Master of Science / Department of Physics / Christopher M. Sorensen / An easier, cheaper and scalable method to obtain silver nanoparticles, AgNPs, directly from the bulk material has been obtained. Two different solvents were tried, water and ethylene glycol, the coating agent was polyvinylpyrrolidone, PVP, and two different silver sizes were used, micron size powder and silver shots, millimeter size. It was seen that changing the size of bulk silver, the temperature of reaction, the amount of oxygen, the concentration of PVP and its molecular weight all had an important influence in the synthesis of nanoparticles. Different morphologies could be obtained when these parameters were adjusted ranging from spheres to triangles and hexagons. A complex mechanism is proposed: during the first step, bulk silver is oxidized by oxygen in solution, forming a thin layer of oxidized silver on the surface. Then, PVP acts as a reducing agent at the oxidized surface, where silver becomes Ag⁰ again. At the same time that PVP reduces the oxidized silver back to metallic silver; it coordinates with the silver atoms acting as a protecting agent. That coordination between PVP and silver pulls out the atoms and produces a detachment of silver atoms from the bulk surface. These silver-PVP complexes in solution later combine to form silver nanospheres and evolve to rods first and then triangles and hexagon with longer reaction time.

After hydrolyzing zinc acetate in methanol solution, spherical ZnO nanoparticles in the size range from about 2.5 to 5 nm were synthesized by maintaining a ZnO concentration of 0.02M. Compared to ZnO nanoparticles prepared via other methods, the particles prepared using our novel colloidal chemistry exhibit narrow size distribution and a high sensitivity to the surrounding environment. The structure and composition of the white powders precipitated from the colloidal solution can vary, depending on how the powder samples are prepared. Factors such as desorption and adsorption of methanol, binding of water and exposure to humid air have been studied to correlate to the structure and composition observed from the precipitated powder. Methanol desorption rate and excess KOH on the particle surface have played an important role in the structural changes. Furthermore, upon annealing, the white precipitate is recovered to wurtize ZnO. XRD and TEM are used to study the structural transformation of ZnO nanoparticles.

No description available.

>Magister Scientiae - MSc / Nitric oxide (NO) plays a vital role as a biological messenger in biological systems. However, NO detection and quantification have always posed significant complications. There is, therefore, a need to develop new materials or technologies that can be used for sampling and determination of NO species in aqueous environments. The use of Schiff base complexes incorporated onto electrodes to make an electrochemical sensor has been explored as an effective method for the determination and quantification of NO in aqueous solutions. The motivation is based on the precedent of denatured cytochrome C as a suitable complexing site for electron-rich species. The ligands and metals complexes used in this work aim to mimic the square planar arrangement of Fe in denatured cytochrome. It is believed that the accessibility of the haem Fe in this configuration is at the heart of the analyte interactions leading to favourable signal transduction. In preparing the Schiff base and corresponding metal complexes, a microwave-assisted synthetic method, was employed. / 2025

The objectives of this project were to synthesise semi-conducting ceramic nanoparticles including zinc oxide (ZnO) and aluminium doped zinc oxide (AZO) through a wet chemistry route to obtain nanoparticles with a controlled size and morphology. Wet chemistry methods (co-precipitation method and hydrothermal method) were used to synthesise ZnO and AZO particles. In the synthesis, various compounds and morphologies were synthesised. ZnO, Zn(OH)2 and unknown phases were co-precipitated, with only ZnO obtained following hydrothermal treatment. Morphologies ranging from platelets, flower-like, nanorods and microflowers were obtained. Particle sizes as small as 11 nm were characterised. Nanorod and nanosphere AZO particles were also synthesised with the results indicated the average grain size decreasing with increasing Al atomic content. Three orthogonal arrays were carried out to investigate the effects of the reaction parameters on the size and morphology of ZnO particles. The applicability of the orthogonal array was successful, with the optimum parameters of both hydrothermal experiments showing an increase in aspect ratio. The L/D ratio of ZnO nanorods obtained in the confirmation experiment increased to 9.4 which was larger than the ZnO synthesised using other reaction conditions (1.0 8.0). Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were used to characterise the properties of the obtained particles. Morphology, crystallinity and particle size were all characterised.

