The work presented in this thesis involves the application of room temperature ionic liquids (RTILs) as solvents for use in electrochemical experiments. Initially, the fundamentals of electrochemistry is presented, followed by a comprehensive overview of RTILs in terms of their properties, applications and their behaviour as electrochemical solvents compared to conventional aprotic solvents. The results of 8 original studies are then presented as follows: X-Ray photoelectron spectroscopy is used to quantify the concentration of bromide ions in an ionic liquid, and is independently confirmed by potential-step chronoamperometry. The reaction mechanisms and kinetics for the electrochemical reduction of some aromatic nitro compounds (namely nitrobenzene and 4-nitrophenol) are determined. The electrochemistry of phosphorus trichloride and phosphorus oxychloride is studied in detail for the first time, due to the unusual stability of these highly reactive compounds in RTILs. The reductions and oxidations of sodium and potassium nitrate are studied, giving rise to 'melt'-like behaviour. The electrodeposition of sodium oxide on platinum is also demonstrated. The electrochemical oxidation of nitrite and the oxidation and reduction of the toxic gas, nitrogen dioxide, is presented. The oxidation of hydrogen gas is studied in ten RTILs with a range of different cations and anions, and contrasting interactions with the RTIL anions are seen. The electrochemical oxidation of ammonia gas is studied in five RTILs with different anions and a general reaction mechanism is suggested. The reduction of benzoic acid is studied in six RTILs, and the kinetics of the dissociation step are found to be very fast. The first five studies are all carried out in one particular ionic liquid, and the reactions and mechanisms are compared to that observed in conventional aprotic solvents. The last three studies employ several RTILs with different cations and anions to look at the contrasting interaction of protons with the RTIL cation/anion and ultimately help to understand the pH properties of the solvent. The overall findings from the work in this thesis are that some reactions and mechanisms (e.g bromide, nitro derivatives and ammonia) are generally the same in RTILs as in conventional aprotic solvents, but other species (e.g. nitrates, phosphorus derivatives) show remarkably different behaviour. It has also been demonstrated that RTILs are suitable media for the detection of nitrogen dioxide, hydrogen and ammonia gases. This suggests that RTILs could potentially offer many advantages when employed as solvents in electrochemical reactions and in amperometric gas sensors.

The electropolymerisation of a range of indole derivatives results in the formation of redox active films. These redox films have been observed to be highly luminescent. Earlier studies have investigated electrochemical and photophysical properties, for potential applications such as fast response potentiometric sensors or novel materials for light emitting devices. The work in this thesis extends this approach to electrochemical and computational studies of a range of novel redox-active aromatic systems. This work has exploited the continuing increase of computing power, employing powerful quantum computational models to complement and augment electrochemical methods. Density Functional Theory has been used to show that prediction of oxidation potentials in good agreement with experimental values is achievable for a wide range of aromatic systems. Calculation of the electron spin density of the radical cations has also helped to elucidate the likely coupling locations for the formation of electroactive layers. It is observed that the nature of substituents and additional hetero groups to the aromatic systems can have a profound effect on electron spin density distributions. The redox-active species formed from indole dimers and 5-methylindolocarbazole have also been characterised. The species formed from electropolymerisation of 5- methylindolocarbazole has been found to be a mixture of three isomers of a 5- methylindolocarbazole dimer. Full characterisation of the product of the electropolymerisation of indole dimers was not possible; fluorescence work however suggests this to be a species with a greater degree of conjugation than either indole dimers or trimers. It is thought likely that this product is either a tetramer or longer chain polymer. This work demonstrates the applicability of a combination of computational and electrochemical methods to the characterisation of novel heteroaromatic systems.

