This research investigated the mechanism, kinetics and feasibility of nitrate, arsenate, and trichloroethylene inactivation on zerovalent iron (ZVI), mixed-valent iron oxides, and boron doped diamond film electrode surfaces, respectively. Nitrate ( ) is a common co-contaminant at sites remediated using permeable reactive barriers (PRBs). Therefore, understanding nitrate reactions with ZVI is important for understanding the performance of PRBs. This study investigated the reaction mechanisms of with ZVI under conditions relevant to groundwater treatment. Tafel analysis and electrochemical impedance spectroscopy were used to probe the surface reactions. Batch experiments were used to study the reaction rate of with freely corroding and cathodically protected iron wires. The removal kinetics for the air formed oxide (AFO) were 2.5 times slower than that of water formed oxide (WFO).This research also investigated the use of slowly corroding magnetite (Fe3O4) and wustite (FeO) as reactive adsorbent media for removing As(V) from potable water. Observed corrosion rates for mixed valent iron oxides were found to be 15 times slower than that of zerovalent iron under similar conditions. Electrochemical and batch and column experiments were performed to study the corrosion behavior and gain a deeper understanding on the effects of water chemistry and operating parameters, such as, empty bed contact times, influent arsenic concentrations, dissolved oxygen levels and solution pH values and other competing ions. Reaction products were analyzed by X-Ray diffraction and XPS to determine the fate of the arsenic.This research also investigated use of boron doped diamond film electrodes for reductive dechlorination of trichloroethylene (TCE). TCE reduction resulted in nearly stoichiometric production of acetate. Rates of TCE reduction were found to be independent of the electrode potential at potentials below -1 V with respect to the standard hydrogen electrode (SHE). However, at smaller overpotentials, rates of TCE reduction were dependent on the electrode potential. Short lived species analysis and density functional simulations indicate that TCE reduction may occur by formation of a surface complex between TCE and carbonyl groups present on the surface.

<p>The primary goals of this research were to investigate the electrochemical behavior of carbon nanostructures of varying morphology, identify morphological characteristics that improve electrochemical capacitance for applications in energy storage and neural stimulation, and engineer and characterize a boron-­doped diamond (BDD) electrode based electrochemical system for disinfection of human liquid waste. </p><p>Carbon nanostructures; ranging from vertically aligned multiwalled carbon nanotubes (MWCNTs), graphenated carbon nanotubes (g-­CNTs) to carbon nanosheets (CNS); were synthesized using a MPECVD system. The nanostructures were characterized by using scanning electron microscopy (SEM) and Raman spectroscopy. In addition to employing commonly used electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), a new technique was developed to evaluate the energy and power density of individual electrodes. This facilitated comparison of a variety of electrode materials without having to first develop complex device packaging schemes. It was found that smaller pore size and higher density of carbon foliates on a three-dimensional scaffold of carbon nanotubes increased specific capacitance. A design of experiments (DOE) study was conducted to explore the parametric space of the MWCNT system. A range of carbon nanostructures of varying morphology were obtained. It was observed that the capacitance was dependent on defect density. Capacitance increased with defect density.</p><p>A BDD electrode was characterized for use in a module designed to disinfect human liquid waste as a part of a new advanced energy neutral, water and additive-free toilet designed for treating waste at the point of source. The electrode was utilized in a batch process system that generated mixed oxidants from ions present in simulated urine and inactivated E. Coli bacteria. Among the mixed oxidants, the concentration of chlorine species was measured and was found to correlate to the reduction in E. Coli concentration. Finally, a new operating mode was developed that involved pulsing the voltage applied to the BDD anode led to 66% saving in energy required for disinfection and yet successfully reduced E. Coli concentration to less than the disinfection threshold.</p> / Dissertation

