• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 138
  • 51
  • 25
  • 21
  • 4
  • 3
  • 3
  • 2
  • 1
  • 1
  • Tagged with
  • 285
  • 285
  • 257
  • 60
  • 60
  • 54
  • 51
  • 41
  • 40
  • 38
  • 37
  • 33
  • 32
  • 31
  • 30
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Avaliação da corrosão em juntas soldadas de fios dissimilares Ni-Ti/Ti-Mo obtidas pelo processo de TIG. / Evaluation of corrosion in weld joints of dissimilar Ni-Ti / Ti-Mo wires obtained by the TIG process.

COSTA, Josiane Dantas. 16 March 2018 (has links)
Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-16T19:08:32Z No. of bitstreams: 1 JOSIANE DANTAS COSTA - DISSERTAÇÃO PPGEQ 2015..pdf: 2694660 bytes, checksum: b1f464f2e8b29d82a5339c5bd52471b3 (MD5) / Made available in DSpace on 2018-03-16T19:08:32Z (GMT). No. of bitstreams: 1 JOSIANE DANTAS COSTA - DISSERTAÇÃO PPGEQ 2015..pdf: 2694660 bytes, checksum: b1f464f2e8b29d82a5339c5bd52471b3 (MD5) Previous issue date: 2015-09-29 / A liga de Ni-Ti, conhecida por Nitinol, é constituída dos elementos níquel e titânio e vem sendo bastante aplicada nas mais diversas áreas: aeroespacial, automotiva, construção civil, dispositivos médicos e ortodônticos. Esse potencial de aplicação decorre das propriedades particulares de efeito de memória de forma e superelasticidade, associada a uma boa resistência à corrosão e excelente biocompatibilidade. Com intuito de aumentar as aplicações desse material em dispositivos médicos, o desenvolvimento de tecnologias de união torna-se necessário para possibilitar a fabricação das mais diferentes formas geométricas e combinações entre materiais similares e dissimilares. Nesse contexto, é fundamental que se realize estudos sobre a resistência a corrosão da região em que foi feita a união (junta), principalmente quando utilizados processos de soldagem, já que podem deixar falhas induzindo a uma maior suscetibilidade a corrosão. Diante disto, neste trabalho foi realizada a união de fios ortodônticos de Ni-Ti com fios ortodônticos de Ti-Mo através do processo de soldagem TIG (“Tungsten Inert Gas”) autógeno. Como se trata de biomateriais, este estudo teve como objetivo geral avaliar a resistência à corrosão dos fios comerciais íntegros e da junta soldada Ni-Ti/Ti-Mo em solução salina tamponada SBF (“Saline Buffered Phosphate”) que simula o sangue humano, para verificar se a soldagem afetaria a resistência a corrosão das juntas. Os resultados obtidos revelaram que o processo da soldagem TIG utilizado neste trabalho gerou juntas soldadas de excelente qualidade, apresentando uma resistência à corrosão superior à dos fios íntegros. O planejamento experimental utilizado para verificar a influência da temperatura e do tempo do tratamento térmico nos resultados de corrosão, gerou um experimento ótimo com temperatura de 350°C e um tempo de 40 minutos. Este resultado foi confirmado através dos ensaios de espectroscopia de impedância eletroquímica. / The Ni-Ti alloy, known as Nitinol, is made of nickel and titanium elements and has been widely applied in several areas: aerospace, automotive, construction, medical and orthodontic appliances. Nitinol's application potential is due to its particular superelasticity properties and shape memory effect associated with a good corrosion resistance and excellent biocompatibility. In order to increase the applications of this material in medical devices, the development of joining technologies is necessary to enable manufacture of the most different geometric shapes and combinations of similar and dissimilar materials. In this context, it is essential to conduct studies on the corrosion resistance of the region where the union (joint) was done, especially when welding processes are used, as they can leave gaps leading to greater susceptibility to corrosion. With this in mind, this work carried out the union of Ni-Ti orthodontic wire with Ti-Mo orthodontic wire through the autogenous TIG (Tungsten Inert Gas) welding process. As biomaterials are involved, this study aimed to evaluate the corrosion resistance of the upright commercial wire and welded joint Ni-Ti/Ti-Mo in buffered saline solution SBP (Saline Buffered Phosphate) which simulates human blood, to check if the welding would affect the corrosion resistance of the joint. The results revealed that the TIG welding process used in this work generated welds of excellent quality, having a corrosion resistance higher than that of intact wires. The experimental design used to determine the influence of temperature and time of heat treatment on the results of corrosion generated a great experiment with temperature of 350 ° C and a time of 40 minutes. This result was confirmed by means of electrochemical impedance spectroscopy test.
232

