Philosophiae Doctor - PhD (Chemistry) / Electrochemiluminescence (ECL) is a light-emitting process generated by electrochemical redox reactions and has been widely used as an analytical tool, especially in the field of biosensing, that is, immunoassays and DNA-probe assays. Thus, the scope of this work was to develop a simple, sensitive ECL immunosensor for cardiac injury and to study and present insights into newly fabricated platforms for bioanalytical applications by using ECL as detection mechanism. / 2021-08-31

Orientador: Dayse Iara dos Santos / Banca: Manuel Henrique Leite / Banca: Alejandra Hortencia Miranda González / Resumo: Materiais nanoestruturados vêm sendo amplamente estudados pela comunidade científica, devido às suas propriedades únicas obtidas com o controle da síntese dos materiais. Por meio do controle experimental, esses materiais podem ser utilizados em numerosas áreas, tais como na eletrônica e na fotônica. Dentre os vários métodos químicos, o processo poliol vem sendo utilizado devido à fácil obtenção de nanopartículas de óxidos e metais na sua forma elementar. O presente trabalho teve como objetivo a síntese do óxido de zinco nanoestruturado por meio do método poliol. Diferentes precursores metálicos, tais como acetato de zinco dihidratado, nitrato de zinco hexahidratado, sulfato de zinco monohidratado e cloreto de zinco anidro e diferentes tempos de permanência da síntese foram utilizados para verificar possíveis interferências dos ânions precursores na síntese e na morfologia do óxido de zinco quando obtido. Os materiais obtidos das sínteses foram caracterizados por difração de raios X (DRX), análises térmicas (TG/DTA), medidas de adsorção de gás nitrogênio, microscopia eletrônica de varredura (MEV), microscopia eletrônica de varredura de alta resolução (MEV-FEG) e cronopotenciometria. Por meio destas técnias mostrou-se a viabilidade da obtenção do óxido de zinco nanoestruturado dd maneira direta a partir do acetato de zinco, através de refluxo em etilenoglicol por 2, 4 e 8 horas seguido de lavagem e centrifugação. A menor nanoestrutura encontrada apresentou partículas com dimensão de aproximadamente 25 nm e formato poliédrico, as quais foram observadas pelo FEG. A técnica de cronopotenciometria, representada por meio das curvas de carga/descarga mostraram que a utilização do compósito contendo o óxido de zinco sintetizado apresenta melhores resultados quando comparados ao uso... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nanostructered materials have been extensively studied by the scientific community due to their unique properties obtained by controlled synthesis of materials. By means of the control of parameters, this new materials can be used in a number of applications in electronic and photonic technology. Among the several methods to obtain nanoparticles or nanostructured materials, the polyol method has been applied because it shows easy procedures to produce nanostructured oxides and elemental metals. The aim of this work is the synthesis of nanostructured zinc oxide, one of the most multifunctional oxides, by the polyol method. Different precursors salts like zinc acetate dihydrate, zinc nitrate hexahydrate, zinc sulfate monohydrate and zinc chloride anhydrate, as well as several times of reflux, were used to investigate the influence of the precursos anions on the synthesis and on the morphology of the crystals of zinc oxide whenever produced. The obtained powders were characterized by X-ray diffraction (DRX), thermal analyses (TG/DTA), and measurements of 'N IND. 2' gas adsorption, scanning electronic and field emission microscopy (MEV and FEG) and chronopotentiometry. These techniques showed the possibility of producing nanostructured zinc oxide in direct way from the reflux in etylenglycol for 2, 4 and 8 hours, followed by washing and centrifugation. The smallest nanostructure observed by FEG presented around 25 nm polyhedral particles. The chronopotentiometry, present charge/discharge curves showing better results for the electrode made of polimer composite containing ZnO nanoparticles than the obtaining results for the oxide alone. The best results showed reversibility of the lithium-ion cell upon 20 cycles, applying 3 μΑ electric current and showing a charge potential up to 4.2 V. / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Mestre

Philosophiae Doctor - PhD / In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode. / South Africa