Nanoparticle-functionalized electrodes have attracted attention in areas such as energy production and storage, sensing, and electrosynthesis. The electrochemical properties of these electrodes depend upon the nanoparticle properties, e.g., core size, core morphology, surface chemistry, as well as the structure of the nanoparticle/electrode interface, including the coverage on the electrode surface, choice of electrode support, and the interface between the nanoparticle and the electrode support. Traditionally used methods of producing nanoparticle-functionalized electrodes lack sufficient control over many of these variables, particularly the nanoparticle/electrode interface. Tethering nanoparticles to electrodes with molecular linkers is a strategy to fabricate nanoparticle-functionalized electrodes that provides enhanced control over the nanoparticle/electrode structure. However, many existing tethering methods are done on catalytically active electrode supports, which makes isolating the electrochemical activity of the nanoparticle challenging. Furthermore, previous work has focused on larger nanoparticles, yet smaller nanoparticles with core diameters less than 2.5 nm are of interest due to their unique structural and electronic properties. This dissertation addresses both of these gaps, exploring small nanoparticle electrocatalysts that are molecularly tethered to catalytically inert electrodes. This dissertation first reviews and compares the methods of fabricating nanoparticle-functionalized electrodes with a defined molecular interface in the context of relevant attributes for electrochemical applications. Next, a new platform approach to bind small gold nanoparticles to catalytically inert boron doped diamond electrodes through a defined molecular interface is described, and the influence of the nanoparticle/electrode interface on the electron transfer properties of these materials is evaluated. The next two studies build upon this platform to evaluate molecularly tethered nanoparticles as oxygen electroreduction catalysts. The first of these two describes the systematic study of atomically precise small gold clusters, highlighting the influence of atomic level differences in the core size and the electrode support material on the catalytic properties. The second study extends the platform approach to study small bimetallic silver-gold nanoparticles produced on the electrode surface and highlights the influence of the structural arrangement of the metals on the catalytic activity. Finally, future opportunities for the field of molecularly tethered nanoparticle-functionalized electrodes are discussed. This dissertation includes previously published and unpublished co-authored material. / 2019-01-27

>Magister Scientiae - MSc / The main aim of this study is to investigate theelectrochemical determination of two beneficial (selenium and zinc) and two toxic (chromium and vanadium) metals in the potable water within the City of Cape Town's distribution area. The Water Laboratory of the City's Scientific Services Branch analyses for these metals in their elemental state, using the Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). This is a standard method used for the detection of trace metals. The most sensitive voltammetric method for determining these metals is by adsorptive stripping voltammetry, using a thin mercury film electrode with a glassy carbon support. This voltammetric method is used for quantitative determination of specific ionic species. Because of mercury's toxicity it is not really favoured for trace metals anymore. Many other possibilities are under investigation, e.g. bismuth-film, modified glassy carbon and antimony electrodes. The boron-doped diamond (BDD) electrode has distinct advantages when used to determine metal concentrations. Advantages of BDD electrodes include lower detection limit, speciation and wider potential window. In this study cyclic voltammetry (CV) was used to determine the copper, cadmium and lead concentrations in potable water by means of square wave voltammetry (SWV) and a bare glassy carbon electrode (GCE). Furthermore, a boron-doped diamond electrode (BDDE) was used to investigate the possibilities of determining selenium, chromium and vanadium by SWV. Real samples (potable water samples) were analysed electrochemically to qualify and quantify these metals and determine whether they comply with the SANS 241:2006 drinking water guidelines.The copper, cadmium, lead and selenium peaks appear very close to the theoretical values, which indicate that these metals can be detected by SWV method, but further analysis with more samples is advised. Even though responses were observed for vanadium and chromium, it was not reliable and requires further investigation. Further studies into the analyses of zinc are also advised.

La pollution causée par le rejet industriel de métaux lourds a engendré la mise en place de réglementations concernant les concentrations en eaux de surfaces de ces polluants fortement toxiques. Des appareillages permettant la quantification des métaux lourds existent d'ores et déjà mais présentent de nombreux inconvénients comme leur coût, l'emploi d'un personnel qualifié ou encore des mesures différées dues à des échantillonnages spécifiques. L'électroanalyse représente, dans le domaine de la détection des métaux lourds, une des alternatives les plus prometteuses à ce jour.Les travaux présentés portent donc sur la mise au point d'un dispositif complet d'électroanalyse, tenant compte des problèmes de spéciation liés à la présence de la matière organique, permettant la quantification de deux métaux lourds fortement relargués par l'industrie : le plomb et le nickel. / Heavy metals industrial wastes involved the establishment of regulations concerning those toxic pollutants concentrations in surface water. Devices allowing heavy metals quantification already exist. Unfortunately, they revealed some gaps as their price, the need for qualified employees or even deferred results because of specific sampling procedures. Nowadays, in the heavy metals detection field, electroanalysis appears as a promising alternative. The work here discussed concerns the study of a global electroanalysis equipment, taking into account speciation issues related to organic matter presence, allowing heavy metals quantification in industrial runoffs of lead and nickel.