Synthèse et caractérisations électrochimiques de nouveaux matériaux pour anodes d'électrolyseurs à haute température / Synthesis and electrochemical characterizations of new materials for high temperature electrolyser anodes

Chauveau, Florent 15 December 2009 (has links)
L’électrolyse de la vapeur d’eau à haute température (EHT) est une voie permettant de produire de l’hydrogène d’une grande pureté et avec un fort rendement, ceci sans émission de CO2. Un des verrous actuels de cette technologie est la forte surtension associée à la réaction d’oxydation des ions O2- qui se déroule à l’électrode à oxygène (anode). L’objectif de ce travail était de concevoir de nouveaux matériaux d’anode possédant des propriétés de conductivité mixte (i.e. électronique et ionique), dans le but d’obtenir des surfaces de réaction plus importantes afin de diminuer cette surtension. A cet effet, une étude comparative a été réalisée sur huit oxydes (ferrites et nickelates de terres rares). Après synthèse et mise en forme, ces matériaux ont fait l’objet de caractérisations physico-chimiques puis électrochimiques en demi-cellules symétriques sous atmosphère unique afin de déterminer ceux présentant les meilleures propriétés sous courant nul et sous polarisation anodique. Quatre composés de structure dérivée de type K2NiF4 ont ainsi été sélectionnés pour être caractérisés de façon plus approfondie en cellules complètes à électrolyte support en conditions EHT (750 - 850°C). Il a ainsi été possible d’obtenir, pour une tension de cellule de 1,3 V une densité de courant de 0,9 A/cm² à 850°C, soit près de deux fois plus qu’avec une cellule identique comportant comme matériau d’anode un composite commercial optimisé à base de LaMnO3 substitué au strontium. / High temperature steam electrolysis (HTSE) is a way to produce hydrogen with a high purity, with noteworthy efficiency and without CO2 emission. Nowadays, a blocking point concerning this technology is the high overvoltage related to the oxidation of the O2- ions occurring at the oxygen electrode (anode). The aim of this work was to design new anode materials with mixed conducting properties (i.e. electronic and ionic), in order to obtain larger reaction areas and to lessen this overvoltage. In this aim, eight compounds (ferrites and rare earth nickelates) were investigated. After synthesis and shaping, these compounds were characterized using physical, chemical and electrochemical analyses in symmetrical half cells, under single atmosphere, in order to determine which ones have the best properties under zero current and under anodic polarization. Four compounds of structure derived from K2NiF4-type were then selected to be more accurately characterized in complete electrolyte supported cells, under HTSE conditions (750 - 850°C). It was then possible to obtain, for a 1.3 V cell voltage, a current density of 0.9 A/cm² at 850°C, which is nearly two times larger than the one obtained with a same cell including a commercial composite material based on strontium substituted LaMnO3 as anode.
233

Intégration de matériaux oxydes innovants dans une cellule IT-SOFC / Integration of innovative oxide materials in an IT-SOFC