L'utilisation de la thermoélectricité passe par une amélioration du rendement du module thermoélectrique à travers l'optimisation de ses dimensions et l'augmentation du facteur de mérite des matériaux thermoélectriques, mais aussi par une réduction des coûts de synthèse et de mise en forme. Dans le cadre de cette thèse nous nous sommes intéressés à la synthèse de β–Zn4Sb3 nanométrique par une méthode de chimie douce à faible dépense énergétique. Nous avons étudié la mise en forme de ce matériau par des technologies d'impression qui permettent d'atteindre les dimensions optimales et présentent un coût réduit. β-Zn4Sb3 est obtenu en deux étapes : une synthèse à reflux suivie d'un traitement thermique à 400°C sous vide secondaire. La composition chimique (DRX, affinement Rietveld), la morphologie (MEB, TEM) et la stabilité en température (spectroscopie Raman) de la poudre sont étudiées. β-Zn4Sb3 ainsi obtenu est densifié par SPS et ses propriétés thermoélectriques sont mesurées montrant une augmentation du facteur de mérite pour des températures inférieures à 100°C. Au dessus de cette température, la présence de porosité et de zinc augmente la résistivité électrique et la conductivité thermique et les échantillons ont un facteur de mérite de 0,6 à 400°C. Enfin, la poudre est mise en forme par sérigraphie et atomisation sur substrat en verre et en Kapton. Le β-Zn4Sb3 montre une forte résistivité électrique juste après impression mais l'application de traitement mécanique et thermique permet de la diminuer. Le facteur de mérite estimé des dépôts est de 0,06 à 400°C. Cependant le faible coût de mise en forme et la possibilité d'automatisation rendent ces techniques viables. / Use of thermoelectricy involves an increase of the module efficiency. In this purpose we need to optimize the dimension of the module and to increase the figure of merit of thermoelectric materials. But we also need to reduce the synthesis and shaping cost. Within the framework of this thesis, we focused on the synthesis of β-Zn4Sb3 nanoparticles by a low energy technique: wet chemistry. We also studied the shaping of this material by printing technologies. These cost-effective technologies allow reaching optimized dimensions. β-Zn4Sb3 is synthesized in two steps: a reflux synthesis flowed by a thermal treatment at 400 °C under vacuum. Chemical composition (XRD, Rietveld refinement), morphology (SEM, TEM) and thermal stability of the powder are studied. The as product β-Zn4Sb3 is densified by SPS and we measured its properties. They show an increase of the figure of merit for temperatures below 100 °C. However above this temperature the presence of zinc and porosity increase electric resistivity and thermal conductivity, leading to a figure of merit of 0.6 at 400 °C. Finally the powder is shaped by two printing technologies: screenprinting and atomization on glass and Kapton substrate. Just after printing the samples show a high electrical resistivity but a decrease is observed after mechanical and thermal treatment. The estimate figure of merit of printing β-Zn4Sb3 is 0.06 at 400 °C. However the printing techniques are cost-effective and allow mass production, which make them still interesting.

