Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-10-01Bitstream added on 2014-06-13T20:14:08Z : No. of bitstreams: 1 gabrieljunior_s_me_ilha.pdf: 1458989 bytes, checksum: 61fbe8b93b56e59134558e478f7ab91e (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente trabalho descreve a preparação, caracterização e as aplicações eletroanalíticas de silsesquioxanos e dendrímeros modificados suportados na superfície da sílica gel. A primeira etapa consistiu em ancorar o silsesquioxano ([H2N(CH2)3]8Si8O12) e o dendrímero Hexadecaamino Poli(propileno)imina (DAB-Am- 16) na superfície da 3-cloropropil sílica gel. Os materiais obtidos, SAC e SD, respectivamente, foram caracterizados pelas técnicas de Infravermelho (FTIR), RMN 29Si e 13C no estado sólido e Energia Dispersiva de Raios-X (EDX). A segunda etapa foi interagir o SAC e o SD com íons de Cu2+ e Ni2+ e posterior complexação com substâncias eletroativas, tais como: ferricianeto de potássio e nitroprussiato de sódio formando, dessa forma, os complexos binucleares: CuHCFSAC, NiHCFSAC, CuNPSAC, CuHCFSD, NiHCFSD e CuNPSD que foram caracterizados por Infravermelho (FTIR) e voltametria cíclica (VC). Os espectros na região do Infravermelho dos materiais supracitados exibiram freqüências próximas ou iguais a 2090 cm-1, atribuídas ao estiramento n(C N) característico do hexacianoferrato e nitroprussiato formados na superfície da SAC e SD. Utilizou-se estes materiais na construção do eletrodo de pasta de grafite os quais foram testados na oxidação eletrocatalítica de substâncias biologicamente importantes tais como a dipirona sódica e nitrito de sódio após um rigoroso estudo sobre o comportamento voltamétrico. O eletrodo de pasta de grafite contendo o CuHCFSAC exibiu dois pares redox com potenciais médios (Em) de: (Em)1= 0,29 V e (Em)2= 0,72 V vs Ag/AgCl (KCl =1.0 molL-1; v = 20 mV s-1) ambos atribuídos aos processos redox Cu(I)/Cu(II) e [Fe(II)(CN)6]4- / [Fe(III)(CN)6]3-, respectivamente, valores estes bem próximos para o CuHCFSD. Os eletrodos de NiHCFSAC e NiHCFSD exibiram... / This work describes the preparation, characterization and electroanalytical properties of modified silsesquioxanes and dendrimers supported onto the silica gel surface. The first step was to anchor the silsesquioxane [(H2N(CH2)3] 8Si8O12) and dendrimer Hexadecaamino Poly(propylene)imine (DAB-Am-16) onto the 3-chloropropyl silica gel surface. The materials obtained, SAC and SD, respectively, were characterized by infrared (FTIR), 29Si NMR and 13C solid state and Energy Dispersive X-ray (EDX). The second step was interact the SAC and SD with Cu2+ and Ni2+ ions and subsequent complexation with electroactive substances, such as: ferricyanide of potassium and sodium nitroprusside forming binuclear complexes: CuHCFSAC, NiHCFSAC, CuNPSAC, CuHCFSD, NiHCFSD and CuNPSD which were characterized by Infrared (FTIR) and cyclic voltammetry (CV). The spectra in the infrared region of the above materials exhibited frequencies near or equal to 2090 cm-1 assigned to stretching n(C N) characteristic of nitroprusside and hexacyanoferrate formed onto the SD and SAC surface. We used these materials in the construction of carbon paste electrode which were tested in the electrocatalytic oxidation of biologically important substances such as sodium dipyrone and sodium nitrite after a rigorous study about voltammetric behavior. The graphite paste electrode containing CuHCFSAC exhibited two redox couples with midpoint potentials (Em) of: (Em)1 = 0.29 V and (Em)2 = 0.72 V vs. Ag/AgCl (KCl = 1.0 mol L-1, v = 20 mV s-1) both assigned to the redox processes Cu(I)/Cu(II) and [Fe(II)(CN)6]4- / [Fe(III)(CN)6]-3, respectively, values very near to the CuHCFSD. The electrodes of NiHCFSAC and NiHCFSD each exhibited two redox couples with midpoint potentials (Em): (Em)1 = 0.29 V and (Em)2 = 0.51 V vs Ag/AgCl (KCl = 1.0 mol L-1, v = 20 mV s- 1) both... (Summary complete electronic access click below)

