Nanomatériaux à base de magnésium et de métaux de transition pour un stockage efficace de l'hydrogène. Le magnésium est un élément de choix pour le stockage de l’hydrogène à l’état solide en raison de sa grande abondance dans la croûte terrestre et de ses fortes capacités de sorption massique et volumétrique de l’hydrogène. Cependant, la réaction de sorption souffre d'une cinétique lente et l'hydrure formé est trop stable pour des applications fonctionnant sous conditions ambiantes. Le premier problème peut être résolu en développant des composites associant deux hydrures, MgH2 et TiH2, à l'échelle nanométrique. Ces matériaux sont synthétisés par broyage mécanique sous atmosphère réactive. Cette technique permet la formation des nanocomposites et leur hydrogénation en une seule étape. De plus, ces matériaux peuvent être produits à grande échelle pour les besoins des applications. Les travaux ont été menés en trois parties : i) l’optimisation de la teneur en TiH2 dans le système (1-y)MgH2+yTiH2. Ceci a été accompli en ajustant la teneur en titane (0,0125 ≤ y ≤ 0,3 mole), tout en conservant une bonne cinétique, une réversibilité de l'hydrogène et une durée de vie utile. Les données montrent que la valeur y = 0,025 offre le meilleur compromis pour développer les propriétés les plus adéquates; ii) l'extension à d’autres métaux de transition pour le système 0,95MgH2 + 0,05TMHx (TM: Sc, Y, Ti, Zr, V et Nb), en évaluant la contribution de chaque additif sur la cinétique, sur la réversibilité de l'hydrogène et sur la durée de vie en cyclage; iii) la conception d'un dispositif de cyclage automatique capable de réaliser des centaines de sorption/désorption dans le but de mesurer la durée de vie des hydrures métalliques. Le travail a été effectué à l'aide de nombreuses méthodes expérimentales. Pour la synthèse, le broyage réactif sous atmosphère d'hydrogène a été principalement utilisé. La structure cristalline et la composition chimique des nanomatériaux ont été obtenues à partir de l'analyse par diffraction des rayons X (DRX). La taille et la morphologie des particules ont été déterminées par microscopie électronique à balayage et spectroscopie de rayons X à dispersion d'énergie (SEM / EDS). Les propriétés thermodynamiques, cinétiques et cycliques de la sorption d'hydrogène ont été déterminées par la méthode de Sieverts / Mg/transition-metal nanomaterials for efficient hydrogen storageMagnesium metal is a prominent element for solid-state hydrogen storage due to its large abundance in earth’s crust and its high weight and volumetric hydrogen uptakes. However, hydrogen sorption suffers from sluggish kinetics and the formed hydride is too stable for applications working under ambient conditions. The former issue can be solved by developing composites combining two hydrides, MgH2 and TiH2 at the nanoscale. These materials are synthesized by mechanical milling under reactive atmosphere. By this technique, the formation of nanocomposites and their hydrogenation can be obtained in a single-step. Moreover, these materials can be produced at large scale for application purposes. The work focused on three topics: i) the optimization of the TiH2 content in the (1-y) MgH2+yTiH2 system. This was accomplished by optimizing the titanium content (0.0125≤y≤0.3 mole), while keeping good kinetics, hydrogen reversibility and cycle-life. The data show that y=0.025 is the best compromise to fulfill the most practical properties; ii) the extension to other transition metals for the system 0.95MgH2+0.05TMHx (TM: Sc, Y, Ti, Zr, V and Nb), evaluating the contribution of each additive to kinetics, hydrogen reversibility and cycle-life; iii) the conception of an automatic cycling device able to carry out hundreds of sorption cycles whit the aim of measuring the cycle-life of metal hydrides. The work was done using manifold experimental methods. For synthesis, reactive ball milling under hydrogen atmosphere was primarily used. The crystal structure and the chemical composition of nanomaterials was determined from X-ray diffraction (XRD) analysis. Particle size and morphology were obtained by Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS). Thermodynamic, kinetic and cycling properties toward hydrogen sorption were determined by the Sieverts method

