Différentes méthodes de synthèses ont été mises au point pour contrôler la forme et la composition des nanoparticules. L’effet de la nature et la concentration des surfactants, des solvants, la température et le temps de synthèse a également été étudié. Les poudres ont été caractérisées par diffraction des rayons X et microscopie électronique à transmission, couplée à la spectroscopie d'énergie dispersive. Des propriétés catalytiques et de détection ont été évaluées respectivement en présence de faibles concentrations de CO et de NO2 dans de l’air synthétique.Des nanooctaèdres de CoxFe3-xO4 ( x=1, 1,5 et x = 1,8 ) de 15-20 nm ont été produits par synthèse hydrothermale en utilisant différents surfactants (CTAB, SDS et PVP). Des nanocubes de tailles différentes de CoFe2O4 ont été produits par synthèse solvothermique en utilisant l'oléylamine comme surfactant. La poudre de CoxFe3-xO4 avec x = 1,5 a une activité plus élevée pour la conversion du CO que les nanooctaèdres x=1, et la conversion a lieu à plus basse température dans le cas des nanocubes. Les nanocubes présentent une sensibilité inférieure de détection au NO2 à celle des nanooctaèdres, ce qui indique que les faces {111} sont plus réactives que les faces {100} dans les nanoparticules de ferrites de cobalt. / Different synthesis methods such as hydrothermal, solvothermal and thermal decomposition were developed to control nanoparticles shape and composition. The influence of synthesis parameters such as the nature of surfactants, the solvents, temperature and time of synthesis were also investigated. The powders were characterized by X-ray Diffraction and Transmission Electron Microscopy coupled with Dispersive Energy Spectroscopy. The catalytic and detection properties were evaluated in presence of CO and NO2 in synthetic air. CoxFe3-xO4 (x = 1, 1.5 ) nanooctahedra with 15-20 nm were produced by hydrothermal synthesis using different surfactants (CTAB, SDS and PVP). Nanocubes of CoFe2O4 were successfully obtained by solvothermal synthesis using oleylamine as surfactant. Nanooctahedra of CoxFe3-xO4 with x = 1.5 have higher activity for the CO conversion than those with x=1, and the conversion starts at lower temperature for the nanocubes. The nanocubes show lower sensitivity for the detection of NO2 than the nanooctahedra which indicates that the {111} faces are more reactive than the {100} ones in cobalt ferrites nanoparticles.

The focus of this thesis was on the synthesis, characterization and application of ceria nanocubes. This thesis is divided into two main sections; the first section investigates the electronic properties of ceria nanocubes, and the second explores their catalytic applications towards alcohol oxidation reactions. The first project of this thesis consisted of the X-ray characterization of hydrothermally synthesized ceria nanocubes of various sizes. For the first time, the electronic properties of such nanocubes were systematically studied using high resolution XPS and XANES. It was found that the concentration of Ce3+ present within the nanocubes was independent of the particle size, as well as the Ce precursor used during synthesis. Throughout the analysis of the Ce 3d and 4d XPS spectra, it was observed that the surface of the ceria nanocube samples was undergoing photoreduction/damage over time. This damage was attributed to the samples’ exposure to high intensity X-ray radiation. This was confirmed through examination of the Ce M4,5- and N4,5-edge XANES spectra. From these results, it was clear that the concentration of Ce3+ on the surface of the ceria nanocubes was independent of particle size. This fact may become important when investigating their potential catalytic activity. The second project of this thesis concentrated on the analysis of the catalytic activity of a variety of CeO2, Au and Au/CeO2 catalysts towards the oxidation of benzyl alcohol. The low temperature oxidation reactions were studied using 1H NMR spectroscopy. It was observed that Au NPs, Au/bulk CeO2, and Au/CeO2 nanocubes in water and K2CO3 were active catalysts for this oxidation reaction at 60°C in both air and O2 (g) atmospheres. Surprisingly, however, the Au/bulk CeO2 and Au/CeO2 nanocube catalysts showed very similar activities. It was also found that ceria nanocubes alone, and Au25(SR)18/bulk CeO2 showed no activity for this reaction under similar conditions. It was determined that below a substrate to catalyst ratio of ~ 1500:1, the Au/CeO2 catalysts, which showed the highest activities, were mass-transport limited with respect to the O2 in the system. The turnover frequencies of the supported catalysts were approximately double those of the unsupported NPs. Furthermore, these reactions have indicated that activating Au25(SR)18/CeO2 for catalysis is a non-trivial task, and more work needs to be done to understand the activation of such clusters.

