This work explores the blending of e-textile technology with the porous electrode of polymer electrolyte membrane fuel cells (PEMFCs) and with smart wound patches to allow monitoring and in-situ diagnostics. This work includes contributions to understanding water transport and conductivity in the carbon cloth gas diffusion layer (GDL), and further developing thread-based relative humidity (RH) and temperature sensors, which can be sewn on a cloth GDL in PEMFCs. We also explore the application of the developed RH and temperature sensors in wearable biomonitoring. First, an experimental prototype is developed for evaluating water transport, thermal conductivity and electrical conductivity of carbon cloth GDLs under different hydrophobic coatings and compressions. Second, we demonstrate the addition of external threads to the carbon cloth GDL to (1) facilitate water transport and (2) measure local RH and temperature with a minimal impact on the physical, microstructural and transport properties of the GDL. We illustrate the roll-to-roll process for fabricating RH and temperature sensors by dip-coating commodity threads into a carbon nanotubes (CNTs) suspension. The thread-based sensors response to RH and temperature in the working environment of PEMFCs is investigated. As a proof-of-concept, the local temperature of carbon cloth GDL is monitored in an ex-situ experiment. Finally, we optimized the coating parameters (e.g. CNTs concentration, surfactant concentration and a number of dipping) for the thread-based sensors. The response of the thread-based sensors in room conditions is evaluated and shows a linear resistance decrease to temperature and a quadratic resistance increase to RH. We also evaluated the biocompatibility of the sensors by performing cell cytotoxicity and studying wound healing in an animal model. The novel thread-based sensors are not only applicable for textile electrochemical devices but also, show a promising future in wearable biomonitoring applications. / Graduate

Les sols agricoles représentent près de 66 % des émissions anthropiques de protoxyde d’azote (N₂O), 3ème gaz responsable de l’effet de serre additionnel. La variabilité des émissions mesurées au champ est élevée. La structure du sol impacte à la fois la production et le transport du N₂O dans le profil de sol. L’objectif de cette thèse était de comprendre le rôle de l’état structural du sol sur la variabilité spatiale des émissions de N₂O. La démarche utilisée associe deux types d’expérimentations en laboratoire - à l’échelle d’un bac de 0,3 m² x 0,1 m et sur une maquette de parcelle agricole de 10 m² x 0,3 m en sol nu - à un travail de modélisation intégrant des processus physiques, chimiques et biologiques dans le profil de sol et le ruissellement, le tout à une résolution temporelle fine. Ce travail a mis en évidence une hiérarchie entre les processus de production et de transport, qui évolue avec le temps et les conditions environnementales : dans des conditions favorables à la dénitrification, la production de N₂O augmente avec la masse volumique en lien avec une augmentation de la part de porosité remplie d’eau, jusqu’à une certaine limite. Le modèle déterministe a montré que la dynamique de la pluie et du ruissellement associé modifie l’intensité et la dynamique des émissions de N₂O, celles-ci étant plus tardives dans les zones avales recevant du ruissellement. Enfin, ce travail a confirmé la complexité du déterminisme des émissions de N₂O et a permis de souligner l’intérêt de caractériser la structure du sol et les émissions à une haute résolution spatiale pour améliorer la qualité des modèles prédictifs. / Agricultural soils account for 66 % of anthropogenic nitrous oxide emissions (N₂O), the 3rd greenhouse gas emitted from anthropogenic activities. N₂O emissions variability measured in-situ is quite high. Soil structure affects both N₂O production processes and N₂O movements through the soil profile. The main goal of this work was to understand the part of soil structure in soil N₂O spatial variability. Two kinds of laboratory experiments were designed: rainfall experiments on soil trays of 0.3 m² x 0.1 m and on a 10 m² x 0.3 m box with a slope. A modelling approach with a short time step was combined, involving representation of physical, chemical and biological soil processes as well as a representation of surface runoff.This work highlighted a hierarchy between N₂O production and N₂O transportation processes, which evolve with time and environmental conditions: under conditions that favor denitrification, N₂O production increases with soil bulk density due to an increase in the water-filled pore space, until a threshold limit. The deterministic modelling approach showed that rainfall dynamic and resulting runoff affect soil N₂O emissions, those emissions occurring later downslope. Finally, this work highlighted the complexity of soil N₂O emissions determinism and we pointed out that the description of soil structure at a high spatial resolution would be useful to improve modelling quality.

