The discovery of an unexpectedly large thermopower accompanied by low resistivity and low thermal conductivity in NaxCoO2 raised significant research interest in these materials and let to a number of experimental and theoretical investigations. This interest has strongly been reinforced by the discovery of superconductivity in the hydrated compound Na0.35CoO2 •1.3H2O in 2003, and thus, NaxCoO2 experiences an again increasing attention. The similarity of the Na cobaltates to the high temperature superconductors (HTSC) - both are transition metal oxides and adopt a layered crystal structure with quasi-two-dimensional (Cu,Co)O2 layers - is an important aspect of the research activities. In contrast to the HTSC cuprates however, the CoO2 layers consist of edge sharing CoO6 octahedra which are distorted in such a way that the resulting local symmetry is trigonal. The trigonal coordination of the Co sites results in geometric frustration which favours unconventional electronic ground states. The geometrically frustrated CoO2 sublattice also exists in the nonhydrated parent compound NaxCoO2, which has been investigated in this work. The intercalation of water into the parent compound is expected to have little effect on the Fermi surface beside the increase in two dimensionality due to the effect of expansion. Upon lowering the symmetry from cubic to trigonal, the t2g states split into states with eg_and a1g symmetry. Measurements of polarisation and temperature dependent soft X-ray absorption have been performed on a wide doping range of NaxCoO2 single crystals. Beside the Co L_2,3-edges, the O K-edge and the Na K-edge have been measured. These measurements show strong polarisation dependencies especially for the excitations into the lower lying a1g energy level. In addition to that, also an unexpected polarisation dependence for higher energies has been observed, which should be absent in trigonal symmetry. These results point towards a deviation of the local trigonal symmetry of the CoO6 octahedra, which is temperature independent in a temperature range between 25 K and 372 K. This deviation was found to be different for Co3+ and Co4+ sites, which leads to a polaronic electron transport. Furthermore, a strong hybridisation between the Co and O ions has been found. In order to shed further light on the electronic structure of NaxCoO2, the electronic spectrum of a CoO6 cluster has been calculated including all interactions between 3d orbitals as well as hopping processes between Co and O and O and O ions. The ground state for two electronic occupations in the cluster (i.e. Co3+ and Co4+) that correspond nominally to all O in the O−2 oxidation state, and Co+3 or Co+4 has been obtained. Then, all excited states obtained by promotion of a Co 2p electron to a 3d electron, and the corresponding matrix elements are calculated. A fit of the observed experimental spectra is good and points out a large Co-O covalence and cubic crystal field effects, that result in low spin Co 3d configurations. The results indicate that the effective hopping between different Co atoms plays a major role in determining the symmetry of the ground state in the lattice. Remaining quantitative discrepancies with the XAS experiments are expected to come from composition effects of itineracy in the ground and excited states. Beside these points, results of photoemission spectroscopy, magnetisation measurements as well as resonant and non-resonant X-ray diffraction using high energy X-rays are shown and discussed. / Die Entdeckung unerwartet großer Thermokraft bei gleichzeitigem niedrigem Widerstand und niedriger thermischen Leitfähigkeit in NaxCoO2 führte zu einem großen wissenschaftlichem Interesse an diesen Materialien und zu einer großen Anzahl an experimentellen und theoretischen Arbeiten. Dieses Interesse steigerte sich noch einmal nach der Entdeckung von Supraleitung in der hydrierten Verbindung Na0.35CoO2 •1.3H2O im Jahre 2003. Die Ähnlichkeit der Na Kobaltate zu den Hochtemperatur-Supraleitern (HTSL) – beides sind Übergangsmetalloxide mit einer geschichteten Kristallstruktur in der quasi zwei dimensionale (Cu,Co)O2 Ebenen enthalten sind – ist ein wichtiger Aspekt moderner wissenschaftlicher Arbeiten. Im Gegensatz zu den HTSL Kupraten bestehen die CoO2 Ebenen aus CoO6 Oktaedern die über ihre Kanten verbunden sind und in der Art verzerrt sind, dass die resultierende Symmetrie trigonal ist. Die trigonale Anordnung der Co Plätze führt zu einer geometrischen Frustration und unkonventionellen elektronischen Grundzuständen. Diese geometrisch frustrierten CoO2 Untergitter existieren ebenfalls in den nicht hydrierten Mutterverbindungen NaxCoO2, welche in dieser Arbeit untersucht wurden. Interkalierung von Wasser in die Mutterverbindung hat nur einen kleinen Einfluss auf die Fermi Oberfläche und führt zu einem Anstieg des zwei dimensionalen Charakters durch den Effekt der Ausdehnung. Durch Verminderung der Symmetrie von kubisch zu trigonal splitten die vormals entarteten t2g Zustände auf in Zustände mit eg und a1g Symmetrie. Zur Bestimmung der elektronischen Struktur