abstract: In this dissertation, combined photo-induced and thermionic electron emission from low work function diamond films is studied through low energy electron spectroscopy analysis and other associated techniques. Nitrogen-doped, hydrogen-terminated diamond films prepared by the microwave plasma chemical vapor deposition method have been the most focused material. The theme of this research is represented by four interrelated issues. (1) An in-depth study describes combined photo-induced and thermionic emission from nitrogen-doped diamond films on molybdenum substrates, which were illuminated with visible light photons, and the electron emission spectra were recorded as a function of temperature. The diamond films displayed significant emissivity with a low work function of ~ 1.5 eV. The results indicate that these diamond emitters can be applied in combined solar and thermal energy conversion. (2) The nitrogen-doped diamond was further investigated to understand the physical mechanism and material-related properties that enable the combined electron emission. Through analysis of the spectroscopy, optical absorbance and photoelectron microscopy results from sample sets prepared with different configurations, it was deduced that the photo-induced electron generation involves both the ultra-nanocrystalline diamond and the interface between the diamond film and metal substrate. (3) Based on results from the first two studies, possible photon-enhanced thermionic emission was examined from nitrogen-doped diamond films deposited on silicon substrates, which could provide the basis for a novel approach for concentrated solar energy conversion. A significant increase of emission intensity was observed at elevated temperatures, which was analyzed using computer-based modeling and a combination of different emission mechanisms. (4) In addition, the electronic structure of vanadium-oxide-terminated diamond surfaces was studied through in-situ photoemission spectroscopy. Thin layers of vanadium were deposited on oxygen-terminated diamond surfaces which led to oxide formation. After thermal annealing, a negative electron affinity was found on boron-doped diamond, while a positive electron affinity was found on nitrogen-doped diamond. A model based on the barrier at the diamond-oxide interface was employed to analyze the results. Based on results of this dissertation, applications of diamond-based energy conversion devices for combined solar- and thermal energy conversion are proposed. / Dissertation/Thesis / Ph.D. Physics 2013

