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La thèse est consacrée à la synthèse et à l’étude des propriétés des matériaux hybrides inorganique-organique à base de polyaniline (PANI) et de polypyrrole (PPy) avec des nanoparticules TiO2 (rutile et anatase) et SnO2 applicables à détection l'ammoniac et aux amines. La croissance directe du polymère sur la surface des nanoparticules a permis l’obtention de matériaux nanocomposites avec une structure “core-shell” qui diffère du mélange mécanique simple par une distribution plus uniforme des polymères et une interaction plus forte entre les composants source. L’objet de la recherche est le processus de formation de nanocomposites de polyaniline et de polypyrrole avec des oxydes métalliques. L’objectif de la recherche est de révéler les particularités de la formation et les propriétés des matériaux composites nanostructurés à base de polymères conducteurs et nanoparticules d’oxydes métalliques sensibles à l’ammoniac et aux amines. Les méthodes de recherche incluent le RedOx et la surveillance du pH, FTIR et UV-spectroscopie, SEM, TEM, thermogravimétrie, chromatographie liquide, mesures de conductivité et tests de capteurs. La nouvelle approche d’étude de la cinétique du processus de polymérisation de l'aniline par la surveillance simultané du RedOx et du pH du milieu réactionnel a été proposée. Pour la première fois, on a montré l’influence des acides sulfoniques et des oxydes métalliques sur le procédé de polymérisation de l’aniline et les caractéristiques moléculaires du polymère obtenu. En outre, une corrélation linéaire entre le contenu en nanoparticules et la durée réciproque des stades séparés de la polymérisation a été démontrée. Les nanocomposites “core-shell” formés ont une sensibilité à l’ammoniac et aux amines environ 2 fois supérieure à celle du polymère pur. Les nouveaux matériaux développés peuvent être utilisés dans la fabrication de couches actives des capteurs chimiorésistifs. / The thesis is devoted to the synthesis and investigation of properties of inorganic-organic polyaniline (PANI) and polypyrrole (PPy) based hybrid materials with TiO2 (rutile and anatase) and SnO2 nanoparticles applicable for ammonia and amines detection. The direct polymer growth on the surface of nanoparticles allowed obtaining of nanocomposite materials with a “core-shell” structure which differs from simple mechanical mixture by more uniform polymer distribution and stronger interaction between source components.The object of research is the process of formation of polyaniline and polypyrrole nanocomposites with metal oxides. The research goal is to reveal formation peculiarities and properties of nanostructured composite materials based on conducting polymers and metal oxides nanoparticles that are sensitive to ammonia and amines. Research methods include RedOx and pH monitoring, FTIR and UV-spectroscopy, SEM, TEM, thermogravimetry, liquid chromatography, conductivity measurements and sensor tests.The new approach to study kinetics of aniline polymerization process by simultaneous RedOx and pH monitoring of reaction medium was proposed. For the first time the influence of sulfonic acids and metal oxides on the aniline polymerization process and molecular characteristics of the obtained polymer was shown. For the first time a linear correlation between the nanoparticles content and reciprocal duration of separate stages of polymerization was shown. Formed "core-shell" nanocomposites have sensitivity to ammonia and amines of about 2 times higher than the pure polymer. Developed new materials can be used in the manufacturing of chemoresistive sensors' active layers.