von NaxCoO2 wurden polarisations- und temperaturabhängige Messungen der Röntgenabsorption im weichen Röntgenbereich für einen großen Dotierungsbereich durchgeführt. Neben den Co L_2,3-Kanten wurden auch die O K-Kante und die Na K-Kante gemessen. Sie zeigen eine starke Polarisationsabhängigkeit speziell für Anregungen in die niederenergetischen a1g Level. Zusätzlich wurde eine unerwartete Polarisationsabhängigkeit bei höheren Energien gefunden, die für trigonalen Symmetrie so nicht auftauchen dürfte. Diese Ergebnisse weisen auf eine Abweichung von der lokalen trigonalen Symmetrie der CoO6 Oktaeder hin, welche Temperatur unabhängig ist in einem Temperaturbereich zwischen 25 und 372 Kelvin. Diese Abweichung ist unterschiedlich für Co3+ und Co4+ Ionen was wiederum auf einen polaronischen Transport hinweist. Zusätzlich wird deutlich, dass eine starke Co-O Hybridisierung existieren muss. Um weiteres Informationen über die elektronische Struktur von NaxCoO2 zu erhalten, wurde das elektronische Spektrum eines CoO6 Oktaeders berechnet in dem alle Wechselwirkungen zwischen 3d Orbitalen sowie Hüpfprozesse zwischen Co und O sowie O und O Ionen enthalten sind. Der Grundzustand für zwei elektronische Besetzungen in einem Cluster (d.h. Co3+ und Co4+) wurde bestimmt für O Ionen mit einer nominellen O-2 Oxidation sowie Co3+ und Co4+ Ionen. Im angeregten Zustand werden die entsprechenden Anregungen eines Co 2p Elektrons in einen unbesetzten 3d Zustand berücksichtigt und die entsprechenden Matrixelemente berechnet. Ein Fit an den experimentellen Daten ist gut und weist auf eine starke Co-O Kovalenz und auf einen starken Einfluss des kubischen Kristallfeldes hin, der zu einer Low-Spin Co 3d Konfiguration führt. Die Ergebnisse zeigen, dass ein effektives Hüpfen zwischen benachbarter Co Ionen eine große Rolle für die Symmetrie des Grundzustandes im Gitter spielt. Quantitative Unterschiede zwischen den experimentellen und theoretischen Daten kommen anscheinend von itineranten Effekten im Grund- und angeregten Zustand. Zusätzlich zu den oben kurz beschriebenen Ergebnissen werden in dieser Arbeit weitere Ergebnisse der Photoemissionsspektroskopie, der Magnetisierung sowie aus resonanter und nicht resonanter Röntgenbeugung mit harter Röntgenstrahlung gezeigt und diskutiert.

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No. of bitstreams: 1 curcio_al_me_rcla.pdf: 1672370 bytes, checksum: fd59b862449a04ac385f3661da6430f3 (MD5) Previous issue date: 2016-02-29 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Nanocristais tem sido extensivamente investigados nos últimos anos devido à sua ampla gama de aplicações em vários dispositivos tais como sensores, células solares, lasers, fotocatalisadores, fotodetectores, detectores de infravermelhos, diodos emissores de luz, materiais eletroluminescentes e outros materiais emissores de luz. Semicondutores nanocristalinos apresentam propriedades eletrônicas intermediárias entre aqueles de estrutura molecular e sólidos macrocristalinos, proporcionando uma ampla gama de aplicações. Entre estes materiais, o sulfeto de zinco (ZnS) puro ou dopado tem recebido notável atenção por causa de suas propriedades estruturais ópticas, versatilidade e potencial para várias aplicações tecnológicas. O ZnS é um típico semicondutor II-VI, com um gap direto de 3,6 eV à temperatura ambiente e aproximadamente 40 meV de energia de gap, sendo um bom material luminescente utilizado em telas, sensores e lasers. Como material de gap largo, o ZnS pode facilmente hospedar diferentes metais de transição como centros luminescentes. Entre estes íons de metais de transição para estruturas dopadas, os íons Cu2+e Mn2+ são atraentes pelas emissões de luz características e por apresentarem propriedades eficientes para aplicações como luminóforos. A inserção desses íons na estrutura do ZnS proporcionam defeitos que resultam em emissão no verde para os íons Cu2+e emissão no laranja para os íons Mn2+. Neste estudo, as amostras de ZnS pura e dopadas com Cu2+ e Mn2+ foram preparados pelo método solvotermal, que demonstra ser um processo eficaz para preparar nanopartículas. Uma vez preparadas, as estruturas das amostras nanoestruturadas foram caracterizadas e correlacionada s com propriedades fotoluminescentes. Os resultados de difração de raios X mostram que as amostras de ZnS foram cristalizadas completamente sem a presença de fases secundárias e os difratogramas correspondem à estrutura blenda cúbica de zinco com grupo espacial F-43m. Os espectros de XANES (X-ray Absorption Near Edge Structure) teóricos e experimentais na borda K do Zn indicam que a incorporação de átomos de Mn na matriz ZnS causam a formação de vacâncias de Zn e S, a qual é confirmada por ajustes de espectros EXAFS (Extended X-ray Absorption Fine Structure). Estas vacâncias estão relacionadas com um desvio para o vermelho observado no pico do espectro de fotoluminescência devido a adição de Mn na estrutura do ZnS. Para o ZnS puro, o pico é centrado em ~ 504 nm, relativo as vacâncias de S na amostra nanoestruturada. À medida que se aumenta a porcentagem de Mn na matriz