A caracterização ex situ e in situ de eletrodos constituídos de IrO2-Nb2O5 revelou que a morfologia, a atividade eletrocatalítica para a reação de desprendimento de O2 (RDO) e a performance para a reação de formação de O3 (RFO) são fortemente dependentes da composição nominal da camada ativa. Baseados em estudos preliminares, escolheu-se a composição IrO2-Nb2O5 (45:55 % mol) para uma extensiva investigação da RDO/RFO, avaliando a influência das variáveis de preparo do eletrodo, da temperatura e da composição do eletrólito. Propôs-se um mecanismo eletródico para RDO/RFO, considerando a influência da composição do eletrólito e dos sítios ativos superficiais. Demonstrou-se que a introdução de PF6- no eletrólito de suporte aumenta significativamente o rendimento da RFO através da inibição da RDO no domínio dos elevados sobrepotenciais. O segundo material eletródico investigado foi o eletrodo de diamante dopado com boro (DDB) de origem comercial. Este material apresenta área superficial e rugosidade sensivelmente maiores que os reportados na literatura, sendo que as diversas análises demonstram um filme de boa qualidade. O pré-tratamento da superfície de DDB resulta na remoção de impurezas e na oxidação da superfície, alterando o caráter hidrofóbico do eletrodo. Sua condutividade e comportamento eletroquímico são dependentes da concentração superficial de transportadores de carga, relacionado diretamente ao potencial aplicado. Desta forma, este eletrodo de DDB altamente dopado apresenta comportamento próximo ao de um metal em potenciais mais anódicos. Os estudos cinéticos em diversos eletrólitos e temperaturas demonstram que o eletrodo de DDB caracteriza-se pela quase ausência de sítios de adsorção ? causa dos elevados sobrepotenciais e energias de ativação para a RDO. De forma surpreendente, a introdução de flúor-ânions no eletrólito resulta na diminuição da energia de ativação para a RDO e da eficiência de corrente para a RFO. Este último parâmetro é função direta da ?eletronegatividade absoluta? dos flúor-ânions. Altas concentrações de NaF alteram a condutividade do eletrólito e a hidrofobicidade do eletrodo, afetando o comportamento cinético do ânodo. Em eletrólitos contendo KPF6, entretanto, a entropia de ativação eletroquímica parece exercer um pronunciado efeito sobre a energia de ativação da RDO. No mecanismo proposto para o eletrodo de DDB, destaca-se a importância da interação entre o principal intermediário da RDO/RFO, HO·, e a superfície do filme. / Ex situ and in situ characterisation of IrO2-Nb2O5 electrodes reveal morphology, electrocatalytical activity for the oxygen evolution reaction (OER) and electrochemical ozone production (EOP) performance are strongly dependent on nominal composition of the oxide film. Based on preliminary studies, the electrode IrO2-Nb2O5 (45:55 mol%) composition was chosen to conduct an extensive OER/EOP investigation, analysing the influence of: electrode preparation procedure, temperature and electrolyte composition. An electrode mechanism for OER/EOP is proposed taking into account the influence of the electrolyte composition and the active surface sites. It is demonstrated that the introduction of PF6- into the electrolyte increases significantly the EOP performance due to inhibition of the OER in the high overpotential domain. The second electrode material investigated is a commercial sample of the boron doped diamond electrode (BDD). This material presents surface area and roughness considerably higher than those reported in literature, however several analyses demonstrate the good quality of the film. The pre-treatment of the BDD surface results in the removal of impurities and surface oxidation, which alters the hydrophobic character of the film. Its conductivity and electrochemical behaviour depend on the surface charge carriers concentration that is directly related to the applied potential. Therefore, this heavily doped BDD sample presents a behaviour resembling a metal at more anodic potentials. Kinetic investigations of several electrolytes and temperatures show BDD electrode is characterised by the almost absence of adsorption sites ? the main cause of the high overpotentials and activation energies for OER. Surprisingly, the introduction of fluoro-anions into the electrolyte results in lower activation energies for OER and lower EOP current efficiency. The latter parameter is directly related to the ?absolute electronegativity? of the fluoro-anions. High NaF concentrations modify the electrolyte conductivity and electrode hydrophobicity. However, in electrolytes containing PF6-, the electrochemical activation entropy seems to exert a pronounced effect on the activation energy for OER. In the proposed OER/EOP mechanism at BDD electrode, a key parameter is the interaction between the main intermediate, HO·, and the electrode surface.

In this thesis, the diffusion of lithium was studied on boron-doped diamond (BDD) as a potential anode material in lithium ion batteries (LIB). The initial interaction between deposited lithium and BDD thin films was studied using X-ray Photoelectron Spectroscopy (XPS). Diffusion is directly linked to reactions between lithium and carbon atoms in the BDD-lithium interface. By measuring binding energies of core-electrons of carbon and lithium before and after deposition, these reactions can be analyzed. Scanning Electron Microscopy (SEM) was used to study the BDD surface and the behaviour of deposited lithium. Experiments show that a chemical interaction occurs between lithium and carbon atoms in the surfacelayers of the BDD. The diffusion of lithium is discussed from spectroscopic data and suggests that surface diffusion is occurring and no proof of bulk diffusion was found. The results do not exclude bulk diffusion in later states but it was not found in the initial interaction at the interface after depositing lithium. SEM images show that lithium clusters in the nanometer range are formed on the BDD surface. The results of this study give insights in the initial diffusion behaviour of lithium at the BDD interface and possible following events are discussed.