Morandi, Anne 04 April 2013 (has links)
Cette thèse vise à évaluer le potentiel d'un nouveau couple cathode / électrolyte pour une application en IT-SOFC (700°C), par le biais de l’élaboration et du test de cellules à anode support de configuration planaire. Les matériaux concernés sont l'électrolyte BaIn0.3Ti0.7O2.85 (BIT07), de structure perovskite, et les nickelates de terres rares Ln2-xNiO4+ (LnN, Ln = La, Nd, Pr) en tant que cathodes ; ces matériaux ont montré des propriétés prometteuses dans des travaux préliminaires effectués à l'IMN et l'ICMCB. La première partie de cette thèse porte sur la mise en place d'un protocole d'élaboration de cellules complètes utilisant des techniques bas coûts et industrialisables (cellules de taille 3 x 3 cm2) : l’anode Ni / BIT07 a été élaborée par coulage en bande, l'électrolyte BIT07 par vacuum slip casting et les cathodes par sérigraphie. Les mesures électrochimiques réalisées sur une première génération de cellules ont mis en évidence la nécessité d'ajouter une couche barrière de GDC entre les cathodes LnN et l'électrolyte BIT07. Les meilleures performances ont été obtenues pour une cellule BIT07 / Ni | BIT07 | GDC | PrN, avec une densité de puissance à 700°C et 0.7 V de 176 mW cm-2 pour une faible résistance de polarisation de 0. 29 Ω cm2. La principale limitation des performances a été identifiée comme étant la résistance interne du banc de test, donnant lieu à des valeurs de résistances séries anormalement élevées. Cette cellule a été opérée avec succès durant plus de 500 heures sous courant, avec néanmoins une vitesse de dégradation extrapolée élevée de l’ordre de 27% / kh. / This thesis aimed at assessing the potential of a novel cathode / electrolyte couple for IT-SOFC applications (700°C), through the elaboration and testing of planar anode-supported cells. The materials involved were the perovskite-structured BaIn0.3Ti0.7O2.85 (BIT07) electrolyte and the rare earth nickelate Ln2-xNiO4+ (LnN, Ln = La, Nd, Pr) cathodes, both materials having shown promising properties in preliminary work done at the IMN and the ICMCB. The first part of this thesis concerned the implementation of a cell elaboration protocol using low-cost and scalable shaping techniques (cell size 3 x 3 cm2); namely, the Ni / BIT07 anodes were elaborated by tape casting, the BIT07 electrolyte by vacuum slip casting and the cathodes by screen printing. Comparison of electrochemical results for a first and second generation of cells highlighted the usefulness of adding a GDC buffer layer in between the LnN cathodes and the BIT07 electrolyte. The best performance has been obtained for a cell BIT07 / Ni | BIT07 | GDC | PrN, with a power density at 700°C and 0.7 V of 176 mW cm-2 for a competitive polarisation resistance of 0.29 Ω cm2. The main limitation of the performance has been determined to be related to the internal resistance of the test setup, giving anomalously high series resistances. This cell has been successfully operated beyond 500 hours under current, although with a fairly high extrapolated degradation rate of 27% / kh.
234

Conception innovante de cathodes à base de nickelates de terres rares pour piles à combustible à oxyde électrolyte solide / Innovative design of rare earth nickelates as cathodes for solid oxide fuel cells