Constitutive relationships are developed to describe the water transport characteristics of the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). Additionally, experimental fixtures and procedures for the determination of the constitutive relationships are presented. The water transport relationships are incorporated into analytical models that assess the impact of the water transport relations and that make PEMFC performance predictions. The predicted performance is then compared to experimental results. The new constitutive relationships are significantly different than the currently popular relationships used in PEMFC modeling because they are derived from experiments on actual PEMFC gas diffusion layer materials. In prior work, properties of the GDL materials such as absolute permeability, liquid water relative permeability, porosity, and capillary behavior are often assumed or used as adjustment parameters in PEMFC models to simplify the model or to achieve good fits with polarization data. In this work, the constitutive relations are not assumed but are determined via newly developed experimental techniques. The experimental fixtures and procedures were used to characterize common GDL materials including carbon papers and carbon cloths, and to investigate common treatments applied to these materials such as the bulk application of a hydrophobic polymer within the porous structure. A one-dimensional model is developed to contrast results based on the new constitutive relations with results based on commonly used relationships from the PEMFC literature. The comparison reveals that water transport relationships can have a substantial impact on predicted GDL saturation, and consequently a significant impact on cell performance. The discrepancy in saturation between cases can be nearly an order of magnitude. A two-dimensional model is also presented that includes the impact of the compressed GDL region under the shoulder of a bipolar plate. Results show that the compression due to the bipolar plate shoulder causes a significant increase in liquid saturation, and a significant reduction in oxygen concentration and current density for the paper GDL. In contrast, compression under the shoulder has a minimal impact on the cloth GDL. Experimental inputs to the 2-D model include: absolute permeability, liquid water relative permeability, the slope of the capillary pressure function with saturation, total porosity, GDL thickness, high frequency resistance, and appropriate Tafel parameters. Computational polarization curve results are compared to experimental polarization behavior and good agreement is achieved. / Ph. D.

The gas diffusion layer (GDL) is one of the key components in a polymer electrolyte membrane (PEM) fuel cell. It performs several functions including the transport of reactant gases and product water to and from the catalyst layer, conduction of both electrons and heat produced in the catalyst layer, as well as mechanical support for the membrane. The overarching goal of this work is to thoroughly examine the GDL structure and properties for use in PEM fuel cells, and more specifically, to determine how to characterize the GDL experimentally ex-situ, to understand its performance in-situ, and to relate theory to performance through controlled experimentation. Thus, the impact of readily measured effective water vapor diffusivity on the performance of the GDL is investigated and shown to correlate to the wet limiting current density, as a surrogate of the oxygen diffusivity to which it is more directly related. The influence of microporous layer (MPL) design and construction on the fuel cell performance is studied and recommendations are made for optimal MPL designs for different operating conditions. A method for modifying the PTFE (Teflon) distribution within the GDL is proposed and the impact of distribution of PTFE in the GDL on fuel cell performance is studied. A method for characterizing the surface roughness of the GDL is developed and the impact of surface roughness on various ex-situ GDL properties is investigated. Finally, a detailed analysis of the physical structure and permeability of the GDL is provided and a theoretical model is proposed to predict both dry and wet gas flow within a GDL based on mercury intrusion porosimetry and porometry data. It is hoped that this work will contribute to an improved understanding of the functioning and structure of the GDL and hence advance PEM fuel cell technology.

Este trabalho descreve o estudo da geração eletroquímica do H2O2 em eletrólito ácido (H2SO4 (0,1 mol L-1) + K2SO4 (0,1 mol L-1)) e eletrólito alcalino (KOH 1,0 mol L-1) utilizando eletrodo de difusão gasosa (EDG), sendo este fabricado com carbono Printex 6L e modificado com 3,0; 5,0 e 10,0% de ftalocianina de cobalto (II) ou cobre (II). Os experimentos foram realizados em uma célula eletroquímica de compartimento único contendo eletrodo de referência Ag/AgCl, contra eletrodo de Pt e como eletrodo de trabalho foi utilizado o EDG. Nos testes de eletrólise a potencial constante (-0,4 V ≤ E ≤ -1,4 V) durante 90 minutos com O2 pressurizado a 0,2 Bar, a concentração de H2O2 alcançou valor máximo de 178 mg L-1 a - 1,0 V (vs. Ag/AgCl) para o EDG não modificado em eletrólito ácido e em eletrólito alcalino, o valor máximo foi de 3.370 mg L-1 a -1,1 V (vs. Ag/AgCl). Quando incorporada a porcentagem de 5,0% de ftalocianina de cobalto (II) à massa do EGD verificou-se que a concentração de H2O2 alcança valor máximo em 331 mg L-1 a -0,7 V (vs. Ag/AgCl), o que representa um aumento de 86,0% no rendimento da produção de H2O2 em meio ácido, além de uma diminuição de 300 mV no potencial aplicado para formação da espécie oxidante. Para o estudo da degradação eletroquímica foram utilizados os corantes amaranto e tartrazina com concentração de 100 mg L-1. Para o estudo do processo eletro-Fenton