Synthesis And Application Of 1-D Silica-based Mesoporous Materials Templated From Amphiphilic Block Copolymers

Throughout the glorious development history of more than 20 years in the field of mesoporous materials, numerous ordered mesostructured materials with various morphologies and compositions have been prepared. As a representative example of 1-D nanomaterials, silica nanotubes belong to the most favorable nanostructures because of their remarkable physicochemical properties and potential applications in the scope of heterogeneous catalysis, drug delivery, confined synthesis, nano-electronical devices and environmental monitoring sensors.Previously, silica nanotubes were mostly synthesized by using different templates, whose preparation procedures were generally complex and time-consuming. A few protocols were based on surfactants using soft-templating approach, where the dimensions of the obtained nanotubes were nonuniform, which restricts their wide applications in the domain of materials and biology. On the other hand, previous work on soft-templating syntheses through the traditional EISA or EIAA method are mainly focused on the core/shell type nanostructured materials based on single spherical micelles or just their aggregated counterparts. However, up to now, seldom work on the cooperative self-assembly of diblock copolymers with the corresponding inorganic species into elongated tubular mesostructures, like nanotubes, and systematic structure directing roles of amphiphilic diblock copolymers in the formation of mesostructures was reported. Further probing into the synthesis and application of 1-D silica-based nanomaterials templated by amphiphilic diblock copolymers is not only of academic interests, but also can lead to construction of more novel nano-materials in the near future.In this work, we developed a shear stress-regulated process for synthesizing of silica nanotubes and their derived ordered packing array based on previously reported EIAA method. A direct carbonization of the as-made silica/template composites, followed by a removal of silica shells, can give rise to uniform carbon nanotubes. Homogeneous small gold nanoparticles were successfully introduced onto the surface of the interior cavities of the ethenyl-modified silica nanotubes, owing to their highly accessible hollow one-dimensional (1-D) channels. The obtained Au/E-SNTs catalysts showed superior performance in catalyzing the epoxidation of styrene with high conversion and selectivity towards styrene oxide. We believe that, this present shear stress-regulated assembly route can be probably further extended to other soft-templating syntheses system for rationally tailoring the micelle particles growth patterns, by just simply varying the extent of agitation of the synthesis system.In chapter 2, large-pore ordered mesoporous carbon and titania were templated by amphiphilic diblock copolymers PEO-b-PS, using resol and titanium isopropoxide as the framework precursors, respectively. The obtained large-pore ordered mesoporous carbon materials feature a face center cubic mesostructure with rather large pore of about 23 nm. The synthesized large-pore ordered mesoporous titania materials possess thermally stable and highly crystalline frameworks.In chapter 3, we developed a shear stress-regulated process for synthesizing of silica nanotubes and their derived ordered packing array based on previously reported EIAA method. Notably, the as-made silica/template composites can be further spontaneously packed into an ordered hollow mesostructure by adding minor amount of organosilanes such as BTEE into the synthesis system. The hollow silica mesostructures have two-dimensional hexagonal symmetry, seemly similar to the mesoporous silica SBA-15, but they show uniform bimodal large mesopores at 20 and 34 nm.In chapter 4, the application of the above-mentioned silica nanotubes and their derived ordered packing array in the scope of templating synthesis and functional nanocomposites materials were investigated. A direct carbonization of the as-made silica/template composites, followed by a removal of silica shells, can give rise to uniform carbon nanotubes. Homogeneous small gold nanoparticles were successfully introduced onto the surface of the interior cavities of the ethenyl-modified silica nanotubes, owing to their highly accessible hollow one-dimensional (1-D) channels. The obtained Au/E-SNTs catalysts showed superior performance in catalyzing the epoxidation of styrene with high conversion and selectivity towards styrene oxide. This novel shear stress-regulated assembly route is a significant enrichment in understanding of the formation mechanism of ordered mesostructured materials and may lead to the discovery and construction of more novel nano-materials in the near future.In chapter 5, the whole thesis is summarized.