Reactivity studies of plasma-synthesized aluminum trifluoride and electrochemical synthesis of non-stoichiometric silver selenide nanowire arrays

A high surface area aluminum trifluoride material ("plasma-AIF3 ") has previously been synthesized in our laboratory by decomposition of zeolitic precursors in fluorine-containing, low-temperature plasmas. The characterization of the halogen exchange reactivity of this unique fluoride material is presented in Part 1 of the dissertation. A gas flow reactor was designed and built to study the isothermal and temperature-dependent halogen exchange activity of plasma-AIF3, with comparisons being made to the well-known halogen exchange catalyst beta-AIF3. Isothermal experiments showed that plasma-AIF3 is an active halogen exchange catalyst for the dismutation of dichlorodifluoromethane, while temperature-programmed reaction (TPR) experiments revealed a lower temperature onset of activity with plasma-AIF3 when compared to beta-AIF3.; The existence of two distinct active sites for halogen exchange on aluminum fluoride is proposed, with sites characteristic of plasma-AIF3 and R-AIF3 having lower and higher temperature onsets of activity, respectively. TPR data for hydrated plasma-AIF3 showed a significant attenuation of the lower temperature active sites, while the higher temperature site remained relatively unchanged in activity. Temperature-programmed X-ray diffraction of plasma-AIF3 revealed the existence of beta-AIF 3 crystallites at temperatures between 225 and 500°C, thus rationalizing the existence of the higher temperature active site (associated with beta-AIF 3) in plasma-AIF3 during heating. Plasma-AIF3 also displayed a high affinity for crystalline hydrate formation with extended exposure to moist air, and TPR experiments performed on commercially available AIF3·3H2O produced plots similar in shape and features when compared to plasma-AIF3. The thermal transformation processes of the trihydrate suggest the origin of the lower temperature active site to be associated with an amorphous bulk AIF3 structure.; Part 2 of the dissertation summarizes the current efforts made toward the template-assisted electrodeposition of Ag2+deltaSe nanowire arrays for fundamental and exploratory studies of the magnetoresistance in non-stoichiometric silver chalcogenides. Silver selenide can be difficult to electrodeposit due in part to the highly facile plating of silver metal from aqueous solutions. A new electrodeposition solution is proposed, containing AgNO3 and SeCl4 as the metal precursors, dimethyl sulfoxide (DMSO) as the solvent and tetrabutylammonium chloride (TBACl) as a supporting electrolyte. The electrodeposition of Ag2Se from this solution and a previously reported solution using NaNO3 as supporting electrolyte was investigated using cyclic voltammetry and X-ray diffraction analysis of electrodeposited thin films.; Cyclic voltammograms of solutions containing only AgNO3 and TBACl in DMSO showed one redox couple corresponding to the deposition and stripping of Ag metal, while the NaNO3-based solution showed an additional redox couple believed to involve the generation of negatively-charged Ag nanoparticles. Thin film electrodeposition of Ag metal from DMSO-based solutions produced non-dendritic deposits, and may be a useful alternative bath solvent for the silver plating industry. Solutions containing only SeCl 4 and TBACl in DMSO were studied by cyclic voltammetry, and revealed important potential ranges within which elemental Se is stable with respect to oxidation and reduction. The proposed mixed-metal electrodeposition solution was also analyzed with cyclic voltammetry, and the reductive formation of Ag2Se was found to occur at potentials between -0.55 V and -0.70 V (vs. Pt/0.1 M Nal, 0.05 M I2 (DMSO)).; Using the results from the electroanalysis of the electrodeposition solutions, nanowire arrays of Ag2+deltaSe were successfully grown by electrodeposition into porous alumina membranes at room temperature (22°C) using an applied voltage of -0.70 V (vs. Pt/0.1 M Nal, 0.05 M I2 (DMSO)). Scanning electron microscopy...