L'objectif principal de ce travail était l'étude systématique de plusieurs groupes de matériaux conducteurs protoniques: Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), Ba₂Nb₁₋ₓY₁₊ₓO₆₋₅, et BaZr₀.₈₅Y₀.₁₅O₃₋₅ (BZY15). Nous avons développé une voie de synthèse pour chaque groupe de matériaux tels que le procédé de combustion sol-gel, la synthèse lyophilisation et le procédé de complexation de citrate-EDTA modifié des nanopoudres pures et des céramiques denses ont été obtenus après ces synthèses suives d'un processus de frittage classique. La structure et la composition des produits obtenues ont été caractérisées par diffraction des rayons X (XRD) et microscopie électronique à balayage (MEB). La variation de la conductivité en fonction de la température a été étudiée par spectroscopie d'impédance, ainsi que la dépendance en fonction de pO₂ et pH₂O. Pour la famille de Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), nous avons étudié l'influence de la nature et la quantité de dopant sur les propriétés structurales et électriques. Les résultats indiquent une solution solide possible jusqu'à 10% de taux du substituant. Selon les observations au MEB, la taille des grains est augmente le taux de substitution. En ce qui concerne les propriétés électriques, nous avons constaté une augmentation de la conduction avec le taux de substitution. Tous les composés présentent une bonne stabilité en milieu humide, sous hydrogène et CO₂. Dans le cas des matériaux Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅, les propriétés physico-chimiques des matériaux synthétisés ont été caractérisées par la diffraction des rayons X et par MEB. La taille moyenne des grains a considérablement augmenté avec l'augmentation du taux de Y³⁺. Les propriétés de conduction ont été légèrement améliorées avec la substitution partielle de niobium par l'yttrium. La stabilité de Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ composés a été étudiée sous différentes atmosphères et conditions. Les propriétés de conduction ionique restent modestes ce qui a été explique par des simulations de dynamique moléculaire. Enfin, nous avons étudié l'influence d'emploi d'un additif ZnO et NiO lors de la synthèse de BZY15, les adjuvants de frittage pouvant être utilisés pour abaisser la température de frittage. L'oxyde de zinc comme un adjuvant de frittage permet de diminuer de 300 °C la température de frittage et d'augmenter légèrement la conduction ionique. / The main objective of the present work was the systematic study of several groups of materials: Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), Ba₂Nb₁₋ₓY₁₊ₓO₆₋₅, and BaZr₀.₈₅Y₀.₁₅O₃₋₅ (BZY15) as proton conductors. We developed a synthesis route for each group of materials such as sol-gel combustion method, freeze-drying synthesis and modified citrate-EDTA complexing method. Pure nanopowders and dense ceramics were obtained after these syntheses plus a classical sintering process. The structure and composition of the obtained products were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The temperature dependences of the conductivity were investigated by impedance spectroscopy as a function of pO₂ and pH₂O. For the family of Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), we studied the influence of dopant nature and content on the structural and electrical properties. Results indicate that the substitution possible till 10 % of doping content. According to the SEM observations, the grain size is increased with increasing dopant content. Concerning electrical properties, we found an increase of conduction with increasing dopant content. All compounds present a good stability in humid, hydrogen and CO₂ containing atmosphere. In case of Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ materials, the physico-chemical properties of synthesized materials have been characterized by the XRD and SEM techniques. The average grain size increased significantly with increasing amount of Y³⁺. Conduction properties were slightly improved with the partial substitution of niobium by yttrium. The stability of Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ compounds was investigated under different atmospheres and conditions. The ionic conduction in this case is quite low, which has been explained by futher molecular dynamics simulations. Finally, we studied the influence of an ZnO and NiO additives on the sintering of BZY15, being these sintering aids used to lower the sintering temperature. Zinc oxide as a sintering aid lowers the sintering temperature by 300 °C and slightly increases the bulk and total conductivity of BZY15.

The design of biomaterials, historically initiated and developed by physicians and engineers, in the last decades has slowly shifted toward a more biochemical based approach. For the replacement, repair and regeneration of tissues scientists are now focusing on materials that stimulate specific biological response at the molecular level. These biomaterials have already shown interesting applications in cell proliferation, differentiation, and extracellular matrix production and organization when the material modifications are designed to elicit specific interactions with cell integrins. In the present work we propose the application of this strategy for the development of blood-compatible materials. We first identified, in the coagulation cascade a key enzyme that constitute a valuable biological target for the development of anti-thrombogenic compounds. Piperazinyl-amide derivatives of N-alfa-(3-trifluoromethyl-benzenesulfonyl)-L-arginine were synthesized as graftable thrombin inhibitors. These inhibitors provided a spacer arm for surface grafting and a fluorine tag for XPS (X-ray photoelectron spectroscopy) detection. The possible disturbance of biological activity due to a variable spacer-arm fixed on the N-4 piperazinyl position was evaluated in vitro against human alfa-thrombin, in silico by molecular modelling and via X-ray diffraction study. Selected inhibitors, having inhibition potency in the mM range, were grafted on polyesters surface via wet chemistry and photochemical activation treatments. Wet chemistry surface grafting was performed by specific hydroxyl chain-ends activation and resulted in bioactive molecules fixation of 20-300pmol/cm2. The photochemical grafting was performed using a molecular clip providing an aromatic azide, for nitrene insertion into a polymer, and an activated ester for grafting of tag compounds. This grafting technique resulted in a dramatic increase in fixed bioactive signals (up to nmol/cm2). The material blood-compatibilization induced by the surface fixation of the inhibitors, was measured by a static blood clot weight measurement test. The wet chemistry grafting technique resulted in moderate blood-compatibilization while by the photochemical grafting method important decrease in surface blood clot formation was observed. In the latter case, the blood response to material contact was found to be strongly affected by the polyester surface photo-degradation induced by the activation treatment.

