Este trabalho apresenta a preparação de filmes nanoestruturados de óxido de manganês e de vanádio por diferentes técnicas e a sua caracterização eletroquímica utilizando diferentes líquidos iônicos como eletrólito. Os filmes de óxido de manganês foram preparados por automontagem camada-por-camada e por eletrodeposição assistida por molde de nanoesferas de poliestireno. Os filmes de óxido de vanádio foram preparados também por automontagem camada-por-camada e por deposição eletroforética. Diversos aspectos relacionados ao uso dos líquidos iônicos como eletrólitos foram discutidos: os resultados obtidos para os filmes de óxido de manganês por automontagem camada-por-camada mostraram que os íons do líquido iônico participam do processo de compensação de carga superficialmente e que o cátion do líquido iônico, apesar de mais volumoso, apresenta coeficiente de difusão maior que o Li+, formando uma barreira à intercalação dos mesmos na estrutura do material. A partir dos resultados obtidos para os filmes de óxido de manganês por eletrodeposição assistida por nanoesferas de poliestireno, foi possível verificar que o desempenho do sistema depende da natureza do líquido iônico utilizado, sendo possível obter desempenho superior aos solventes orgânicos convencionais com um dos líquidos iônicos utilizados do ponto de vista da ciclabilidade. Desempenho superior aos eletrólitos convencionais também foi observado para os filmes de óxido de vanádio obtidos por automontagem camada-por-camada. Por fim, a caracterização eletroquímica em líquidos iônicos dos filmes de óxido de vanádio obtidos por deposição eletroforética mostrou que não apenas o uso de nanopartículas, mas também o modo de deposição das mesmas influencia no desempenho eletroquímico do sistema. De maneira geral, os resultados obtidos mostraram que o uso de filmes nanoestruturados e de líquidos iônicos como eletrólitos constituem alternativas promissoras para a obtenção de dispositivos de armazenamento e conversão de energia de alto desempenho e segurança. / This work presents the preparation of manganese and vanadium oxides nanostructured films by different techniques and their electrochemical characterization in different ionic liquids based electrolytes. Manganese oxide films have been prepared by self-assembly layer-by-layer and by electrodeposition assisted by polystyrene nanospheres template. Vanadium oxide films have been also prepared by self-assembly layer-by-layer deposition and by electrophoretic deposition. Several aspects related with the use of ionic liquids as electrolytes have been discussed: the obtained results from layer-by-layer deposition of manganese oxide have shown that ionic liquid ions also participate in the charge compensation process, but only superficially; in spite of ionic liquid cation been larger than Li+, it moves faster, achieving the electrode surface before, being a barrier for Li+ intercalation. From the results obtained for the manganese oxide prepared by template assisted electrodeposition, it was possible to notice that electrochemical performance is dependent on the ionic liquid structure, being possible to achieve higher performance than with conventional organic solvent electrolyte with one of the studied ionic liquid. Superior performance in comparison with conventional electrolyte has also been achieved for vanadium oxide films prepared by layer-by-layer deposition from the point of view of cyclability. Finally, the electrochemical characterization of vanadium oxide films prepared by electrophoretic deposition in ionic liquids has shown that not only the use of nanoparticles but also the deposition method employed influences the electrochemical performance. To conclude, the obtained results have shown that the use of nanostructured films and ionic liquids as electrolytes are promising alternatives for the obtention of high performance energy storage and conversion devices.

Um estudo refinado dos filmes derivados do gel de pentóxido de vanádio foi realizado por meio de técnicas espectroscópicas e microscópicas visando compreender melhor as características deste material na escala microscópica. Foi demonstrado que o gel de pentóxido de vanádio é uma suspensão de nanopartículas anisotrópicas que se mantêm estáveis mesmo em altas concentrações. As propriedades estruturais e espectroscópicas destas nanopartículas foram revistas e discutidas no estado da arte. Em paralelo foi possível investigar fenômenos como a transição de fase induzida por laser e desenvolver aplicações tecnológicas em áreas como litografia e sensoriamento de gases. Ficou destacada nesta tese o grande potencial de investigação da microscopia Raman confocal na área de nanomateriais. / A refined study of films derived from vanadium pentoxide gel was carried out based on spectroscopic and microscopic techniques, aiming a better understanding of this material on a microscopic scale. It was demonstrated that the vanadium pentoxide gel consists of a suspension of anisotropic nanoparticles which remains stable even at high concentrations. The structural and spectroscopic properties of such nanoparticles were reviewed and discussed, providing new insights at the state of the art. It was also investigated the occurrence of some relevant phenomena, such as the laser induced phase transition, and to develop new technological applications in areas such as gas sensing and lithography. The collection of results described in thesis highlighted a great research potential of confocal Raman microscopy, in the field of nanomaterials.

