Orientador: Devaney Ribeiro do Carmo / Resumo: O presente trabalho descreve a preparação, caracterização e aplicação eletroanalítica de um metalosilsesquioxano ligado em uma sílica mesoporosa (MCM-41) e em uma zeólita (H-FAU-Si/Al 40) com hexacianoferrato de níquel adsorvido em sua superfície. Algumas técnicas espectroscópicas como: Espectroscopia no infravermelho por transformada de Fourier (FTIR), Microscopia eletrônica de varredura (MEV), Espectroscopia por Energia Dispersiva de Raios X (EDS) e Voltametria cíclica, foram utilizadas na caracterização dos materiais formados. Os espectros na região do Infravermelho para o MTTiPNiH e ZTTiPNiH apresentaram as bandas de seus precursores (TTiP, MCM-41 e H-FAU-Si/Al 40), apenas duas absorções diferiram dos demais espectros, uma em, aproximadamente, 2168 cm-1 e outra a 2098 cm-1, tais resultados foram atribuídos ao estiramento ν (C≡N). Para o MTTIPNiH, através das micrografias pode-se observar partículas com tamanhos variados, entre 0,30 µm a 0,60 µm. Para o ZTTiPNiH as micrografias apresentaram um pequeno aumento no tamanho de partículas, aproximadamente de 50 nm, quando comparado a seus precursores. O EDS determinou a composição química semi-quantitativa dos elementos carbono, oxigênio, silício, titânio, fósforo, níquel e ferro, presentes em ambas as amostras. O eletrodo de pasta de grafite exibiu um par redox bem definido com potencial de médio padrão (E°’) de +0,53 V e +0,51 V para o MTTiPNiH e ZTTiPNiH, respectivamente, atribuído ao processo redox FeII(CN)6 / FeIII(CN)6 em... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This research describes the preparation, characterization and electroanalytical application of a metalosilsesquioxane bonded in mesoporous silica (MCM-41) and in zeolite (H-FAU-Si/Al 40) with nickel hexacyanoferrate adsorbed on their surface. Techniques as fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and cyclic voltammetry were used in the characterization of the synthesized materials. The spectra in the infrared region for MTTiPNiH and ZTTiPNiH showed the bands of their precursors (TTiP, MCM-41 and H-FAU Si/Al 40), only two absorption differed from the others spectra, one at, approximately, 2168 cm-1 and another at 2098 cm-1 , which were attributed to stretching ν(C≡N). For MTTIPNiH through the micrographs can be observed particles with varied sizes between 0.30 µM to 0.60 µm. For ZTTiPNiH the micrographs showed a small increase in particle size, approximately, 50 nm, as compared to their precursors. EDS determined the semi-quantitative chemical composition of carbon, oxygen, silicon, titanium, phosphorus, nickel and iron present in both samples. The carbon paste electrode exhibited a well-defined redox couple with E°' = +0.53 V and +0.51 V for MTTiPNiH and ZTTiPNiH, respectively, attributed to the redox process FeII(CN)6 / FeIII(CN)6 in presence of nickel. Carbon paste electrode modified with MTTiPNiH showed electrocatalytic activity to dipyrone and sulfite. However the carbon paste electrode... (Complete abstract click electronic access below) / Doutor

Capteur électrochimique basé sur des matériaux carbonés fonctionnalisés, pour la détection de deux micropolluants faisant partie des substances prioritaires de la Directive Cadre européenne sur l’Eau (DCE2000/60/CE) : le plomb et l’anthracène. Les capteurs électrochimiques permettent d’atteindre des limites de détection et une sélectivité adéquates pour l’analyse de micropolluants dont les concentrations sont de l’ordredu μg/L, et sont simples d’utilisation pour des analyses in situ à moindre coût comparés aux appareils d’analyses conventionnels. Leur robustesse est un paramètre important afin de permettre des mesures en continu ou semi-continu dans les eaux. Cette thèse propose tout d’abord le développement du capteur pour la détection du plomb. La formulation d’une encre conductrice de carbone est étudiée pour la sérigraphie de ’électrode réceptrice, permettant ainsi de contrôler la composition de l’encre et d’étudier l’influence de la phase carbonée sur les propriétés électrocatalytiques des électrodes. La fonctionnalisation des électrodes par greffage électrochimique d’un sel de diazonium est également étudiée afin de maîtriser la sensibilité et la reproductibilité des électrodes greffées, en contrôlant l’épaisseur et la qualité des couches. Avec cet objectif, la fonctionnalisation dans un liquide ionique protique qui permet le contrôle de la monocouche en modulant la viscosité de ce milieu a été étudiée. Les électrodes greffées montrent des performances analytiques améliorées notamment en termes de répétabilité et de reproductibilité. Enfin ce travail de thèse porte également sur le développement du capteur pour la détection électrochimique de l’anthracène, molécule sans fonctions chimiques. Les électrodes sont, dans ce cas, fonctionnalisées par un polymère à empreinte moléculaire, matériau connu pour sa très grande sélectivité. Les performances de ce capteur, dont la sélectivité est basée uniquement sur le facteur de forme de la molécule, pour la détection de l’anthracène sont alors mises en évidence. / Electrochemical sensor based on functionalized