homogêneo foram utilizados 0,05; 0,1 e 0,15 mmol de Fe2+ ou Fe3+ e para o processo eletro-Fenton heterogêneo em meio alcalino foi utilizado 0,15 mmol das nanopartículas do tipo Fe3-xCuxO4 (0 ≤ x ≤ 0,25). As eletrólises foram realizadas a potencial constante em -0,7 V (vs. Ag/AgCl) no EDG modificado com 5,0% de ftalocianina de cobalto (II) sob fluxo constante de O2 durante 90 minutos no processo eletro-Fenton homogêneo enquanto no processo eletro-Fenton heterogêneo o EDG não modificado foi utilizado e as eletrólises foram realizadas a -1,1 V (vs. Ag/AgCl). Todos os ensaios eletroquímicos foram realizados em um potenciostato PGSTAT- 302 acoplado a um com módulo de alta corrente BSTR-10A e controlado por meio do software GPES (Metrohm Autolab). As nanopartículas Fe3-xCuxO4 (0 ≤ x ≤ 0,25) foram caracterizadas por Análise de Ativação de Neutrons (AAN), DRX, BET, XPS e MET. As amostras dos corantes foram analisadas por espectrofotometria UV/Vis, cromatografia líquida de alta eficiência (CLAE) e teor de carbono orgânico total (COT). Em termos de descoloração, houve uma pequena diminuição no espectro dos corantes quando utilizado H2O2 eletrogerado em meio ácido o que não ocorre na degradação quando utilizado o processo eletro-Fenton homogêneo sendo mais evidente quando utilizado Fe2+, alcançando uma descoloração máxima de 80,0 e 99,2% respectivamente para os corantes amaranto e tartrazina. O decaimento da concentração por CLAE foi bastante eficiente quando utilizado o processo eletro-Fenton, com melhores resultados para Fe2+ e Fe3-xCuxO4 (x= 0,25) sendo a cinética dos processos de pseudo-primeira ordem. Foram identificados os subprodutos formados durante a degradação dos corantes durante o processo eletro-Fenton homogêneo. Os maiores valores de remoção de COT (67,3%) e consumo energético (CE) (370 kwh kg-1 foram obtidos para o processo utilizando íons Fe2+ e as nanopartículas Fe3-xCuxO4 (x=0,25) respectivamente para o corante amaranto. Os valores da concentração de ferro residual solúvel estão dentro do limite permitido segundo a Resolução CONAMA nº 430/2011. Para o processo eletro-Fenton heterogêneo, a concentração de H2O2 residual e consumida diminuiu e aumentou respectivamente com o aumento do valor de \"x\" na espinela da Fe3-xCuxO4 (0 ≤ x ≤ 0,25). / This work describes the electrogeneration of H2O2 study in acidic medium (H2SO4 (0.1 mol L-1) + K2SO4 (0.1 mol L-1)) and alkaline medium (KOH 1.0 mol L-1) using gas diffusion electrode (GDE), being these GDE manufactured with the Printex 6L carbon and modified with percentages of 3.0, 5.0 and 10.0% of cobalt (II) phthalocyanine or copper (II) phthalocyanine. The experiments were performed in an electrochemical cell single compartment containing the reference electrode Ag/AgCl, platinum counter electrode and the working electrode was used the GDE. In tests electrolysis at constant potential (-0.4 V ≤ E ≤ - 1.4 V) for 90 minutes pressurized with O2 at 0.2 Bar, H2O2 concentration reached a maximum value at 178 mg L-1 to -1.0 V (vs. Ag/AgCl) for GDE unmodified in acid electrolyte and alkaline electrolyte, the maximum value was 3,370 mg L-1 at potential -1.1 V (vs. Ag/AgCl).When incorporated percentage of 5.0% of cobalt (II) phthalocyanine to mass GDE, it is verified that the concentration of H2O2 reaches maximum value at 331 mg L-1 at -0.7 V (vs. Ag/AgCl), which represents increase in yield of 86.0% relative to Printex 6L carbon in acidic medium, addition to a decrease of 300 mV at potential applied to the formation of oxidizing species. To study the electrochemical degradation were amaranth and tartrazine dyes with concentration of 100 mg L-1. To study the homogeneous electro-Fenton process were used 0.05; 0.1 e 0.15 mmol de Fe2+ or Fe3+ and to heterogeneous electro-Fenton process in alkaline medium was used 0.15 mmol of Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles. The electrolysis were performed at constant potential -0.7 V (vs. Ag/AgCl) in the GDE modified with 5.0% of cobalt (II) phthalocyanine under constant flow of O2 for 90 minutes in the homogeneous electro-Fenton process while in the heterogeneous electro-Fenton process, GDE unmodified was used and the electrolysis were performed at -1.1 V (vs. Ag/AgCl). All electrochemical tests were performed using a potentiostat/galvanostat model PGSTAT 302 coupled to a BSTR-10A current booster and controlled by GPES software (Metrohm Autolab). The Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles were characterized by Neutron Activation Analysis (NAA), XRD, BET, XPS and TEM. The samples of the dyes were analyzed by spectrophotometry UV/Vis, high performance liquid chromatography (HPLC) and total organic carbon (TOC). In terms of discoloration, was a small decrease in the spectrum of the dye when used H2O2 in acidic medium which doesn\'t occur in the degradation when used homogeneous electro-Fenton process being more evident when used Fe2+, reaching a maximum discoloration of 80.0 and 99.2% respectively for amaranth and tartrazine dyes. The decay concentration by HPLC was very efficient when using the electro-Fenton process with better results for Fe2+ and Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles being the kinetics of the process of pseudo-first order. Were identified by-products formed during the degradation of dyes during the homogeneous electro-Fenton process. The higher values of TOC removal (67.3%) and energy consumption (EC) (370 kWh kg-1) were obtained to process using Fe2+ ions and Fe3-xCuxO4 (x= 0.25) nanoparticle respectively for amaranth dye. The values of residual soluble iron concentrations are within the permissible limit according to CONAMA Resolution nº 430/2011. To the heterogeneous electro-Fenton process, the residual and consumed concentration of H2O2 decreased and increased respectively with increasing value of \"x\" in the spinel of Fe3-xCuxO4 (0 ≤ x ≤ 0.25).