Considerando a relevância dos trabalhos onde se utiliza eletrodos quimicamente modificados e o pequeno número de estudos envolvendo cocaína e seus interferentes (cafeína, teobromina e lidocaína), por técnicas eletroquímicas ou piezelétricas, este estudo tem como objetivo o desenvolvimento de eletrodos de ouro e platina quimicamente modificados com compostos da classe das cucurbiturilas (CB[5], CB[6] e CB[7]) para a detecção de cocaína. A técnica de microbalança de cristal de quartzo foi empregada a fim de se estudar cocaína padrão e seus interferentes, em fase gasosa. Os eletrodos de ouro foram quimicamente modificados com cucurbiturilas e o modificador CB[6] apresentou os melhores resultados. Medidas por voltametria cíclica foram realizadas utilizando-se um potenciostato Autolab III acoplado a um computador, com eletrodo de ouro e platina atuando como eletrodo de trabalho, Ag/AgCl como eletrodo de referência e eletrodo espiral de platina como eletrodo auxiliar, com velocidade de varredura de 0,1 V.s-1 (100 mV.s-1). Os parâmetros voltamétricos foram otimizados para tornar as análises mais rápidas e sensíveis sem perda de qualidade ou intensidade do sinal voltamétrico. O eletrodo de platina quimicamente modificado com filme de cucurbit[6]urila apresentou aumento da corrente de pico catódica quando estudado frente à cocaína, teobromina e lidocaína. Análises com eletrodo de platina sem modificador químico apresentaram limite de detecção de 4,14.10-6 mol.L-1 e limite de quantificação de 1,38.10-5 mol.L-1 , para a cocaína, e na presença do modificador químico CB[6] apresentou limite de detecção de 1,36.10-6 mol.L-1 e limite de quantificação de 4,54.10-6 mol.L-1 . Eletrodos de ouro com ou sem a presença de modificadores químicos não apresentaram sinal para nenhum analito. / Considering the importance of chemically modified electrodes and the small amount of the cocaine study and their interfering (caffeine, theobromine and lidocaine) using electrochemical and piezoelectric techniques, this study aims to investigate the development of the gold and platinum electrodes chemically modified by cucurbiturils (CB[5], CB[6] and, CB[7]) in order to detect cocaine. The Quartz Crystal Microbalance technique was employed in order to study in gas phase the standard samples of cocaine and their interfering. Gold electrode was chemically modified with cucurbiturils films and the CB[6] modifier showed the best results. The cyclic voltammetric measurements were performed using a Autolab III potentiostat coupled to a computer, being gold and platinum as the working electrode, Ag/AgCl as the reference electrode and platinum wire as counter electrode, using a scan rate of 0,1 V.s-1 (100 mV.s-1). The voltammetric parameters were optimized in order to make the analysis faster and more sensitive without loss of intensity and quality of the voltammetric signal. The platinum electrode modified by cucurbit[6]uril film showed an increase of cathodic current peak when electrode was exposed to cocaine, theobromine and lidocaine. Analysis employed platinum working electrode without chemical modifier showed a detection limit of 4.14 . 10-6 mol.L-1 and quantification limit of 1.38 . 10-5 mol.L-1 for cocaine and with chemical modifier CB[6] showed a detection limit of 1.36 . 10-6 mol.L-1 and quantification limit of 4.54 . 10-6 mol.L-1 . Gold electrodes with or without chemical modifiers showed no response for any analyte.