Esta tese tem como foco o desenvolvimento de procedimentos analíticos automáticos, visando as determinações fotométricas de vanádio e de estanho em águas e em alimentos empregando o processo de multicomutação em fluxo. Um microcontrolador da família PIC e um programa escrito em linguagem Visual Basic 6.0 foram empregados para controle dos dispositivos e aquisição de dados. A unidade de detecção foi construída empregando LED de alto brilho e celas de fluxo com longo caminho óptico (50-200 mm) para ganho em sensibilidade. O módulo de análises, empregando bombas solenoide como propulsores de fluido e o fotômetro foram integrados, formando uma unidade compacta. A determinação de vanádio em águas, mineral e de rio, foi baseada na redução do V(V) à V(IV) com ácido ascórbico e posterior complexação com Eriocromo Cianina R (ECR). Empregando uma cela de 150 mm, o sistema apresentou resposta linear de 0,02 a 1,00 mg L-1, limite de detecção estimado em 13 ?g L-1, coeficiente de variação de 0,87% (n=10) e frequência analítica de 47 determinações por hora. Recuperações entre 89 e 109% foram obtidas para adição de V(V) nas amostras de águas. O procedimento para a determinação de estanho em alimentos foi desenvolvido empregando bomba de multi-seringa como unidade de propulsão de fluidos, cela de fluxo com caminho óptico de 200 mm e parada de fluxo de 50 s. Baseado na reação do Sn(IV) com o violeta de pirocatecol (PCV) na presença de surfactantes, o sistema apresentou resposta linear de 0,10 a 1,25 mg L-1, limite de detecção estimado em 0,04 mg L-1, coeficiente de variação de 1,30% (n=10) e frequência analítica de 49 determinações por hora. Recuperações entre 95 e 115% foram obtidas com a adição de Sn(IV) às amostras de alimentos. / Automatic analytical procedures for photometric determinations of vanadium in water and tin in foods were developed using the multicommutation flow analysis process. A microcontroller of the PIC family and a software written in Visual Basic 6.0 language were used for devices control and data acquisition. Detection unit was designed to use high brightness LED and long optical pathlength flow cells (50-200 mm) to improve sensitivity. The flow analysis module using solenoid mini-pumps as fluid propelling devices and the photometer were integrated in order to form a compact unit. The determination of vanadium in mineral and river waters was based on the reduction of V(V) to V(IV) with ascorbic acid and subsequent complexation with Eriochrome Cyanine R (ECR). Employing flow cell of 150 mm, the system presented linear response between 0.02 and 1.00 mg L-1, detection limit of 13 ?g L-1, variation coefficient of 0.87% (n=10) and sampling throughput of 47 determinations per hour. Recoveries between 89 and 109% were attained for vanadium spiked to mineral and river water. The procedure for determination of tin in foods was development employing a multi-syringe pump as fluid propelling device, a flow cell with optical pathlength of 200 mm and stop flow of 50 s. The procedure was based on the reaction of Sn(IV) with pyrocatechol violet (PCV) in the presence of surfactants, presented linear response between 0.10 and 1.25 mg L-1, detection limit of 0.04 mg L-1, variation coefficient of 1.30% (n=10) and sampling throughput of 49 determination per hour. Recoveries between 95 and 115% were attained for tin spiked samples