Este trabalho descreve o estudo da geração eletroquímica do H2O2 em eletrólito ácido (H2SO4 (0,1 mol L-1) + K2SO4 (0,1 mol L-1)) e eletrólito alcalino (KOH 1,0 mol L-1) utilizando eletrodo de difusão gasosa (EDG), sendo este fabricado com carbono Printex 6L e modificado com 3,0; 5,0 e 10,0% de ftalocianina de cobalto (II) ou cobre (II). Os experimentos foram realizados em uma célula eletroquímica de compartimento único contendo eletrodo de referência Ag/AgCl, contra eletrodo de Pt e como eletrodo de trabalho foi utilizado o EDG. Nos testes de eletrólise a potencial constante (-0,4 V ≤ E ≤ -1,4 V) durante 90 minutos com O2 pressurizado a 0,2 Bar, a concentração de H2O2 alcançou valor máximo de 178 mg L-1 a - 1,0 V (vs. Ag/AgCl) para o EDG não modificado em eletrólito ácido e em eletrólito alcalino, o valor máximo foi de 3.370 mg L-1 a -1,1 V (vs. Ag/AgCl). Quando incorporada a porcentagem de 5,0% de ftalocianina de cobalto (II) à massa do EGD verificou-se que a concentração de H2O2 alcança valor máximo em 331 mg L-1 a -0,7 V (vs. Ag/AgCl), o que representa um aumento de 86,0% no rendimento da produção de H2O2 em meio ácido, além de uma diminuição de 300 mV no potencial aplicado para formação da espécie oxidante. Para o estudo da degradação eletroquímica foram utilizados os corantes amaranto e tartrazina com concentração de 100 mg L-1. Para o estudo do processo eletro-Fenton homogêneo foram utilizados 0,05; 0,1 e 0,15 mmol de Fe2+ ou Fe3+ e para o processo eletro-Fenton heterogêneo em meio alcalino foi utilizado 0,15 mmol das nanopartículas do tipo Fe3-xCuxO4 (0 ≤ x ≤ 0,25). As eletrólises foram realizadas a potencial constante em -0,7 V (vs. Ag/AgCl) no EDG modificado com 5,0% de ftalocianina de cobalto (II) sob fluxo constante de O2 durante 90 minutos no processo eletro-Fenton homogêneo enquanto no processo eletro-Fenton heterogêneo o EDG não modificado foi utilizado e as eletrólises foram realizadas a -1,1 V (vs. Ag/AgCl). Todos os ensaios eletroquímicos foram realizados em um potenciostato PGSTAT- 302 acoplado a um com módulo de alta corrente BSTR-10A e controlado por meio do software GPES (Metrohm Autolab). As nanopartículas Fe3-xCuxO4 (0 ≤ x ≤ 0,25) foram caracterizadas por Análise de Ativação de Neutrons (AAN), DRX, BET, XPS e MET. As amostras dos corantes foram analisadas por espectrofotometria UV/Vis, cromatografia líquida de alta eficiência (CLAE) e teor de carbono orgânico total (COT). Em termos de descoloração, houve uma pequena diminuição no espectro dos corantes quando utilizado H2O2 eletrogerado em meio ácido o que não ocorre na degradação quando utilizado o processo eletro-Fenton homogêneo sendo mais evidente quando utilizado Fe2+, alcançando uma descoloração máxima de 80,0 e 99,2% respectivamente para os corantes amaranto e tartrazina. O decaimento da concentração por CLAE foi bastante eficiente quando utilizado o processo eletro-Fenton, com melhores resultados para Fe2+ e Fe3-xCuxO4 (x= 0,25) sendo a cinética dos processos de pseudo-primeira ordem. Foram identificados os subprodutos formados durante a degradação dos corantes durante o processo eletro-Fenton homogêneo. Os maiores valores de remoção de COT (67,3%) e consumo energético (CE) (370 kwh kg-1 foram obtidos para o processo utilizando íons Fe2+ e as nanopartículas Fe3-xCuxO4 (x=0,25) respectivamente para o corante amaranto. Os valores da concentração de ferro residual solúvel estão dentro do limite permitido segundo a Resolução CONAMA nº 430/2011. Para o processo eletro-Fenton heterogêneo, a concentração de H2O2 residual e consumida diminuiu e aumentou respectivamente com o aumento do valor de \"x\" na espinela da Fe3-xCuxO4 (0 ≤ x ≤ 0,25). / This work describes the electrogeneration of H2O2 study in acidic medium (H2SO4 (0.1 mol L-1) + K2SO4 (0.1 mol L-1)) and alkaline medium (KOH 1.0 mol L-1) using gas diffusion electrode (GDE), being these GDE manufactured with the Printex 6L carbon and modified with percentages of 3.0, 5.0 and 10.0% of cobalt (II) phthalocyanine or copper (II) phthalocyanine. The experiments were performed in an electrochemical cell single compartment containing the reference electrode Ag/AgCl, platinum counter electrode and the working electrode was used the GDE. In tests electrolysis at constant potential (-0.4 V ≤ E ≤ - 1.4 V) for 90 minutes pressurized with O2 at 0.2 Bar, H2O2 concentration reached a maximum value at 178 mg L-1 to -1.0 V (vs. Ag/AgCl) for GDE unmodified in acid electrolyte and alkaline electrolyte, the maximum value was 3,370 mg L-1 at potential -1.1 V (vs. Ag/AgCl).When incorporated percentage of 5.0% of cobalt (II) phthalocyanine to mass GDE, it is verified that the concentration of H2O2 reaches maximum value at 331 mg L-1 at -0.7 V (vs. Ag/AgCl), which represents increase in yield of 86.0% relative to Printex 6L carbon in acidic medium, addition to a decrease of 300 mV at potential applied to the formation of oxidizing species. To study the