Filmes de óxidos de molibdênio, com ou sem a inclusão de metais, foram eletroquimicamente depositados sobre eletrodos de carbono vítreo em solução de Mo(VI) com pH ajustado em 2,5 ou 3,0. Estes filmes foram caracterizados por Soft X-ray Spectroscopy (SXS), X-ray Diffraction (XRD) e Rutherford Backscattering Spectroscopy (RBS). A coordenação local dos sítios de Mo foram analizadas. As configurações estruturais locais do Mo foram avaliadas quando diferentes números de ciclos de potencial foram empregados na modificação dá superfície do eletrodo. Alguns metais (Pt, Pd, Rh e Cu) foram codepositados com as espécies de Mo e seu efeito nos materiais obtidos foi investigado. O grau de ocupação do orbital 4d do Mo foi examinado como um indicador da existência de interações entre o Mo e o metal codepositado. A incorporação de Pt no filme de óxidos na superfície de um eletrodo de ouro foi caracterizada por espectroscopia PIXE. O eletrodo modificado por óxidos de molibdênio foi estudado em faixas de potencial positivas frente à oxidação de nitrito (NO2-) e de óxido nítrico (NO). A relação entre a porosidade do filme e a presença de água em seus interstícios foi examinada e a capacidade de retenção de NO e NO2 foi também investigada. O eletrodo modificado foi usado como um sensor amperométrico em um sistema de injeção em fluxo (FIA) e o método foi empregado na determinação de nitrito em amostras de lingüiça. A oxidação de H2O2 foi investigada em superfície recoberta por filme de óxidos de Mo com Pt codepositada. O efeito do pH, do potencial e do tempo de pré-redução do filme de Pt e MoOx foi discutida. O comportamento eletroquímico dos filmes codepositados de Rh, Pd, Pt ou Cu e MoOx foi caracterizados comparativamente pela redução do iodato e pela oxidação do nitrito e do etanol nestes substratos. H4MogO26 foi empregado para preparar filmes contendo molibdênio e sua resposta eletroquímica foi comparada com as obtidas com o filme depositado por procedimento usual. O filme de óxidos de molibdênio foi usado com sucesso na imobilização de um complexos de Ru(III) na superfície de carbono vítreo. / Molybdenum oxide films with and without metal inclusion were electrochemically deposited on glassy carbon electrodes from Mo(VI) solutions at pH 2.5 or pH 3.0. These films were characterized by Soft X-ray Spectroscopy (SXS), X-ray Diffraction (XRD) and Rutherford Backscattering Spectroscopy (RBS). The local coordination of Mo sites was analyzed. The Mo local structure configurations were evaluated when different number of potential cycles were employed in the modification of the electrode surface. Some metaIs (Pt, Pd, Rh and Cu) were codeposited with the Mo species and their effect on the obtained material was investigated. The occupancy leveI of the 4d orbital of Mo was examined as an indicator of interactions between Mo and codeposited metals. The incorporation of Pt in the oxide film at a gold electrode surface was characterized by PlXE spectroscopy. The electrode modified by molybdenum oxides was studied at positive potential ranges for the oxidation of nitrite (NO2-) and nitric oxide (NO). The relationship between the porosity of the film and its water content was exarnined and the entrapment of NO and NO2 was also investigated. The modified electrode was used as an amperometric sensor in a flow injection configuration and the method was employed in the deterrnination of nitrite in sausage samples. The oxidation of H2O2 was investigated at surfaces covered by the Mo filrn with codeposited Pt. The effect of pH and potential and time of pre-reduction on the response of the film with Pt was discussed. The electrochemical behaviour of codeposited films of Rh, Pd, Pt or Cu and Mo MoOx was characterized comparatively for the reduction of iodate and the oxidation of nitrite and ethanol. 4MogO26 was also employed to prepare films containing molybdenum and their electrochemical responses were compared with those obtained by using the film electrodeposited by the usual procedure. The molybdenum oxide film was successfully used for the immobilization of Ru(III) complex at glassy carbon surfaces.

