Design and applications of metal oxide nanostructures from electrospun carbon templates.

摘要

This dissertation outlines advances in the design, fabrication, characterization and application of metal oxide/polymer composite fibers, metal oxide polymer coaxial fibers, and metal oxide fibers and tubes. Their preparation was based on the electrospinning technique, in which metal oxide precursors were incorporated into polymer solutions and electrospun to yield composite fibers or coated onto the walls of polymer fiber templates to yield coaxial fibers. The calcination of composite fibers and coaxial fibers yield metal oxide nanofibers and nanotubes, respectively. These materials were characterized for their unique chemical, physical, catalytic, magnetic, optical, and mechanical properties. These materials were also found to have enormous surface to volume ratios invaluable in heterogeneous catalysis.;Electron-hole recombination is a major practical problem facing the use of titanium dioxide (TiO2) as a photocatalyst in environmental remediation. We describe the use of surface modified anatase TiO2 nanofibers with gold (Au) nanoparticles in the photodegradation of methyl orange and methyl red as organic pollutants. The TiO2 nanofibers were generated by electrospinning of a composite solution of polymethylmethacrylate and titanium isopropoxide followed by calcination at 500°C. The dimensions of TiO2 nanofibers and Au nanoparticles were 150+/-50 nm and 20+/-10 nm, respectively. Au loaded TiO2 catalyst exhibited an enhanced photocatalytic activity in photodegradation of methyl orange and methyl red under UV irradiation compared to neat TiO2.;The TiO2 nanofibers were also used as catalyst supports for palladium (Pd) nanoparticles due to their high aspect ratio and ease of fabrication. Pd nanoparticles were deposited in situ onto TiO2 support by aqueous incipient wetness impregnation. The size of the nanoparticles was ∼5-10 nm in diameter. Pd nanoparticles supported on TiO2 (Pd/TiO 2) were applied as heterogeneous catalysts in the Heck reaction. The Pd/TiO2 showed an enhanced catalytic activity and selectivity at 140°C for trans-stilbene with yields greater than 94% compared to 80% of Pd nanoparticles on carbon supports. This was attributed to high surface area, porosity and high dispersion of Pd nanoparticles supported on TiO2 nanofibers.;Metal oxide nanotubes were fabricated using the TUbes by Fiber Templating (TUFT) approach in which electrospun nanofibers were used as exo-templates. Zinc oxide, titanium dioxide and zirconium dioxide were deposited as colloidal suspensions onto electrospun polymer fibers. The average diameter of the templates was ∼250+/-100 nm. Thermal degradation of the template core yields metal oxide sub-micron tubes with diameters ∼350-450 nm and a wall thickness ∼50-100 nm. Similarly, Co doped ZnO and TiO2 nanotubes were fabricated via the sol-gel process and characterized for optical and magnetic properties.;The integration of Vertically Aligned Carbon Nanotubes (VACNTs) in processor chips as thermal interface materials for the management of heat dissipation was also investigated due to their superior thermal and electrical conductivity. VACNTs were successfully synthesized via Catalytic Thermal Chemical Vapor Deposition (CTCVD) method. Pd capping of VACNTs tips, meant to lower interfacial resistance between CNTs and a heat sink, was not successful. This was due to poor surface wetting of CNTs which require surface modification of the CNTs to facilitate Pd capping via electroless plating.