electrochemical degradation were amaranth and tartrazine dyes with concentration of 100 mg L-1. To study the homogeneous electro-Fenton process were used 0.05; 0.1 e 0.15 mmol de Fe2+ or Fe3+ and to heterogeneous electro-Fenton process in alkaline medium was used 0.15 mmol of Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles. The electrolysis were performed at constant potential -0.7 V (vs. Ag/AgCl) in the GDE modified with 5.0% of cobalt (II) phthalocyanine under constant flow of O2 for 90 minutes in the homogeneous electro-Fenton process while in the heterogeneous electro-Fenton process, GDE unmodified was used and the electrolysis were performed at -1.1 V (vs. Ag/AgCl). All electrochemical tests were performed using a potentiostat/galvanostat model PGSTAT 302 coupled to a BSTR-10A current booster and controlled by GPES software (Metrohm Autolab). The Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles were characterized by Neutron Activation Analysis (NAA), XRD, BET, XPS and TEM. The samples of the dyes were analyzed by spectrophotometry UV/Vis, high performance liquid chromatography (HPLC) and total organic carbon (TOC). In terms of discoloration, was a small decrease in the spectrum of the dye when used H2O2 in acidic medium which doesn\'t occur in the degradation when used homogeneous electro-Fenton process being more evident when used Fe2+, reaching a maximum discoloration of 80.0 and 99.2% respectively for amaranth and tartrazine dyes. The decay concentration by HPLC was very efficient when using the electro-Fenton process with better results for Fe2+ and Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles being the kinetics of the process of pseudo-first order. Were identified by-products formed during the degradation of dyes during the homogeneous electro-Fenton process. The higher values of TOC removal (67.3%) and energy consumption (EC) (370 kWh kg-1) were obtained to process using Fe2+ ions and Fe3-xCuxO4 (x= 0.25) nanoparticle respectively for amaranth dye. The values of residual soluble iron concentrations are within the permissible limit according to CONAMA Resolution nº 430/2011. To the heterogeneous electro-Fenton process, the residual and consumed concentration of H2O2 decreased and increased respectively with increasing value of \"x\" in the spinel of Fe3-xCuxO4 (0 ≤ x ≤ 0.25).

Os processos oxidativos avançados (POA) são uma alternativa para complementar os processos clássicos de tratamento de efluentes que podem não ser eficientes para remoção de alguns tipos de poluentes como, por exemplo, os poluentes emergentes. Os POA se baseiam na geração de espécies altamente reativas (radicais hidroxila), a partir de peróxido de hidrogênio (H2O2), que oxidam os poluentes. O H2O2 pode ser eletrogerado in situ pela reação de redução de oxigênio (RRO) no meio reacional. O uso de eletrodos de difusão gasosa (EDG) altamente porosos proporciona o suprimento de oxigênio na interface eletrodo/solução podendo aumentar a velocidade da RRO. O uso de modificadores como quinonas e azocompostos imobilizados à matriz de carbono dos EDG podem aumentar a geração de H2O2. Portanto, os modificadores orgânicos Sudan Red 7B (SR7B), metil-p-benzoquinona (MPB), ácido antraflávico (AA) e antraquinona-2-ácido carboxílico (A2CA) foram adicionados em diferentes teores ao carbono Printex L6 (CP) e microcamadas porosas destes materiais foram estudados por voltametria cíclica e de varredura linear em eletrodo de disco-anel rotatório (RRDE). Os materiais contendo 0,5% de SR7B e 5,0% de MPB levaram a aumento na eficiência de geração de H2O2 para 86,2 e 85,5%, respectivamente, em relação ao CP puro que levou a 82,8%. EDG de CP modificados com 0,5% de SR7B foram construídos com telas metálicas em sua faces externas e a aplicação de densidades de corrente de 75, 100 e 150 mA cm-2 levou a uma maior eletrogeração de H2O2. Em densidades de corrente de 75 mA cm-2, o EDG modificado gerou 1020,1 mg L-1 de H2O2 com consumo energético de 118,0 kWh kg-1 de H2O2, constante cinética aparente de 37,3 mg L-1 min-1 e eficiência de corrente de 17,9%, enquanto o EDG de CP puro gerou menor concentração de H2O2; 717, 3 mg L-1, com maior consumo energético; 168,5 kWh kg-1, menor constante cinética aparente; 21,4 mg L-1 min-1, e menor eficiência de corrente; 12,6%. Portanto, o EDG modificado poderia ser empregado em sistemas que precisem de altas gerações de H2O2. / The advanced oxidation processes (AOP) are an alternative to the classical processes of treatment of effluents that may not be effective for the removal of some types of pollutants such as emerging pollutants. The AOP are based on the highly reactive species (hydroxyl radicals) from hydrogen peroxide (H2O2), which oxidize pollutants. H2O2 can be electrogenerated in situ by the oxygen reduction reaction (ORR) in the reaction medium. The use of highly porous gas diffusion electrodes (GDE) provides the supply of oxygen at the