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Thesis (Ph. D.)--Johns Hopkins University, 1934. / Biography. Bibliography: p. 44.

Thesis (Ph. D.)--Johns Hopkins University, 1934. / Biography. Bibliography: p. 44.

In this research various techniques were used to study surface groups on carbon electrodes, including the spectroscopic techniques UV-Vis-NIR, FTIR, PAS, XPS and XAS, as well as the Boehm titration. The methods determined to give the best insight to the surface functionalities on the carbon were XPS, XAS and the Boehm titration. The Boehm titration methodology was standardized before use. An in situ method of examining surface groups using spectroscopy during electrochemistry was attempted. Spectroelectrochemistry is a useful way to gain information on how electrochemistry affects electrodes during experimentation; however, it was unsuccessful for the carbon used and remains to be developed. Polymerization of the copolymer of PANI and PPy as a potential electrode material for ECs was achieved by electrochemical cycling and was studied through spectroelectrochemical measurements. Overall, the research completed included the initial stages to studying electrodes for electrochemical capacitors using analytical, non-electrochemistry techniques in conjunction with electrochemistry.

The work presented on this thesis is focused on studies of the kinetics of electron transfer in bilayer lipid membranes (BLMs). Three different types of BLM were studied: i) tethered, ii) pore suspended (commonly known as ‘black’) and iii) based on the avidin – biotin interaction (these are part of the wider group of polymer cushioned BLMs). In order to produce tethered BLMs (tBLMs) of the best quality possible, self – assembled monolayers (SAMs) of a thiolipid (1,2 dipalmitoyl-sn-glycero-phosphothioethanol (DPPTE)) and of the same thiolipid mixed with L α phosphatidylcholine (EggPC) were characterised and their behaviour compared to that of SAMs of two alkanethiols (1 – heptanethiol and 1 – dodecanethiol). The SAMs that were formed by a mixture of lipids (DPPTE+EggPC) presented better kinetic parameters and were the chosen to produce tBLMs. Tethered BLMs were made by using the SAM described above as the lower leaflet; the second leaflet was deposited by vesicle fusion, the vesicles were made of EggPC. tBLMs are commonly used as model membranes, however in biophysical studies free-standing membranes or ‘black’ lipid membranes are more realistic models of cellular processes. The rates of electron transfer in both types of bilayer lipid membranes are compared. These BLMs were modified using two very important mitochondrial membrane associated molecules – ubiquinone-10 (UQ10) and α-tocopherol (VitE). The studies involved the use three redox couples, Fe(CN)_6^(3-/4-), Ru(NH_3 )_6^(3+/2+) and NAD+/NADH using cyclic voltammetry and electrochemical impedance spectroscopy. The NAD+/NADH couple is of particular interest as it is the key to several important biochemical processes. The last type of BLM that was studied was the BLMs based on the avidin – biotin interaction. Avidin was deposited on a platinum surface by electrodeposition and then vesicles composed of EggPC and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (sodium salt) (DOPE(B)) are burst by applying +0.7V (vs. Ag/AgCl, KCl 3.5M), leading to the formation of a supported BLM. The vesicles used had methylene blue (MB) inside; its release, when the vesicles burst, was monitored by cyclic voltammetry and UV-Vis. The kinetic parameters were determined based on the EIS measurements using Fe(CN)_6^(3-/4-) and Ru(NH_3 )_6^(3+/2+) as redox couples.

