Ionic transport properties of template-synthesized gold nanotube membranes

Ionic transport in nanotubes exhibits unique properties due to the strong interactions between ions and the nanotube surface. The main objective of my research is to explore and regulate the ionic transport in gold nanotube membranes.;Chapter 1 overviews a versatile method of fabricating nanostructured materials, called the template synthesis. Important parameters of the template synthesis are introduced such as templates and deposition methods. The template synthesis method is used to prepare membranes used in this dissertation.;Chapter 2 describes a method to increase the ionic conductivity in membranes containing gold nanotubes with small diameter (4 nm). The gold nanotube membrane is prepared by the electroless plating of gold in a commercially available polycarbonate membrane. Voltages are applied to the gold nanotube membrane and fixed charges are injected on the gold nanotube walls. We show that ionic conductivity of the gold nanotube membrane can be enhanced in aqueous potassium chloride (KCl) solution at negative applied voltages. When the most negative voltage (-0.8 V vs. Ag/AgCl) is applied to the membrane, the ionic conductivity of the solution inside the gold nanotube (94 mS.cm-1) is comparable to that of 1 M aqueous KCl, over two orders of magnitude higher than that of the 0.01 M KCl contacting the membrane.;Chapter 3 explores another important transport property of the gold nanotube membrane -- ion permselectivity. When the permselective membrane separates two electrolyte solutions at different concentrations, a membrane potential is developed and measured by the potentiometric method. Surface charge density and the ion mobilities are estimated by fitting the experimental data with a pre-existing model. The surface charge density of the gold nanotube membrane in this research is estimated to be 2 muC/cm2.;Chapter 4 describes voltage-controlled ionic transport in a gold/polypyrrole membrane doped with sodium dodecylbenzene sulfonate (DBS). Polypyrrole (PPy) films doped with DBS are electropolymerized on both sides of a polycarbonate membrane template. The gold/PPy membrane is oxidized at 0.6 V (vs. Ag/AgCl) and reduced at -0.7 V. We show that the gold/PPy (DBS) membrane can be switched between dielectric-film characteristics in oxidized form and a high conductance state in reduced form.