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

O zinco vem sendo utilizado, já há bastante tempo, como revestimento protetor e decorativo para peças metálicas [1]. No entanto, cada vez mais a indústria busca revestimentos protetores que sejam mais resistentes à corrosão, que tenham boas características de soldabilidade, pintabilidade e, principalmente baixo custo. Os métodos mais comuns pelos quais os revestimentos de zinco são aplicados são imersão a quente, eletrodeposição e aspersão térmica. O presente trabalho tem como objetivo caracterizar a morfologia dos revestimentos Galvanized (GI), Galvannealed (GA) e Zn-55Al de zinco obtidos pelo processo de imersão a quente, verificar o comportamento eletroquímico e analisar o comportamento corrosivo dos revestimentos pelas técnicas de Potenciometria e Eletrodo Vibratório (SVET). Os resultados demonstraram que é possível a análise das fases por voltametria em microcélula no revestimento em que as fases foram crescidas, porém, não é possível aplicar a técnica nas diferentes fases formadas nos revestimentos industriais devido à espessura dos revestimentos. Não foi observado influência da luz Ultravioleta-visível na taxa de corrosão dos revestimentos estudados por SVET e esta técnica mostrou-se satisfatória para grandes aumentos e pequenas áreas. As análises por SVET demonstraram a possibilidade de analisar a corrosão localizada em diferentes fases intermetálicas nos revestimentos. / Zinc has been used for quite some time, as decorative and protective coating for metal parts. However, the industry increasingly seeks protective coatings that are more resistant to corrosion, have good weldability characteristics, and especially low cost. The most common methods by which zinc coatings are applied are hot dipping, electroplating and thermal spraying. The present work aims to characterize the morphology of the coatings Galvanized (GI), galvannealed (GA) and Zn-55Al of zinc obtained by hot dip process, check the electrochemical behavior and analyze the behavior of coatings for corrosion techniques of pots and Vibrating electrode (SVET). The results showed that it is possible to analyze the phases by microcell voltammetry in the coating in which the phases were grown, however, is not possible to apply the technique in the different phases formed in industrial coatings due to the thickness of coatings. There was no influence of UV-VIS in the corrosion rate of the coatings studied by SVET and this technique was satisfactory for large and small areas increases. The analysis by SVET demonstrated the possibility of analyzing the localized corrosion in different intermetalic phases in coatings.

Les biopiles représentent une solution attractive et ambitieuse pour développer des systèmes alternatifs de conversion d'énergie. Ce travail décrit la construction d'une biopile à éthanol/O2 (oxydation de l'éthanol à l'anode et réduction de l'oxygène à la cathode) avec des électrodes tridimensionnelles possédant une surface spécifique élevée. Le point de départ a été la fabrication et l'optimisation de bioélectrodes enzymatiques par immobilisation d'enzymes et de médiateurs sur des nanofibres de polyacrylonitrile, préparées par la méthode d'électrospinning, et recouvertes d'or. Ces bioélectrodes à base de nanofibres (biocathode et bioanode) ont été assemblées pour construire et caractériser une biopile à éthanol/O2 qui a fourni une densité de puissance de 1600 µW/cm2 par la méthode de polarisation et 210 µW/cm2 par imposition de résistances au système. Enfin, nous avons décrit la fabrication de la première biopile miniaturisée à éthanol/oxygène avec des enzymes immobilisées sur électrodes Au en s'appuyant sur les concepts de la microfluidique. La biopile microfluidique la plus performante a délivré 90 µW/cm2. Afin d'augmenter la puissance délivrée par ces systèmes miniaturisés, des résultats préliminaires ont été obtenus sur l'empilement en série ou en parallèle de biopiles fonctionnant avec des enzymes en solution. / Biofuel cells represent an attractive and ambitious option for developing alternative systems of energy conversion. This work describes the construction of an ethanol/O2 biofuel cell (ethanol oxidation at the anode and oxygen reduction oxygen at the cathode) from tridimensional electrodes with high specific surface area. The starting point was the synthesis and the optimization of the enzymatic bioelectrodes on gold electrodes by immobilizing enzymes and mediatorson polyacrylonitrile nanofibers, obtained by electrospinning method, and recovered by gold nanoparticles. The bioelectrodes (bioanode and biocathode) based on nanofibers have been assembled to build and to characterize an ethanol/O2 biofuel cell that has delivered a power density of 1600 µW/cm2 by the polarization method, and 210 µW/cm2 by imposing resistances to the system. Finally, we have described the production of the first miniaturized ethanol/O2 biofuel cell with immobilized enzymes at Au electrodes based on microfluidic concepts. The best microfluidic biofuel cell has delivered 90 µW/cm2. In order to increase the power delivered by these miniaturized systems, preliminary results have been obtained by stacking biofuel cells, working with enzymes in solution, in series or parallel.

