Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (M. Phil.)--University of Hong Kong, 1992.

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2008. / Title from PDF t.p. (viewed Aug. 17, 2009). Includes bibliographical references. Also issued in print.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Ohio University, March, 2006. / Title from PDF t.p. Includes bibliographical references (p. 57-58)

Thesis (M.Sc. (Chemistry)) - Rhodes University, 2007.

Carbon electrodes have found widespread use in electrochemistry due to its broad versatility and low cost amongst other advantages. Recent innovations in carbon materials have added new dimensions to their utility in electrochemical applications. This thesis aims to investigate aspects of carbon materials, in particular boron-doped diamond (BDD) and nanocarbon composites, mainly for electrochemical analysis and energetics studies. The electrochemical behaviour of estradiol and other endocrine disrupting compounds was examined on the BDD electrode with different surface pretreatments, as well as on a nanocarbon-modified BDD electrode. It was shown that the precise control of surface chemical termination enabled the electrode to be tuned to exhibit diffusional or adsorptive voltammetry at oxidised and hydrogenated BDD interfaces respectively. Adsorption effects were also observed on the modified electrode leading to significant pre-concentration of the analyte onto the nanocarbon and a corresponding lowering of the limit of detection by ca three orders of magnitude to nanomolar levels. Surface modification of the BDD electrodes was then explored using a simple and convenient dropcast technique to deposit microcrystalline copper phthalocyanine onto the electrode. The influence of the surface chemical termination towards the interaction with the modifier compound was demonstrated in relation to the oxygen reduction reaction. Hydrogen terminated BDD modified in such a manner was able to significantly decrease the overpotential for the cathodic reaction by ca 500 mV when compared to the unmodified electrode while modified oxidised BDD showed no such electrocatalysis, signifying greater interaction of the phthalocyanine modifier with the hydrogenated surface. The lack of a further conversion of the peroxide product was attributed to its rapid diffusion away from the triple phase boundary (comprising the phthalocyanine microcrystallite, aqueous solution and BDD electrode) at which the reaction is expected to exclusively occur. Next carbon composites were studied in the form of carbon paste electrodes (CPEs). The practicality of a nanocarbon paste was established by cyclic voltammetry with several well-characterised redox systems commonly used to test electrode activity and was found to exhibit comparable behaviour to the more typical graphitic formulation. Reversible uptake of some analytes was observed at the CPEs, giving rise to complex double peak voltammetry. This uptake phenomenon was then further examined at the nanocarbon paste electrode to monitor the transfer of species between two dissimilar liquid phases. The interfacial behaviour gave rise to voltammetric peaks which were assigned to species originating from the aqueous, binder and carbon phases respectively and this enabled the measurement of Gibbs energies of transfer between oil and aqueous phases. Finally the effect of different ionic liquids as binder for carbon-ionic liquid composite electrodes was studied. Some ionic liquids were demonstrated to offer benefits in comparison to oil in the fabrication of carbon paste type electrode due to an increased adsorption of analytes. The ionic “liquid” (with a melting point above room temperature) <i>n</i>-octyl-pyridinium hexafluorophosphate [C₈py][PF₆] was shown to be useful in combination with carbon nanotubes as a composite electrode or as a modifier to a screen-printed electrode to significantly enhance the sensitivity of electrochemical detection via adsorptive stripping voltammetry. Overall the carbon-based electrodes studied have demonstrated excellent utility as electrode materials in the areas of electrochemical sensing and energetics investigations.

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Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Bitstream added on 2014-06-13T19:44:55Z : No. of bitstreams: 1 milare_e_dr_araiq.pdf: 10181929 bytes, checksum: 3f94f7f763de7735f2990b5223234de8 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Eletrodos laminares de Ir ou Pt-Ir(30%) foram empregados como substratos para deposição eletroquímica de Hg, a partir de soluções contendo íons Hg(I), e remoção deste Hg por meio de voltametria cíclica (VC) ou térmica (termogravimetria / termogravimetria derivada - TG/DTG e calorimetria exploratória diferencial - DSC). A superfície dos eletrodos foi caracterizada empregando-se as técnicas complementares de análise: microscopia eletrônica de varredura (imagens SEM, microanálise por EDX e mapas de distribuição de elementos), microscopia eletrônica de transmissão (imagens TEM, microanálise por EDX e difração de elétrons), difratometria de raios X (XRD) e espectroscopia fotoeletrônica de raios X (XPS). Os voltamogramas cíclicos obtidos para o sistema Ir/Hg mostram até 3 picos na região de varredura de potenciais decrescentes, que foram atribuídos a: deposição de Hg em regime de subpotencial (UPD); deposição de Hg volumétrico, e redução de óxidos. A curva de I-E para a varredura de potenciais crescentes mostra até 6 picos, dependendo do tratamento empregado, que foram atribuídos a: oxidação de Hg volumétrico a Hg(I); oxidação de Hg(I) a Hg(II); oxidação de Hg presente no filme sobre a superfície do substrato a Hg(II); oxidação de Hg presente na sub-superfície do eletrodo a Hg(II); formação de óxidos. Os voltamogramas cíclicos obtidos para o sistema Pt-Ir(30%)/Hg mostram até 4 picos na varredura de potenciais decrescentes, que foram atribuídos a: deposição de Hg em regime de subpotencial (UPD) e redução de óxidos, concomitantemente; deposição eletroquímica de Hg volumétrico, e formação de produtos de interação Hg-substrato. Na varredura de potenciais crescentes a curva I-E mostra até 6 picos, dependendo do tratamento empregado, atribuídos a: oxidação de Hg volumétrico a Hg(I); oxidação... / Laminar electrodes of Ir or Pt-(30%)Ir were used as substrates for electrodeposition of Hg from Hg(I)-containing solutions, and Hg removal, using cyclic voltammetry (CV) or thermal analysis (thermogravimetry / derivated thermogravimetry - TG/DTG and differential scanning calorimetry- DSC). The electrode surface was characterized using complementary techniques for surface analysis: scanning electron microscopy (SEM images, EDX microanalysis and mapping of elements), transmission electron microscopy (TEM images, EDX microanalysis and electron diffraction), X ray diffratometry (XRD) and X ray photoelectron spectroscopy (XPS). The cyclic voltammograms of the Ir/Hg system shows at least 3 peaks in the cathodic potential scan, which were attributed to: underpotential deposition of Hg (UPD); bulk Hg deposition, and; reduction of oxides. In the anodic potential scan up to 6 peaks can be observed (depending on the treatment used), which were attributed to: bulk Hg oxidation to Hg(I); oxidation of Hg(I) to Hg(II); oxidation of Hg film formed on the substrate surface to Hg(II); oxidation of Hg from the sub-surface to Hg(II); the formation of oxides. The cyclic voltammograms obtained for the Pt-(30%)Ir/Hg system show up to 4 peaks in the cathodic potential scan, which were attributed to: underpotential deposition of Hg (UPD) and the reduction of oxides, concomitantly; bulk Hg deposition, and; the formation of products of Hg-substrate interaction. In the anodic potential scan up to 6 peaks could be recorded (depending on the electrode treatment), which were attributed to: bulk Hg oxidation to Hg(I); oxidation of Hg film from the substrate surface to Hg(II); the formation of oxides and decomposition of intermetallic compounds formed by Hg-substrate interactions, and Hg removal from substrate and decomposition of Pt/Hg intermetallic compounds. The Hg was also deposited at an open-circuit potential...(Complete abstract click electronic access below)

The main tasks of this thesis were to evaluate a number of amperometric enzyme electrode chemistries for the selective and sensitive detection of L-lactate, and apply mass fabrication technologies to reproducibly manufacture sensors in a controllable manner. The sensors studied were based on the use of lactate oxidase with a range of modified-carbon electrodes. Noble metals, hexacyanoferrate (111) or Prussian Blue were used to modify carbon electrodes for the electro-catalytic determination of hydrogen peroxide, the product of the reaction of lactate oxidase with L-lactate. Tetrathiafulvalene was employed as an artificial mediator between the enzyme and the electrode. Polypyrrole was tested as a means of immobilising lactate oxidase and to achieve direct charge transfer to the underlying carbon electrode. The characteristics of the sensor responses to hydrogen peroxide, L-lactate and ascorbate were compared, in relation to the electrochemical electrode area. From this investigation, it was confirmed that screen-printed electrodes were more reproducible to manufacture than hand-fabricated electrodes. For screen-printed rhodinised-carbon electrodes, an operating potential of +400 mV (SCE) was selected. Interference from ascorbic acid and sensitivity to hydrogen peroxide were determined to be 26 μA.mM⁻¹.cm⁻² and 27 μA.mM⁻¹.cm⁻², respectively. Screen-printed carbon electrodes modified with platinum, rhodium or palladium were selected for further investigation. Rhodium on carbon performed the best in ten-ns of sensitivity and selectivity at low potentials, and different formations of rhodium-carbon complexes were studied. Although rhodium electroplated onto carbon screen-printed electrodes was examined, printing inks made from a preformed powder of rhodium on carbon-graphite proved to be the preferred route of electrode fabrication. Screen printing, ink-jet printing and Cavro solution deposition were employed to fabricate the amperometric enzyme electrodes. These sensors were composed of rhodinised carbon and lactate oxidase in a water-based electrode ink with a protective outer membrane layer. Each stage, from ink preparation to membrane composition, was developed empirically. The sensitivity, stability and reproducibility of the working electrode was improved by altering it to a homogeneous ink, consisting of carbon graphite powder, rhodinised carbon powder (5% Rh by weight), hydroxyethyl cellulose (2% w/v) and lactate oxidase in the weight ratio of 2:8:18:1. A layer of cellulose acetate (2% w/v in a 1:1 solution of acetone to cyclohexanone) and an outer coating of a polyurethane called Pellethane (1% to 4% w/v in dimethyl formamide and tetrahydrofuran) improved the selectivity, sensitivity and detection range of the sensor, allowing it to operate in physiological solutions with reduced passivation from protein adsorption. The sensor design was revised to allow its passage through a catheter and operation within a blood vessel; it was manufactured on flexible material using screen printing and Cavro solution deposition techniques. These miniature sensors, with a working surface of 0.5 x 15 mm, were capable of linearly measuring lactate up to 3 mM in buffer solutions with an average sensitivity of 44.8 nA.mM⁻¹ L-lactate. To test the sensor operation in physiological solutions, a flow injection system was employed. A planar three-electrode card used in this system was manufactured using screen printing and Cavro solution deposition techniques. L-lactate concentrations up to 6.4 mM were sensitively and, after minor correction, accurately determined in undiluted plasma and whole blood samples. This thesis has therefore made progress toward mass fabricating an amperometric enzyme electrode device suitable for the determination of L-lactate concentrations in vitro.