Sharma, Rakesh 24 November 2016 (has links)
Des oxydes appartenant au type structural Ruddlesden-Popper (RP) sont des matériaux de cathode prometteursdes piles à combustible à oxyde électrolyte solide (SOFC) fonctionnant à température intermédiaire (~ 500-700 °C). L’objectif de cette thèse est l’élaboration de conducteurs ioniques et électroniques, mixtes (MIEC) tels que la solution solide, La2-xPrxNiO4+δ, 0 ≤ x ≤ 2, des phases RP de formule Lan+1NinO3n+1 (n= 1, 2 and 3) et les composites associés à la cérine gadoliniée, Ce0.9Gd0.1O2-δ (CGO).Une microstructure et une architecture innovantes de ces électrodes ont été obtenues avec succès en utilisant l’atomisation électrostatique (ESD) et la sérigraphie (SP). La structure, la composition, la non-stoechiométrie en oxygène et la microstructure de ces matériaux ont été caractérisées par diffraction des rayons X, par spectroscopie de rayons X à dispersion d'énergie, par analyse thermogravimétrique et par microscopie électronique à balayage. Les propriétés électrochimiques et la stabilité chimique de ces électrodes à oxygène sont discutées en fonction de leur architecture et de la composition en utilisant la spectroscopie d'impédance électrochimique (SIE) et la diffraction des rayons X, respectivement. Enfin, une cellule complète SOFC intégrant la cathode LaPrNiO4+δ a été testée.Mots Clés: Pile à combustible à haute température (SOFC), Conducteur ionique et électronique mixte (MIEC), Cathode, Nickelates, Ce0.9Gd0.1O2-δ (CGO), Microstructure de type corail, Design architectural, Interfaces, Stabilité chimique, Atomisation électrostatique (ESD), Sérigraphie (SP), Spectroscopie d’impédance électrochimique (EIS). / Layered Ruddlesden-Popper type (RP) oxides are promising cathodes for solid oxide fuel cells operating at intermediate temperature (~500 - 700 °C).This thesis is focused on the synthesis of mixed ionic-electronic conducting materials such as pure La2-xPrxNiO4+δ, 0 ≤ x ≤ 2, higher order Lan+1NinO3n+1 (n= 1, 2 and 3) RP phases and composites adding Ce0.9Gd0.1O2-δ (CGO) component. An innovative microstructure and architecture of these electrodes were successfully prepared using electrostatic spray deposition (ESD) and screen-printing (SP) processes. These materials were evaluated through structural, compositional, oxygen non-stoichiometry and microstructural characterizations using X-ray diffraction, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and scanning electron microscopy. The electrochemical properties and chemical stability of these oxygen electrodes are discussed according to the architectural design and composition using electrochemical impedance spectroscopy (EIS) and X-ray diffraction, respectively. Finally, a single SOFC based on LaPrNiO4+δ cathode has been tested.Keywords: Solid Oxide Fuel cell(SOFC), Mixed Ionic and Electronic Conductor (MIEC), Cathode, Nickelates, Ce0.9Gd0.1O2-δ (CGO), Coral-type microstructure, architectural design, interfaces, chemical stability, Electrostatic Spray Deposition (ESD), Screen-Printing (SP), Electrochemical Impedance Spectroscopy (EIS).
235

Caractérisation croisée de la double couche électrique se développant à l'interface solide/liquide (304L/NaCl) pour différents états de surface / Cross-characterization of the electrical double layer at the solid (304L Stainless Steel) / liquid (NaCl solution) interface for different surface states