Um suporte catalítico superparamagnético nanoestruturado do tipo \"core-shell\" constituído de núcleos de magnetita revestidos por sílica, obtido por uma microemulsão reversa, foi utilizado como plataforma para o ancoramento de cátions de metais de transição que serviram como precursores na obtenção de nanopartículas de Rh(0), Pt(0) e Ru(0). A superfície do suporte de sílica foi funcionalizada com um aminosilano que permitiu um aumento significativo na quantidade dos íons metálicos sequestrada das soluções aquosas dos sais dos metais estudados. Os nanocatalisadores foram empregados em reações de hidrogenação de alquenos e cetonas em fase líquida e puderam ser facilmente separados pela aplicação de um campo magnético, que foi realizada pelo contato de um imã de neodímio com a parede do reator contendo o catalisador e o produto. A técnica de separação magnética utilizada foi capaz de isolar completamente o sólido da fase líquida, fazendo com que a utilização de outros métodos de separação como filtração e centrifugação, comumente utilizados em sistemas heterogêneos líquidos, fossem completamente dispensados. As reações de hidrogenação foram realizadas utilizando-se hidrogênio molecular como agente redutor e dispensou a utilização de agentes redutores mais drásticos como hidretos metálicos que não atendem aos princípios verdes em demanda na nossa sociedade.Todos os sólidos catalíticos desenvolvidos mostraram uma excelente possibilidade de reutilização que comprovou a estabilidade da fase ativa do catalisador, destaca-se a hidrogenação do benzeno pelo catalisador magnético de Rh(0) que pôde ser utilizado por até 20 vezes (número total de rotação igual a 10.240), sem queda significativa de atividade, com freqüência de rotação chegando a 1.167 h-1. A ocorrência de lixiviação de espécies cataliticamente ativas, que é comum em catálise heterogênea em fase líquida, não foi observada nas reações de hidrogenação estudadas. Este fato pode ser atribuído às condições reacionais brandas utilizadas, à forte aderência das nanopartículas metálicas ao suporte funcionalizado com grupos NH2 e ao eficiente método de separação magnética empregado. O procedimento de separação catalisador-produto, além de não fazer uso de métodos físicos de separação mais agressivos como uma centrifugação, permitiu o isolamento dos componentes dentro do próprio reator, descartando a exposição do catalisador à condições atmosféricas e o uso de solventes extras durante o procedimento de separação. / A core-shell superparamagnetic catalytic support comprised of magnetite nanoparticles recovered by silica was obtained using a reverse microemulsion. The material was used as a framework for anchoring transition metal cations that were used for the fabrication of Rh(0), Pt(0) and Ru(0) nanoparticles. The catalysts were employed in the hydrogenation of alkenes and ketones in liquid phase and they showed to be easily recoverable from liquid systems by placing a small neodymium magnet on the reactor wall. The magnetic separation technique provided a complete isolation of the catalyst from the liquid phase containing the products. It also made the use of other separation techniques, commonly used in achieving product separation in liquid-solid heterogeneous systems, such as filtration and centrifugation completely unnecessary. The surface of the silica support was modified with an aminosilane leading to a substantial increasing in the metal uptake from aqueous solutions of Rh, Pt and Ru salts. The hydrogenation reactions were carried out using molecular hydrogen as the reducing agent and they did not require any drastic reducers such as metal hydrides that would go against the principles of green chemistry. The stability of the catalysts were evidenced by the outstanding recycling properties. A single portion of the Rh0 catalyst for instance could be used for up to 20 times in the hydrogenation of benzene (TON: 10,240), and no significant loss in the catalytic activity was observed giving TOF values of up to 1167 h-1. Leaching of active catalytic species which is commonly encountered in heterogeneous solid-liquid systems was also absent in the hydrogenation reactions studied and this finding can be attributed to the mild reaction conditions used, the adherence of Rh, Pt and Ru nanoparticles to the magnetic support functionalized with NH2- groups and the efficient magnetic separation method used in isolating the product that dismiss the use of extra solvents and more aggressive separation methods such as a centrifugation.

