Controlling the Nanoscopic and Macroscopic Properties of Inorganic Tubes: Towards Advanced Applications in Materials Science

• Other Authors: Makki, Rabih Mohammad (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Chemistry; Biochemistry
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-6963

Materials synthesis far from thermodynamic equilibrium can yield hierarchical order that spans from molecular to macroscopic length scales. Here we study the formation of microscopic and macroscopic inorganic tubes during spatially controlled reaction processes. The underlying chemistry involves the precipitation of amorphous silica and metal hydroxides during the mixing of silicate solutions and metal ions with insoluble hydroxides. The conventional method involves the addition of a metal salt crystal into an aqueous silicate solution. However the random shape and size as well as the continuous, and hence transient, dissolution of the crystal hamper the quantitative and systematic analysis of the system, and limit the potential applications of the obtained structures. To overcome these problems, we employ small (micro-scale) polymer beads. These beads are produced by emulsification techniques and then loaded with metal salt by simple equilibration in aqueous solution. Once exposed to the sodium silicate solution, a thin colloidal membrane starts to grow around the entire bead from which microtubes emerge. For the copper sulfate-silicate system, tube formation is only observed above a critical bead radius that is inversely proportional to the initial loading concentration. The formed tubes have inner radii down to 3 m, reach lengths of 0.5 mm, and grow at speeds of up to 50 m s1. Moreover, tubes pinned to air bubbles can induce directional bead motion. We also describe a new approach that establishes control over the growth velocities of macroscopic silica-metal oxide/hydroxide tubes. Our approach is demonstrated for the injection of acidic cupric sulfate solution into a large volume of basic sodium silicate solution. The forming tube is pinned to a gas bubble that is held at the end of a hollow glass rod. The tube's linear growth follows the speed of the glass rod while its radius is self-selected according to volume conservation of the injected solution. Depending on the experimental conditions, tube growth occurs at either the moving gas bubble or the stationary glass capillary. Oscillatory modulations of the growth velocity provoke the formation of hollow nodules on the outer tube surface. These nodules form after each rapid velocity decrease at exponentially decaying rates and seem to be energetically favored over a sudden isotropic increase in tube radius. We also demonstrate a simple and facile method for the production of straight copper(oxide)-silica tubes. The tubes are produced for different oxidation states of copper (i.e., Cu, CuO, and Cu2O). For these experiments, copper hydroxide-silica tubes are first prepared by injecting cupric sulfate solution into sodium silicate solution and pinning a growing tube to a "free" rising air bubble. The obtained tubes are then heated to form copper(II), or copper(I), oxide-silica tubes. Finally, copper-silica tubes are produced by adding a diluted sulfuric acid solution over the copper(I) oxide-silica tubes. Thermogravimetric analyses confirm the heat-induced decomposition of copper hydroxide within the original tubes while X-ray diffraction certifies the composition of the modified tubes. Lastly, the velocity-controlled approach is applied to the synthesis of iron oxide-silica tubes. Transmission electron microscopy and X-ray diffraction, as well as Raman and Mössbauer spectroscopy reveal magnetite nanoparticles in the range of 5−15 nm. Optical data suggest that the magnetite particles follow first-order nucleation−growth kinetics. The hollow tubes exhibit superparamagnetic behavior at room temperature, with a transition to a blocked state at TB = 95 K for an applied field of 200 Oe. Heat capacity measurements yield evidence for the Verwey transition at 20 K. Finally, we show a remarkable dependence of the tubes' magnetic properties on the speed of the pinning rod and the injection rate employed during synthesis === A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Fall Semester, 2012. === November 5, 2012. === Chemical Gardens, Magnetite, Polymer Beads, Self-Propelled, Silica Tubes, Verwey Transition === Includes bibliographical references. === Oliver Steinbock, Professor Directing Dissertation; Paul Trombley, University Representative; Naresh Dalal, Committee Member; Susan Latturner, Committee Member.