Self-assembly of nanoparticles is a promising route to form complex, nanostructured materials with functional properties. Nanoparticle assemblies characterized by a crystallographic alignment of the nanoparticles on the atomic scale, i.e. mesocrystals, are commonly found in nature with outstanding functional and mechanical properties. This thesis aims to investigate and understand the formation mechanisms of mesocrystals formed by self-assembling iron oxide nanocubes. We have used the thermal decomposition method to synthesize monodisperse, oleate-capped iron oxide nanocubes with average edge lengths between 7 nm and 12 nm and studied the evaporation-induced self-assembly in dilute toluene-based nanocube dispersions. The influence of packing constraints on the alignment of the nanocubes in nanofluidic containers has been investigated with small and wide angle X-ray scattering (SAXS and WAXS, respectively). We found that the nanocubes preferentially orient one of their {100} faces with the confining channel wall and display mesocrystalline alignment irrespective of the channel widths.  We manipulated the solvent evaporation rate of drop-cast dispersions on fluorosilane-functionalized silica substrates in a custom-designed cell. The growth stages of the assembly process were investigated using light microscopy and quartz crystal microbalance with dissipation monitoring (QCM-D). We found that particle transport phenomena, e.g. the coffee ring effect and Marangoni flow, result in complex-shaped arrays near the three-phase contact line of a drying colloidal drop when the nitrogen flow rate is high. Diffusion-driven nanoparticle assembly into large mesocrystals with a well-defined morphology dominates at much lower nitrogen flow rates. Analysis of the time-resolved video microscopy data was used to quantify the mesocrystal growth and establish a particle diffusion-based, three-dimensional growth model. The dissipation obtained from the QCM-D signal reached its maximum value when the microscopy-observed lateral growth of the mesocrystals ceased, which we address to the fluid-like behavior of the mesocrystals and their weak binding to the substrate. Analysis of electron microscopy images and diffraction patterns showed that the formed arrays display significant nanoparticle ordering, regardless of the distinctive formation process.  We followed the two-stage formation mechanism of mesocrystals in levitating colloidal drops with real-time SAXS. Modelling of the SAXS data with the square-well potential together with calculations of van der Waals interactions suggests that the nanocubes initially form disordered clusters, which quickly transform into an ordered phase. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

Catalysis has an effect on almost every aspect of our lives. They are used to help grow the food we eat, clean the water we drink and produce the fuels our civilisation is so dependent upon. Homogeneous catalysts, those in the same phase as the reaction medium, are highly selective as a result of their tuneable nature, for example through changes to ligands in a metal complex. However, their separation from the reaction medium can become a problematic, costly, non-green issue, overcome through the use of heterogeneous catalysts which can be removed and recycled by simple separation techniques such as filtering and sedimentation. A major limitation on understanding the behaviour of heterogeneous catalysts is the presence of different active sites due to different exposed crystal surface, concentration of defects and morphological variations. With such considerations, the first section of this thesis focuses on the synthesis of discrete and well-defined nanostructured materials (ceria and titanate) using a single-step hydrothermal method. Nanostructured ceria with different morphologies (particles, rods and cubes), present a high oxygen storage capacity and thermal stability. Their oxidation catalytic activity was assessed using CO oxidation as a model reaction as a function of their physical and chemical properties, tuned by morphological control at the nanoscale. An inverse relationship is observed between crystallite size and rates of reaction normalised per surface area. Smaller crystallites present a constrained geometry resulting in a higher concentration of defects, highly active catalytically due to their unsatisfied coordination and high surface energy. The surface to bulk oxygen ratio generally increased as the surface area increased, however, ceria nanorods present a higher surface oxygen content than that which would be predicted according to their surface area, likely due to the selective exposure of the (110) and (100) dominating crystal surfaces presenting more facile oxygen atoms in their surface. Additionally a relationship between surface to bulk oxygen ratios and activation energies was also ascribed to the more facile nature of oxygen atoms on these surfaces and their more readily formed oxygen vacancies as a result. This activity is as a result of the formation of oxygen vacancies being the rate-controlling step. The thermal stability of nanostructured ceria (particles, rods and cubes) was also studied to investigate their performance under cyclic high temperature applications. For this, the materials were pre-treated at 1000 °C under different atmospheres (inert, oxidative and reducing). In all cases, the materials sinter, consequently resulting in a dramatic decrease in surface area. Interestingly, their catalytic activity per surface area towards CO oxidation, seems to be maintained, although those materials pre-treated under inert and oxidising atmospheres became inactive in consecutive catalytic runs. However, nanostructured ceria pre-treated at 1000 °C under hydrogen appeared to maintain its activity per surface area. The presence of hydrogen during thermal treatment does not only facilitate the removal of surface oxygen, but also the bulk oxygen, resulting in a rearrangement of the structure that facilitates its catalytic stability. Titanate nanotubes were shown to be inactive for CO oxidation and thus were used in the second part of this thesis as a support for platinum nanoparticles to study the effect of the structure and metal-support interaction on the resulting catalytic activity. The study focuses on the effect of different loading methods (ion exchange and incipient wetness impregnation) of platinum nanoparticles on the resulting metal particle size, dispersion, metal-support interaction and consequently their resulting catalytic activity. Ion exchange consistently resulted in smaller nanoparticles with a lower dispersion of sizes and more active catalyst, both in terms of turnover frequency values and activation energy, compared with incipient wetness impregnation. The catalytic activity of the platinum supported on titanate nanotubes increases as the metal particle size decreases to a size value (between 1 and 2.5 nm) below which a dramatic decrease in activity is observed. Despite initial differences in catalytic activity between the different catalysts, it was observed that after initial reactions to 400 °C, the activation energy was independent of metal loading weight and was instead inherent of the loading method, suggesting the presence of similar active sites.