4 ABSTRACT Methods for the determination of five isomers of aminonitrophenol were developed, based on the technique of differential pulse voltammetry (DPV) and HPLC with amperometric detection. As the working electrodes, boron-doped diamond film electrode (BDDFE) and glassy carvon paste electrode (GCPE) were employed. Preliminary electrode testing was performed by cyclic voltammetry. The methods were aimed to the determination of all five aminonitrophenol isomers in hair dyes and to the determination of 2-amino-4- nitrophenol and 4-amino-2-nitrophenol in body fluids after solid phase extraction. From the voltammetric methods, the one using BDDFE for the cathodic determination in hair dyes exhibits sufficient selectivity. The performance of chromatographic methods was found suitable for the determination of aminonitrophenols in both observed matrices. The applicability of the developed methods was successfully confirmed by the determination of tested analyted in real samples of hair dyes and spiked samples of urine. Preceding measurements are described, dealing with the determination of other oxidizable compounds, containing phenolic or aniline moieties on BDDFE. The obtained results confirm that in some cases, BDDFE shows more resistance to fouling than other carbon-based electrodes, but in most cases, the...

Le dépôt de ZnO sur diamant est actuellement assuré par des méthodes physiques (ALD, sputtering, CVD) coûteuses et complexes à mettre en oeuvre. La réalisation de ces dépôts de ZnO peut également être effectuée via des procédés plus doux tels que le procédé électrochimique qui représente une alternative intéressante car peu coûteux, et facile à mettre en oeuvre. L’électrodépôt de ZnO a été très largement étudié sur divers substrats, notamment pour des applications dans le domaine du photovoltaïque. Toutefois, seule une étude a été réalisée concernant l’électrodépôt de ZnO sur diamant alors que de nombreuses applications découlent de telles structures : dispositifs à ondes acoustiques de surface (SAW), photo-détecteurs UV ou bien biocapteurs. L’objectif de la thèse réside ainsi dans l’étude de l’électrodépôt de ZnO sur substrat diamant dopé bore en se basant sur le procédé mis en évidence par le groupe de Lincot dans les années 1990. Cette technique consiste à réduire, en présence d’ions Zn2+, l’oxygène dissous pour former des hydroxydes et a fortiori ZnO par réaction des hydroxydes et des ions Zn2+.Le diamant étant un substrat complexe en raison notamment de son grand gap (5,4 eV), un important dopage est nécessaire pour pouvoir l’étudier dans le domaine de l’électrochimie. Dans un premier temps, les conditions d’électrodépôt de ZnO sur diamant (température, potentiel électrique) ont été déterminées avant d’envisager l’étude de l’influence de divers paramètres expérimentaux. Par la suite, l’influence de la composition du bain a été étudiée puisque les concentrations et la nature des précurseurs de zinc et de l’électrolyte support ont été étudiées, permettant de former toute une variété de structures de ZnO sur diamant. Enfin, la dernière partie de la thèse s’est focalisé sur l’influence de la chimie de surface du diamant sur la morphologie, la structure et l’adhérence des dépôts de ZnO formés. L’état de surface initialement hydrogéné du diamant a été modifié en utilisant des traitements électrochimiques conduisant à la formation de groupements oxydés. / Currently, ZnO deposition on diamond is obtained by physicals methods (ALD, sputtering, CVD) which are expensive and difficult to implement. The realization of these ZnO deposits can also be made by softer methods such as electrodeposition which represents an interesting alternative because of its low cost. ZnO electrodeposition has been already studied on several substrates especially for photovoltaic devices. However, only one study has been realized concerning ZnO electrodeposition on diamond while many applications derived from these structures: surface acoustic wave sensors, UV photodetectors, and biosensors. The aim of this work is the study of ZnO electrodeposition on boron doped diamond by following the process highlighted by Lincot et al in 1990s. This process is based on the oxygen reduction reaction leading to the formation of hydroxides which react with Zn2+ cations to form ZnO. Diamond is a complex substrate which presents a large gap of 5.4 eV requiring an important doping to allow its use in electrochemistry. At first, ZnO electrodeposition conditions (temperature, electrical potential) have been determined. The influence of deposition bath has then been studied by varying nature and concentrations on zinc precursor and electrolyte support. Results indicate the possibility to obtain different ZnO/diamond structures by varying theses parameters. Finally, the influence of the surface termination of diamond on ZnO structures, shape and adherence has been investigated by modifying the H-terminated surface on O-terminated surface by using electrochemical treatments.