| Popis: |
This dissertation reports the synthesis of ordered mesoporous organosilicas, with surface and bridging groups, obtained under microwave conditions. The study was focused on the usage of microwave irradiation to synthesize high quality organosilica mesostructures, and to monitor their adsorption and surface properties by varying chemical composition as well as time and temperature of hydrothermal synthesis. Specifically, channel-like and cage-like ordered mesoporous organosilicas with various surface and bridging groups were synthesized under microwave conditions. Also, microwave-assisted synthesis of cage-like ordered mesoporous silicas was carried out and improved. For the purpose of comparison, analogous mesostructures were prepared by using conventional heating instead of microwave irradiation. This study shows that the removal of polymeric template from as-synthesized cage-like siliceous mesostructures requires a combination of extraction with acidified ethanol and thermal treatment in flowing nitrogen at about 350 °C. The microwave-assisted synthesis was successfully used to screen a wide range of temperatures and time in order to establish optimal conditions for the preparation of SBA-16. It is noteworthy that this synthesis requires only 8-18 hours instead of the 48 hours normally used. The resulting cage-like materials exhibited high surface area, large pore volume and large pore diameters. The attachment of vinyl, ureidopropyl and mercaptopropyl groups into siliceous pore walls of SBA-15 and SBA-16 mesostructures was successful under microwave conditions. Mono- and bi-functional channel-like and cage-like organosilicas prepared under microwave irradiation showed comparable or improved adsorption properties (for instance, larger pore volume and pore size and higher specific surface area) than those obtained for the corresponding samples synthesized using conventional heating. The microwave-assisted synthesis of periodic mesoporous organosilicas with ethane, isocyanurate and disulfide bridging groups was also explored. Similarly as in the case of organosilicas with pendant groups, the co-condensation synthesis under microwave irradiation afforded ordered mesostructures having organosiliceous framework with high surface area and large pore volume. This work demonstrates the attractiveness of the microwave technique for the synthesis of ordered mesoporous organosilicas. |