The design of biomaterials, historically initiated and developed by physicians and engineers, in the last decades has slowly shifted toward a more biochemical based approach. For the replacement, repair and regeneration of tissues scientists are now focusing on materials that stimulate specific biological response at the molecular level. These biomaterials have already shown interesting applications in cell proliferation, differentiation, and extracellular matrix production and organization when the material modifications are designed to elicit specific interactions with cell integrins. In the present work we propose the application of this strategy for the development of blood-compatible materials. We first identified, in the coagulation cascade a key enzyme that constitute a valuable biological target for the development of anti-thrombogenic compounds. Piperazinyl-amide derivatives of N-alfa-(3-trifluoromethyl-benzenesulfonyl)-L-arginine were synthesized as graftable thrombin inhibitors. These inhibitors provided a spacer arm for surface grafting and a fluorine tag for XPS (X-ray photoelectron spectroscopy) detection. The possible disturbance of biological activity due to a variable spacer-arm fixed on the N-4 piperazinyl position was evaluated in vitro against human alfa-thrombin, in silico by molecular modelling and via X-ray diffraction study. Selected inhibitors, having inhibition potency in the mM range, were grafted on polyesters surface via wet chemistry and photochemical activation treatments. Wet chemistry surface grafting was performed by specific hydroxyl chain-ends activation and resulted in bioactive molecules fixation of 20-300pmol/cm2. The photochemical grafting was performed using a molecular clip providing an aromatic azide, for nitrene insertion into a polymer, and an activated ester for grafting of tag compounds. This grafting technique resulted in a dramatic increase in fixed bioactive signals (up to nmol/cm2). The material blood-compatibilization induced by the surface fixation of the inhibitors, was measured by a static blood clot weight measurement test. The wet chemistry grafting technique resulted in moderate blood-compatibilization while by the photochemical grafting method important decrease in surface blood clot formation was observed. In the latter case, the blood response to material contact was found to be strongly affected by the polyester surface photo-degradation induced by the activation treatment.