ZnS, uma emissão no amarelo-laranja centrada em ~ 590 nm pode ser observada, associada com a transição 4T1-6A1 no interior de níveis 3d de Mn2+. A adição de íons Cu2+ ao ZnS resulta em um alargamento no pico do espectro de fotoluminescência decorrente de emissão no azul-verde, que está relacionada a recombinação de elétrons de níveis de defeitos mais profundos dos estados t2 do Cu próximos da banda de valência. / Nanocrystals has been extensively investigated in recent years due to its wide range of applications in various devices light emitting materials such as sensors, solar cells, lasers, photocatalysts, photodetectors, IR detectors, light emitting diodes and others. Nanocrystalline Semiconductors have electronic properties between those intermediate molecular macrocristalinos and solid structure, providing a wide range of applications. Among these materials, zinc sulfide (ZnS) pure or doped has received considerable attention because of its optical structural properties, versatility and potential for several technological applications. The ZnS is a typical II-VI semiconductor with a direct band gap of 3.6 eV at room temperature and about 40 meV in energy gap, and a good luminescent material for constrution of displays, lasers and sensors. As wide band gap material, ZnS can easily host different transition metals as luminescent centers. Among these ions of transition metal doped structures, Cu2+ and Mn2+ ions are attractive for light emission characteristics and for having effective properties for applications such as phosphors. The addition of these ions in ZnS structure provide defects that result in emission in the green for the Cu2+ ions and emission in orange for the Mn2+ ions. In this study, samples of pure ZnS and doped with Cu2+ and Mn2+ ions were prepared by solvotermal method, which demonstrate to be an effective process for preparing nanoparticles. Once prepared, the structures of the nanostructured samples were characterized and correlated with photoluminescent properties. The results of X-ray diffraction showed that the ZnS samples were completely crystallized without the presence of secondary phases and XRD patterns correspond to the structure of zinc blende to cubic space group F-43m. spectra XANES (X-ray Absorption Near Edge Structure) theoretical and experimental in the Zn K edge indicates that the inclusion of Mn atoms in the ZnS matrix cause the formation of Zn and S vacancies, which is confirmed by spectral adjustments EXAFS (Extended X-ray Absorption Fine Structure). These vacancies are associated with a red shift observed in the photoluminescence spectrum peak due to the addition of Mn in ZnS structure. For pure ZnS, the peak is centered at ~ 504 nm concerning the vacancies in the S nanostructured sample. As it increases the percentage of Mn in the ZnS matrix, in yellow-orange emission centered at ~ 590 nm can be observed, associated with the transition 4 T1- 6A1 inside 3d levels of Mn2+. Adding Cu2+ to the ZnS results in a broadening of the peak of the photoluminescence spectrum due to emission in blue-green, which is related to recombination deeper defect levels of electrons of t2 Cu states near the valence band.

Made available in DSpace on 2016-06-02T19:56:50Z (GMT). No. of bitstreams: 1 5035.pdf: 2696735 bytes, checksum: 1e1df725e495abb44c7ceab896e17284 (MD5) Previous issue date: 2013-03-12 / Universidade Federal de Sao Carlos / Particle size effect and Ce addition on the catalytic properties of Cu/Al2O3catalysts were investigated for the water gas shift reaction (WGS). The catalysts were prepared by dry impregnation of an aqueous solution of nitrates of the respective metals on alumina, synthesized by sol-gel method. Samples were prepared with 5, 10 and 15% w/w of metallic copper and 12% w/w of CeO2. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR) spectroscopy, X-ray absorption (XAS). The WGS reaction was performed with reagents ratio of H2O:CO = 1:3 with temperature range from 200 to 350° C. The crystallites CuO were not detected by XRD. As the Cu content increased, the crystallite size of CeO2 decreased with a fluorite type structure from 7.4 to 3.4 nm. The results of TPR showed that the interaction Cu-O-Al was crucial to reduce temperature and ceria addition on the catalysts did not affect the temperature reduction of the CuO. The XANES in situ results along the WGS reaction showed that metallic Cu predominated and ceria was partially reduced. EXAFS results showed that the Cu particle size increased from 0.65 to 0.91 nm with an increased load of copper from 5 to 15%, respectively. After the reduction, step prior to reaction, the catalysts were not completely reduced. The degree of reduction increased with the Cu particle size and it was also dependent on the temperature and the oxidation potential of mixing of the reactants. The addition of ceria did not change the degree of reduction of samples Cu/Al2O3. The results suggest that the Cu particles have a reduced Cu core covered with an oxide layer. The catalytic activity increased as the Cu particle size decreased, which can be associated