The main aim of the work reported is the design of proof-of-concept of at point-of-use hydrogen peroxide electrogeneration from air. The experimental work discussed within this thesis explores five major areas: the kinetics of electrocatalysis, ion-pairing, change of solvent media, the electrode surface modication by a redox mediator, and the electrochemical reduction of oxygen within enhanced mass transport systems. The electrocatalytic rates and mass transport of two oxygen reduction redox meditors, viz. anthraquinone and methyl viologen, are studied in aqueous solutions. The investigation is facilitated through the use of a boron-doped diamond electrode, allowing the catalytic response to be clearly delineated from that of the direct oxygen reduction process. The use of simulation software is highlighted in combination with experimental voltammograms to extract kinetic data. Specifically, the voltammetric features, such as the `reverse' peak and the `split waves', are given particular attention. Consequently, it is possible to deconvolute the electrocatalytic reaction mechanisms. The reactivity of the viologen radical cation is comparable to the semiquinone radical anion in aqueous solution ((4.8~6)x10^9 M^-1 s^-1), but over a far wider pH range (pH 2.5 - pH 8.5). The change of local proton concentration, and sequential electron transfers play key roles here. Moreover, the reduced reactivity of semiquinone is observed upon formation of ion-pairs with tetrabutylammonium cations in alkaline solutions. The electro-reduction of oxygen and its mediated pathways are also investigated in non-aqueous media; in particular the thermodynamics, the kinetics, and mass transport involved in these processes. Through a variable temperature study in electrolytic acetonitrile solution, the oxygen dissolution is quantitatively shown to be an endothermic process. Moreover, the diffusion coeficients and concentration of oxygen upon change of acetonitrile mole fraction is also explored in water-acetonitrile mixtures. The rates of bimolecular reactions are extracted from simulation programs, involving semiquinone in anhydrous acetonitrile and viologen radical cation in ethanol, and show a 3 - 4 orders of magnitude reduction compared to that in aqueous solution. Although the solubility of oxygen is ca. 6 - 8 times larger in non-aqueous solvents, the much reduced homogeneous rates limit the electrogeneration of hydrogen peroxide in pure organic media. Novel surface modification methodologies for graphitic surfaces with covalently attached anthraquinonyl groups are studied and characterised. The anthraquinonyl-modified carbon surfaces show much reduced overpotentials required for oxygen reduction. In the final chapter, utilising the new surface modification methodology and novel designs, two gravity-feed flow cells for electrochemical reduction of oxygen in aqueous solutions are proposed and characterised, one based upon the tubular electrode geometry. The other exhibits much enhanced current conversion by using a porous reticulated vitreous carbon electrode. The latter may provide a prototype hydrodynamic system to produce dilute hydrogen peroxide solution at point-of-use.

Nowadays, nanostructures fixed on solid substrates and colloidal nanoparticles permeate through all areas of human life, in area of sensors and detection as well. This dissertation thesis deals with the fabrication of nanostructures on the surface of planar electrodes via self-ordered nanoporous template of aluminum trioxide. The nanofabrication, as one of many possible techniques, is used to increase the active surface area of electrodes by creating unique surface types with specific properties. These electrodes are very perspective in the applications, such as biomolecules electrochemical detection and measurement. The transformation of aluminum layer into non-conductive nanoporous template in the process of anodic oxidation is a fundamental technique employed to obtain the array of nanostructures in this thesis. The fabrication of high quality nanoporous membranes with narrow pore size distribution on various types of metallic multilayers is one of the key experimental parts in this work. Several problems associated with the production of the thin-film systems, including the dissolving the barrier oxide layer, are discussed and solved. Another part of this work deals with the use of nanoporous membrane as a template for the production of metallic nanostructures via electrochemical metal ions deposition directly into the pores. The obtained nanostructures as nanowires, nanorods or nanodots are characterized by the scanning electron microscopy and energy-dispersive or wavelength X-ray spectroscopy. The electrode surface, modified by gold nanostructures suitable for the detection of biomolecules, has been chosen for the electrochemical measurements, due to the gold biocompatibility. The nanostructured electrodes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The effect of nanostructured surface geometrical parameters, including the size of the electrochemically active area, on the results of electrochemical measurements has been observed and compared to flat gold electrodes. Two model biomolecules, namely guanine and glutathione, have been chosen for the study of potential application of these nanostructures in biosensors.

Magister Scientiae - MSc (Chemistry) / Pollutants such as polycyclic aromatic hydrocarbons (PAHs) are known for their toxic effects which may lead to the cause of degenerative diseases in both humans and animals. PAHs are widespread in the environment, and may be found in water, food, automotive industry and petrochemical industries to name but a few sources. Literature reports have highlighted industrial workplace exposure to PAHs as a leading cause for development of cancer in workers. Particularly, workers in the petrochemical industry are adversely affected and the incidence of skin and lung cancer in this population group is high. The United States of America in its guidelines developed by environmental protection agency (EPA) has identified 18 PAHs as priority pollutants. Among these are anthracene, benzo[a]pyrene and pyrene which have been selected as the focal point of this study due to their significance in the petrochemical industry. Due to the carcinogenic and mutagenic properties reported in literature for certain PAHs, there have been monitoring procedures taken in most countries around the world. The commonly used analytical methods for the detection of PAHs from industrial samples are high performance liquid chromatography (HPLC) coupled to fluorescence detection, membrane filtration, ozonation and reverse osmosis. Analysis of PAHs from the petrochemical industry is typically performed by HPLC method as well as sono-degredation in the presence of oxygen and hydrogen peroxide.