Templating Preparation Of Mesoporous Fibers And The Studies On Encapsulation Of Functional Materials

Recently, investigation on morphology of mesoporous silica has attracted considerable attention. For many applications, these mesoporous materials should be controlled not only on the nanometer scale of the pore structure but also on the micrometer scale of the morphology. A diversity of mesoporous silica with defined morphology, like films, spheres, fibers or tubules, has been demonstrated. Due to the combination of ordered mesopores and high aspect ratio, hollow or solid fibers are particularly interesting for potential application in optical devices, nanofluidics, and hosts for chemical species. Early approaches to mesoporous silica fibers employed direct synthesis through one-phase or two-phase reaction. The one-phase synthesis usually starts from a dilute solution of silica-surfactant and the fiber diameter is in a wide range, depending on the synthesis conditions. The two-phase reactions utilize the oil-water interface under acidic condition and the fibers have a single-crystal-like mesostructure with diameters from 1 to 40 m. Presently, three problems remain to be resolved: (1) There are many effects that influence the products, so it is difficult to control the microscopic and macroscopic properties of the fibers independently. (2) The fibers are self-dispersed and disordered. (3) The diameter and length of fibers are in wide ranges. In this word, template synthesis and the self-assembly of mesophasesare combined to yield a novel method for preparing ensembles of parallel hollow mesoporous silica fibers. These fibers with hierarchical organization can easily be prepared using surfactants as structure-directing agent and anodic aluminium oxide (AAO) membranes as hard template. The microscopic and macroscopic properties of the fibers can be independently controlled. The diameter and length of mesoporous fibers is corresponding to pore diameter and thickness of AAO membrane. Because the pore diameter, thickness, and pore density of the AAO membrane can be controlled by varying the anodization procedure, fiber array with any desired characteristics could be prepared. The internal architecture of mesoporous nanofibers can be controlled by varying the component of precursor solution.Among all metals, copper plays an essential role since it shows unique physical properties such as high electrical conductivity and is widely used as interconnects in electronic circuits. So far, various types of Cu nanostructures like films, nanoparticles, and nanowires have been successfully fabricated using chemical and physical method. However, synthesis of copper nanotube has not been reported yet. The template synthesis method pioneered by C. R. Martin is one of the important processes for fabricating metal nanostructures. However, this procedure usually results in solid metal wires instead of hollow tubes unless the pore surface is modified specially. In this wore, an effective method for preparing ordered metal nanotube arrays with open ends by electroless deposition in AAO templates is described as a four-step procedure, i.e., pore-wall modification, polish treatment, sensitization-activation and electroless deposition. The AAO membranes were first functionalized with silane containing amine group. Then the membranes were polished to expose the unmodified surface to prevent the formation of the densely metallic film on the membrane surface. In order to obtain Cu tubes, a catalyst must be applied to the pore surface, so the metal preferentially deposits on the pore walls. This was accomplished by a two-step process. The modified alumina membranes were first sensitized with Sn2+ sensitizer, which binds to the surface via complexationwith surface amine group. It was then activated with Pd2+, resulting in the formation of Pd nanoparticles on the surface of the template. Finally, the Pd-coated membrane was immersed in a Cu plating bath. Cu deposited onto the pore surface from solution. The amine group functional procedure on the pore surface is a key step for nanotube growth. It seems that the interaction between the alumina por...