This thesis presents experimental work with the primary aim of developing new approaches for the detection and characterisation of nanoparticles via electrochemical methods. The first chapter introduces the fundamental aspects of electrochemistry while the second chapter discusses the need for nanoparticle detection methods and the nonelectrochemical and electrochemical techniques that are currently used in the measurement of nanoparticles. A novel way to quantify silver nanoparticles in aqueous solution is proposed via nanoparticle-electrode impact experiments. In this technique a suitably potentiostatted electrode is immersed in a nanoparticle solution so as to bring about the oxidation or reduction of a single nanoparticle upon its collision with the electrode surface. This “direct” nanoparticle impact technique is then employed to detect laboratory synthesised silver nanoparticles in seawater. It is further shown that this method is capable of sizing silver nanoparticles contained in a commercially available cleaning product. Commercial silver nanoparticles are subsequently monitored via a sticking and stripping technique where homemade gold electrodes fabricated from CDs are immersed in a seawater sample spiked with nanoparticles prior to stripping voltammetry. The reduction of hydrogen peroxide on the surface of silver nanoparticles impacting upon an electrode is also examined. This “indirect” nanoparticle detection method is shown to provide an accurate route to nanoparticle sizing. A Fickian model is subsequently proposed to describe nanoparticle transport to the substrate electrode in both direct and indirect nanoparticle detection techniques. The importance of determining the proportion of nanoparticles which adhere to the electrode surface upon impact is highlighted and the sticking coefficient of a gold nanoparticle at a carbon surface determined. This technique to monitor nanoparticle sticking is optimised by chemical modification of the substrate electrode in order to achieve a “sticky” surface improving the rate of silver nanoparticle sticking. Finally, the nanoparticle collision method is shown to be applicable to C₆₀ nanoparticles where their detection and sizing is achieved in non-aqueous conditions. The methods developed in this thesis make a significant contribution to the promising application of electrochemical techniques in the detection and characterisation of single nanoparticles.

The separation of oxidation-reduction reactions into individual half-cells with a resulting "mixed potential" is well known as a dissolution mechanism for metals; however, the mechanism by which non-conducting crystals lose ions to the solution has been studied only slightly.

An iodine surface layer has been prepared on Ru(poly) and Ru(0001) electrodes by exposure to iodine vapor in UHV and polarizing in a 0.1 M HClO4/0.005 M KI solution, respectively. A saturation coverage of I on a Ru(poly) electrode passivates the Ru surface against significant hydroxide, chemisorbed oxygen or oxide formation during exposure to water vapor over an electrochemical cell in a UHV-electrochemistry transfer system. Immersion of I-Ru(poly) results in greater hydroxide and chemisorbed oxygen formation than water vapor exposure, but an inhibition of surface oxide formation relative that of the unmodified Ru(poly) surface is still observed. Studies with combined electrochemical and XPS techniques show that the iodine surface adlayer remained on top of the surface after cycles of overpotential electrodeposition/dissolution of copper on both Ru(poly) and Ru(0001) electrodes. These results indicate the potential bifunctionality of iodine layer to both passivate the Ru surface in the microelectronic processing and to act as a surfactant for copper electrodeposition. The electrodeposition of Cu on Ru(0001) or polycrystalline Ru was studied using XPS with combined ultrahigh vacuum/electrochemistry methodology (UHV-EC) in 0.1 M HClO4 with Cu(ClO4)2 concentrations ranging from 0.005 M to 0.0005 M, and on polycrystalline Ru in a 0.05M H2SO4/0.005 M CuSO4/0.001 M NaCl solution. The electrochemical data show well-defined cyclic voltammograms (CV) with a Cu underpotential deposition (UPD) peak and overpotential deposition (OPD) peak. XPS spectra of Ru electrodes emersed from perchloric acid solution at cathodic potentials indicate that ClO4- anions dissociate to yield specifically adsorbed Cl and ClOx species. Subsequent Cu deposition results in the formation of a thin, insoluble Cu(II) film with Cu(I) underneath. In contrast, similar deposition on polycrystalline Ru in the sulfuric acid/Cu sulfate solution with NaCl added yields only Cu(0), indicating that the formation of Cu(II) and Cu(I) involves both Cl and perchlorate interactions with the deposited Cu. A pre-adsorbed layer of iodine on the Ru(0001) surface inhibits perchlorate dissociation in iodide-free electrolyte and leads to the deposition of Cu(0) in the perchlorate bath. XPS depth profile analysis demonstrates that the iodine monolayer "floats" on top of the deposited film, in agreement with previous results, effectively protecting the Cu film from air oxidation.