In this paper, metal-enhanced fluorescence (MEF) technique is used to lower the detection limit of carcinoembryonic antigen (CEA) which is able to be utilized in forecasting the risk of having certain kinds of cancers, especially colon and rectal cancer. By incubating silver nanocubes (Ag NCs) on the surface of the chips, the detection limit goes down to below 1ng/mL of CEA. Also, when combining MEF with surface acoustic wave (SAW) devices, the incubation time between antigen and antibody will decrease significantly with the fluorescence signal keeping similar or higher level.

Alloys, intermetallic compounds and multi-metal oxides are generally made by traditional solid-state methods that often require melting or grinding/pressing powders followed by high temperature annealing (> 1000 degrees C) for days or weeks. The research presented here takes advantage of the fact that nanoparticles have a large fraction of their atoms on the surface making them highly reactive and their small size virtually eliminates the solid-solid diffusion process as the rate limiting step. Materials that normally require high temperatures and long annealing times become more accessible at relatively low-temperatures because of the increased interfacial contact between the nanoparticle reactants. Metal nanoparticles, formed via reduction of metal salts in an aqueous solution and stabilized by PVP (polyvinylpyrrolidone), were mixed into nanoparticle composites in stoichometric proportions. The composite mixtures were then annealed at relatively low temperatures to form alloy and intermetallic compounds at or below 600 degrees C. This method was further extended to synthesizing multi-metal oxide systems by annealing metal oxide nanoparticle composites hundreds of degrees lower than more traditional methods. Nanoparticles of Pt (supported or unsupported) were added to a metal salt solution of tetraethylene glycol and heated to obtain alloy and intermetallic nanoparticles. The supported intermetallic nanoparticles were tested as catalysts and PtPb/Vulcan XC-72 showed enhanced catalytic activity for formic acid oxidation while Pt3Sn/Vulcan XC-72 and Cu3Pt/y-Al2O3 catalyzed CO oxidiation at lower temperatures than supported Pt. Intermetallic nanoparticles of Pd were synthesized by conversion chemistry methods previously mentioned and were supported on carbon and alumina. These nanoparticles were tested for Suzuki cross-coupling reactions. However; the homocoupled product was generally favored. The catalytic activity of Pd3Pb/y-Al2O3 was tested for the Heck reaction and gave results comparable to Pd/y-Al2O3 with a slightly better selectivity. Conversion chemistry techniques were used to convert Pt nanocubes into Ptbased intermetallic nanocrystals in solution. It was discovered that aggregated clusters of Pt nanoparticles were capable of converting to FePt3; however, when Pt nanocubes were used the intermetallic phase did not form. Alternatively, it was possible to form PtSn nanocubes by a conversion reaction with SnCl2.