CAMPOS, Othon Souto. Estudo Mecanístico da Eletrodeposição de Cádmio em Meio de Sulfato Ácido. 2011. 46 f. Dissertação (Mestrado em química)- Universidade Federal do Ceará, Fortaleza-CE, 2011. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-06-02T19:41:14Z No. of bitstreams: 1 2011_dis_oscampos.pdf: 938891 bytes, checksum: 170c80aaa846defc16b0b360c53792fb (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-07-20T20:01:55Z (GMT) No. of bitstreams: 1 2011_dis_oscampos.pdf: 938891 bytes, checksum: 170c80aaa846defc16b0b360c53792fb (MD5) / Made available in DSpace on 2016-07-20T20:01:55Z (GMT). No. of bitstreams: 1 2011_dis_oscampos.pdf: 938891 bytes, checksum: 170c80aaa846defc16b0b360c53792fb (MD5) Previous issue date: 2011 / This work describes a mechanistical proposition for cadmium electrodeposition in acid sulfate medium on platinum substrate using electrochemical techniques. The cadmium electrodeposition studies were carried in sodium sulfate 1 mol L–1 medium containing cadmium sulfate 10–2 mol L–1, which the pH of the solutions were adjusted with analytical grade sulfuric acid. The pH interval of the work solutions were ranged between 1 and 3. In all studied medium, the potentiostatic polarization curves showed a diffusional plateau which obeys the Levich equation. The interfacial pH studies showed the influence of acid–base equilibrium of bisulfate ion with the formation of a coordination compound Cd(HSO4)+ in platinum electrode. It is proposed that the cadmium ion associated in acid–base equilibrium of bisulfate ion, deposits as cadmium bisulfate at an irreversible step, and followed by a reversible metallic deposition of cadmium with the leaving of bisulfate ion, and this step is slower than the first one. Then, a mathematical model was calculated for the mechanism proposed, and qualitative studies were carried regarding to the polarization curve and electrochemical impedance spectroscopy behavior. / Este trabalho descreve uma proposição mecanística para a deposição de cádmio em meio de sulfato ácido sobre substrato de platina utilizando técnicas eletroquímicas. Os estudos de eletrodeposição de cádmio foram feitas em meio de sulfato de sódio 1 mol L–1 contendo 10–2 mol L–1 de sulfato de cádmio, em que o pH das soluções foi ajustado com ácido sulfúrico PA. O intervalo de pH das soluções de trabalho foi variado entre 1 e 3. Em todos os meios estudados, as curvas de polarização potenciostática mostraram a formação de um patamar difusional que obedece a equação de Levich. Os estudos de pH local revelaram a influência do equilíbrio ácido–base do íon bissulfato com formação de compostos de coordenação Cd(HSO4)+ no eletrodo de platina. Propõe-se que o íon cádmio, associado ao equilíbrio ácido–base do íon bissulfato, deposita como bissulfato de cádmio numa etapa irreversível, e seguida pela deposição de cádmio metálico reversível com a saída do íon bissulfato, sendo esta última etapa mais lenta que a primeira. Desse modo, foi calculado um modelo matemático para o mecanismo proposto, sendo realizados estudos qualitativos em relação ao comportamento da curva de polarização e do espectro de impedância eletroquímica.