This thesis investigates the chemistry of 25 ascidian species collected from Algoa Bay, South Africa with a concerted focus on metal accumulation by these ascidians and the possible interaction of these metals with ascidian metabolites. Chapter 2 details the screening techniques employed to establish the presence of nitrogenous metabolites (1H- 15N HMBC), hyper-accumulated metal ions (ICP-MS) and potential metal ion/ ascidian metabolite complexes (LC-ICP-MS/ESI-MS). Unfortunately, exhaustive attempts to detect intact metal ion/ascidian metabolite complexes through the use of liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICPMS/ ESI-MS) were unsuccessful. However, the LC-ICP-MS/ESI-MS data obtained for the crude organic extracts of six of the Algoa Bay ascidian species, Distaplia skoogi, Aplidium monile, Aplidium sp., Didemnum sp., Leptoclindines sp. and Polycitor sp. enabled identification of a number of ten halogenated metabolites, namely the indoles 2.28-2.30, and the tyramine and tyrosine derivatives (2.31-2.33, 2.41, 2.43, 2.44 and 2.46), within the ascidian extracts. This study confirmed that LC-ICP-MS/ESI-MS is a powerful tool for the dereplication of halogenated metabolites in complex mixtures especially where these compounds are present in very small amounts. This study is also the first report of these compounds (eight of which are known) in African ascidians. Compounds 2.32 and 2.46 have not been reported before from a marine source. Compounds 2.28-2.30 and 2.33 were present in sufficient amounts in the respective ascidian extracts to allow their isolation and structure elucidation using standard spectroscopic techniques Chapter 3 explores the ability of ascidians to accumulate a wide range of metal ions at concentrations which are often orders of magnitude higher than those of the surrounding sea water. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total ion concentrations of 24 metals in 25 Algoa Bay ascidian species. To the best of our knowledge this is the largest and most extensive investigation of metal concentrations in a group of different ascidians occurring in the same area. Hypotheisizing that the metal ion concentrations for each ascidian specimen screened may represent a unique fingerprint for each specimen principal component analysis (PCA) was used in an attempt to establish whether there were spatial, temporal or phylogenetic relationships associated with the metal concentration fingerprints of the ascidians that formed part of this study. The PCA results showed that there were no statistically significant relationships between ascidian metal ion concentrations and either the collection year or the collection site of the ascidians. However, species from the family Didemnidae provided the clearest statistical evidence supporting a phylogenetic relationship between these ascidians and their hyperaccumulated metal ion profiles. Furthermore, these results suggested that ascidian species are indeed actively concentrating metal ions from the surrounding sea water and are not simply sinks for passively accumulated metal ions. Interestingly, the concentration of vanadium in the set of ascidians studied did not appear to correlate with any of the other metals accumulated by these ascidians suggesting that there is possibly a unique method employed for the accumulation of vanadium by ascidians. Chapter 4 investigated this possibility further after the nucleosides 4.10, 4.11, 4.13, 4.15, 4.17 and 4.40 were isolated from the vanadium accumulating ascidian Aplidium monile. Studies into the interactions between nucleosides and vanadyl are unfortunately rare and usually qualitative in nature with limited information provided about the stability or structures of the complexes formed. The vanadyl accumulating aplousobranch ascidians e.g. Aplidium monile dominated our study of Algoa Bay ascidians therefore providing us with the rationale to investigate the relatively little studied binding ability and stability of vandyl-nucleoside complexes. Potentiometric studies were conducted to determine the stability constants of complexes formed between the oxovanadium ion vanadyl (VO2+) and the commercially available nucleosides 4.10-4.14. The data afforded by this analysis clearly confirmed the complexity of the vanadyl/nucleoside complexation and suggested that guanosine (4.12) formed the most stable complex with oxovanadium ions. We were also able to establish a third protonation constant for the hydroxyl moiety in 4.12 with a logK 8.87 which has not been previously reported. Finally, Chapter 5 revisited the cytoxicity two Algoa Bay ascidians, Clavelina sp. and Atriolum marinense the extracts from which produced promising bioactivity results in previous studies against oesophageal cancer cells. The HP-20 fractionated extracts of Clavelina sp. and Atriolum marinense proved to be similalrly cytotoxic to breast cancer cells. With the exception for the 100% acetone(aq)fractions the NMR data for both species suggested that most active non polar fractions were dominated by what appeared to be structurally unremarkable fatty acid glycerides and as such were not pursued further. Purification of the 100% acetone(aq)fraction of A. marinense resulted in the isolation of a styrene trimer, 5.1, common to both ascidian extracts. The NMR simulation software WIN-DAISY was employed to confirm the structure of 5.1. Attempts to establish if 5.1 was an isolation artefact or a product of marine pollution were inconclusive