The ability to grow materials in the nanometric size regime with controlled shape and size provide a fundamental synthetic challenge, while allowing for evaluation of such unique nanostructures in multiple applications. In this dissertation, colloidal sodium lanthanide fluoride (NaLnF4) nanocrystals are described with an overall emphasis on i) size control, ii) surface chemistry related towards their applications as nano-bioprobes, and iii) the synthesis and fundamental aspects of epitaxial layer growth generally referred as core-shell nanocrystals. Chapter 1 provides a brief overview on the basic aspects of colloidal nanocrystals. In Chapter 2, synthesis and surface modification of colloidal sodium lanthanide fluoride nanocrystals, epitaxial growth, and their applications in optical and magnetic resonance imaging is reviewed. Chapter 3 describes a phase transfer protocol utilizing polyvinylpyrrolidone and subsequent silica coating of initially hydrophobic upconverting nanocrystals. This protocol is extended in Chapter 4 using end-group functionalized polyvinylpyrrolidone and demonstrates tunability of surface charge and functional groups on upconverting nanocrystals for targeted labeling of human prostate cancer cells. The synthesis of size-tunable NaGdF4 nanocrystals below 10 nm is described in Chapter 5. These nanocrystals are evaluated for their efficacy in magnetic resonance imaging (MRI), and a fundamental insight into the effect of surface gadolinium ions in T1 MRI contrast enhancement is presented. Chapter 6 demonstrates the synthesis of tunable, epitaxial layers on upconverting (core) nanocrystals. A novel synthetic strategy is demonstrated, by deliberate defocusing and self-focusing of differently sized nanocrystals driven by the common physical phenomenon of Ostwald ripening. Utilizing the contraction of lanthanide ions along the series, a fundamental investigation on the effect of compressive/tensile strain epitaxial layer growth is presented in Chapter 7. The fundamental rule of minimal lattice mismatch for epitaxial growth takes into account only the magnitude of mismatch and not the sign of mismatch caused by a compressive/tensile strained layer. A strong asymmetric effect between the compressive/tensile layer growth given the same magnitude of lattice mismatch is observed, demonstrating the necessity of including the sign of mismatch to generate isotropic (conformal)/ pseudomorphic (coherent) epitaxial growth. Finally, in Chapter 8 conclusions and possible future work are discussed. / Graduate / 0494

Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. In this work, a combination of TEM (transmission electron microscopy), XRD (X-ray Powder Diffractometry), EDS (Energy disperse X-ray spectroscopy), SQUID (Superconducting Quantum Interference Device), TGA (Thermograviometric analysis), UV-visible absorption spectroscopy and Faraday rotation were employed to characterize the morphology, structure, composition and magnetic properties of the products. HRTEM images show clear core-shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Au-coated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And all the above characterizations show that in this sample, there are no Fe oxides inside the particle.

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There have been many applications of cerium oxide in oxidation catalysis but the understanding of its role in catalysis is rather limited. This research is concerned with the use of nano-size cerium oxide in methane steam reforming reaction. It is found that addition of cerium oxide to the commercial supported Ni catalysts can dramatically reduce the undesirable carbon deposition (through surface oxidation), which is thermodynamically favorable under low steam conditions. In order to understanding the fundamental role of oxidation activity of the cerium oxide, different sizes of nano-crystallined cerium oxides have been carefully prepared by micro-emulsion technique. Their reactivity is clearly shown to be size dependent. We found that ceria particle sizes of lower than 5.1 nm are able to activate molecular oxygen, which accounts for the unprecedentedly reported critical size effect on oxidation. Characterizations by EPR, XPS, TPR suggest that a substantially large quantity of adsorbed oxygen species (O₂ ^-) is preferentially formed in the small size ceria from air. Also, it is found that the oxygen vacancies are formed in the interface of metal and oxide, and the strength of the metal oxide interaction may influence the formation of the efficient oxygen vacancies, which are responsible for the adsorbed surface oxygen.

The design of core/shell nanoparticles is of great interest for a wide range of applications. The primary focus of this dissertation is on the design and optimization of two synthetic routes. The first one is an aqueous reduction method using sodium borohydride and sodium citrate. This method was extended to design two types of core/shell nanoparticles, both of which have many applications in bio-sensing, magnetic resonance imaging, and magnetically guided SERS for the identification of environmental threats. The first, Fe/Ag core/shell nanoparticles were designed using a novel one-pot method by varying the AgNO3 addition time in the system. For example, if AgNO3 is added five minutes after the start of the reaction, the already formed Fe nanoparticles serve as seeds for heterogeneous nucleation and growth of Ag nanoparticles. The result of the synthesis was 50 nanometer spherical particles with a narrow size distribution. The second type, Fe/SiO2/Au core/shell nanoparticles were designed using a two-step method. First, 150 nanometer spherical Fe nanoparticles were synthesized followed by the addition of tetraethylorthosilicate (TEOS). This created a Fe/SiO2 core/shell nanoparticle to which HAuCl3 was added. In both cases, Fe/Ag and Fe/SiO2/Au, the formed nanoparticles were characterized and tested for the application as SERS active materials. The second part of this dissertation work was focused on using the polyol method to design bimetallic Cu/Ni, Fe/FeOx, and Co/C core/shell nanoparticles. In each case, the polyol method provided an easy one-pot reaction to synthesize these novel nanomaterials. The design of the Cu/Ni nanoparticles allowed for further insight into the polyol mechanism by independently investigating the factors that govern the formation of elemental Cu and Ni nanoparticles. By understanding the ability of the polyols to easily prepare metal and metal oxide nanoparticles, we were able to manipulate a one-pot reaction to design an aqueous ferrofluid consisting of Fe/FeOx nanoparticles. These spherical 15 nanometer particles were studied for their potential application as MRI contrast agents. In addition, the aqueous ferrofluid served as a precursor for the design of magnetic/luminescent core/shell nanoparticles. Finally, the polyol method was extended to create Co/C nanoparticles for permanent magnet applications.

