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Chemical Modification of Porous Alumina for Nanowire Templating and NEXAFS Spectroscopy of Aqueous ATP

  • Author(s): Kelly, Daniel Nicholas
  • Advisor(s): Stacy, Angelica M
  • Saykally, Richard J
  • et al.
Abstract

Part One: Chemical Modification of Porous Alumina for Nanowire Templating:

A modified sol-gel technique and subsequent polymer coating technique was used to modify the size of nanowires grown via electrodeposition in porous alumina templates. The porous alumina film is initially soaked in a water-containing solution prior to exposure to a different solution of 3-aminopropyltriethoxysilane in toluene. The amount of water in the aqueous solution correlates with the thickness of silane coating observed after exposure to the organic solution. The pH of the aqueous solution influences the coating thickness as well, primarily as a function of film density. Other factors such as silane concentration, silane exposure time, and aqueous co-solvent choice did not influence the coating thickness.

After coating porous alumina with APTES, polymethylmethacrylate (PMMA) was coupled to amines at the material surface through an aminolysis reaction. No proton-transfer catalyst was necessary for the transformation. Thickness of polymer films were related to initial pore diameter in the modified porous alumina. Dissolution of PMMA-treated porous alumina templates under alkaline conditions yielded no nanostructures, supporting the covalent attachment of the PMMA to the pore wall. Amide-related peaks were also observed using infrared spectroscopy.

Several nanowire systems were grown in the aforementioned chemically modified, electrode-backed porous alumina templates. Nickel, bismuth telluride, and bismuth antimony nanowires were grown electrochemically using previously established methods. Nanowire diameters were smaller in modified templates in accordance with the coating procedures applied to the porous alumina.

Part Two: NEXAFS Spectroscopy of Aqueous ATP:

NEXAFS spectroscopy at the nitrogen and carbon K-edges was used to study the hydration of adenosine triphosphate in liquid microjets. Total electron yield spectra were recorded as a function of concentration, pH, and the presence of sodium, magnesium, and copper ions (Na+/Mg2+/Cu2+). Significant spectral changes were observed upon protonation of the adenine ring, but not under conditions that promote π-stacking, such as high concentration or presence of Mg2+, indicating NEXAFS is insensitive to the phenomenon. Intramolecular inner-sphere association of Cu2+ did create observable broadening of the nitrogen spectrum, whereas outer-sphere association with Mg2+ did not.

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