Nanocatalysis has emerged in the last decades as an interface between homogeneous and heterogeneous catalysis, offering simple solutions to problems that conventional materials have not been able to solve. In fact, nanocatalyst design permits to obtain structures with high superficial area, reactivity and stability, and at the same time presenting good selectivity and facility of separation from reaction mixtures. In this work, we prepared hybrid structures comprising gold, palladium and silver nanoparticles (Au, Pd and Ag NPs), titanate nanosheets (TixO2), graphene oxide (GO), and partially reduced graphene oxide (prGO). We focused on bi- and tri-components hybrids, namely TixO2, M/(pr)GO and M/TixO2/(pr)GO (M = Au, Pd or Ag) and developed facile, versatile and environment-friendly preparation methods with an emphasis on control over physicochemical features such as size, shape and composition. In order to exploit the catalytic applications, we employed the reduction of 4-nitrophenol as a model reaction, followed by visible-light assisted oxidation of p-aminothiophenol (PATP). With these tests, we unraveled metal-support interactions and cooperative effects that render hybrid structures superior to their individual counterparts. / A nanocatálise surgiu nas últimas décadas como uma interface entre catálise homogênea e heterogênea, oferecendo soluções simples a problemas que os materiais convencionais não conseguiram resolver. De fato, o design de nanocatalisadores permite obter estruturas com grande área superficial, reatividade e estabilidade, e ao mesmo tempo apresentando boa seletividade e facilidade de separação de misturas reacionais. Neste trabalho apresentamos a preparação de estruturas híbridas compostas por nanopartículas de ouro, paládio e prata (Au, Pd e Ag NPs), nanofolhas de titanato (TixO2), óxido de grafeno (GO) e óxido de grafeno parcialmente reduzido (prGO). Focamos em híbridos do tipo M/TixO2, M/(pr)GO e M/TixO2/(pr)GO (M = Au, Pd ou Ag) e desenvolvemos métodos de preparação simples, versáteis e ambientalmente amigáveis, com ênfase no controle sobre tamanho, forma e composição. Para explorar as potencialidades catalíticas utilizamos a redução do 4-nitrofenol como reação modelo, e em seguida a oxidação assistida por luz do p-aminotiofenol (PATP). Com esses testes, investigamos interações metal-suporte e efeitos cooperativos que tornam as estruturas hibridas superiores a cada um dos materiais que as compõem.

This dissertation is directed towards the fundamental understanding of the controlled synthesis of noble-metal (silver, gold, and palladium) and metal oxide (manganese and copper oxide) nanostructures as well as their applications in heterogeneous and plasmonic catalysis. In the first part of this work (Section 1), we provided a general background concerning the science of controlled nanomaterials, their syntheses, properties, and applications in catalysis and plasmonic catalysis. Then, we describe and developed a series of protocols for the synthesis of these nanomaterials with controlled sizes and structures (spheres, cubes, rods, shells, flowers, dendrites, and tadpoles), mainly focusing on the mechanistic understanding of their formation and how physical and chemical parameters (size, shape, composition, surface morphology) may influence/modify their catalytic properties (Sections 2 and 3). In Section 4, we turned our attention for the design of simple protocols for the synthesis of advanced nanomaterials that are interesting for green catalytic transformations applications. In this case, we envisioned the use of MnO2-Au nanomaterials (nanowires and nanoflowers) displaying several properties (unique pore structure, high surface area, ultrasmall Au NPs at the surface, high concentration of oxygen vacancies and Auδ+ species, strong metal-support interactions, and uniform shapes and sizes) that are desirable for catalyzing a series of green oxidation reactions in mild conditions (low temperatures and molecular oxygen or atmospheric air as the oxidants). In Section 5, we have demonstrated that catalysis and optical properties can be merged together to improve catalytic processes, the so called-plasmonic catalysis. This allowed us the use of visible light as the energy input to drive chemical transformations in mild conditions and then provide new insights regarding the various factors that affect SPR-mediated catalytic activities in plasmonic nanostructures. Finally, in Section 6, we focused our attention on how important is to introduce both nanoscience and the synthesis/characterization of nanomaterials having controlled physicochemical features to undergraduate students. Specifically, we have described simple laboratory experiments for the synthesis of nanomaterials (gold nanospheres and Cu(OH)2/CuO nanowires) displaying uniform sizes and shapes in order to investigate and explain their optical properties, catalytic activities and formation mechanisms. / Não consta resumo na publicação.