Continued emission of green house gases has energized research activity worldwide to develop efficient ways to harness renewal energy. The availability of large scale energy storage technologies is essential to make renewal energy a reliable source of energy. Redox flow batteries show potential in this direction. These batteries typically need expensive membranes which need replacement be-cause of fouling. The recently proposed soluble lead redox flow battery (SLRFB), in which lead ions deposit on electrodes in charge cycle and dissolve back in discharge cycle, can potentially cut down the cost of energy storage by eliminating membrane. A number of challenges need to be overcome though. Low cycleability, residue formation, and low efficiencies are foremost among these, all of which require an understanding of the underlying mechanisms. A model of laminar flow-through SLRFB is first developed to understand buildup of residue on electrodes with continued cycling. The model accounts for spatially and temporally growing concentration boundary layers on electrodes in a self consistent manner by permitting local deposition/dissolution rates to be controlled by local ion transport and reaction conditions. The model suggests controlling role for charge transfer reaction on electrodes (anode in particular) and movement of ions in the bulk and concentration boundary layers. The non-uniform current density on electrodes emerges as key to formation of bare patches, steep decrease in voltage marking the end of discharge cycle, and residue buildup with continuing cycles. The model captures the experimental observations very well, and points to improved operational efficiency and decreased residue build up with cylindrical electrodes and alternating flow direction of recirculation. The underlying mechanism for more than an order of magnitude increase in cycle life of a beaker cell battery with increase in stirrer speed is unraveled next. Our experiments show that charging with and without stirring occurs identically, which brings up the hitherto unknown but quite strong role of natural convection in SLRFB. The role of stirring is determined to be dislodgement/disintegration of residue building up on electrodes. The depletion of active material from electrolyte due to residue formation is offset by “internal regeneration mechanism”, unraveled in the present work. When the rate of residue formation, rate of dislodging/disintegration from electrode, and rate of regeneration of active material in bulk of the electrolyte becomes equal, perpetual operation of SLRFB is expected. The identification of strong role of free convection in battery is put to use to demonstrate a battery that requires stirring/mixing only intermittently, during open circuit stages between charge and discharge cycles when no current is drawn. Inspired by our experimental finding that the measured currents for apparently diffusion limited situations (no external flow) are far larger than the maxi-mum possible theoretical value, the earlier model is modified to account for natural convection driven by concentration gradient of lead ions in electrolyte. The model reveals the presence of strong natural convection in battery. The induced flow in the vicinity of the electrodes enhances mass transport rates substantially, to the extent that even in the absence of external flow, normal charge/discharge of battery is predicted. The model predicted electrochemical characteristics are verified quantitatively through voltage-time measurements. The formation of flow circulation loops driven by electrode processes is validated qualitatively through PIV measurements. Natural convection is predicted to play a significant role in the presence of external flow as well. The hitherto unexplained finding in the literature on insensitivity of charge-discharge characteristics to electrolyte flow rate is captured by the model when mixed mode of convection is invoked. Flow reversal and wavy flow are predicted when natural convection and forced convection act in opposite directions in the battery. The effect of the presence of non-conducting material (PbO on anode) on the performance of SLRFB is studied using a simplified approach in the model. The study reveals the presence of charge coup de fouet phenomenon in charge cycle. The phenomenon as well as the predicted effect of depth of discharge on the magnitude of charge coup de fouet are confirmed experimentally.

In this diploma thesis was analysed layer of corroded material created on refractory lining of reactors for mazut gasification. Samples of corroded material were analysed for SiO2, Al2O3, ZrO2, Fe2O3 a TiO2. Corroded material was further analysed by x-ray and IR spectroscopy to acquire more precise data about chemical composition. This thesis studies the exact effect of microstructure on static corrosion kinetics in system SiO2-Al2O3.

Bauelemente auf Basis von AlGaN/GaN-Heterostrukturen bieten vielversprechende Eigenschaften für Hochfrequenz- und leistungselektronische Anwendungen. Dazu zählen die hohe Elektronenmobilität im zweidimensionalen Elektronengas (2DEG) und eine hervorragende Durchbruchsfeldstärke. Die effiziente ohmsche Kontaktierung der Source- und Drain-Gebiete von Hetero-Feldeffekttransistoren mit Gate-Dielektrikum (MISHFETs) stellt jedoch eine Herausforderung dar. In dieser Arbeit werden unterschiedliche Kontaktstapel auf Basis von Ti/Al/Ni/Au und V/Al/Ni/Au hinsichtlich ihrer Eignung als ohmsche Kontaktierung verglichen. Mit Hilfe von elektrischen und mikrostrukturellen Methoden werden die Vorgänge bei der Ausbildung des elektrischen Kontakts untersucht. Während der etablierte Ti-haltige Kontaktstapel einen Hochtemperaturschritt bei mindestens 800°C benötig, um einen hinreichend guten Kontaktwiderstand zu erzielen, lässt sich mit der V-basierten Metallisierung eine Reduzierung der notwendigen Temperatur um bis zu 150 K erreichen. Die so optimierten Kontakte werden als Source- und Drain-Metallisierung für MISHFETs genutzt. Es wird gezeigt, dass die Reduzierung der Formierungstemperatur bei V-haltigen Kontakten einen positiven Effekt auf die Eigenschaften der Bauelemente hat. So wird die Schädigung des 2DEGs minimiert und es können Transistoren mit geringerem Leckstrom und höherem An/Aus-Verhältnis des Drain-Stroms hergestellt werden.

<p>Electrospinning has gained immense interests in recent years due to its potential application in various fields, including energy storage application. The V₂O₅/GO as a layered crystal structure has been demonstrated to fabricate nanofibers with diameters within a range of ~300nm through electrospinning technique. The porous, hollow, and interconnected nanostructures were produced by electrospinning formed by polymers such as Polyvinylpyrrolidone (PVP) and Polyvinyl alcohol (PVA), separately, as solvent polymers with electrospinning technique. </p> <p> </p> <p>In this study, we investigated the synthesis of a graphene-modified nanostructured V₂O₅ through modified sol-gel method and electrospinning of V₂O₅/GO hybrid. Electrochemical characterization was performed by utilizing Arbin Battery cycler, Field Emission Scanning Electron Microscopy (FESEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), Mercury Porosimetery, and BET surface area measurement. </p> <p> </p> <p>As compared to the other conventional fabrication methods, our optimized sol-gel method, followed by the electrospinning of the cathode material achieved a high initial capacity of <b>342 mAh/g</b> at a high current density of 0.5C (171 mA/g) and the capacity retention of ~80% after 20 cycles. Also, the prepared sol-gel method outperforms the pure V₂O₅cathode material, by obtaining the capacity almost two times higher.</p> <p>The results of this study showed that post-synthesis treatment of cathode material plays a prominent role in electrochemical performance of the nanostructured vanadium oxides. By controlling the annealing and drying steps, and time, a small amount of pyrolysis carbon can be retained, which improves the conductivity of the V₂O₅ nanorods. Also, controlled post-synthesis helped us to prevent aggregation of electro-spun twisted nanostructured fibers which deteriorates the lithium diffusion process during charge/discharge of batteries.</p>

No description available.

Plazmonika, tedy vědní obor zabývající se interakcí světla s kovovými materiály, nabízí ve spojení s nanotechnologiemi nezvyklé možnosti, jak světlo ovládat a využívat. Výsledkem tohoto spojení může být například zaostřování světla pod difrakční limit, zesilování emise nebo absorbce kvantových zářičů, či extrémně citlivá detekce molekul. Tato práce se zabývá zejména možnostmi využití plazmoniky pro vývoj plošných optických prvků, tzv. metapovrchů, a pro fotokatalytické aplikace založené na plazmonicky generovaných elektronech s vysokou energií, tzv. horkých elektronech. Nejprve jsou vysvětleny teoretické základy plazmoniky a je poskytnut přehled jejích nejvýznamnějších aplikací. Poté jsou představeny tři studie zabývající se využitím plazmonických nanostruktur pro ovládání fáze a polarizace světla, pro vytváření dynamicky laditelných metapovrchů, a pro foto-elektrochemii s horkými elektrony. Společným prvkem těchto studií je pak používání pokročilých, resp. v rámci těchto oblastí netradičních, materiálů, jako např. oxidu vanadičitého nebo dichalkogenidů přechodných kovů.