carbon materials, for the detection of two micropollutants, lead and anthracene, which are among of the priority substances of the European Framework Directive on Water(DCE 2000/60 / EC). Electrochemical sensors allow to achieve detection limits and selectivities for the analysis of micropollutants whose concentrations are of the order of μg/L. They are easy to use for in situ analyzes at lower costs compared to those of the conventional analysis equipment. Their robustness is an important parameter in order to allow continuous or semi-continuous measurements in water. First of all, this thesis proposes the development of a sensor for lead detection. The conductive carbon ink formulation is studied for the screen-printing of the receiving electrode, thus allowing to control the ink composition and to study the influence of the carbon phase on the electrocatalytic properties of electrodes. Functionalization of electrodes by electrochemical grafting of a diazonium salt is also studied in order to control the sensitivity and reproducibility of grafted electrodes, by controlling the thickness and the quality of the layers. With this aim it has been studied the functionalization in a protic ionic liquid in order to allow the control of the monolayer bymodulating the viscosity of this medium. The grafted electrodes show improved analytical performance especially in terms of repeatability and reproducibility. Finally, this work reports the development of a sensor for the electrochemical detection of anthracene, a molecule without chemical functions. In this case, a molecularly imprinted polymer, a material known for its very high selectivity, functionalizes the electrodes.Having a selectivity is only based on the form factor of the molecule, the performance of the sensor developed for the detection of anthracene is also highlighted.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Nesta tese foi demonstrado que a associação da técnica eletroanalítica Voltametria de Redissolução Anódica de Onda Quadrada (SWASV, do inglês, Square-Wave Anodic Stripping Voltammetry) com a Análise por Injeção em Batelada (BIA, do inglês, Batch- Injection Analysis) permite o desenvolvimento de métodos analíticos para a determinação de metais (Cu, Cd, Pb, Hg e Zn) em amostras de etanol combustível e biodiesel. Metais podem ser incorporados aos biocombustíveis em processos de armazenagem e transporte, podendo causar danos irreversíveis ao biocombustível, o qual pode danificar motores e causar problemas ambientais. Logo, justifica-se o presente trabalho pela necessidade do desenvolvimento de métodos analíticos visando o controle de qualidade em relação ao teor de metais nestas amostras, preferencialmente métodos de fácil manuseio, rápidos, de baixo custo e robustos. BIA-SWASV permitiu a determinação direta (sem qualquer diluição da amostra) de Cd, Pb, Cu e Zn em etanol combustível empregando eletrodos de Au e filme de Hg. Limites de detecção na faixa de 0,6 a 5 pg L-1, faixa linear de 12,5 a 200 pg L-1 e valores de recuperação entre 87 e 109% foram obtidos para análises de 1 mL de amostra e tempo de deposição de 90 s (tempo total de cada medida de ~200 s). O tempo de injeção da amostra pela micropipeta eletrônica usada no sistema BIA foi de 40 s, ou seja, a deposição dos metais ocorreu mesmo após o término da injeção (transporte difusional das espécies ao eletrodo). Além disso, esta tese apresenta a associação de eletrodos impressos (SPE, do inglês, Screen-Printed Electrode) ao sistema BIA visando o desenvolvimento de métodos analíticos com características portáteis. Este sistema foi combinado a outros componentes que funcionam com uso de baterias como, pipetas eletrônicas, mini-potenciostatos e computador laptop, e aplicado à determinação de metais (Pb, Cu e Hg) em amostras de biodiesel após digestão ácida. Empregaram-se nos experimentos SPE’s com tinta condutora de Au (SPGE, do inglês, Screen-Printed Gold Electrode) como eletrodo de trabalho, reduzindo o volume de amostra a 200 pL (em eletrodos convencionais utilizou-se 1000 pL) com tempo de injeção de 40 s (velocidade de injeção de 5 gL s-1) e, nestas condições, obtiveram-se limites de detecção abaixo de 1,0 gg L-1 (equivalente a 6 gg g-1), faixa linear entre 20 e 280 gg L-1 e valores de recuperação entre 90 e 110% para amostras de biodiesel fortificadas. O baixo consumo de amostra no sistema BIA prolongou o tempo de vida útil do SPGE para um dia inteiro de análises (210 injeções). O sistema BIA associado a técnicas eletroanalíticas permitiu o desenvolvimento de métodos analíticos de baixo custo, simples, precisos, que empregam pequeno volume de amostra, portáteis (sobretudo com o emprego de SPE’s), que podem ser aplicados para a determinação de rotina e em campo de metais em amostras de etanol combustível e biodiesel. / In this thesis it is shown that the association of electroanalytical technique Square- Wave Anodic Stripping Voltammetry (SWASV) with Batch-Injection Analysis (BIA) allows the development of analytical methods for determination of metals (Cu, Cd, Pb, Hg and Zn) in ethanol fuel and biodiesel samples. Metals can be incorporated into biofuels