electrode/solution interface, which can increase the RRO speed. The use of modifiers such as quinones and azocompounds immobilized on the carbon matrix of GDE may increase H2O2 generation. Therefore, the organic modifiers Sudan Red 7B (SR7B), methyl-p-benzoquinone (MPB), anthraflavic acid (AA) and anthraquinone-2-carboxylic acid (A2CA) were added in different contents to carbon Printex L6 (CP) and microporous layers of these materials were studied by cyclic voltammetry and linear sweep voltammetry on a rotating ring- disc electrode (RRDE). Materials with 0.5% of SR7B and 5.0% of MPB increased the current efficiency for electrogeneration of H2O2 to 86.2 and 85.5%, respectively, in relation to pure CP that leaded to 82.8%. GDE of CP modified with 0.5% of SR7B were constructed with metallic screens on their outer faces and an application of current densities of 75, 100 and 150 mA cm-2 led to a greater electrogeneration of H2O2. At current densities of 75 mA cm-2, the modified GDE generated 1020.1 mg L-1 of H2O2 with energy consumption of 118.0 kWh kg-1 of H2O2, apparent kinetic constant of 37.3 mg L-1 min-1 and current efficiency of 17.9%, while GDE of pure CP generated lower H2O2 concentration; 717, 3 mg L-1, with higher energy consumption; 168.5 kWh kg-1, lower apparent kinetic constant; 21.4 mg L-1 min-1, and lower current efficiency; 12.6%. Therefore, the modified GDE could be applied in systems that require high generations of H2O2.

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-02-15T14:00:25Z No. of bitstreams: 1 Nattany Tayany Gomes de Paula.pdf: 885461 bytes, checksum: 787ab63496a1306c113ee5c12e2dac92 (MD5) / Made available in DSpace on 2017-02-15T14:00:25Z (GMT). No. of bitstreams: 1 Nattany Tayany Gomes de Paula.pdf: 885461 bytes, checksum: 787ab63496a1306c113ee5c12e2dac92 (MD5) Previous issue date: 2015-03-12 / Sulfites are considered food additives that after chemical reaction releasing sulfur dioxide (SO2), sulfite ion (SO32-), or bisulfite ion (HSO3-). These additives act as antioxidants in food, in the control of bacterial growth and enzymatic and non-enzymatic browning reactions during processing and storage. Although widely used in the food industry, the use of sulfite as a preservative causes some problems, reducing the nutritional quality of foods processed and in some cases are caused adverse effects to human health. In this work it is proposed to determine sulfite in samples of processed juices and wines through an analytical flow system with biamperometric detection. The system was built employing a peristaltic pump, proportional injector, a Gas Diffusion Cell (GDC) and Reagent Generation Cell (RGC) and polyethylene tubes with an internal diameter of 0.8 mm for making the analytical path. The RGC was coupled to a potentiostat for applying current to the electrochemical generation of triiodide ions. For detection it was used a biamperometric detector, adapted to a coulometer for applying the constant potential. For the data acquisition and processing was performed using a software developed in Lab View® language. The analysis method was based on a redox reaction between the I3- ions SO32- and providing a decrease of the generated current by the pair and this decrease in the signal is proportional to the concentration of SO32- ions. After the system optimization, the proposed procedure was operated with KI concentrations of 0.25 mol L-1, HCl 1.0 mol L-1, Na2SO4 and 0.1 mol L-1, with 0.25 mA current applied in RGC and the length of the sampling loop was of 20 cm. In the proposed procedure, a linear response was obtained between 1 and 12 mg L-1 of sulfite E = - (0,2371 ± 0,0028) C + (6,7097 ± 0,0182), R = -0,9997), LD = 0,26 mg L-1 and LQ = 0,86 mg L-1, relative standard deviation less than 2% (n = 10), with sampling frequency of 40 h−1. Potential interfering studies demonstrated the selectivity of the proposed method. Addition and recovery tests with samples of juices and wines were performed to give results of recovery between 91.63 and 110.34%, demonstrating the possibility of operation of the proposed procedure in real samples. / Os agentes sulfitantes ou sulfitos são considerados aditivos alimentares que, após reação química, liberam dióxido de enxofre (SO2), íon sulfito (SO32-) ou íon bissulfito (HSO3-). Estes aditivos são agentes multifuncionais e atuam como antioxidantes em alimentos, no controle do crescimento bacteriano e de reações (enzimáticas e não enzimáticas) de escurecimento durante o processamento e estocagem. Mesmo sendo muito utilizado na indústria de alimentos, o emprego de sulfitos como conservantes provoca alguns problemas, reduzindo a qualidade nutricional dos alimentos tratados e em alguns casos são provocados efeitos adversos à saúde humana. Neste trabalho propõe-se determinar sulfitos em amostras de sucos industrializados e vinhos empregando um sistema de análise em fluxo com detecção biamperométrica. O sistema foi