with the presence of the redox couple Cu+/Cu0. This provides a possibility of CO oxidation and its reoxidation due to water activation. The ceria addition also increased catalytic activity and it is probably attributed to activation of the water on the surface of ceria, followed by transfer of oxygen from its structure to the oxidation of CO in an interface Cu-CeO2. / O efeito do tamanho da partícula de Cu e a adição de céria nas propriedades catalíticas dos catalisadores de Cu/Al2O3 foram investigados para a reação de deslocamento gás água (WGS). Os catalisadores foram preparados por impregnação da solução alcoólica dos respectivos nitratos dos metais em alumina, sintetizada pelo método sol-gel. As amostras foram preparadas com teores de Cu de 5, 10 e 15% m/m e 12% m/m de CeO2. Os catalisadores foram caracterizados por difração de raios X (DRX), redução a temperatura programada (TPR) e espectroscopia de absorção de raios X (XAS). A reação de WGS foi realizada com a razão de reagentes H2O:CO = 3:1 em temperaturas entre 200 e 350ºC . Os cristalitos de CuO não foram detectados por DRX. Com o aumento do teor de Cu de 5 para 15% m/m verificou-se um decréscimo no tamanho de cristalitos de CeO2 com uma estrutura do tipo fluorita de 7,4 para 3,4 nm. A interação Cu-O-Al foi determinante na temperatura de redução dos catalisadores e a adição da céria não afetou a temperatura da redução do CuO. Os resultados de XANES in situ mostraram que ao longo da reação de WGS o Cu na forma metálica foi predominante e a céria encontrava-se parcialmente reduzida. Os resultados de EXAFS mostraram que o tamanho das partículas de Cu aumentou de 0,65 para 0,91nm com o aumento do teor do cobre de 5 para 15%, respectivamente. Após a etapa de redução que antecede a reação, os catalisadores não se encontraram completamente reduzidos. O grau de redução aumentou com o tamanho da partícula de Cu e mostrou-se dependente também da temperatura e do potencial de oxidação da mistura dos reagentes. A adição da céria não modificou o grau de redução das amostras de Cu/Al2O3. Tais resultados sugerem que as partículas de cobre apresentam um núcleo reduzido com óxido de cobre na superfície. A atividade catalítica aumentou com a diminuição do tamanho de partícula de Cu, o que pode estar associado à maior presença do par redox Cu+/Cu0 nas menores partículas. Este possivelmente proporciona a oxidação do CO, reduzindo o Cu+ ao Cu0 e a reoxidação ocorre devido à ativação da água. A adição da céria também aumentou a atividade catalítica, a qual foi atribuída provavelmente à ativação da água nas vacâncias de oxigênio da céria, seguida da transferência de oxigênio de sua estrutura para a oxidação do CO em uma interface Cu-CeO2.

Les batteries lithium ions sont la technologie de référence pour le stockage électrochimique de l’énergie. Cependant, les matériaux cathodiques de ces batteries comme LiCoO2, LiMn2O4 ou LiFePO4 présentent une capacité spécifique limitée (<160 mAh/g). De nombreux composés sont à l’étude pour améliorer cette performance dont le fluorure de fer (III) en raison de sa capacité théorique de 711 mAh.g-1. Ce travail présentera la synthèse de FeF3 par différentes méthodes de fluoration. Les matériaux obtenus seront comparés en termes de structures et de liaison (DRX, Mössbauer, spectroscopies IR et Raman) mais aussi de texture (isothermes d’adsorption à l’azote à 77K). Les propriétés électrochimiques des matériaux obtenus seront également comparées et testées. Enfin, l’étude du mécanisme électrochimique de cette famille de composés sera menée via une méthode de caractérisation « in operando » : la spectroscopie d’absorption des rayons X (XAS). / The lithium-ion batteries are the current solution for electrochemical energy storage. However, their performances are limited by the cathode materials, such as LiCoO2, LiMn2O4 or LiFePO4 of specific capacity lower than 160 mAh/g. Many materials are good candidates to improve this capacity such as iron trifluoride of theoretical capacity of 711 mAh.g-1. This work will present the synthesis of FeF3 through different fluorination ways. The resulting materials will be characterized owing to their structure by XRD, Mössbauer, Raman and IR spectroscopies and their texture by nitrogen adsorption isotherms at 77K and SEM. After that, the electrochemical properties will be evaluated and compared. Finally, the study of the electrochemical mechanism of this family of compounds will be led with a method of characterization “in operando” : the X-rays absorption spectroscopy (XAS).

