered mesoporous silica materials with an extremely high content of organic sulfonic groups exhibit comparable activities with liquid concentrated sulfuric acid in the catalytic esterification of cyclohexanol with acetic acid. This approach would open a door for the application of mesoporous silica materials with an extremely high content of organic sulfonic groups as solid acidic catalysts on large molecular conversion with high activities.Currently there is a great interest in enzyme immobilization to enhance enzyme stability, reusability, and easy separation from the reaction mixture. And we use a general and facile approach"fish-in-net"for the encapsulation of lactase in ordered mesoporous silica, where the enzymes are entrapped in macroporous cages connected by uniform mesoporous channels. In our experiment, although the catalytic activities are not as perfect as the free enzyme, they still exhibit a certain activities, which show our method for immobilization is effective.