construído empregando-se uma Bomba Peristáltica, um Injetor Proporcional, uma Câmara de Difusão Gasosa (CDG) e uma Câmara de Geração de Reagente (CGR). A CGR foi acoplada a um potenciostato para a aplicação de corrente necessária para a geração eletroquímica de íons triiodeto. Para detecção foi utilizado um detector biamperométrico. Para o tratamento e aquisição de dados, foi utilizado um software desenvolvido em linguagem Lab View®. A metodologia de análise foi baseada em uma reação de oxirredução entre os íons SO32- e I3-, que proporciona uma diminuição da corrente biamperométrica gerada pelo par redox I3-/I-, sendo essa diminuição de corrente proporcional a concentração de íons SO32-. Após a otimização do procedimento proposto obteve-se as melhores condições: 0,25 mol L-1 de KI, 1,0 mol L-1 de HCl, 0,1 mol L-1 de Na2SO4, corrente de 0,25 mA aplicada na CGR e volume de amostra de 100 μL. Nestas condições, obteve-se uma resposta linear entre 1 e 12 mg L-1 de sulfito (I = - (0,2371 ± 0,0028) C + (6,7097 ± 0,0182), R = -0,9997), LD = 0,26 mg L-1 e LQ = 0,86 mg L-1, desvio padrão relativo menor que 2% (n = 10), com frequência de amostragem de 40 determinações por hora. Estudos de potenciais interferentes demonstraram a seletividade do método proposto. Testes de adição e recuperação com amostras de sucos e vinhos foram realizados, obtendo-se resultados de recuperação entre 91,63 e 110,34%, demonstrando a possibilidade de operação do procedimento proposto em amostras reais.

Biocélulas a combustível (BFCs) são definidas como dispositivos bioeletroquímicos que utilizam componentes biológicos, como enzimas ou microrganismos, para converter energia química em energia elétrica. Neste estudo, reporta-se o desenvolvimento de um bioeletrodo composto por fibras flexíveis de carbono (FFC) modificadas com a enzima álcool desidrogenase (ADH), o qual foi utilizado juntamente com a levedura Saccharomyces cerevisiae , sendo enzima e microrganismos usados como biocatalisadores cooperativos para bioprodução e oxidação de etanol. A glicose é oxidada pelas células de levedura sob condições anaeróbias, e o etanol formado pela fermentação alcóolica é, em seguida, oxidado a acetaldeído pela enzima ADH. A oxidação de etanol pela ADH resulta ainda, na redução da molécula de nicotinamida adenina dinucleotídeo, NAD+ a NADH. Posteriormente, o NADH formado nessa reação é eletroquimicamente oxidado a NAD+ na superfície do bioeletrodo de FFC baseado em ADH (FFC-ADH). Avaliou-se a influência da temperatura e do pH na bioeletrocatálise de etanol pela ADH e a melhor resposta obtida foi em 40 ºC e pH 8,5. Além disso, obteve-se uma excelente correlação linear entre os valores de concentração de etanol e densidade de corrente, indicando que a resposta bioeletrocatalítica da ADH é diretamente proporcional à concentração de etanol produzido a partir da fermentação. O conceito de que microrganismos e enzimas podem trabalhar cooperativamente para produzir uma nova classe de bioeletrodos, foi introduzido nesse trabalho. Por fim, demonstrou-se, que o bioeletrodo cooperativo pode ser aplicado com sucesso em uma BFC, utilizando o biocátodo de difusão de gás contendo a enzima bilirrubina oxidase (BOx) imobilizada em sua superfície. / Biofuel cells (BFCs) are defined as bioelectrochemical devices that use biological components, such as enzymes or microorganisms, to convert chemical energy into electric energy. In this study, we report the development of a bioelectrode composed of flexible carbon fibers (FCF) modified with the enzyme alcohol dehydrogenase (ADH) together with Saccharomyces cerevisiae yeast, being enzyme and microorganisms used as cooperative biocatalysts for bioproduction and oxidation of ethanol. Glucose is oxidized by the yeast cells in anaerobic conditions, and ethanol is produced through alcoholic fermentation and then it is oxidized to acetaldehyde by the ADH enzyme. The ethanol oxidation by ADH also results in the reduction of the nicotinamide adenine dinucleotide molecule, NAD+ to NADH. Subsequently, the NADH produced in this reaction is electrochemically oxidized to NAD+ on the surface of the FCF bioelectrode based on ADH (FCF-ADH). The influence of temperature and pH on the bioelectrocatalysis of ethanol was evaluated and the best performance was found at 40 ºC and pH 8.5. Additionally, the results demonstrated an excellent linear correlation between the ethanol concentration and the current generated, which indicates that the bioelectrocatalytic response of ADH is directly proportional to concentration of ethanol produced from the fermentation. The present study has introduced the concept that microorganisms and enzymes can work cooperatively to produce a new class of bioelectrodes. Finally, it has been demonstrated that the cooperative bioelectrode can be applied successfully to BFC using a gas-diffusion biocathode containing the bilirubin oxidase enzyme (BOx) immobilized on its surface.