Hydrogen fuel is one of the most important areas of research in the field of renewable energy development and production. Hydrogen gas can be generated by fuel cells, water electrolyzers, and heterogeneous nanoscale catalysts. It can be burned to directly release chemical energy or condensed for storage and transport, providing fuel for combustion devices or storing excess energy generated by renewable sources such as wind turbines and concentrated solar power assemblies. While platinum is the most active catalyst for hydrogen reduction, its high cost significantly deters its utilization in advanced photocatalytic materials. One approach to mitigating this expense is optimizing the morphology and placement of nanostructured platinum catalysts. Highly crystalline, morphologically-controlled platinum nanoparticles (Pt NPs) have been effectively utilized to increase hydrogen generation efficiency in a variety of nanocomposite materials. However, synthesis routes to high-quality Pt NPs can be dangerous and difficult to replicate. Furthermore, utilization of the Pt NPs in nanocomposite materials is hindered by lack of control over catalyst placement. Nanopeapods are versatile nanocomposites that offer a high degree of control over catalyst placement as well as the potential for interesting new properties arising from the interaction between the catalyst and a semiconductor. Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) consist of linear arrays of Pt NPs encapsulated within the scrolled semiconductor hexaniobate. Pt@HNB NPPs offer significant advantages over similar composites by utilizing the isolated reduction environment of the encapsulated Pt NP arrays to decrease kinetic competition and surface crowding. This work describes the design, fabrication, and implementation of the new nanocomposite platinum@hexaniobate nanopeapods for sensitized hydrogen production under visible light irradiation. The following chapters present facile microwave heating syntheses of highly crystalline Pt nanocubes and Pt@HNB NPPs with consistent morphology and high catalyst loading. A detailed study is also presented of the optical properties of the Pt nanocubes, which produced a UV-range absorbance band that indicates the formation of a localized surface plasmon resonance. Most significantly, preliminary results from visible light photolysis indicate that sensitized Pt@HNB NPPs produce hydrogen in quantities comparable to published systems, and that alteration of experimental parameters may result in even greater yields.

<p>The functionalization of nonwoven electrospun polymeric fibers with metallic nanostructures has enabled the design of novel nanocomposite materials used in a wide range of applications. In particular, designs based on incorporating established antimicrobial species such as copper and silver have potential applications as antimicrobial filtration membranes, leveraging on the convoluted fiber assembly and high surface area–to–volume ratios of the constitutive fibers. Electroless deposition based on spontaneous electrochemical reactions offers a facile and tunable methodology for surface–confined growth of metallic nanostructures on the non–planar substrate architectures presented by nonwoven electrospun fibers. </p> <p>Firstly, this work explores, in a broad sense, the effects of two different seed catalyst chemistries, palladium and silver, on the evolution of copper nanoparticles on electrospun polyacrylonitrile fibers. Copper nanoparticle coverage and conformity; deposition kinetics; modifications in the surface chemistry of the PAN fibers; and thermal stability of the resultant nanocomposites were examined. Secondly, qualitative and quantitative assessment of the interfacial adhesion between the copper nanostructures and PAN fibers were undertaken by exploiting the elastic mismatch between both phases during tensile deformation. For copper nanocubes on nanofibers, the adhesion energy is estimated to be between 0.48 J/m² and 1.0 J/m² using strain and growth based adhesion models.</p> <p>Macroscopically, the compliant nature of the nonwoven fiber mats makes them susceptible to out-of-plane deformation during water filtration processes which may alter their size exclusion configuration for effective filtration. A bulge testing device is built and implemented to simulate and characterize hydraulic flow – induced deformation in the electrospun PAN fiber mats. The pressure–deflection relationships of the mats show a sub-linear dependence in contrast to classical continuum materials. The macroscopic mat behavior was governed by the properties of the constituent fibers, with an apparent mat bending rigidity dependent on the fiber diameters.</p> <p> Lastly, the nonwoven fiber mats functionalized with copper nanoparticles were evaluated for use as potential antimicrobial microfiltration membranes. The fiber mats displayed high water flux and high separation efficiency for model 3 μm particles, with separation factors reaching above 99%.</p>