Doctor of Philosophy / Department of Chemistry / Takashi Ito / Polymer thin films have played an important role in our everyday lives ranging from industrial to biomedical applications. In this thesis, two major topics based on polymer thin films including photopolymerized self-assembled monolayer and nanoporous thin films derived from diblock copolymer are discussed. In the first part of this thesis, a well-packed self-assembled monolayer with phosphonic acid as head group and diacetylenic functional group in the tail formed on AlGaN/GaN surface. According to water contact angle and UV/Vis absorption spectroscopy data, the stability of this self assembled monolayer on oxidized AlGaN/ GaN surface can be improved by photopolymerization of SAMs. The photopolymerization efficiency of the SAMs is effected by the position of polymerization functional group in the alkyl chain. In the second part of this thesis, PS-b-PMMA diblock copolymer thin films were prepared, characterized and applied as a template for electron transfer efficiency determination. The surface COOH group in nanoporous thin films derived from PS-b-PMMA were modified with ferrocene redox moieties having different linker lengths in the organic phase. The surface functionalization efficiency was quantitatively assessed by measuring the monovalent probe cations released from the surface COOH groups via cation-exchange processes using highly- sensitive analytical techniques including spectrofluorometry and inductively coupled plasma mass spectrometry (ICP-MS). The surface coverage of the redox moieties is an important parameter to determine the electron hopping efficiency. The electron propagation resulted from electron hopping across relatively large spacing that was controlled by the motion of anchored redox sites. The longer linker led to the larger physical displacement range of anchored ferrocene moieties, facilitating the approach of the adjacent ferrocene moieties within a distance required for electron self-exchange reaction. Faradic currents originating from redox-involved electron hopping through the ferrocene moieties anchored onto the insulator surface decreased with increasing the concentration of beta-cyclodextrin ([beta]-CD) in aqueous solution. The current could be recovered by adding redox-inactive guest molecules of [beta]-CD to the solution.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1994 / A quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. The basis for quantitative description involves conducting a voltage balance over the galvanic couple. The contributions to the voltage balance include the galvanic couple cell emf, kinetic descriptions of the anodic and cathodic half reactions, the voltage characteristics 'of mineral-mineral contacts and solution voltage losses. The rates of the anodic and cathodic half' reactions were modelled by the Butler-Volmer equation and ti1ediffusion equation. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. TIle galvanic couples were constructed. as rotating ring disc electrodes and hence electrolyte voltage losses were negligible. Three galvanic couples, copper-platinum, copper-pyrite and galena-pyrite, were electrochemically characterised under different conditions of ferric concentration, electrode rotation rate and temperature. The effect of illumination on the anodic dissolution of galena was investigated. The electrochemical model is in good agreement with experimentally measured galvanic currents. Galvanic interaction is a dynamic function and various models are developed which account for dynamic behaviour in galvanic cells. / MT2017

L’objectif de ces travaux est de comprendre et modéliser le comportement en corrosion de l’acier Uranus S1N en milieu acide nitrique chaud et concentré. La littérature montre que cet acier présente un comportement en corrosion particulier, en comparaison à d’autres aciers comme l’acier 304L. Les aciers 304L et Uranus S1N ont une composition chimique similaire à l’exception du silicium (moins de 1% pour le 304L et 4% pour l’Uranus S1N). En milieu acide nitrique seul, l’acier 304L présente une vitesse de corrosion plus faible que celle de l’acier Uranus S1N. Cette tendance s’inverse lorsque l’on ajoute des ions oxydants au milieu. Les mécanismes physico-chimiques en jeu ne semblent pas clairement établis. On souhaite comprendre quel est l’effet de l’enrichissement en silicium conduisant à cette différence de comportement. Les phénomènes de réduction et d'oxydation sont comparés entre les deux aciers pour différentes conditions : acide nitrique pur, présence de vanadium pentavalent, présence de chrome hexavalent. On montre que la présence de Si diminue les cinétiques de réduction et donc empêche l'acier Uranus S1N de se trouver dans son domaine transpassif même en conditions très oxydantes. Puis la couche passive de l'acier Uranus S1N est étudiée à travers trois jeux d'expériences. D'une part ses caractéristiques thermodynamiques sont étudiées par la mesure du potentiel d'activation de l'acier. D'autre part, sa composition chimique, sa