during storage and transportation processes, which can damage engines and cause environmental problems. Therefore, it becomes necessary to develop analytical methods aiming the quality control of metals in these samples, preferably methods that are easy to operate, fast, inexpensive and robust. BIA-SWASV allowed direct determination (no dilution of the sample) of Cd, Pb, Cu and Zn in fuel ethanol employing Au and Hg film electrodes. Detection limits in the range of 0.6 to 5 pg L"1, linear range from 12.5 to 200 pg L-1 and recovery values of between 87 and 109% were obtained for analysis of 1 mL of sample and deposition time of 90 s (total time of each measurement of ~200 s). The time of sample injection by the electronic micropipette used by the BIA system was 40 s, that is, the deposition of metal occurred even after the end of injection (diffusional transport of species to the electrode). In addition, in this thesis it is presented the combination of Screen-Printed Electrodes (SPE) to the BIA system aimed to the development of analytical methods with portable characteristics. This system was combined with other components that operate using batteries as electronic pipettes, mini- potentiostat and laptop computer, and applied to the determination of metals (Pb, Cu and Hg) in biodiesel samples after acid digestion. It was used in the experiments SPE's with Au conductive ink as a working electrode (SPGE), reduced the volume of sample to 200 pL (in conventional electrodes was used 1000 pL) with injection time of 40 s (injection rate of 5 pL s-1), and in these conditions, detection limits lower than 1,0 pg L-1 (equivalent to 6 pg g-1), linear range between 20 and 280 pg L-1 and recovery values between 90 and 110% for biodiesel fortified samples were obtained. The low sample consumption extended the lifetime SPGE’s for a whole day of analysis (210 injections). BIA system associated with electroanalytical techniques allowed the development of inexpensive,simple, accurate, portable (especially with the use of SPE's) analytical methods, employing reduced sample volume, which can be applied for the routine and on-site determinations of metals in ethanol fuel and biodiesel samples. / Tese (Doutorado)

Цель работы состояла в определении оптимальных значений диаметра и массы углеродных нанотрубок (УНТ) в нафионсодержащей модифицирующей пленке для получения наилучших электрохимических и аналитических характеристик толстопленочных углеродсодержащих электродов (ТУЭ). В ходе работы синтезированы многостенные УНТ со средним диаметром dср ≈ 23 нм методом каталитического пиролиза этанола и проведена кислотная очистка полученного материала от металлических частиц катализатора и других модификаций углерода. Аналогичным способом обработаны коммерческие УНТ с dср ≈ 147 и 16 нм от Sigma-Aldrich. Успешно изготовлены 36 типов ТУЭ без УНТ и на основе УНТ в условиях варьирования массового содержания УНТ в диапазоне MУНТ = 0,3-10,0 мкг на поверхности ТУЭ. Аттестация поверхностей электродов проведена методами оптической и электронной микроскопии. Изучены электрохимические характеристики изготовленных ТУЭ методами циклической вольтамперометриии и импедансной спектроскопии. Выполнено определение ионов железа (III) в модельном растворе методом адсорбционной инверсионной вольтамперометрии. Установлены оптимальные значения среднего диаметра УНТ dср ≥ 23 нм и массы УНТ MУНТ = 5,0-10,0 мкг на поверхности ТУЭ для получения наилучших электрохимические и аналитические характеристики. Разработанные ТУЭ на основе УНТ могут применяться для определения ионов тяжелых металлов в реальных водах с концентрацией меньшей предельно-допустимых значений, установленных нормативными документами. / The aim is to determine the optimal values of the diameter and weight of carbon nanotubes (CNT) in modifier film containing Nafion for the best electrochemical and analytical characteristics of the thick film of carbon-containing electrodes (TFCE). Multi-walled CNT with an average diameter dav ≈ 23 nm were synthesized by the catalytic pyrolysis of ethanol and purified from the metal catalyst particles and other modifications of carbon, using mixture of concentrated sulfuric and nitric acids. Commercial CNT with dav ≈ 147 and 16 nm from Sigma-Aldrich were treated by a similar procedure. The batch of 36 types of TFCE without CNT and based on CNT varied by weight of CNT (MCNT) on TFCE surface in the range of 0,3-10,0 μg was made. The electrode surfaces were studied by optical and electron microscopy. The electrochemical characteristics of obtained TFCE by cyclic voltammetry and electrochemical impedance spectroscopy were investigated. The detection of Fe (III) ions in a model solution was carried out by adsorptive stripping voltammetry. The optimal values of the average diameter of CNT dav ≥ 23 nm and a weight of CNT on TFCE surfaces MCNT = 5,0-10,0 μg were determined. These parameters allow us to reach the best electrochemical and analytical characteristics of modified TFCE. Developed TFCE based on CNT may be used for the detection of heavy metal ions in real water with a concentration of less maximum permissible values, established by regulations.