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[pt] Recentemente, os nanocristais semicondutores, também conhecidos como pontos quânticos, tornaram-se muito atrativos em abordagens de detecção por fotoluminescência devido as suas propriedades ópticas peculiares, tais como fluorescência intensa e com perfil estreito, comprimento de onda máximo ajustável através do controle do tamanho das partículas e maior fotoestabilidade em comparação com os corantes orgânicos convencionais. As nanopartículas sintetizadas foram avaliadas como sondas fotoluminescentes (na forma de dispersão aquosa) para a determinação de captopril, histamina, canamicina e tiroxina (analitos não fotoluminescentes na temperatura ambiente) evitando o uso de procedimentos complexos de derivatização química e permitindo quantificações de forma simples e com sensibilidade. Nanopartículas de CdTe modificadas com o ácido tioglicólico (TGA) e com o ácido 2-mercaptopropiônico (2MPA) e também nanopartículas de ZnS modificadas com L-cisteína foram sintetizadas pela abordagem em fase aquosa coloidal. Estas foram caracterizadas usando métodos microscópicos e espectroscópicos adequados. A fotoluminescência da nanopartícula 2MPA-CdTe foi consideravelmente mais intensa quando na presença de captropil. Sob condições ótimas, o modelo de calibração (isoterma de ligação de Langmuir) foi linear até 4,8 x 10-4 mol L-1 com constante de equilíbrio de ligação de 3,2 x 104 L mol-1 e limite de detecção (LOD) de 6,2 x 10-6 mol L-1 (1,3 (micro)g mL-1). Aplicações em soro sanguíneo humano fortificado com captropil e em formulações farmacêuticas foram demonstradas. A fotoluminescência das nanopartículas de TGA-CdTe foi reduzida (supressão) após adição de diferentes concentrações de histamina seguindo o modelo de Stern- Volmer. A resposta linear cobriu uma faixa de concentração até 5,7 x 10-4 mol L-1, com LOD de 9,6 x 10-6 mol L-1 (1,1 (micro)g mL-1). A abordagem proposta foi utilizada para determinação de histamina em carne de atum. Já a presença de aminoglicosídeos aumentou a fluorescência das nanopartículas de TGA-CdTe (seguindo o modelo da isoterma da adsorção de Langmuir). A kanamicina foi o aminoglicosídeo escolhido para estudar o efeito do aumento da intensidade da fotoluminescência das nanopartículas de TGA-CdTe disperso em solução aquosa. A faixa linear estendeu-se até 8,2 x 10-7 mol L-1 com LOD de 2,5 x 10-8 mol L-1 (14,2 ng mL-1). As constantes de ligação entre diversos aminoglicosídeos e TGACdTe foram calculadas e indicou que existe uma relação entre o número de grupos amino primários disponíveis e o aumento da luminescência. Essa abordagem foi aplicada com sucesso para a análise de amostras de leite e água de riacho, ambos fortificados com kanamicina, usando procedimento de extração em fase sólida com um polímero impresso molecularmente (MIP). A intensidade da fotoluminescência da nanopartícula cisteína-ZnS em solução contendo brometo de cetiltrimetilamônio (CTAB) foi reduzida (quenched) após adição de tiroxina. A redução total do sinal (quenching) seguiu o modelo de Stern-Volmer com resposta linear até 4,0 x 10-6 mol L-1 de concentração do analito, o LOD foi 6,2 x 10-8 mol L-1 (48,3 ng mL-1). A dispersão aquosa da cisteína-ZnS foi usada como sonda óptica para a determinação de tiroxina em formulações farmacêuticas e em saliva humana fortificada com analito. / [en] Recently, semiconductor nanocrystals, also known as quantum dots, have become very attractive for photoluminescence based sensing approaches due to their unique optical properties like intense photoluminescence with narrow profile, maximum wavelength adjustable by the control of particle size and higher photostability in comparison of conventional organic dyes. Different synthesized nanoparticles were evaluated as photoluminescent probes (as aqueous dispersions) for the determination of captopril, histamine, kanamycin and thyroxine (nonphotoluminescent analytes at room-temperature) avoiding the use of complex chemical derivatization procedures and enabling simple and sensitive quantifications. Thioglycolic acid (TGA) and 2-mercapoprionic acid (2MPA) modified CdTe nanoparticles and L-cysteine modified ZnS nanoparticles were synthesized via the colloid aqueous phase route. Their characterization was made using proper microscopic and spectroscopic methods. The emission intensity of 2MPA-Cdte is greatly enhanced in the presence of captopril. Under optimum