morphologie et sa structure sont mis en lumière par la correlation de différentes techniques in-situ et ex-situ cohérentes. Enfin, la rupture de passivité à haut potentiel est observée car le Si est suspecté responsable de la disparition de l'attaque intergranulaire. Ces trois axes d'études de l'oxyde protecteur de l'acier Uranus S1N font appel à des techniques in-situ originales comme l'Atomic emission spectro electrochemistry permettant de coupler la mesure électrochimique à l'analyse élémentaire en ligne, mais également à des techniques d'analyses ex-situ telles que la spectroscopie à photoélectrons X ou la spectroscopie d'énergie dispersive sur lame mince. / This work aims at understanding the corrosion behavior of the Uranus S1N stainless steel (SS) in hot and concentratred nitric acid. The Uranus S1N SS is a 304L type SS (18Cr-15Ni) added by 4 wt.% of Si. In pure nitric acid, the 304L SS dissolves slower. In other words, Si enhances the corrosion rate of the SS. But when oxidizing species are added, the 304L dissolves at a much higher rate than the Uranus S1N. Mecanisms involving Si that bring to this phenomenon are not clearly established. The purpose of this thesis project is to elucidate the role of Si in the spontaneous corrosion of the SS in pure nitric acid and in presence of oxidizing species. Reduction and oxydation phenomena are compared, through I-V curves measurements, between both steels, for different conditions : pure nitric acid, presence of pentavalent vanadium, hexavalent chromium. It was shown that Si diminishes the reduction kinetics and prevents the Uranus S1N SS to be shifted to its transpassive domain even when conditions are largely oxidizing. Then the oxide layer was investigated through three sets of experiments. Firstly, thermodynamics of the oxides where characterized by measuring the activation potential of the SS. Secondly, their chemical composition, thickness and structure were investigated coupling congruent in-situ and ex-situ measurements. Eventually, high potential passivity breakdown was investigated to understand why Si inhibits the intergranular attack at the surface. These three investigations rely on coupling original in-situ techniques as the atomic emission spectroelectrochemistry (electrochemical measurements coupled to elemental on line analysis) and ex-situ surface analysis as X-Ray photoelectron spectroscopy or Energy dispersive X-ray spectroscopy on cross-section thin blades.

Orientador: Edward Ralph Dockal / Banca: Assis Vicente Benedetti / Banca: Stanlei Ivair Klein / Banca: Osvaldo Antônio Serra / Banca: Éder Tadeu Gomes Cavalheiro / Resumo:Nesta tese estudou-se complexos organocobaloximas, com o grupo orgânico sendo derivado de benzilas substituídas do tipo [RCo(DMG)2py] onde R é 3-F∅CH2, 3-CH3O∅CH2, 4-Cl∅CH2, 3,5-CF3CF3∅CH2, 3-CN∅CH2, 3-Cl∅CH2, 3,4-Cl,Cl∅CH2 e C6F5CH2, por meio das técnicas de espectrometria de massas, análise térmica e voltametria cíclica. Os complexos foram sintetizados através de reação entre dimetilglioxima (DMGH), piridina, cloreto de hexaaquocobalto(II) em meio alcalino e atmosfera inerte, para gerar um composto Co(I) e posterior reação deste último com o respectivo reagente. Todos os compostos foram caracterizados por meio de técnicas espectroscópicas de ressonância magnética nuclear de 1H e de 13C, infravermelho e visível-ultravioleta, além de análises elementares de carbono, hidrogênio, nitrogênio e cobalto. Foram realizados espectros de massas de alguns complexos por meio da "ionização por spray de elétrons seguida de decomposição do íon formado por colisão com um gás" (ESI-MS-CID-MS), para se obter informações de massa molecular e estruturais. Os espectros dos compostos estudados apresentaram características comuns, mostrando que as fragmentações dos ligantes axiais R e py ocorrem quase que simultaneamente. Também foram realizadas análises térmicas por TG e DSC e os complexos investigados apresentaram comportamento semelhante, com a decomposição ocorrendo em três etapas, onde os dois primeiros estágios são atribuídos às perdas dos ligantes axiais, seguido da eliminação parcial do ligante equatorial dimetilglioxima. O resíduo final foi identificado como sendo Co3O4, no qual parte dos oxigênios presentes provém da dimetilglioxima e não incorporados da atmosfera. Ensaios de voltametria cíclica realizados com os complexos em meio de acetonitrila sugerem que a oxidação dos complexos é um processo quasi reversível...