First reported in 1992, ordered mesoporous materials exhibit unique features, such as regular pore geometry, high surface area, and large pore volume, and have shown great potential in various applications. This dissertation combines the knowledge from the field of ordered mesoporous materials and several other research areas to design advanced hybrid porous materials for controlled release and catalysis applications.
The demand for better treatment of illness has led to ever-increasing efforts in the development of efficient drug delivery system that can transport drug molecules to the targeted site and release the loading in a controlled manner. The emerging ordered mesostructured materials exhibit great potential in controlled release because of their stable structures, large surface areas, tunable pore sizes and pore volumes, well-defined surface properties, and biocompatibility. The great diversity in surface functionalization offers mesoporous silica a unique advantage in site-specific delivery and stimuli-responsive release. My research is focused on developing novel controlled release systems using physiologically compatible chemical or physical stimuli by integrating organic materials with inorganic nanostructured porous materials. The release system uses mesoporous materials as reservoir and functional organic or nanomaterials as valves to perform the controlled responsive functionalities. With this strategy, a series of stimuli responsive and physiologically compatible release systems have been developed, which provide a promising new direction in the bio-applications of nanostructured materials.
Poly(4-vinyl pyridine) is coated on mesoporous silica through facile "grafting to" method. The grafted polymer nanoshell works as pH-sensitive barrier to control the release of trapped molecules from mesoporous silica. We also use nanoparticle as capping agent to block the silica mesopore by pH-responsive acetal linker to obtain acid-sensitive delivery system. By designing a polymeric network (capable of being cross-linked and de-cross-linked) as a "gatekeeper" at the pore opening of mesoporous silica-based materials, a series of hybrid porous materials for controlled release have been developed. For example, the pore of silica materials loaded with guest molecules are blocked by the addition of cystamine, a disulfide-based bifunctional primary amine, which allows polymer chains around the silica surface to be cross-linked. The polymeric network thus formed around the pore opening can be reopened by cleaving the disulfide bond of cystamine in the presence of disulfide reducing agents such as dithiothreitol (DTT), leading to the redox-controlled release. The further introduction of cyclodextrin introduced into the polymer network expands the responsive diversity by supramolecular host-guest interaction, which is sensitive to photoirradiation, redox signal, or competitive binding.. In addition, cavitands are introduced into the hybrid system and work as supramolecular releasing trigger.
Sulfonated ordered mesoporous carbons have been synthesized by covalent attachment of sulfonic acid containing aryl radicals on the surface of mesoporous carbons. The hybrid materials work as novel solid acid catalysts, which show stable and highly efficient catalytic performance in biodiesel production.