Les métaux lourds et les radionucléides sont présents dans différents écosystèmes du monde à cause de contaminations naturelles ou des activités anthropiques. L’utilisation de micro-organismes pour restaurer ces écosystèmes pollués, processus connu sous le nom de bioremédiation, suscite beaucoup d’intérêt, spécialement aux pH proches de la neutralité. Les minéraux de fer qui encroûtent les bactéries neutrophiles du fer, notamment les Oxydes de Fer Biogéniques (BIOS en anglais), ont une structure très faiblement cristalline, qui en plus de leur grande surface et réactivité font d’eux d’excellents supports pour le piégeage de polluants inorganiques. Dans cette thèse nous avons étudié les différents mécanismes de piégeage de l’uranium uranium par la bactérie neutrophile Sphaerotilus natans, choisie comme modèle bactérien de micro-organismes du fer capables de filamenter en formant des gaines. S. natans peut croître sous forme de cellules individuelles ou formant des filaments. Ces derniers ont été utilisés pour étudier la biosorption d’U(VI) et sa sorption sur les BIOS. De plus, la sorption d’U(VI) sur les analogues abiotiques de ces minéraux de fer a été testée. Afin d’utiliser les filaments de S. natans pour piéger l’U(VI), il était nécessaire d’identifier les facteurs induisant la filamentation de S. natans. L’influence de l’oxygène a été établie en utilisant des techniques de biologie moléculaire et nos résultats ont démontré que tandis qu’en condition d’oxygène saturé elle croît sous forme de cellules individuelles, une diminution modérée d’oxygène à ~ 3 mg O2.L-1 la fait croître sous la forme désirée, des filaments de S. natans.Les BIOS attachés aux filaments de S. natans ainsi que ses analogues abiotiques ont été analysés pas XAS au seuil K du Fe. Les deux matériaux identifiés sont des phosphates de fer(III) amorphes avec une faible proportion de fer(II), qui présentent une réactivité élevée pour le piégeage de polluants inorganiques. L’EXAFS au seuil LIII de l’U a montré la même structure pour les couches O, tandis que celles P, Fe et C étaient différentes en fonction des sorbants. Une étude intégrée qui combine des techniques expérimentales avec des calculs de spéciation a permis de décrire les isothermes d’adsorption de l’U(VI) en utilisant un modèle de complexation de surface. Ces résultats suggèrent que les groupes phosphoryles et carboxyles sont les groupes fonctionnels principaux pour la biosorption d’U(VI) par des filaments de S. natans. Les résultats de cette thèse vont aider à comprendre les processus contrôlant l’immobilisation de l’U(VI), soit par la biosorption sur S. natans, la sorption sur les BIOS ou la sorption sur les phosphates de fer, et en conséquence le devenir de l’U en conditions neutres / Heavy metals and radionuclides are present in some ecosystems worldwide due to natural contaminations or anthropogenic activities. The use of microorganisms to restore those polluted ecosystems, a process known as bioremediation, is of increasing interest, especially under near-neutral pH conditions. Iron minerals encrusting neutrophilic iron-related bacteria, especially Bacteriogenic Iron Oxides (BIOS), have a poorly crystalline structure, which in addition to their large surface area and reactivity make them excellent scavengers for inorganic pollutants. In this PhD work we studied the different mechanisms of uranium scavenging by the neutrophilic bacterium Sphaerotilus natans, chosen as a model bacterium for iron-related sheath-forming filamentous microorganisms. S. natans can grow as single cells and filaments. The latter were used to investigate U(VI) biosorption and U(VI) sorption onto BIOS. In addition, uranium sorption onto the abiotic analogues of such iron minerals was assessed. In order to use S. natans filaments for U(VI) scavenging, it was necessary to identify factors inducing S. natans filamentation. The influence of oxygen was ascertained by using molecular biology techniques and our results revealed that while saturated oxygen conditions resulted in single cell growth, a moderate oxygen depletion to ~ 3 mg O2.L-1 led to the desired filamentous growth of S. natans. BIOS attached to S. natans filaments as well as the abiotic analogues were analysed by XAS at Fe K-edge. Both materials were identified as amorphous iron(III) phosphates with a small component of Fe(II), with a high reactivity towards scavenging of inorganic pollutants. In addition, EXAFS at the U LIII-edge revealed a common structure for the O shells, while those for P, Fe and C were different for each sorbent. An integrated approach combining experimental techniques and speciation calculations made it possible to describe U(VI) adsorption isotherms by using a surface complexation model. These results suggested the role of phosphoryl and carboxyl groups as the main functional groups involved in the U(VI) biosorption by S. natans. The results of this PhD work will help to better understand the processes governing U(VI) immobilization, either by S. natans biosorption, sorption onto BIOS or sorption onto iron phosphates, an thus the fate of uranium in near-neutral pH environments