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this thesis organocobaloxime complexes, with the organic group being derived from a substituted benzyl, of the type [RCo(DMG)2py] where R is 3-F∅CH2, 3-CH3O∅CH2, 4-Cl∅CH2, 3,5-CF3,CF3∅CH2, 3-CN∅CH2, 3-Cl∅CH2, 3,4-Cl,Cl∅CH2 and C6F5CH2, were studied by the techniques of spectrometry of mass, thermal analysis and cyclic voltammetry. The complexes were synthesized by the reaction between dimethylglioxime (DMGH) pyridine, hexaaquocobalt(II) chloride in a medium alkaline and inert atmosphere, to generate a compound Co(I) and the posterior reaction of the latter with the respective reagent. All the compounds were characterized by the spectroscopic techniques of nuclear magnetic ressonance of 1H and of 13C, infrared and visible-ultraviolet, and elementary analyses of carbon, hydrogen, nitrogen and cobalt. Mass spectra were obtained for some complex by the "ionization for eletrons spray followed by decomposition of the ion formed by collision with a gas" (ESI-MSCID- MS), to obtain molecular mass and structural information. The spectra of the studied compounds presented common characteristics, showing that the fragmentations of the axial ligands R and py almost happen simultaneously. Thermal analyses were also performed by TG and DSC and the investigated complexes presented similar behavior, with the decomposition ocurring in three stages. The first two stages are attributed to the loss of the axial ligands, followed by the partial elimination of the equatorial ligand dimethylilglioxime. The final residue was identified as Co3O4, in which part of the oxigen present came from dimethylglioxime and not from of the atmosphere. Cyclic voltammetry studies of the complexes in acetonitrile showed that the oxidation of the complexes, occurs by an quasi-reversible process with transfer of an electron. The oxidized species is decomposed then, with the rupture of the Co-C bond. / Doutor

Orientador: Hebe de Las Mercedes Villullas / Banca: Estevam Vitorio Spinacé / Banca: Germano Tremiliosi Filho / Banca: Margarida Juri Saeki / Banca: Auro Atsushi Tanaka / Resumo: Neste trabalho, as reações de oxidação de metanol e etanol foram estudadas respectivamente sobre nanocatalisadores de Pt-Ru e Pt-Sn suportados em carbono. Os estudos para cada sistema foram realizados com aproximadamente o mesmo tamanho de partícula e mesma composição total e diferentes quantidades das fases liga e óxido. Catalisadores Pt-Sn com diferentes composições também foram estudados. Os catalisadores foram preparados pelos métodos de microemulsão e poliol modificado e as quantidades das fases liga e óxido foram modificadas por tratamentos térmicos em diferentes atmosferas. O crescimento das partículas foi evitado utilizando-se condições brandas de temperatura, de modo que este estudo foi conduzido na ausência dos efeitos de tamanho de partícula. A caracterização das propriedades físicas foi realizada por difração de raios X (DRX), microscopia eletrônica de transmissão (TEM), calorimetria exploratória diferencial (DSC), espectroscopia de fotoelétrons excitados por raios X (XPS) e espectroscopia de absorção de raios X dispersivos (DXAS) in situ. O comportamento eletroquímico geral dos nanocatalisadores foi avaliado por voltametria cíclica em solução ácida e as atividades eletrocatalíticas frente às reações de oxidação de metanol e etanol foram estudadas por varredura linear de potencial e cronoamperometria. Cromatografia líquida de alta eficiência (HPLC) foi utilizada para analisar quantitativamente os produtos de oxidação do metanol sobre os catalisadores Pt-Ru. Os resultados obtidos com os catalisadores Pt-Ru mostram claramente que a presença de espécies oxidadas de Ru é necessária para melhorar a atividade eletrocatalítica frente à oxidação de metanol. A oxidação de CO adsorvido também foi estudada, sendo que ambas as reações mostraram-se bastante... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, methanol and ethanol oxidation were studied on carbon-supported Pt-Ru and Pt- Sn nanocatalysts respectively. For each system, the studies were carried out with nearly the same particle size and identical overall composition, and different amounts of oxide and alloyed phases. For some Pt-Sn catalysts, overall composition was also varied. The catalysts were synthetized by microemulsion and modified poliol methods, and the amounts of alloyed and oxide phases were modified by heat treatments in different atmospheres. Because particle growth was avoided using mild temperature conditions, the study reported here was conducted in the absence of particle size effects. Characterization of physical properties was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and in situ dispersive X-ray absorption spectroscopy (DXAS). The general electrochemical behavior of the nanocatalysts was evaluated by cyclic voltammetry in acidic solution, and the electrocatalytic activities for the oxidation of methanol and ethanol were studied by linear potential sweeps and chronoamperometry. High performance liquid chromatography (HPLC) was used to assess the yields of soluble products of methanol oxidation on the Pt-Ru catalysts. The results obtained for the Pt-Ru catalysts clearly evidence that the presence of oxide species is necessary to enhance the electrocatalytic activity for methanol oxidation. Oxidation of adsorbed CO was also measured. Both reactions, methanol and adsorbed CO oxidation, were found to be very sensitive to the surface changes produced by the heat treatments. Interestingly, the best catalyst for methanol oxidation was not found to be the most efficient for the... (Complete abstract click electronic access below) / Doutor