O desgaste de máquinas e seus componentes têm grande influência econômica em diversos setores da indústria. Diante dessa situação, tem sido feitos estudos visando desenvolver novos materiais e revestimentos que apresentem maior resistência ao desgaste. O revestimento é um dos métodos mais utilizados quando se procura garantir a uma superfície alguma propriedade mecânica que não é intrínseca ao metal base. O objetivo deste trabalho é realizar um estudo comparativo de ligas de diferentes composições químicas, através do desenvolvimento de um consumível para soldagem manual ao arco elétrico a ser aplicado especialmente para o recobrimento de superfícies submetidas ao desgaste abrasivo. Os eletrodos desenvolvidos foram compostos pela combinação de cromo-carbono e tungstênio-carbono misturados em um revestimento base com rutilo-carbonato de cálcio-fluorita, resultando em eletrodos revestidos com sete diferentes composições. A comparação e avaliação da resistência à abrasão foi feita com base nos dados obtidos no ensaio de desgaste abrasivo, segundo a norma ASTM G65-91, e também baseada nos resultados da composição química, microestrutura e análise microestrutural dos revestimentos. Os resultados mostraram que os depósitos com maior resistência ao desgaste abrasivo foram obtidos com eletrodos com as composições contendo carbono e 7% de tungstênio e carbono e 1,5% de cromo. Esses mesmos depósitos foram os que apresentaram valores mais elevados de microdureza, e em sua microestrutura pode-se perceber a formação de maior quantidade de carbonetos. / The wear in machines and equipments is one of the main sources of economic losses. Nowadays many studies have been conducted to develop new materials and coverages to produce wear resistance. The hardfacing is one of most common methods to produce a deposit having properties not intrinsic to that of the base material. The main objective of this work is to study the viability of using different alloys compositions to produce covered electrodes for shielded metal arc welding (SMAW) resistant to abrasive wear. The covered electrodes were produced adding chromiumcarbon and tungsten-carbon to rutile-calcium carbide-fluorite base. Comparison and evaluation of wear resistance of the developed electrodes was based in ASTM G65-91 wear tests, deposit chemical compositions and the resultant microstructures. The results shown that electrodes containing additions of C-W 7 % and C-Cr 1.5 % produced best performance of wear test deposits. These compositions produced deposits containing the higher amounts of carbides and exhibit higher hardness values.