conditions, the calibration model (Langmuir binding isotherm) was linear up to 4.8 x 10-4 mol L-1 with equilibrium binding constant of 3.2 x 104 L mol-1 and limit of detection (LOD) of 6.2 x 10-6 mol L-1 (1.3 (micro)g mL-1). Applications in captopril fortified human serum and in pharmaceutical formulations were demonstrated. The photoluminescence of TGA-CdTe nanoparticles was quenched by histamine in a concentration dependent manner (Stern-Volmer model). The linear response covered the concentration range up to 5.7 x 10-4 mol L-1 with LOD of 9.6 x 10-6 mol L-1 (1.1 (micro)g mL-1). The proposed method was used for the analysis of tuna fish. The presence of aminoglycosides enhanced the photoluminescence of the TGA-CdTe nanoparticles (following a Langmuir binding isotherm model). Kanamycin was used as a model aminoglycoside in order to study its effect on the photoluminescence enhancement of TGA-CdTe quantum dots dispersed in aqueous solution. The linear range extended up to 8.2 x 10-7 mol L-1 with LOD of 2.5 x 10-8 mol L-1 (14.2 ng mL-1). Binding constants were calculated for several aminoglycosides indicating that there is a relationship between the number of available primary amino groups and the increasing in photoluminescence. This approach was successfully applied for determination of kanamycin fortified milk and in stream water samples after solid phase extraction using a molecular imprinted polymer produced using a kanamycin template. The photoluminescence intensity of cysteine-ZnS in solution containing cetyltrimethyl ammonium bromide (CTAB) was quenched by thyroxine. The overall quenching followed a Stern-Volmer model with linear response coveing an analyte concentration range up to 4.0 x 10-6 mol L-1. LOD was 6.2 x 10-8 mol L-1 (48.3 ng mL-1). The aqueous dispersion of cysteine-ZnS was used as optical probe for the determination of thyroxine in pharmaceutical formulations and in analyte fortified human saliva.

The first part of this dissertation deals with the application of a luminescence quenching method to measure diffusion and permeation coefficients of oxygen in polymers. Most luminescence oxygen sensors do not follow linearity of the Stern-Volmer (SV) equation due to heterogeneity of luminophore in the polymer matrix, thus the complexity of data analysis is increased. To circumvent this limitation, inverted fluorescence microscopy is utilized in this work to investigate the SV response of the sensors at the micron-scale. In these diffusion experiments, oxygen concentration is measured by luminescence changes in regions with high SV constants and good linearity. Thus, we avoid numerical complexity of combining nonlinear SV equation with a diffusion model. This technique allows us to measure oxygen diffusion properties in different type of polymers like transparent, opaque, free-standing polymers and polymers that cannot be cast into free standing films and polymer composites. In the second part of this thesis, we have explored the effect of Ag-Cu alloy nanoparticles on the emission intensity of luminophores at their close proximity. Alloy nanoparticles offer additional degrees of freedom for tuning their optical properties by altering atomic composition and atomic arrangement and thus can be an attractive option for manipulating signal of a wide range of luminophores. In this work, surface plasmon resonance spectrum of Ag-Cu alloy nanoparticles deposited by sputtering was easily tuned in wide wavelength range by varying one experimental condition- annealing temperature. Large metal enhanced luminescence for different luminophores viz Alexa Fluor 594 and Alexa Fluor 488 were achieved at the vicinity of Ag-Cu nanoparticles when maximum spectral overlap between SPR spectra of Ag-Cu nanoparticles and the emission and absorption spectra of the luminophores occur. We also studied the effect of composition of Ag-Cu nanoparticles synthesized by the polyol process on the luminescence of low quantum yield dye Cy3. In the third part of this thesis, quenching effect of Cu nanoparticles on CdSe/ZnS nanocrystal quantum dots has been explored. As Cu nanoparticles have comparable dielectric properties with gold nanoparticles, they are expected to show similar quenching effects. It was found that Cu is an efficient quencher of fluorescence from CdSe/ZnS quantum dots and the quenching effect is due to resonance energy transfer from quantum dots to Cu nanoparticles.