Im Rahmen dieser Arbeit wurde die Wechselwirkung von halophilen Mikroorganismen mit Uran unter Verwendung verschiedener spektroskopischer, mikroskopischer und molekularbiologischer Methoden untersucht. Ausgewählte Vertreter halophiler Mikroorganismen waren dabei das moderat halophile Bakterium Brachybacterium sp. G1 sowie zwei extrem halophile Archaea der Gattung Halobacterium. Für das extrem halophile Archaeon H. noricense DSM15987T wurde auch die Wechselwirkung mit den trivalenten Metallionen Europium und Curium untersucht. Es konnte festgestellt werden, dass die Bioassoziation von Uran durch das untersuchte Bakterium und die beiden Archaea in unterschiedlicher Art und Weise erfolgte. Für den niedrigeren Urankonzentrationsbereich (30 - 50 μM) konnte für das moderat halophile Bakterium der Prozess der Biosorption nachgewiesen werden, welcher nach 2 h abgeschlossen war. Mittels in situ ATR FT-IR war ausschließlich die Anbindung von Uran an Carboxylgruppen detektierbar. Die Assoziation desselben Radionuklids an die Zellen der beiden extrem halophilen Archaea erfolgte im Gegensatz dazu in einem mehrstufigen Prozess. Dieser ist bisher in der Literatur nach bestem Wissen nur einmal für ein Bakterium beschrieben. Der mehrstufige Prozess ist gekennzeichnet durch eine erste kurze Assoziationsphase von einer Stunde, gefolgt von einer Freisetzung des Urans in die umgebende Lösung. Nach dieser vierstündigen Desorptionsphase setzte ein erneuter Assoziationsprozess ein. Bei höheren Urankonzentrationen (85 - 100 μM) wurde mit zunehmender Kontaktzeit mehr Uran assoziiert, ohne dass Desorptionsprozesse erkennbar waren. Um den mehrstufigen und konzentrationsabhängigen Assoziationsprozess von Uran an H. noricense DSM15987T auf molekularer Ebene aufzuklären, wurden Fluoreszenzmikroskopie, Elektronenmikroskopie gekoppelt mit EDX – Analyse sowie in situ ATR FT-IR, TRLFS und XAS komplementär eingesetzt und diese mikroskopischen und spektroskopischen Methoden durch die molekularbiologische Methode der Proteomik ergänzt. Mikroskopisch konnte eine Agglomeration der Zellen detektiert werden. Diese war mit zunehmender Inkubationszeit sowie bei höherer Urankonzentration stärker ausgeprägt. Mit den spektroskopischen Methoden konnte die Anbindung von Uran an carboxylische Funktionalitäten nachgewiesen werden. Zusätzlich war eine Phosphatspezies, strukturell analog dem U(VI) Mineral Meta-Autunit, nachweisbar. Die Fraktionsanalyse zeigt, dass bei niedriger Urankonzentration diese Phosphatspezies dominant ist. Demgegenüber überwiegt bei einer höheren Urankonzentration die carboxylische Spezies. Dies kann mit der verstärkten Agglomeration und der damit einhergehenden Freisetzung von EPS, wozu auch carboxylische Funktionalitäten in Form von verschiedenen Zuckerderivaten gehören, erklärt werden. Eine Bestätigung der Bildung eines Uran-Phosphat-Minerals erfolgte mit TEM/EDX. Die erhaltenen spektroskopischen und mikroskopischen Nachweise des Uran-Phosphat-Minerals konnten auch erstmalig mit molekularbiologischen Ergebnissen in Übereinstimmung gebracht werden. Dabei war mit Hilfe der Proteomik eine Uran-induzierte Änderung der Expression von Enzymen des Phosphatmetabolismus nachweisbar. Zusätzlich wurde die Interaktion von H. noricense DSM15987T mit trivalenten Metallen untersucht. Dabei kam das radioaktive Element Curium und sein analoges Lanthanid Europium zum Einsatz. Es konnte festgestellt werden, dass es sich bei der Assoziation von Europium, anders als beim Uran, nicht um einen mehrstufigen Prozess handelt. Jedoch ist auch hier nicht von einer reinen Biosorption auszugehen, da die Assoziation relativ langsam erfolgt. Mit TRLFS konnten drei zellassoziierte Spezies extrahiert werden. Durch den Vergleich mit Referenzspektren fand eine Zuordnung zu einer phosphatischen und einer carboxylischen Spezies statt. Bei der Assoziation von Curium an das halophile Archaeon konnten zwei Spezies identifiziert werden, welche allerdings auf Grund der geringen Anzahl an vorhandenen Referenzspektren nicht eindeutig zugeordnet werden konnte. Mit der vorliegenden Arbeit konnte gezeigt werden, dass die bisher in der Literatur noch nicht beschriebene Kombination von spektroskopischen, mikroskopischen und molekularbiologischen Methoden zur Aufklärung der Uraninteraktion mit Mikroorganismen notwendig ist. So können stattfindende Prozesse zusätzlich durch eine veränderte Proteinexpression erklärt werden. Zusammenfassend ist zu sagen, dass die Art und Weise der Wechselwirkung eines Radionuklids mit einem Mikroorganismus stark vom jeweiligen Mikroorganismus abhängt. Daher ist es zukünftig wichtig die unter Endlagerbedingungen aktiven dominanten Vertreter zu identifizieren, um daraus resultierend die bedeutenden Stoffwechselwege abzuleiten und letztendlich thermodynamische Daten für die Sicherheitsanalyse zu generieren. Das in dieser Arbeit untersuchte Bakterium wird aufgrund seiner geringen Salztoleranz, trotz seiner starken Biosorption des Urans, eher eine untergeordnete Rolle für das Migrationsverhalten der Radionuklide im Salzgestein spielen. Demgegenüber sind Halobacterium Spezies auf Grund ihrer hohen Salztoleranz und ihres ubiquitären Vorkommens in weltweiten Salzvorkommen ein dominanter Mikroorganismus in Steinsalz. Die untersuchten extrem halophilen Archaea tragen dabei zu einer Immobilisierung des Urans (z. Bsp. durch Biomineralisierung und Bioreduktion) und somit zur Rückhaltung von im Salzgestein freigesetzten Radionukliden bei. Inwiefern diese Transformationsprozesse auch für andere sechswertige Actinide wie PuO22+ und NpO22+ zutreffen, muss in weiteren Experimenten geklärt werden.