>Magister Scientiae - MSc / In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures. / South Africa

This graduate work deals with the study and preparation of gel polymer electrolytes with flame retardants for lithium-ion batteries. The theoretical part describes the types of electrolytes, their features, benefits, how they differ and where they are used in detail. The basis of this section is gel electrolytes with flame retardants, to measure their electrical and electrochemical properties. The experimental part deals with the preparation of samples of gel electrolytes with different percentages of flame retardant, where varied species of flame retardants and measuring their electrical conductivity and potential windows. Impedance spectroscopy, cyclic voltammetry and dynamic-analytical thermal analysis were selected as measuring methods.

This master's thesis deals with a topic of determination of the most suitable ratio of cathode materials for the lithium-sulfur systems. The first two chapters provide a general introduction to the topic of electrochemical energy sources and present the commonly used primary and secondary battery systems with emphasis on their characteristics and applications. The core of the theoretical part is dedicated to lithium-ion and lithium-sulfur batteries, their working principles along with the benefits or drawbacks related to the particular systems, and widely used materials. The experimental part briefly comments on determining the suitable electrode paste preparation method, the subsequent main part is focused on evaluation of electrochemical performance of cells using different ratios of cathode materials. Five samples of cathode materials were prepared, where the sulfur ratio is in range from 64 to 88 wt. %. Finally, the comparison of all prepared ratios in terms of their electrochemical properties is provided.

This diploma thesis deals with the description of individual types of batteries. The first part is focused to primary and secondary batteries, materials for their positive and negative electrodes with a focus on lithium-ion batteries and their changes over time. The next section focuses on a more detailed description of sodium-ion batteries, used electrode materials and to their problems. Practical part is focesed to preparing of electrode materials and to completing of measuring electrochemical cell and to discribing of measuring methodes and to evaluation of measured data.