Die Kombination aus anorganischen Nanopartikeln und Mikrogelen in einem hybriden System erlaubt die Herstellung von Materialien mit vielseitigen neuen Eigenschaften. Im Idealfall weisen solche hybriden Materialien neben den Eigenschaften von beiden indivduellen Systemen zusätzlich synergetische Effekte auf, welche aus den Interaktionen zwischen dem anorganischen Nanopartikel und dem Mikrogel resultieren. Im ersten Teil dieser Arbeit wird eine neuartige und eingängige Methode zur Herstellung von Cu2O@PNIPAM Kern-Schale Nanoreaktoren präsentiert. Die PNIPAM Schale schützt dabei die Cu2O Nanopartikel effektiv vor Oxidation. Die Cu2O@PNIPAM wurden als Photokatalysator zum Abbau von Methylorange unter sichtbarem Licht eingesetzt. Im Vergleich zu den reinen Cu2O Nanopartikeln konnte eine signifikante Steigerung der katalytischen Aktivität festgestellt werden. Desweiteren kann die photokatalytische Aktivität mittels Temperatur durch die thermosensitive PNIPAM Schale abgestimmt werden. Verhältnismäßig geringe Konzentrationen einer Cu2O@PNIPAM wässrigen Lösung (1,5 Gew%) können direkt als neuartige Tinte genutzt werden. Keine zusätzlichen Additive oder organische Lösungsmittel sind für die Strahldruckprozesse vonnöten. Gedruckte Bauelemente bestehend aus den Cu2O@PNIPAM wurden als Gas Sensoren eingesetzt und zeigten eine geringere Nachweisgrenze für NO2 als die reinen Cu2O Nanowürfel. Im zweiten Teil der Arbeit wurden katalytisch aktive Au Nanopartikel an copolymerisierten α –Cyclodextrin (α-CD) Einheiten in einem Poly(N-vinylcaprolactan) (PVCL) Mikrogel immobilisiert. Diese hybriden Partikel sind sehr aktive Katalysatoren für die Reduktion von aromatischen Nitroverbindungen. Die Reduktion von 4-Nitrophenol (Nip) und 2,6-Dimethyl-4-nitrophenol (DMNip) wurden als Modellreaktionen ausgewählt. Durch selektive Bindungseingenschaften der Nitroverbindungen an die α-CD Einheiten konnten verschiedene katalytische Aktivitäten für Nip and DMNip festgestellt werden. / The combination of inorganic nanoparticles and organic microgels in one hybrid system allows for the preparation of new materials with multifunctional properties. Ideally, such hybrid materials reflect both the properties of its individual components and synergetic effects due to the interaction between inorganic nanoparticles and microgels. In the first part of this thesis, the fabrication of Cu2O@Poly(N-isopropylacrylamide) (PNIPAM) core-shell nanoreactors has been presented. It was found that the PNIPAM shell effectively protects the Cu2O nanocubes from oxidation. The core-shell microgels have been used as photocatalyst for the decomposition of methyl orange and a significant enhancement in the catalytic activity has been observed compared with the bare Cu2O nanocubes. Most importantly, the photocatalytic activity of the core-shell nanoreactors can be further tuned by the thermosensitive PNIPAM shell. The aqueous solution of Cu2O@PNIPAM core-shell nanoparticles with quite low solid content (1.5wt. %) can be also directly used as a novel ink material for the inkjet printing without adding any other surfactants and organic solvents. The gas sensor device printed by core-shell nanoparticles is more sensitive to NO2 than that made from the bare Cu2O nanocubes. In the second part, a kind of hybrid microgel has been fabricated by immobilization of catalytically active Au nanoparticles in the α-cyclodextrin (α-CD) modified poly(N-vinylcaprolactam) (PVCL) microgels without addition of reducing agent and surfactant. The hybrid microgels can work efficiently as catalyst for the reduction of aromatic nitro-compounds by using the reduction of 4-nitrophenol (Nip) and 2,6-dimethyl-4-nitrophenol (DMNip) as model reactions. Due to the selective binding property of α-CDs to nitro compounds, the synthesized hybrid microgels show different catalytic activity for the target compounds, 4-nitrophenol (Nip) and 2,6-dimethyl-4-nitrophenol (DMNip), during the catalytic reactions.

Neste trabalho, a estrutura local e média de nanopartículas foi estudada utilizando-se métodos de espalhamento e difração de raios X. Os métodos utilizados foram: Análise da Função de Distribuição de Pares Atômicos (Atomic Pair Distribution Function Analysis, em inglês) para o estudo do ordenamento estrutural de curto alcance, Refinamento de Rietveld e Modelamento Total do Perfil de Difração de Pó para o estudo do ordenamento médio. Os materiais estudados foram: nanopartículas de KY3F10 dopadas com Tb, nanocubos núcleo-camada (core-shell, em inglês) de FeO-Fe3O4 e nanopartículas de ferritas de Mn-Zn. O trabalho teve como objetivo demonstrar como os métodos mencionados podem ser utilizados de forma complementar para fornecer informações de curto, médio e longo alcance usando-se dados de espalhamento e difração de raios X. Neste trabalho, ressalta-se a importância de cada método no estudo da estrutura cristalina e demonstra avanço e desenvolvimento de metodologias para a sua aplicação. / In this work, local and average structure of nanoparticles were studied using X-ray scattering and diffraction methods. The methods used were: Atomic Pair Distribution Function Analysis to study the short-range ordering, Rietveld refinement and Whole Powder Pattern Modelling to study the long-range ordering. The studied materials were: Tb-doped KY3F10 nanoparticles, core-shell FeO-Fe3O4 nanocubes and Mn-Zn ferrite nanoparticles. The objective of this work was to demonstrate how the methods mentioned can be used in a complementary way to provide short, average and long range information about the structure using X-ray scattering and diffraction data. The importance of each method to study the crystalline structure is highlighted demonstrating progress and development of methodologies for its application.