Nuclear energy can be used to reliably generate large quantities of electricity while providing minimal lifetime CO2 emissions. Given the extreme importance of safety in the nuclear industry, it is necessary to have a fundamental understanding of the materials used throughout the nuclear fuel cycle. It is of particular to importance to develop an understanding of these materials at an atomic level. In this thesis, X-ray absorption spectroscopy (XAS), along with several other X-ray based techniques, has been used to study materials that are produced or proposed for use in the nuclear fuel cycle. Uranium mining and milling operations generate large quantities of waste, known as mine and mill tailings. At their McClean Facility in Northern Saskatchewan, AREVA Resources Canada disposes of the tailings waste using the JEB Tailings Management Facility (TMF). AREVA monitors the mineralization of elements of concern (i.e., Ni, As, Fe, Mo, Ra, and U) within the TMF as part of its on-going commitment towards managing the facility’s environmental impact. Molybdenum (Mo) is predicted to mineralize as insoluble powellite (CaMoO4) within the TMF. However, no experimental evidence confirmed the presence of powellite in the TMF. In Chapter 2, the presence of powellite, and other Mo-bearing minerals, was determined using powder X-ray diffraction (XRD), X-ray fluorescence imaging, and Mo K-edge XAS. The results of this study confirmed that powellite was present in the TMF and showed that Mo K-edge XAS was the only effective way to detect the Mo minerals within the TMF. New materials for use as nuclear fuels were also investigated in this thesis. Spent nuclear fuel must be securely stored for long periods of time due to the presence transuranic elements (TRU; i.e., Pu, Am, Np, Cm), and the use of inert matrix fuels (IMF), which consist of actinides embedded in a neutron transparent (inert) material, have been proposed for to “burn-up” or transmute these TRU species. Stabilized ZrO2 materials have been proposed for use in IMF applications, and in Chapter 3 the thermal stability of a series of NdxYyZr1-x-yO2-\delta materials made by a ceramic synthetic route have been studied using powder XRD, scanning electron microscopy (SEM), and X-ray absorption spectroscopy. (Nd was used as a surrogate for Am.) The results of this study showed that the fluorite structure of the NdxYyZr1-x-yO2- \delta materials was stabilized when y >= 0.05, and that the local environment around Zr was independent of composition or annealing temperature. The effect of synthetic method on the thermal stability of the NdxYyZr1-x-yO2-\delta materials was also determined, and this is the subject of Chapter 4. In this study a series of NdxY0.25-xZr0.75O1.88 materials were synthesized using a low-temperature co precipitation synthesis, and these then annealed at 1400 °C and 1500 °C. The as-synthesized and annealed materials were characterized by powder XRD, SEM, and XAS. This study confirmed that the thermal stability of the materials was dependent on synthetic method, and that materials made using a solid-state method were superior to those produced by a solution-based approach. Y-stabilized zirconia has a low thermal conductivity, which is not ideal for a nuclear fuel. The thermal conductivity could be increased if a lighter cation, such as Sc, was used to stabilize the fluorite structure. In Chapter 5, the thermal stability of a series of NdxScyZr1-x-yO2-\delta materials was investigated. The as-synthesized and annealed materials were studied by powder XRD, SEM, and XAS. These results showed that the fluorite structure was only stable in the annealed materials when x+y >= 0.15 and y >= 0.10. The results of this study provided insight into the possible use of scandia-stabilized zirconia for use as an inert matrix fuel. This studies presented in this thesis have used X-ray absorption spectroscopy and a number of other techniques to characterize materials important to the nuclear fuel cycle. The studies presented here were only possible because of the unique information that can be obtained using XAS. This thesis serves to highlight the importance of XAS as a technique and how it can be applied to solve problems related to the material science of the nuclear fuel cycle.

Diluted magnetic semiconductor oxides (DMSOs) have received great attention recently due to their outstanding applications in optoelectronic and spintronic devices. Ever since the initial observation of ferromagnetism at room temperature in cobalt-doped titania, extensive effort is concentrated on preparation of transition metal doped wide band gap semiconductors, especially Mn- doped ZnO. Compared to Mn-doped ZnO, magnetic interactions in SnO! and In!O! semiconductors have been underexplored. SnO! and In!O! semiconductors have many applications, owing to their high charge carrier density and mobility as well as high optical transparency. Investigation on electronic structure changes induced by dopants during the synthesis procedure can effectively influence magnetic interactions between charge carriers. In this work, a combination of structural and spectroscopic methods was used to probe as-synthesized SnO! and In!O! nanocrystals doped with Mn!! and Mn!! as precursors. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy are powerful techniques to explore formal oxidation state of manganese dopant, electronic environment, number of nearest neighbors around the absorbent, and bond lengths to the neighboring atoms. Analysis reveals the presence of multiple oxidation states in the doped nanocrystals, and establishes a relation between !"!! ratio and expansion or contraction of lattice parameters. !"!! Although doping semiconductors are crucial for manipulating the functional properties, the influence of dopants on nanocrystals structure is not well understood. Nanocrystalline films prepared from colloidal Mn-doped SnO! and In!O! nanocrystals through spin coating process exhibit ferromagnetic behavior in temperatures ranging from 5 K to 300 K. Magnetic transformation from paramagnetic in free-standing Mn-doped nanocrystals to strong ferromagnetic ordering in nanocrystalline films is attributed to the formation of extended structural defects, e.g., oxygen vacancies at the nanocrystals interface. Magnetic circular dichroism (MCD) studies clearly show that Mn!! occupies different symmetry sites in indium oxide, when bixbyite and rhombohedral In!O! nanocrystals (NCs) are compared.