Ce travail se concentre sur le développement de systèmes catalytiques capable d’oxyder complètement le méthane à basse température. Le sujet principal concerne la conception d'une nouvelle génération de catalyseurs à base de palladium qui sont résistants aux composés soufrés et à l'eau.<p>Notre objectif a été atteint grâce à l'utilisation d'un support oxyde mixte produit par sol-gel. En effet, nos catalyseurs de palladium supporté sur un oxyde de silicium dopé au titane se sont révélés être résistants à l’empoisonnement au soufre et présentent des performances élevées pour la conversion du méthane.<p>En variant les quantités de TiO2, il a été montré que les performances atteignent un maximum pour une composition en masse de 10% TiO2. Les analyses structurelles et de surface ont montré que nos supports mixtes contiennent des liens Ti-O-Si. Nous pensons que ces liens sont responsables de l’activité accrue du catalyseur.<p>Par ailleurs, les catalyseurs contenant du titane présentent une tolérance supérieure vis-à-vis du SO2 lorsque celui-ci est ajouté aux réactifs ou que le catalyseur est exposé à une atmosphère de SO2 pur à 350°C pendant 15 heures. Nous avons mis en évidence par XPS que les sites Ti-O-Si sont également responsables de cette tolérance aux composés soufrés. Ceci est accompli par l'insertion du SO2 dans le support qui forme des liens soit Ti-O-SOx•••Si soit Si-O-SOx•••Ti. L’analyse XPS a également montré que sur le long terme, l’exposition au SO2 conduit à la formation d’une couche de PdSO4 de 18 à 20 Å. Étonnamment, les catalyseurs sont capables de récupérer entièrement leur activité initiale après ce traitement. Cette régénération se produit grâce à un mécanisme concerté avec le méthane permettant la décomposition totale du PdSO4. Par ailleurs, des études en présence d'eau ont montré que ces propriétés restent inchangées.<p>L'état du palladium a également été étudié et nous a permis de prouver qu’une activation/stabilisation du catalyseur est nécessaire. Celle-ci est réalisée en présence des réactifs par de légères modifications chimiques du support et de la phase de palladium. En effet, l'augmentation de l'activité du catalyseur a été corrélée avec une augmentation des quantités de Ti3+ et Pd0. La présence de palladium métallique dans le catalyseur semble être l'élément clé dans l'activation des liaisons C-H.<p>Enfin, nous avons étudié l'influence de la taille/la dispersion des particules de palladium sur la vitesse de réaction. L'utilisation de synthèses en phase liquide nous a permis de produire des solutions colloïdales de particules de palladium avec des tailles contrôlées. Cette étude a révélé que la combustion du méthane est une réaction sensible à la structure. Néanmoins, un meilleur contrôle de la forme des nanoparticules devrait être réalisé pour déterminer les facteurs structurels influençant la réaction./ The present work focuses on the development of highly efficient catalytic systems able to completely oxidize methane at low temperature in order to comply with modern environmental legislation. The main subject concerns the design of a new generation of palladium-based catalysts that are sulfur and water resistant. <p>Our goal was achieved through the use of a mixed oxide support produced by sol-gel. In fact, palladium-supported on titanium-doped silica catalysts have proven to be sulfur tolerant and exhibit high performances for the methane conversion. <p>Varying the amounts of TiO2 showed that the performance reached an optimum for a 10 wt.% TiO2 loading. According to the structural and surface analyses, the mixed oxides contained Ti-O-Si linkages, believed to be responsible for the better activity as compared to PdO supported on pure oxides. <p>Moreover, the titania-containing catalysts exhibited a superior tolerance towards SO2 when either adding it to the reactants or feeding it as a pure pretreatment atmosphere at 350°C (15 hour on stream). We evidenced using XPS that the Ti-O-Si sites are also responsible for the higher sulfur tolerance of the catalysts by the insertion of SO2 in the support forming either Ti-O-SOx•••Si or Si-O-SOx•••Ti. XPS analyses also evidenced that the long-term SO2-treatment leads to the formation of PdSO4 with a thickness of 18 to 20 Å. However, the catalysts can entirely recover their initial activity after this treatment. This regeneration was proven to be occurring through a concerted mechanism with methane leading to the total decomposition of PdSO4. Moreover, studies in presence of water showed that these properties remained unchanged.<p>The state of the palladium was also investigated and allowed us to evidence that an activation/stabilization of the catalyst is necessary. This is achieved in presence of the reactants by slight and subtle changes in both the support and the palladium phase. The increase of the catalyst activity was correlated with an increase of Ti3+ and Pd0 fractions. The presence of metallic palladium in the catalyst seems to be the key element in the activation of the C-H bonds. <p>Finally, we have studied the influence of the size/dispersion of the palladium particles on the reaction rate. The use of wet-chemistry synthesis allowed us to produce colloidal solutions of palladium with controlled particles sizes. This study revealed that the methane combustion is a structure sensitive or demanding reaction. Nevertheless, a better control of the shape of the nanoparticles should be achieved to determine the structural factor influencing the reaction.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished