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The microstructure and electrochemical behavior of boron doped and undoped ultra thin diamond film electrodes have been studied in this work. The ultra thin diamond films are deposited on porous silicon (PSi) by microwave plasma chemical vapor deposition (MPCVD). In order to enlarge the surface area of diamond electrodes, the deposition of nano structured diamond thin films is performed only in a short time deposition under a negative bias, so that diamond nuclei grew from the tips of PSi nano structures and the thin film surface remained rough and nano fine structured. Diamond thin films were analyzed by Raman spectroscopy and SEM, and then fabricated to the electrode device. From SEM analysis, the morphology of diamond thin films on PSi reveals in the shape of nano rods diamond crystallites. The electro-chemical response was evaluated by performing cyclic voltammetry in the inorganic K4[Fe(CN)6] and a K2HPO4 buffer solution. Boron doped diamond thin film on porous silicon has demonstrated a high redoxidation current of cyclic voltammetry, which may be due to the rough surface providing more electrochemical surface area and more sp2 conducting bonds exposed on the surface.

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Unstable Sn(III) intermediates generated in the Sn(IV)/Sn(II) redox reaction in 2 M HBr + 4 M NaBr media were detected by scanning electrochemical microscopy (SECM) and cyclic voltammetry (CV). In CV, the underpotential deposition of Sn(0) and its stripping peaks severely perturbed the analysis of diffusional reactions. In SECM, however, the detection of diffusional Sn(III) bromide species was clearly observed due to the absence of the perturbation from the surface reactions. The ECEC-DISP mechanism in both the reduction and oxidation reactions was proposed via Sn(III) bromide intermediates. CVs at different concentrations of Sn(IV) and at various scan rates were fit by numerical simulations based on the proposed mechanism with good agreement. Enhanced electrochemical reversibility in the Sn(IV)/Sn(II) redox reaction was observed at the elevated temperature of 80 °C. We attributed such observation to changes in the rate of bromide loss from Sn(IV)Br₆²⁻ to Sn(IV)Br₅⁻ based on the CV simulation. In a similar approach, a short-lived intermediate, presumably bromine anion radical Br₂⁻·, was detected in the Br⁻ /Br₃⁻ electro-oxidation reaction in nitrobenzene solution by SECM and CV. The reaction mechanism was proposed based on a detected Br₂⁻· intermediate as follows: (1) the one electron transfer of Br⁻ to Br·, (2) the dimerization of 2Br· to Br₂, (3) the bromide addition reaction of Br₂ to Br₃⁻ , (4) the bromide addition reaction of Br· to Br₂⁻·, and (5) the Br· addition reaction of Br₂⁻· to Br₃⁻. The simulation based on the proposed mechanism fitted well with the experimental SECM and CV results. At last, the applicability of the Sn/Br system as electrolyte for electrochemical energy storage was tested. A redox flow battery was constructed, where the Sn(IV)/Sn(II) reduction was carried out on the negative electrode, while the Br· /Br₂ oxidation was carried out on the positive electrode during charging. Cyclability was tested up to 35 charge/discharge cycles, and 100 % coulombic efficiency was observed in all cycles. However, only 40 % of voltage efficiency was obtained, mainly due to the large irreversibility of the Sn(IV)/Sn(II) redox reaction in the bromide media.

This study has two aspects. One concerns the development of a sensitive differential pulse polarographic (DPP) method and its use to conduct a preliminary study of natural waters to detect the presence of nitrosoamines, and the second, where the study was carried out in greater detail, is the investigation of the kinetics of reduction of N-nitrosodimethylamine (NDMA) in aqueous solution. An optimization study was first conducted to identify the conditions that give the greatest sensitivity. Conditions investigated were different supporting electrolytes and solvent mixtures. Supporting electrolytes used were 0.10 M solutions of acids, bases and salts, and the solvent mixtures studied were ethanol/water mixtures. The effect of various supporting electrolytes and various ethanol/water mixtures on peak current was studied in order to select the conditions that give the greatest sensitivity for the determination of nitrosoamine concentrations. The lowest nitrosoamine concentration that can be detected in a solution (limit of detection) was determined. The optimum supporting electrolytes for N-nitrosoamines and the C-nitrosoamine were respectively found to be 0.10 M H2S04 and 0.10 M NaOH. Aqueous solutions were also found to give greater sensitivity than ethanol/water mixtures. The presence of nitrosoamines in some natural water samples was then checked using differential pulse polarography (DPP).Concentrations of nitrosoamines in these water samples were determined using the optimum conditions. The analyte analytes studied were 4-nitroso-N,N-dimethylaniline (4NDMA); Nnitrosodibutylamine (NDBA),N-nitrosodi-n-propylamine (NDPA) and N-nitrosodiphenylamine (NDPhA). All four nitrosoamines were detected in some of the selected natural water samples . The kinetics of the electrochemical reduction of NDMA was studied using controlled potential coulometry, linear scan voltammetry (LSV) and cyclic voltammetry (CV). Controlled potential coulometry was first used to determine the number of electrons transferred (n) in the reduction reaction. Two moles of electrons were found to be required for the reduction of one mole of NDMA solution, at a stationary mercury drop electrode (SMDE). The major product obtained, identified by UVNIS spectroscopy, was dimethylamine (DMA). / Ph.D. (Chemistry) North-West University, Mafikeng Campus, 2005

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 154-163) / Microfiche. / xvi, 163 leaves, bound ill. 29 cm

Thesis (MSc.(Chemistry))--University of Pretoria, 2007. / Summary in English. Includes bibliographical references.

Thesis (Ph.D.), Memorial University of Newfoundland, 1998. / Restricted until June 1999. Bibliography: leaves 189-201.

A interação espontânea entre pirita e íons mercúrio foi acompanhada por meio de voltametria cíclica. Eletrodos de carbono grafite e parafina sólida recobertos com grãos de pirita foram mergulhados em soluções contendo íons mercúrio, retirados, lavados e introduzidos na solução de trabalho (solução tampão de ácido acético 0,25M e acetato de sódio 0,25M). Eletrodos que previamente estiveram imersos na solução contendo íons Hg(II) apresentaram um potencial de circuito aberto maior que o potencial típico da pirita na mesma solução. Com o elevado número de novos processos eletroquímicos detectados verifica-se a complexidade do sistema pirita/íons Hg(II) e que mais de uma espécie de mercúrio se deposita espontaneamente sobre o mineral. A possibilidade de formação de sulfeto de mercúrio sobre a pirita foi investigada construindo eletrodos com duas espécies de sulfeto (HgS(preto) e HgS(vermelho)). A resposta eletroquímica do HgS(preto) apresenta processos catódicos e anódicos semelhantes aos processos observados no voltamograma da pirita, após sua interação com íons Hg(II). Entretanto, o perfil eletroquímico do HgS(vermelho) não apresenta qualquer semelhança com voltamograma do sistema pirita/íons Hg(II). Realizou-se estudos para verificar a influência de variáveis químicas (concentração e pH) e físicas (tempo, temperatura e transporte de massa). Observou-se que o transporte de massa acelera o processo de adsorção de espécies de mercúrio sobre a pirita e determinou-se a melhor condição experimental de retirada de íons mercúrio. / The spontaneous interaction between pyrite and mercury ions was studied employing cyclic voltammetry. The electrodes, consisting of solid paraffin and graphite covered by pyrite particles, were immersed in solutions containing mercury ions. After mineral/mercury ions interaction, the electrode was washed and introduced in the working solution (acetic acid 0,25M and acetate of sodium 0,25M). Eletrodes which were immersed in the solution containing mercury ions, presented a open circuit potential more positive than that of the pyrite in the same solution. The high number of new electrochemical processes detected denotes the complexity of the system pyrite/mercury ions and indicates that several species of mercury may deposit spontaneously on the mineral surface. The possibility of formation of mercury sulfide on the pyrite was investigated employing electrodes constructed with HgS(Black) and HgS(red). The electrochemical response of HgS(black) presents cathodic and anodic processes similar to that observed in the voltammogram of pyrite, after interaction with mercury ions. The potentiodynamic profile of HgS(red) it does not present any similarity with the voltammogram of the system pyrite/mercury ions. Studies were carried out to verify the influence of chemical (concentration and pH) and physical variables (time, temperature and mass transport). It was observed that the mass transport accelerates the adsorption process of mercury species on the pyrite surface and the optimal experimental condition for scavenging mercury ions was determined.

>Magister Scientiae - MSc / The tuberculosis (TB) disease to this day remains one of the world’s prominent killerdiseases. Pyrazinamide (PZA) is one of the most commonly prescribed anti- tuberculosis (anti-TB) drugs due to its ability to significantly shorten the TB treatment period from the former nine months to the current six months duration. However, excess PZA in the body causes hepatotoxicity and damages the liver. This hepatotoxicity, together with the resistance of the bacteria to treatment drugs, poor medication and inappropriate dosing, greatly contribute to the high incidents of TB deaths and diseases that are due to side effects (such as liver damage). This brings about the calls for alternative methods for ensuring reliable dosing of the drug, which will be specific from person to person due to inter-individual differences in drug metabolism. A novel biosensor system for monitoring the metabolism of PZA was prepared with a Ni-PPI-PPy star copolymer and cytochrome P450 2E1 (CYP2E1) deposited onto a platinum electrode. The nanobiosensor system exhibited enhanced electro-activity that is attributed to the catalytic effect of the incorporated star copolymer. The biosensor had a sensitivity of 0.142 µA.nM-1, and a dynamic linear range (DLR) of 0.01 nM-0.12 nM (1.231 – 7.386 ng/L PZA). The limit of detection of the biosensor was found to be 0.00114 nM (0.14 ng/L) PZA. From the HPLC peakconcentration (Cmax) of PZA determined 2 h after drug intake is 2.79 – 3.22 ng.L-1,which is very detectable with the nanobiosensor as it falls within the dynamic linear range.