Os processos oxidativos avançados (POA) são uma alternativa para complementar os processos clássicos de tratamento de efluentes que podem não ser eficientes para remoção de alguns tipos de poluentes como, por exemplo, os poluentes emergentes. Os POA se baseiam na geração de espécies altamente reativas (radicais hidroxila), a partir de peróxido de hidrogênio (H2O2), que oxidam os poluentes. O H2O2 pode ser eletrogerado in situ pela reação de redução de oxigênio (RRO) no meio reacional. O uso de eletrodos de difusão gasosa (EDG) altamente porosos proporciona o suprimento de oxigênio na interface eletrodo/solução podendo aumentar a velocidade da RRO. O uso de modificadores como quinonas e azocompostos imobilizados à matriz de carbono dos EDG podem aumentar a geração de H2O2. Portanto, os modificadores orgânicos Sudan Red 7B (SR7B), metil-p-benzoquinona (MPB), ácido antraflávico (AA) e antraquinona-2-ácido carboxílico (A2CA) foram adicionados em diferentes teores ao carbono Printex L6 (CP) e microcamadas porosas destes materiais foram estudados por voltametria cíclica e de varredura linear em eletrodo de disco-anel rotatório (RRDE). Os materiais contendo 0,5% de SR7B e 5,0% de MPB levaram a aumento na eficiência de geração de H2O2 para 86,2 e 85,5%, respectivamente, em relação ao CP puro que levou a 82,8%. EDG de CP modificados com 0,5% de SR7B foram construídos com telas metálicas em sua faces externas e a aplicação de densidades de corrente de 75, 100 e 150 mA cm-2 levou a uma maior eletrogeração de H2O2. Em densidades de corrente de 75 mA cm-2, o EDG modificado gerou 1020,1 mg L-1 de H2O2 com consumo energético de 118,0 kWh kg-1 de H2O2, constante cinética aparente de 37,3 mg L-1 min-1 e eficiência de corrente de 17,9%, enquanto o EDG de CP puro gerou menor concentração de H2O2; 717, 3 mg L-1, com maior consumo energético; 168,5 kWh kg-1, menor constante cinética aparente; 21,4 mg L-1 min-1, e menor eficiência de corrente; 12,6%. Portanto, o EDG modificado poderia ser empregado em sistemas que precisem de altas gerações de H2O2. / The advanced oxidation processes (AOP) are an alternative to the classical processes of treatment of effluents that may not be effective for the removal of some types of pollutants such as emerging pollutants. The AOP are based on the highly reactive species (hydroxyl radicals) from hydrogen peroxide (H2O2), which oxidize pollutants. H2O2 can be electrogenerated in situ by the oxygen reduction reaction (ORR) in the reaction medium. The use of highly porous gas diffusion electrodes (GDE) provides the supply of oxygen at the electrode/solution interface, which can increase the RRO speed. The use of modifiers such as quinones and azocompounds immobilized on the carbon matrix of GDE may increase H2O2 generation. Therefore, the organic modifiers Sudan Red 7B (SR7B), methyl-p-benzoquinone (MPB), anthraflavic acid (AA) and anthraquinone-2-carboxylic acid (A2CA) were added in different contents to carbon Printex L6 (CP) and microporous layers of these materials were studied by cyclic voltammetry and linear sweep voltammetry on a rotating ring- disc electrode (RRDE). Materials with 0.5% of SR7B and 5.0% of MPB increased the current efficiency for electrogeneration of H2O2 to 86.2 and 85.5%, respectively, in relation to pure CP that leaded to 82.8%. GDE of CP modified with 0.5% of SR7B were constructed with metallic screens on their outer faces and an application of current densities of 75, 100 and 150 mA cm-2 led to a greater electrogeneration of H2O2. At current densities of 75 mA cm-2, the modified GDE generated 1020.1 mg L-1 of H2O2 with energy consumption of 118.0 kWh kg-1 of H2O2, apparent kinetic constant of 37.3 mg L-1 min-1 and current efficiency of 17.9%, while GDE of pure CP generated lower H2O2 concentration; 717, 3 mg L-1, with higher energy consumption; 168.5 kWh kg-1, lower apparent kinetic constant; 21.4 mg L-1 min-1, and lower current efficiency; 12.6%. Therefore, the modified GDE could be applied in systems that require high generations of H2O2.