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Ce travail de thèse est consacré à la synthèse électrochimique de films minces d’hydroxydes doubles lamellaires (HDL) et à l’élaboration de biocapteurs enzymatiques à détection ampérométriques, utilisant ces films comme matrices d’immobilisation des enzymes. Des études préalables de synthèse de suspensions de HDLs à partir de la neutralisation de mélange de cations métalliques divalents et trivalents par la soude ont été effectuées. Les solides formés ont été caractérisés par spectroscopie FTIR et par diffraction des rayons X ; leurs compositions ont été déterminées par dosages chimiques et par ICP-OES. Les conditions permettant de former exclusivement un HDL ont été précisées pour plusieurs couples cations divalents / cations trivalents, en présence d’ions bicarbonate ou du complexant EDTA. Les suivis pHmétriques ont permis de définir les compositions d’électrolytes les plus adaptées pour les synthèses électrochimiques des films de HDLs. Des films minces d’Hydrotalcite ou de Pyroaurite ont été obtenus sur substrat conducteur (Pt, Au) par augmentation du pH local résultant de la réduction de l’oxygène dissous ou de l’eau. Les paramètres potentiel, courant et temps de réduction ont été étudiés. Des comportements électrochimiques linéaires de ces électrodes modifiées vis-à-vis de l’ion ferricyanure ou des produits de catalyse enzymatique, H2O2 et NADH, ont été mis en évidence. Deux types de biocapteurs, à glucose ou à lactate, ont été fabriqués par co-déposition électrochimique du film HDL et de l’enzyme, glucose oxydase ou lactate déshydrogénase. Leurs sensibilités ampérométriques pour leur substrat, glucose ou lactate, ont été étudiées en fonction de différents paramètres de préparation ou de fonctionnement. / This work is devoted to the electrochemical synthesis of layered double hydroxides (LDH) thin films and to the development of enzymatic biosensors with amperometric detection, using these films as immobilization matrices of enzymes. Preliminary studies of LDH suspensions synthesis by neutralization of mixed divalent and trivalent metallic cations with sodium hydroxide were performed. The powders were characterized by FTIR spectroscopy and X-ray diffraction, and their compositions were determined by chemical titration and ICP-OES. Conditions for the formation of pure LDH were specified for several couples of divalent / trivalent cations, in the presence of bicarbonate ions or EDTA. The pH titration curves allow the determination of the best suited electrolyte compositions for the electrodeposition of LDHs films. Hydrotalcite or Pyroaurite thin films were obtained on conductive substrates (Pt, Au) from the increase of local pH induced by dissolved oxygen or water electrochemical reduction. The following parameters were studied, potential, current and reduction time. The linear electrochemical behaviour of these LDH-modified electrodes was verified for the oxidation of ferricyanide ions or H2O2 and NADH, the products resulting from bio-catalysed reactions. Two types of biosensors, for glucose or lactate determination, were elaborated by electrochemical co-deposition of LDH film and enzyme, glucose oxidase or lactate dehydrogenase. Amperometric sensitivities for glucose or lactate were studied as a function of preparation and operation parameters.

Magister Scientiae - MSc / TiO2 has been broadly used as a standard photocatalyst due to its high stability, low cost, relatively low toxicity, and excellent photocatalytic performance in comparison to other semiconductor materials. However, the large band gap of TiO2 limits its use as a photocalyst due to the high energy required for excitation of the electrons in the UV region. Research on the reduction of TiO2 band gap to the visible region of the spectrum has been explored with little success. Therefore, this study focusses on shifting the band gap of TiO2 catalyst from the UV region to the visible region by doping with graphene and nitrogen-doped graphene to form TiO2-G and TiO2-NG nanocomposites, respectively. The N-doped graphene support was prepared by doping the graphene oxide with nitrogen through Hydrothermal process, followed by the reduction of the materials. Fourier Tranform Infrared (FTIR) spectroscopy confirmed the successful doping of graphene to N-graphene by the appearance of C-N and N-H vibrational modes on the spectra. The XRD results show the fingerprint patterns of TiO2 and N-graphene, which confirms the successful preparation of the nanocomposites. Morphological studies of the nanocomposites using transmission electron microscopy (TEM) show the TiO2 nanowires dispersed on graphene related supports. The optical band gap of TiO2 from UV-Vis spectroscopy was found to be 3.2eV, which decreased to 2.7eV and 2.5eV upon incorporation of grapheme and N-graphene, respectively. These results prove the success in the achievement of the aim in this study. When electrochemical studies were further conducted on the materials, TiO2-NG was found to possess better electrochemical properties with fast electron kinetics observed on the impendance spectroscopy results. The results obtained justified use of TiO2-NG photocatalyst the optimal material for organic mineralisation in Advanced Oxidation Processes (AOPs).

This thesis describes the application of macro, micro, ultra-microelectrodes and microelectrode arrays to the measurement of trace concentrations of nickel and cobalt in sediment and natural waters by adsorptive cathodic stripping voltammetric methods. In addition the measurement of tin by adsorptive cathodic stripping voltammetry in sediment and natural waters is discussed. Also, the application of macroelectrodes and microelectrode arrays to the measurement of lead, cadmium and zinc in sediment and natural waters by anodic stripping voltammetry is considered. In all cases the determination of the six metals was optimised by investigating the influence of various significant parameters, such as in-situ mercury plating, complexing agent concentration, scan rate, pulse height, accumulation time and potential, buffer concentration and pH. The results obtained for these investigations are discussed in this thesis / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--State University of New York at Binghamton, Dept. of Chemistry, 2006. / Includes bibliographical references.

Thesis (M.E.E.)--University of Delaware, 2006. / Principal faculty advisor: Balaji Panchapakesan, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Insttute, 1955. / Typewritten. Vita. Bibliography: p. 138-143. Also available via the Internet.

Abstract Information science and technology ( IT; Including computer and communication), Biotechnology (BT) and Nanotechnology (NT), are the three main technologies dominant in the 21st century. In nanotechnology, quantum size effects or surface effect (due to enhanced surface to volume ratio) can cause many new and interesting phenomena. In the literature there is also evidence that addition of small metal particles to semiconductors can enhance the optical properties of these semiconductor ¡Vnanoparticle hybrid systems. In this thesis, an electrochemical method is used to fabricate Au and ZnO nanoparticles. To characterize the samples we use various techniques like TEM (for the particle size and crystal structure), XRD (for structure, particle size analysis), Absorbance spectroscopy (for analyzing the optical properties of these systems), Photoluminescence (to study the mechanism of internal emission in the ZnO nanoparticles) On the theoretical part, some calculations based on the Drude model we computed and compared to the experimental absorbance spectrum of the samples.