Nanoscale materials usually present strikingly different properties in comparison with their bulk counterparts, such as quantum size effects, surface plasmon resonance (SPR). To explore new properties as well as for novel applications, nanomaterials are being extensively investigated. This project investigates the interactions of electromagnetic fields with nanoscale materials, particularly gold nanoparticles (GNPs), over a wide range of frequency bands, including static field, 261 kHz, 13.56 MHz, 2.45 GHz, millimetre wave, THz, and the visible light. Especially, the efforts have been devoted to the study of heating effect of GNPs in association with potential biomedical applications. To explain the electromagnetic heating of GNPs, dielectric properties of GNP dispersions has been studied from 100 MHz to 20 GHz, as well as in the millimetre wave and THz ranges. The static field induced effects on the size distribution of GNPs has also been examined using ultra-violet spectroscopy and correlated to SPR. It has been revealed that purified GNPs cannot increase the specific absorption rate substantially at whichever frequency points of 261 kHz, 13.56 MHz, or 2.45 GHz. However, a greater temperature rise has been observed in the impurified GNP dispersions compared to deionisedwater, after 10 min RF treatment at 13.56 MHz. The measurements on dielectric properties show that impurified samples have much higher effective conductivity than that of deionised-water, while the conductivity change of purified ones is very small and not detectable within the measurement accuracy. This observation supports that the heating effect of GNP dispersions is mostly contributed by the impurities and disproves that GNPs can increase the specific absorption rate significantly. The magnetic field heating at 261 kHz suggests that GNPs have very weak magnetic properties. It has been found that a static field can change the size distribution of GNPs. Up to 2 THz, it is measured that the dielectric properties of GNP dispersions have no convincing change compared to deionised-water, implying that the electromagnetic heating of GNP below 2 THz may be insignificant. In addition, it is confirmed that GNPs have strong absorption in the visible light range due to SPR.

Nanocatalysis has emerged in the last decades as an interface between homogeneous and heterogeneous catalysis, offering simple solutions to problems that conventional materials have not been able to solve. In fact, nanocatalyst design permits to obtain structures with high superficial area, reactivity and stability, and at the same time presenting good selectivity and facility of separation from reaction mixtures. In this work, we prepared hybrid structures comprising gold, palladium and silver nanoparticles (Au, Pd and Ag NPs), titanate nanosheets (TixO2), graphene oxide (GO), and partially reduced graphene oxide (prGO). We focused on bi- and tri-components hybrids, namely TixO2, M/(pr)GO and M/TixO2/(pr)GO (M = Au, Pd or Ag) and developed facile, versatile and environment-friendly preparation methods with an emphasis on control over physicochemical features such as size, shape and composition. In order to exploit the catalytic applications, we employed the reduction of 4-nitrophenol as a model reaction, followed by visible-light assisted oxidation of p-aminothiophenol (PATP). With these tests, we unraveled metal-support interactions and cooperative effects that render hybrid structures superior to their individual counterparts. / A nanocatálise surgiu nas últimas décadas como uma interface entre catálise homogênea e heterogênea, oferecendo soluções simples a problemas que os materiais convencionais não conseguiram resolver. De fato, o design de nanocatalisadores permite obter estruturas com grande área superficial, reatividade e estabilidade, e ao mesmo tempo apresentando boa seletividade e facilidade de separação de misturas reacionais. Neste trabalho apresentamos a preparação de estruturas híbridas compostas por nanopartículas de ouro, paládio e prata (Au, Pd e Ag NPs), nanofolhas de titanato (TixO2), óxido de grafeno (GO) e óxido de grafeno parcialmente reduzido (prGO). Focamos em híbridos do tipo M/TixO2, M/(pr)GO e M/TixO2/(pr)GO (M = Au, Pd ou Ag) e desenvolvemos métodos de preparação simples, versáteis e ambientalmente amigáveis, com ênfase no controle sobre tamanho, forma e composição. Para explorar as potencialidades catalíticas utilizamos a redução do 4-nitrofenol como reação modelo, e em seguida a oxidação assistida por luz do p-aminotiofenol (PATP). Com esses testes, investigamos interações metal-suporte e efeitos cooperativos que tornam as estruturas hibridas superiores a cada um dos materiais que as compõem.