Philosophiae Doctor - PhD / Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle under low pressure, costs only slightly higher than methanol and can easily be cracked down into hydrogen and nitrogen. At low temperature, ammonia oxidation on noble metal electrodes is a sluggish reaction and efficient catalysts are required to convert ammonia to nitrogen and hydrogen at reasonable reaction rates. In this thesis, I present polycrystalline and oriented nanoalloys synthesised at room temperature in aqueous media and their catalytic effects on the oxidation of ammonia. The electro-oxidation of ammonia on palladium-goldsilver (PdAuAgNPs) ternary nanoalloys was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV). The PdAuAg nanoalloys were prepared through a facile synthesis with ascorbic acid as a reductant and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of PdCh/HAuCI4.3H20/AgN03 mixtures. UV-visible spectroscopy was used to confirm the complete reduction of the metal ions; absorption peaks observed at 260 nm, 285 nm and 420 nm for Ag", Au3+ and Pd2+ ions respectively, disappeared after reduction indicating a complete reduction of the metal ions to zero-valent nanoparticles. High resolution transmission electron microscopy (HR TEM) revealed the formation of crystalline nonaggregated 25-35 nm sized nanoalloys. The elemental composition of the nanoalloys measured using energy dispersive X-ray spectroscopy (EDX) showed the presence of the three elements; Pd, Au and Ag. The well-dispersed non-agglomerated PdAuAg nanoalloys exhibited a reduced overpotential and a 33%, 400%,82% and 54% increase in current density for ammonia electro-oxidation compared to Pd, PdAg, PdAu nanoparticles and bare Pt electrode, respectively. The much improved current density of the well-dispersed PdAuAg nanoalloys is attributed to the increased electrochemically active surface area of the nanoalloys. This electro catalytic behaviour of the PdAuAg nanoalloys for ammonia oxidation in KOH solutions provides a promising route for development of low-cost and high performance electro catalyst for electro-oxidation of ammoniaMoreover, ammonia oxidation on platinum surfaces has been found to be a very structure sensitive reaction which takes place almost exclusively on Pt(100) surfaces. I report for the first time the preparation of sodium polyacrylate-capped Pt(100)Pd, pte 1OO)Au, pte 1OO)Ir, Pt(IOO)Rh, Pt(100)PdAu, Pt(100)IrAu, Pt(IOO)PdIr and Pt(IOO)RhAu nanoalloys. The reduction of the metal ions to nanoparticles was confirmed by UV-visible spectroscopy while the shapes and the structures of the nanoparticles were studied using HRTEM and CV. HRTEM analysis showed well distributed non-agglomerated 5-20 nm semi-spherical and cubic nanoalloys with lattice fridges on their surfaces indicating the crystalline nature of the nanoalloys. Pt(100) nanoalloy systems showed particles with triangular and cubic shapes. The existence of the preferentially cubic shaped nanoparticles in the samples indicated that the nanoalloys had some (100) sites orientation/a significant amount of (100) sites at their surfaces. The CV of the nanoparticles in the hydrogen adsorption/desorption region (-200 mV to 100 mV vs. Ag! AgCl) was used to obtain qualitative information about the surface structure of the nanoparticles. The voltammogram of oriented Pt(100) nanoparticles showed very clearly the presence of adsorption states associated with (110) sites, (100) domains and (l00) sites at -131 mV, -34 mV and 29 mV, respectively. The companson of this voltammetric profile with that obtained for a Pt(100) single crystal electrode clearly points out that the synthesised Pt nanoparticles have a high density of (100) sites. However, the peak that was observed at 29 mV in the CV of Pt(100) nanoparticles was not present in the vo ltammo grams of the Pt(100) nanoalloy systems confirming the formation of the nanoalloys. The results reported in this work demonstrate the importance of controlling the intrinsic structural properties of Pt nanoparticles; in terms of nature of the active sites and the effect of adding adatoms (such as Au, Pd, Rh, Ir) in order to understand their catalytic properties. The electrochemical activities of these nanoparticles for ammonia oxidation in basic medium showed an increase of over 100% current density compared to Pt electrode. Pt(lOO)RhAu nanoalloys showed the highest catalytic properties while Pt(lOO)PdAu had the lowest as shown in the trend: Pt(lOO)RhAu > Pt(lOO)PdIr > Pt(lOO) > Pt(lOO)IrAu > Pt(lOO)Pd> Pt(lOO)Rh > Pt(lOO)Au > Pt(lOO)Ir > Pt(lOO)PdAu. The synthesised oriented nanoalloys were further interrogated towards the oxidation of hydrazine as a fuel for hydrazine fuel cells. The oriented Pt(lOO) nanoparticles and Pt(lOO) nanoalloy systems exhibited over 1000% increase in current density and reduced oxidation overpotential compared to bare glassy carbon electrode. These excellent catalytic properties are attributed to the increased surface area and the presence of (100) sites which favour the oxidation of hydrazine.

The present work deals with the use of manganese oxide as a catalyst for positive electrode of fuel cells. The theoretical part is to analyze the problem of fuel cells, focusing on lowtemperature fuel cells. Are discussed and the methods of measurement and evaluation of properties of manganese oxide layer. The practical part deals with doping electrolytic manganese dioxide salts of divalent metals and monitoring their behavior in the cyclic voltammetry by the EQCM method.

Nowadays it is attached to a major effort to study applications of nanoparticles in biosensors technology. We studied the effect of gold nanoparticles on the surface of the electrodes by Electrochemical Impedance Spectroscopy method and Cyclic Voltammetry. For impedance measurements was proposed substitute electrical model and cyclic voltammetry method was used to determine the electroactive surface of electrodes.