La modélisation mathématique des systèmes électrochimiques, et en général la modélisa- tion des systèmes fluidiques réactifs en présence de champs électriques, est un problème d’une complexité telle que des solutions analytiques n’existent que dans des cas très simpli- fiés et la solution numérique est, malgré toute la puissance de calcul moderne, encore très difficile. À ce jour, les avancées dans la modélisation au niveau des modèles d’écoulement sont majeures, mais la modélisation couplée de l’écoulement, avec le champ électrique en présence de solutions concentrées demeure encore un défi de taille. Le couplage des diffé- rents champs décrits par les modèles mathématiques devient critique dans les régions où ont lieu les réactions hétérogènes aux interfaces chargées modélisées par l’équation non linéaire de Butler-Volmer. Les logiciels commerciaux modernes commencent à permettre de coupler les modules d’électrochimie avec la mécanique des fluides numérique (CFD), mais l’ impossibilité d’ac- céder au code source ne permet pas au chercheur de modifier à volonté la formulation des modèles. Par conséquent, le projet de recherche actuel vise le développement d’une plate-forme logicielle ouverte (open-source) comme OpenFOAM, qui peut garantir une complète accessibilité au code-source, la liberté des utilisateurs à faire des modifications, la transparence des détails des modèles, et tous les autres développements qui sont requis pour chaque problème rencontré par les chercheurs. Le développement de modèles reposant sur des lois physiques établies permettra la modéli- sation des systèmes électrochimiques complexes, et la compréhension des phénomènes qui s’y déroulent. Il vise la modélisation du transfert de masse d’une cellule où l’écoulement de la solution concentrée (molten salt) est turbulent, biphasique et incompressible, et les réactions électrochimiques de surface sont calculées en utilisant une distribution tertiaire de densité de courant. Le principal enjeu sur le plan scientifique, dans le cadre de ce projet, demeure donc de développer un modèle qui soit bien calé sur le problème technologique visé afin qu’il puisse reproduire de façon réaliste les systèmes électrochimiques. Il vise éga- lement à amener la modélisation à un point où l’outil pourra être utilisé comme instrument de prédiction et de validation de nouveaux concepts des systèmes électrochimiques. / Abstract: The modeling of electrochemical systems, and in general the modeling of reacting flows ex- posed to electric field, is a complex problem to the point that analytic solutions exist only for simplified cases despite the increasing computer power. The state of art shows major improvements in the fluid-dynamics of electrochemical reactors; but the full coupling of the flow with the electric field in presence of concentrated electrolytic solutions still needs to be properly investigated. The coupling gets even more critical along the charged in- terfaces where heterogeneous reactions are modeled through the non-linear Butler-Volmer equation. Commercial software are slowly try to connect electrochemical modules to the well val- idated CFDs, but most of the time costly licenses, and poor accessibility to the source code, do not allow a deep integration between the two. Instead, this research study pro- poses an open-source code implemented in OpenFOAM, that guarantees full accessibility to the source code, user’s modifications, full transparency of the model’s details, and any possible further developments required by the specificity of the problem. The final code implements the mass transfer of a cell where the concentrated solution (molten salt) is a two-phase turbulent incompressible flow and the electrochemical surface reactions consider tertiary current distributions. The aim of this work is to create an open source platform to predict and analyze industrial reactor’s performances. The advanced modeling can be later exploited and used as a validation instrument for new electrochemical concepts.