This dissertation is directed towards the fundamental understanding of the controlled synthesis of noble-metal (silver, gold, and palladium) and metal oxide (manganese and copper oxide) nanostructures as well as their applications in heterogeneous and plasmonic catalysis. In the first part of this work (Section 1), we provided a general background concerning the science of controlled nanomaterials, their syntheses, properties, and applications in catalysis and plasmonic catalysis. Then, we describe and developed a series of protocols for the synthesis of these nanomaterials with controlled sizes and structures (spheres, cubes, rods, shells, flowers, dendrites, and tadpoles), mainly focusing on the mechanistic understanding of their formation and how physical and chemical parameters (size, shape, composition, surface morphology) may influence/modify their catalytic properties (Sections 2 and 3). In Section 4, we turned our attention for the design of simple protocols for the synthesis of advanced nanomaterials that are interesting for green catalytic transformations applications. In this case, we envisioned the use of MnO2-Au nanomaterials (nanowires and nanoflowers) displaying several properties (unique pore structure, high surface area, ultrasmall Au NPs at the surface, high concentration of oxygen vacancies and Auδ+ species, strong metal-support interactions, and uniform shapes and sizes) that are desirable for catalyzing a series of green oxidation reactions in mild conditions (low temperatures and molecular oxygen or atmospheric air as the oxidants). In Section 5, we have demonstrated that catalysis and optical properties can be merged together to improve catalytic processes, the so called-plasmonic catalysis. This allowed us the use of visible light as the energy input to drive chemical transformations in mild conditions and then provide new insights regarding the various factors that affect SPR-mediated catalytic activities in plasmonic nanostructures. Finally, in Section 6, we focused our attention on how important is to introduce both nanoscience and the synthesis/characterization of nanomaterials having controlled physicochemical features to undergraduate students. Specifically, we have described simple laboratory experiments for the synthesis of nanomaterials (gold nanospheres and Cu(OH)2/CuO nanowires) displaying uniform sizes and shapes in order to investigate and explain their optical properties, catalytic activities and formation mechanisms. / Não consta resumo na publicação.

There is a considerable interest in the use of tungsten oxide in the research and development of new materials and devices, such as gas sensors and as photocatalysts. In order to improve the photocatalytic properties of WO3, its combination with metals which allows the preparation of WMxOy materials are believed to be promising photocatalysts under visible light. The present work deals with the synthesis of homo- and hetero-metallic tungsten alkoxide and amide compounds using the single source precursor approach for potential chemical vapour deposition precursors of mixed-metal oxide films.