Dehydrogenation is the catalytic process of removing hydrogen from a saturated hydrocarbon to produce an olefin. Olefins are important feedstocks for the petrochemical industry and can potentially be used to produce fuels through oligomerization. Alloys containing an active metal such as platinum and palladium and a non-catalytic metal offer improved selectivity towards the olefin. This body of work seeks to further the understanding of how heteroatomic bonds in alloys change the rate and selectivity of alloy catalysts used for dehydrogenation.In the first study, a series of Pt-V bimetallic catalysts are synthesized, which are highly selective propane dehydrogenation catalysts. The bimetallic nature of the nanoparticles was verified by in-situX-ray Absorption Spectroscopy(XAS)and the formation of the Pt3V alloy phase was shown by in-situ synchrotronX-ray Diffraction(XRD). A reduction-oxidation differenceXASmethod was used to examine the surface stoichiometry and found that a shell layer of the alloy phase forms when the particles are platinum rich. Electronic modification of Pt was studied by Pt L3edgeX-ray Absorption Near Edge Structure(XANES),X-ray Photoelectron Spectroscopy(XPS), Resonant Inelastic X-ray Scattering (RIXS)andDensity FunctionalTheory(DFT). The spectral changes observed were shown to be due to changes in the energy of the filled and unfilled 5d density of states, and not due to electron transfer. The electronic modifications cause a weakening of adsorbate binding and destabilization of deeply dehydrogenated hydrocarbons, which contributes to the dehydrogenation selectivity.In the second study, alloys between palladium and five different promoters were synthesized and tested as propane dehydrogenation catalysts.The structure ofthe alloy catalysts was characterized by in-situ XAS and in-situ synchrotron XRD.Zinc and indium form alloy structures with site isolated palladium, while gallium, iron and manganese do not. All of the alloys have improved propane dehydrogenation selectivity compared to monometallic palladium. The propylene production turnover rate of the alloys increased by almost an order of magnitude compared to monometallic Pd, but among the alloys the turnover ratesonly varied by a factor of two despite the different structures and electronic modifications inherent to each phase. The site isolated alloys had higher propylene selectivity than those that were not site isolated. The site isolated alloys showed strongerelectronic modification: both in binding strengths and in Pd projected Density of States (pDOS)by DFT than did the non-site isolated alloys. The commonly used computational selectivity descriptor for dehydrogenation, which is the difference in energy between alkene desorption and alkene C-H bond activation energy correctly predicts that the site isolated alloys will have high selectivity but shows weaker trends for alloys without site isolation. A modified selectivity descriptor, involving the C-C bond breaking barrier in the adsorbed alkyne more accurately reflects the high selectivity of the non-site isolated alloys.In a third study,RIXS and XPSare used to examine trends in the electronic modification of platinum alloys with transition metal and post transition metal promoters. All alloys show an increase in the energy transfer maximum, showing that alloying modifies energy the filled and unfilled density of states. The increase in the energy transfer maximum in platinum alloys with 3d metals islargerfor early transition metals, which by DFT show larger shifts in the d-band center. The post transition elements showsignificantlylarger shifts than to the transition elements, partially due to the lack of orbital overlap between the valence p orbitals and Pt 5d orbitals. Platinum has the same number of valence d electrons regardless of promoter or structure, and redistribution of the 5d electron energy brought about by heteroatomic bonds leads to the observed electronic modifications. The positive binding energy shifts measured by XPS reflect these energy changes, which occur due to changes in the Fermi energy of the alloy, initial state effects and intra and extra atomic relaxation (final state effects). The calculated initial state effect shift is correlated to descriptors of the valence d band, such as the d band center.

Ce travail de thèse a pour but d'explorer de nouveaux matériaux de type structural Tavorite et de revisiter certains déjà bien connus. Dans un premier temps, les synthèses de compositions ciblées ont été réalisées selon des procédures variées (voies tout solide, hydrothermale, céramique assistée par sol-gel, broyage mécanique) afin de stabiliser d'éventuelles phases métastables et d'ajuster la microstructure impactant fortement les performances électrochimiques de tels matériaux polyanioniques. Ces matériaux ont ensuite été décrits en profondeur, dans leurs états originaux, depuis leurs structures moyennes, grâce aux techniques de diffraction (diffraction des rayons X sur poudres ou sur monocristaux et diffraction des neutrons) jusqu'aux environnements locaux, en utilisant des techniques de spectroscopie (résonance magnétique nucléaire à l'état solide, absorption des rayons X, infra-rouge et Raman). Par la suite, les diagrammes de phases et les processus d'oxydoréduction impliqués pendant l'activité électrochimique des matériaux ont été étudiés grâce à des techniques operando (diffraction et absorption des rayons X). La compréhension des mécanismes impliqués pendant le cyclage permet de mettre en évidence les raisons de leurs limitations électrochimiques : La synthèse de nouveaux matériaux (composition, structure, microstructure) peut maintenant être développée afin de contrepasser ces limitations et de tendre vers de meilleures performances / This PhD work aims at exploring new Tavorite-type materials and at revisiting some of the well-known ones. The syntheses of targeted compositions were firstly performed using various ways (all solid state, hydrothermal, sol-gel assisted ceramic, ball milling) in order to stabilize eventual metastable phases and tune the microstructure impacting strongly the electrochemical performances of such polyanionic compounds. The materials were then described in-depth, at the pristine state, from their average long range structures, thanks to diffraction techniques (powder X-rays, single crystal X-rays and neutrons diffraction), to their local environments, using spectroscopy techniques (solid state Nuclear Magnetic Resonance, X-rays Absorption Spectroscopy, Infra-Red and/or Raman). Thereafter, the phase diagrams and the redox processes involved during electrochemical operation of the materials were investigated thanks to operando techniques (SXRPD and XAS). The in-depth understanding of the mechanisms involved during cycling allows to highlight the reasons of their electrochemical limitations: the synthesis of new materials (composition, structure and microstructure) can now be developed to overcome these limitations and tend toward better performance.