Solid oxide fuel cells (SOFC) are mainly used as large stationary elec- tricity sources, therefore an every little improvement in their performance leads to considerable savings. In order to understand the fundamentals of the SOFC operation, we have developed a new model describing the main physical processes. The thermodynamical model of SOFC, developed in this thesis, concerns the gas transport, the transport of the charged particles in- cluding the thermoelectric effect and the electrochemical reactions. Linear irreversible thermodynamics is the key modelling framework, in which the dusty gas model and the Butler-Volmer equations are used. A new relation between the electrochemical affinity and the overpotential is introduced into the Butler-Volmer equation. A weakly formulated statinonary system en- dowed with boundary conditions is solved with the finite element method in one dimensional approximation. 1

This thesis primarily focuses on the electrochemical properties of the H₂/H⁺ redox couple, at various metallic electrodes in room temperature ionic liquids. Initially, a comprehensive overview of room temperature ionic liquids, RTILs, compared to conventional organic solvents is presented which identifies their favourable properties and applications, followed by a second chapter describing the basic theory of electrochemistry. A third chapter presents the general experimental reagents, instruments and measurements used in this thesis. The results presented in this thesis are summarized in six further chapters and shown as follows. (1) Hydrogenolysis, hydrogen loaded palladium electrodes by electrolysis of H[NTf₂] in a RTIL [C₂mim][NTf₂]. (2) Palladium nanoparticle-modified carbon nanotubes for electrochemical hydrogenolysis in RTILs. (3) Electrochemistry of hydrogen in the RTIL [C₂mim][NTf₂]: dissolved hydrogen lubricates diffusional transport. (4) The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends. (5) The formal potentials and electrode kinetics of the proton_hydrogen couple in various room temperature ionic liquids. (6) The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a Platinum microelectrode in room temperature ionic liquids. The first two studies show electrochemically formed adsorbed H atoms at a metallic Pt or Pd surface can be used for clean, efficient, safe electrochemical hydrogenolysis of organic compounds in RTIL media. The next study shows the physicochemical changes of RTIL properties, arising from dissolved hydrogen gas. The last three studies looked at the electrochemical properties of H₂/H⁺ redox couple at various metallic electrodes over a range of RTILs vs a stable Ag/Ag⁺ reference couple, using H[NTf₂] and benzoic acid as proton sources. The kinetic and thermodynamic mechanisms of some reactions or processes are the same in RTILs as in conventional organic or aqueous solvents, but other remarkably different behaviours are presented. Most importantly significant constants are seen for platinum, gold and molybdenum electrodes in term of the mechanism of proton reduction to form hydrogen.

Three mathematical models, two of primary alkaline battery cathode discharge, and one of primary alkaline battery discharge, are developed, presented, solved and investigated in this thesis. The primary aim of this work is to improve our understanding of the complex, interrelated and nonlinear processes that occur within primary alkaline batteries during discharge. We use perturbation techniques and Laplace transforms to analyse and simplify an existing model of primary alkaline battery cathode under galvanostatic discharge. The process highlights key phenomena, and removes those phenomena that have very little effect on discharge from the model. We find that electrolyte variation within Electrolytic Manganese Dioxide (EMD) particles is negligible, but proton diffusion within EMD crystals is important. The simplification process results in a significant reduction in the number of model equations, and greatly decreases the computational overhead of the numerical simulation software. In addition, the model results based on this simplified framework compare well with available experimental data. The second model of the primary alkaline battery cathode discharge simulates step potential electrochemical spectroscopy discharges, and is used to improve our understanding of the multi-reaction nature of the reduction of EMD. We find that a single-reaction framework is able to simulate multi-reaction behaviour through the use of a nonlinear ion-ion interaction term. The third model simulates the full primary alkaline battery system, and accounts for the precipitation of zinc oxide within the separator (and other regions), and subsequent internal short circuit through this phase. It was found that an internal short circuit is created at the beginning of discharge, and this self-discharge may be exacerbated by discharging the cell intermittently. We find that using a thicker separator paper is a very effective way of minimising self-discharge behaviour. The equations describing the three models are solved numerically in MATLABR, using three pieces of numerical simulation software. They provide a flexible and powerful set of primary alkaline battery discharge prediction tools, that leverage the simplified model framework, allowing them to be easily run on a desktop PC.