Mastouri, Wejdene 13 December 2017 (has links)
Lorsqu'un solide est en contact avec un liquide, des phénomènes physico-chimiques conduisent à polariser l'interface. Deux zones de charge, de signe opposé, apparaissent à cette interface, une dans le solide et l'autre dans le liquide, formant ainsi la double couche électrique (DCE). Par rapport à la littérature existante, l’originalité de ce travail est de s’intéresser à la DCE à l’interface acier inoxydable 304L /film passif d’oxyde/ solution de NaCl (0.01M) en couplant des caractérisations électrochimiques, électriques et physiques. Une méthodologie de caractérisation par voie électrochimique en utilisant les méthodes de spectroscopie d’impédance (SIE) et de voltammétrie cyclique (CV) a été mise au point pour accéder à deux paramètres: la capacité effective et la densité surfacique de charge. Des modifications de la concentration de l'électrolyte, du potentiel appliqué et de l'état de surface ont ensuite été réalisées : la capacité effective de la DCE dépend principalement de la concentration et du potentiel et la densité surfacique de charge croît avec la concentration. Dans la gamme étudiée, la rugosité a une faible influence sur la capacité effective mesurée. Des analyses physico-chimiques de la surface ont permis de caractériser les films passifs formés sur l'acier, sans révéler de différences significatives entre les surfaces avant et après immersion. Un autre paramètre caractéristique de la DCE, la densité volumique de charge à la paroi, a été aussi déterminé par la méthode d'électrisation par écoulement du liquide. Les 3 méthodes de caractérisation (SIE, CV et électrisation) confirment l'influence de la concentration sur les caractéristiques de la DCE. / When a metal is immersed in an electrolyte, a charge distribution is created at the interface and a potential is set up across the two phases. The separation between charges give rise to what are known as electric double layers (EDL). Compared to the usual solid/liquid interfaces investigated in the literature, this study is dedicated to the EDL at the stainless steel 304L / passive film / NaCl (0.01M) interface by combining electrochemical, electrical and physical methods. First, a methodology has been set up to characterise the EDL by the electrochemical methods: Electrochemical Impedance Spectroscopy (EIS) and cyclic voltammetry (CV). Both the effective capacity and the surface charge density were evaluated. Then, several parameters were investigated such as the electrolyte concentration, the applied potential and the influence on the EDL of the surface preparation. The results showed that the double layer capacitance depends mainly on the concentration of the electrolyte and on the applied potential. The roughness seems to have a poor influence on the measured capacitance. Various physico-chemical analysis were performed in order to characterise the passive films formed at the surface: no significant difference could have been evidence between the surfaces before and after immersion. Finally, the volume charge density was also determined by the liquid flow electrification measurement. Whatever the characterization techniques used (EIS, CV or flow electrification), the same trend was observed with regard to the influence of the concentration on the characteristics of the EDL.
236

Compréhension des mécanismes de (dé)lithiation et de dégradation d'électrodes de silicium pour accumulateur Li-ion et étude de facteurs influents / Understanding of (de)lithiation and degradation mechanisms of silicon electrodes used in Li-ion batteries and study of influent factors

Radvanyi, Etienne 06 February 2014 (has links)
Les travaux de thèse présentés dans ce manuscrit portent sur l’étude d’électrodes de silicium, matériau prometteur pour remplacer le graphite en tant que matériau actif d’électrode négative pour accumulateur Li-ion. Les mécanismes de (dé)lithiation du silicium sont d’abord étudiés, par Spectroscopie des Electrons Auger (AES). En utilisant cette technique de caractérisation de surface, qui permet d’analyser les particules individuellement dans leur environnement d’électrode, nos résultats montrent que la première lithiation du silicium s’effectue selon un mécanisme biphasé cr-Si / a-Li3,1Si tandis que les processus de (dé)lithiation suivants apparaissent complètement différents et sont du type solution solide. Ces mécanismes d’insertion / désinsertion du lithium conduisent à des variations volumiques importantes des particules de matériau actif lors du cyclage, à l’origine d’une détérioration rapide des performances électrochimiques. En combinant plusieurs techniques de caractérisation, les mécanismes de dégradation d’une électrode de silicium sont étudiés au cours du vieillissement. En utilisant en particulier la spectroscopie d’impédance électrochimique et des analyses par porosimétrie mercure, une véritable dynamique de la porosité de l’électrode est mise en évidence lors du cyclage. Un modèle de dégradation, mettant en cause principalement l’instabilité de la Solid Electrolyte Interphase (SEI) à la surface des particules de silicium, est proposé. Pour tenter de stabiliser cette couche de passivation et ainsi améliorer les performances électrochimiques des électrodes de silicium, l’influence de deux paramètres est étudiée : l’électrolyte et le « domaine de lithiation » du silicium, ce dernier paramètre étant associé à l’évolution de la composition du matériau actif lors du cyclage. A l’issue de ces travaux, des performances prometteuses sont obtenues pour des accumulateurs Li-ion comprenant une électrode de silicium. / The work presented here focuses on electrodes made of silicon, a promising material to replace graphite as an anode active material for Li-ion Batteries (LIBs). The first part of the manuscript is dedicated to the study of silicon (de)lithiation mechanisms by Auger Electron Spectroscopy (AES). By using this technique of surface characterization, which allows investigating individual particles in their electrode environment, our results show that the first silicon lithiation occurs through a two-phase region mechanism cr-Si / a-Li3,1Si, whereas the following (de)lithiation steps are solid solution type process. Upon (de)alloying with lithium, silicon particles undergo huge volume variations leading to a quick capacity fading. By combining several techniques of characterization, the failure mechanisms of a silicon electrode are studied during aging. In particular, by using electrochemical impedance spectroscopy and mercury porosimetry analyses, an impressive dynamic upon cycling of the electrode porosity is shown. A model, which mainly attributes the capacity fading to the Solid Electrolyte Interphase instability at the silicon particles surface, is proposed. To try to stabilize this passivation layer and thus improve silicon electrodes electrochemical performances, the influence of two parameters is studied: the electrolyte and the “lithiation domain” of silicon; the latter is associated with the evolution of the active material composition upon cycling. Finally, by using these last results, promising performances are obtained for silicon electrode containing LIBs.
237

Development of electrochemical sensors containing bimerallic silver and gold nanoparticles

Mailu, Stephen Nzioki January 2010 (has links)
Magister Scientiae - MSc / Polyaromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been shown to be teratogenic, mutagenic and carcinogenic and pose serious threats to the health of aquatic and human life. Several methods have been developed for their determination such as immunoassay, gas chromatography and high performance liquid chromatography (HPLC) in combination with fluorescence or absorbance detection. However, these methods are known to manifest underlying disadvantages such as complicated pretreatment, high costs and time consuming processes. In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles. Transmission electron microscopy showed that the synthesized nanoparticles were in the range of 20-50 nm. The properties of the composite formed upon deposition of the nanoparticles on the PPyox film were investigated by electrochemical methods. The PPyox/Ag-AuNPs/GCE sensor showed strong catalytic activity towards the oxidation of anthracene, phenanthrene and pyrene, and was able to simultaneously detect anthracene and phenanthrene in a binary mixture of the two. The catalytic peak currents obtained from square wave voltammetry increased linearly with anthracene, phenanthrene and pyrene concentrations in the range of 3.0 x 10-6 to 3.56 x 10-4 M,3.3 x 10-5 to 2.83 x 10-4 M, 3.3 x 10-5 to 1.66 x 10-4 M and with detection limits of 0.169 μM, 1.59 μM and 2.70 μM, respectively. The PPyox/Ag-AuNPs/GCE sensor is simple, has antifouling properties and is less time consuming with a response time of 4 s. / South Africa
238

The use of cyclodextrin template-based metal oxide nanomaterials in the development of electrochemical sensors for phenolic endocrine disruptor compounds

Masikini, Milua January 2010 (has links)
Magister Scientiae - MSc / Iron oxide nanoparticles were prepared using co-precipitation method in the presence and absence of beta-cyclodextrin β-CD). Such materials were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The TEM shows that the surface morphology has no difference between nanoparticles prepared in the presence and absence of beta-cyclodextrin β-CD), amorphous particles with high surface area and dimensions of about 100 nm by 500 nm. The amorphous states of nanoparticles are confirmed further by XRD. The ATR-FTIR analysis confirms inclusion complex between β-CD and nanoparticles. The nanoparticles synthesized were used to develop an electrochemical sensor for phenolic endocrine disruptors by modifying the surface area of glassy carbon electrode (GCE). Electrochemical characterization of the iron oxide β-CD nano-composites, studied in 0.1 M potassium chloride (KCl) using chronoamperometry,showed that the surface concentration of the adsorbed composite material was 8.5 x 10-8 mol/cm2. Sensor analysis of bisphenol A (BPA) was carried out using cyclic voltammetry (CV) and square wave voltammetry (SWV) based on amperometric techniques which gave a linear range of 0.50 × 10-6 M to 50 × 10-6 M; limit of detection of 0.156 x 10-6 M and order of magnitude of linearity of 2.03. Hence, the sensor was further used to study 4-tert-octylphenol (TOP); the results showed that the sensitivity and the limit of detection were 11.31 nA L/mol and 0.249 x 10-6 M, respectively and order of magnitude of linearity of 2.00. / South Africa
239

Protein phosphatase biosensor for the detection of cyanotoxins associated with algal bloom

Mniki, Nontle Catherine January 2013 (has links)
Magister Scientiae - MSc / The toxicity of microcystin is associated with the inhibition of serine/threonine protein phosphatases 1 and 2A, which can lead to hepatocyte necrosis and haemorrhage. Analysis of microcystin is most commonly carried out using reversed-phase high performance liquid chromatographic methods (HPLC) combined with ultra-violet (UV) detection .The ability of these techniques to identify unknown microcystin in environmental samples is also restricted by the lack of standard reference materials for the toxins. Highly specific recognition molecules such as antibodies and molecularly imprinted polymers (MIPs) have been employed in the pre-concentration of trace levels of microcystin from water and show great potential for the clean-up of complex samples for subsequent analysis. New biosensor technologies are also becoming available, with sufficient sensitivity and specificity to enable rapid ‗on-site‘ screening without the need for sample processing. In this work we constructed a Protein phosphatase biosensor for detection of microcystin-LR in aqueous medium, onto polyamic acid/graphene oxide (PAA: GO) composite electrochemically synthesised in our laboratory. The composites were synthesised at three different ratios i.e. 50:50, 80:20 and 20:80 to evaluate the effect of each component in the search to produce highly conductive mediator platforms. The electrochemistries of the three different composites were evaluated using CV and SWV to study interfacial kinetics of the materials as thin films at the glassy carbon electrode. The phosphatase biosensor parameters were evaluated using CV, SWV, EIS and Uv-vis spectroscopy. The affinity binding of the microcystin-LR to protein phosphatase 2A was investigated using electrochemical impedance spectroscopy which is a highly sensitive method for measuring interfacial kinetics of biosensor systems.
240

Electrochemical actuation potential of diaminophenazine linked pyrrole derivatives

Ward, Meryck January 2013 (has links)
>Magister Scientiae - MSc / A novel monomer (Phenazine-2,3-diimino(pyrrole-2-yl)–PDP) derived from the condensation reaction between 2,3-diaminophenazine and a pyrrole derivative has been synthesized as a hinge molecule in the design of a zig-zag polymer with actuation possibility. The monomer was polymerized chemically and electrochemically to produce the new polymer material – polymerized Phenazine-2,3-diimino(pyrrole-2-yl) PPDP. Two very crucial properties of a good actuator material, relate specifically to its solubility testing and electrical conductivity. The hinged polymer material was studied intensively in terms of its spectroscopy; Fourier Transform Infrared - FTIR, 1H’NMR, thermal properties (Differential Scanning Calorimetry-DSC and Thermogravimetric Analysis-TGA) as well as voltammetry and conductivity. Conductivity was evaluated using three different approaches including; 4 probe measurements, plotting of I/V curves based on potentiostatic measurements and an electrochemical impedance experiment using a dielectric Solartron interface. Electrochemical kinetics of the polymer prepared as a thin film at glassy carbon electrode (GCE) was also done and it was clear that the thin film conductivity was vastly different from the compressed pellet conductivity (thick film). The zig-zag polymer was then further modified by homogeneous inclusion of gold nanoparticles to improve conductivity and solubility, in the thick film arrangement. Conductivity of the thin film was studied by electrochemical impedance spectroscopy with the relative charge transfer values being determined for unmodified and modified polymer systems. The solubility testing of the material plays an important role as it is required for a wide range of experimental applications. The zig-zag polymer showed great promise for applications; in dye sensitized solar cells and free standing interpenetrating polymer network (IPN), solubility testing and electrical conductivity would need to be improved in order to be used in these applications.

Page generated in 0.0752 seconds