Membranas hidrocarbônicas não fluoradas têm sido desenvolvidas para uso em substituição as membranas fluoradas (Nafion®) em células a combustível de eletrólito polimérico (PEMFC), ou em temperaturas superiores a 80 °C, ou em células com adição direta de álcool. Este trabalho teve como objetivo avaliar o desempenho de membranas hidrocarbônicas catiônicas, desenvolvidas para uso em célula a combustível alimentada com etanol (DEFC), e de camadas de difusão gasosa (GDL – Gas Difusion Layer) e eletrodos (GDE – Gas Difusion electrode) preparados para uso com as mesmas. Duas membranas hidrocarbônicas (E-750 e P-730) da empresa FuMATech®/GR foram avaliadas quanto à capacidade de troca iônica e grau de inchamento em água/etanol, quanto a composição química, morfologia, comportamento térmico e visoelástico e condutividade por impedância. As GDLs foram preparadas a partir de uma emulsão aquosa de Teflon® e pó de carbono Vulcan XC-72R®, com e sem agente emulsificante (resina sulfonada), dispersa em ambas as faces do tecido de carbono pelo método de aspersão. Os GDEs foram preparados pela deposição de emulsão catalítica de diferentes eletrocatalisadores sobre as respectivas GDLs do ânodo e catodo. Os GDEs anódico e catódico foram preparados com 1 mg.cm-2 do eletrocatalisador de PtSn/C 20% (75:15) e de Pt/C (20:80), respectivamente, e caracterizados por MEV-EDS. As características fisico-químicas das membranas hidrocarbônicas foram similares às apresentadas pela membrana Nafion®. O desempenho do protótipo de célula unitária DEFC com as membranas FuMATech® foi inferior ao obtido com a membrana Nafion® usando-se GDE comercial. Por outro lado, ensaios com a membrana Nafion® utilizando-se os eletrodos preparados neste trabalho e eletrodos comerciais apresentaram valores de potencial similares. / Non-fluorinated hydrocarbon cationic membranes have been developed for use instead of Nafion® in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), or at higher temperatures than 80 ºC, or in fuel cells fed with alcohol. The aim of this work was to evaluate the performance of commercial non-fluorinated hydrocarbon cationic membranes with potential use in direct ethanol fuel cell (DEFC), and also evaluate the Gas Difusion Layer (GDL) and Gas Difusion electrode (GDE) prepared for use with them. Two hydrocarbon membranes (E-750 and P-730) produced by FuMATech®/GR were analyzed according to their ion exchange capacity, water uptake in water/alcohol solution, morphology, chemical composition, thermal and viscoelastic behaviour, and conductivity by impedance. The GDLs were prepared by spraying an aqueous emulsion of Vulcan carbon/Teflon®, with and without emulsifier agent (sulfonated hydrocarbon resin), in both sides of a carbon fabric. The electrodes were prepared by the respective deposition of the electrocatalysts emulsions on the cathode and anode GDLs. The anodic and cathodic GDEs were prepared with 1 mg.cm-2 of the electrocatalyst of PtSn/C 20% (75:15) and of Pt/C (20:80), respectively, which were characterized by SEM-EDS. The physicochemical properties of the hydrocarbon membranes were similar to the Nafion® membrane ones. The potential values obtained in a DEFC prototype unit cell with FuMATech® membranes were lower than those with Nafion-117 membrane. On the other hand, the performance of the DEFC prototype with Nafion-117 membrane was the same if used GDEs commercial or here prepared.

Lithium-ion batteries (LIBs) are an integral part of consumer electronic devices and electric vehicles. There is a growing need for LIBs with higher capacity, rate performance and cycling stability. At the anode electrode these challenges are being addressed for instance by utilising materials with higher theoretical capacity compared to graphite (372 mAh/g) or by optimising the morphology of materials through nanostructuring of the electrode. In this thesis the former is investigated by synthesising a reduced graphene oxide (rGO) tin sulphide (SnS2) hybrid, and the latter by self-assembly of rGO sodium titanate and rGO titanium dioxide (TiO2) nanorods. In Chapter 2, SnS2 is investigated due to its high theoretical capacity as an anode material (645 mAh/g), low cost and environmental benignity. SnS2 nanoparticles were grown directly on rGO sheets which provide a conductive framework and limit the detachment of tin particles which undergo large volume changes during alloying reactions. However, a fast decrease in capacity was observed. Post-mortem analysis of the electrodes showed that rGO becomes irreversibly passivated suggesting that additional measures to retain effective charge transport between the low weight percent conductive additive and the active phase during cycling are required. An alternative material system based on nanorods of intercalation materials (sodium titanate and TiO2) wrapped by rGO sheets was chosen to investigate self-assembly in anodes to address the low packing density of nanomaterials. A drop-casting method was used to align rGO-sodium titanate nanorods through evaporation driven self-assembly (Chapter 3) which relies on a combination of electrostatic repulsive forces originating from the rGO coating, and liquid crystal phase formation at high concentrations, facilitated by the high aspect ratio nanorods. As reference, non-aligned films were prepared by adjusting the pH of the nanorod dispersion. Freestanding aligned and non-aligned films were converted to rGO-TiO2 (Chapter 4). The volumetric capacity of the self-assembled films was double that of non-aligned films, and up to 4.5 times higher than traditional casted electrodes using the same material. Further, up to rates of 4 C, the self-assembled films outperformed the non-aligned films. These films showed no sign of capacity fading up to 1000 cycles, which together with post-mortem analysis confirms that these assembled structures are maintained during battery cycling.