Fluorescent carbon dots are a new class of carbon nanomaterials that have emerged recently, and have created a lot of interest as a potential competitor to classical semiconductor quantum dots. Carbon dots possess low toxicity, biocompatibility, easy and low-cost synthesis, and good optical properties. They show huge potential as novel and versatile nanomaterials for a wide range of applications such as bioimaging, drug delivery, chemical sensing, photocatalysis, and as sensitizers for photovoltaic solar cells. The main motivation for this research was the need to produce non-toxic, low-cost nanomaterials with good optical and electrical properties for the use in the fabrication of sustainable, inexpensive nanostructured solar cells with good efficiency. The main aims and objectives of this PhD research were: to synthesize fluorescent carbon dots from biomass-derived precursors by using the hydrothermal synthesis method, to understand and explain structural and optical properties of the as-synthesized carbon dots, and to use the carbon dots as sensitizers for nanostructured solar cells. Carbon dots (CDs) were synthesized using hydrothermal synthesis method from polysaccharides (chitosan and chitin), monosaccharide (D-glucose), amino acids (L-arginine and L-cysteine), and from real food waste in the form of lobster shells. Carbon dots were thoroughly characterized to obtain the information about their structural and optical properties. The as-synthesized carbon dots showed polydispersity and quasi-spherical morphology, with particle sizes ranging from 5-17 nm. Carbon dots showed predominantly amorphous nature, and the functional groups from the starting precursors were successfully incorporated into the as-synthesized carbon dots. Diluted solutions of carbon dots were transparent under daylight and showed blue-green photoluminescence emission under UV excitation. All carbon dots showed excitation-dependent photoluminescence emission which was more pronounced for excitation wavelengths larger than 320 nm. Chitosan CDs, L-cysteine CDs and lobster CDs also showed excitation-independent emission for excitation wavelength in the range of 200 - 320 nm. The highest fluorescence quantum yield of (43.3 ± 2.1) % was calculated for L-arginine CDs. It was concluded that the origin of light emission in carbon dots must be governed by the interplay between the absorption due to the carbon cores and the surface functional groups. Considering the application of the as-synthesized carbon dots, two types of solar cells were fabricated. Carbon dots were used as sensitizers for ZnO-nanorod-based and for TiO2-based nanostructured solar cells. Three types of carbon dots (chitosan CDs, chitin CDs and D-glucose CDs) were used as sensitizers for ZnO-nanorod-based solar cells. ZnO nanorods were successfully coated with carbon dots, and the chitosan-CDs-sensitized solar cells showed the efficiency of 0.061 %. When using layer-by-layer coating method, solar cells with combination of chitosan- and chitin-CDs as sensitizers showed the efficiency of 0.077 %. All six types of carbon dots (chitosan CDs, chitin CDs, D-glucose CDs, L-arginine CDs, L-cysteine CDs, and lobster CDs) were used as sensitizers for TiO2-based nanostructured solar cells. TiO2-based solar cells sensitized with carbon dots showed much higher efficiency compared to the ZnO-nanorod-based solar cells. L-arginine-CDs sensitized TiO2-based solar cells showed the highest efficiency of (0.362 ± 0.007) %, which was the best efficiency of all fabricated solar cells. By surveying a range of biomass-derived carbon dots, and demonstrating a clear link between functionalisation and solar cell performance, this PhD research project provides a guide to direct future development of low-cost, biomass-derived sensitizers for nanostructured solar cells.

Total scattering can be used to study crystalline materials, whose structure presents a periodic arrangement of atoms, as well as disordered materials, such as liquids, glasses or nanomaterials. This thesis work reports three experimental case studies in which different analysis methods were chosen as appropriate on a case-by-case basis. This study demonstrates that total scattering combined with modelling and complementary experimental techniques can guide the understanding of the structure of complex nanostructures. X-ray and neutron total scattering data were collected on multi-walled carbon nanotubes continuously filled with iron and analysed using the program PDFgui for refinement of the pair distribution function and molecular dynamics simulations using the program DL_Poly_4. The analyses show that the iron core is mainly composed of ��-Fe and confirms the dependence of the local ordering on the orientation of the crystallographic axes of iron with respect to the nanowire axis. Prussian blue (Fe4[Fe(CN)6]3 · ��H2O) was synthesised in bulk and nanoparticulate phases using deuterated chemicals; the amount of D2O and H2O in the pores and vacancies, as well as polyvinylpyrrolidone remaining in the nanoparticle samples, were estimated, using an ad hoc modelling procedure of the first few peaks in the neutron PDF function. Models of the structure were refined using the programs PDFgui and RMCProfile. In the last case, a 50Å supercell of the bulk structure with randomly distributed stoichiometric vacancies and D2O and H2O molecules occupying both the pores and the vacancies was used as starting atomic configuration. The CaO/CaCO3 family of materials consists of a series of samples that have undergone carbonation and/or calcination. The X-ray and neutron pair distribution function data were compared to the theoretical PDF of the CaO and CaCO3 phase, generated using the program GULP, that produces PDF functions based on the spectrum of phonon frequencies of the material. The analysis shows that the carbonation is almost completed already after 2 minutes of carbonation and the structure remains stable under further carbonation.