This thesis focuses on core/shell nanoparticle catalysts including preparation, characterization and testing performance using direct methanol fuel cell. Core/shell were prepared using noble and non-noble metals. Also some core/ shell nanoparticles supported on silica and different types of carbon were prepared as well in this thesis. Non-noble core/shell nanoparticles including novel Co/Ni, SiO2/Ni using three types of silica and novel SiO2/CoFe were prepared by a new modified sol-gel method using hydrazine in alkali media as the reducing agent to reduce metal chloride through two steps process. Parameters such as temperature, pH of solution and reducing agents, were seen to be of great importance in deciding the morphology of the final product as well as the structure of the core/shell catalyst. Core/shell nanoparticles have been successfully prepared for Co/Ni and SiO2/CoFe for first time by choosing the right parameters. This study presents the unique structure which has not been obtained previously for SiO2/Ni catalyst using commercial silica as core. A novel halo shaped structure was the common feature in the catalysts prepared as indicated by TEM. This study presents as well noble Ru/Pt core/shell nanoparticles supported on three types of carbon by a new modified polyol method for first time. The author of this work is not aware of any studies that have prepared Ru/Pt on carbon powder smaller or equal to 50 nm and Ru/Pt on CMWNT previously. This work presents special structure (crown- jewel shaped) for Ru/Pt on Vulcan XC-72 carbon which was not obtained previously for the same catalyst. Selected catalysts were tested using a direct methanol fuel cell. SiO2/Pt core/shell nanoparticles were prepared for the first time by two different methods, namely a new modified sol-gel and polyol methods with novelty structures halo and crown- jewel shaped respectively. Based on the particles size obtained from TEM images, the modified polyol method seems to have a much greater impact on the particles size than the modified sol-gel method. Based on these findings Ru/Pt, Ru/Pt supported on three different types of carbon and Pt supported on CMWNT were prepared using the new modified polyol method. Pt on CMWNT catalyst was synthesized for the first time successfully by a new modified polyol method and all the particles were found to be well dispersed with a narrow size distribution of an average particles size of 3nm. This catalyst gave promising results on DMFC. Pt supported on CMWNT and Ru/Pt supported on Vulcan and CMWNT were used for the first time as electro-catalysts in DMFC to study the effect of the support on the catalytic activity of catalysts. The results show that Ru/Pt on CMWNT gives better performance than the unsupported Ru/Pt and Ru/Pt on Vulcan XC-72. Using Ru/Pt on CMWNT with higher methanol concentration (anode feed) improved the fuel cell power density when compared with the RuPt commercial catalyst.

Core-shell nanohybrids have wide applications in pollutant degradation. In this study, core-shell nanohybrid was formed through heteroaggregation between neutral nanoparticles (i.e., hematite nanoparticles or HemNPs) and charged nanoparticles (i.e., carboxylated polystyrene nanoparticles or PSNPs). In the dispersant solution of 1 mM NaCl at pH 6.3, HemNPs were neutral and underwent favorable homoaggregation, whereas PSNPs were negatively charged and underwent no homoaggregation. When the two types of particles were mixed, homoaggregation of HemNPs and heteroaggregation between HemNPs and PSNPs took place simultaneously, forming HemNPs-PSNPs heteroaggregates. The transmission electron microscopy images of heteroaggregates show that HemNPs and PSNPs formed core-shell structure in which HemNPs were the cores and PSNPs were the shells. The size of the core-shell nanohybrids can be controlled by varying the concentration ratio of HemNPs to PSNPs. The increase of the size of charged nanoparticles resulted in larger nanohybrids. This new method has lower energy footprint than existing ones. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Semiconductor nanowire field-effect transistors (NWFET) have been recognized as a possible alternative to silicon-based CMOS technology as traditional scaling limits are neared. The core-shell nanowire structure, in particular, also allows for the enhancement of carrier mobility through radial band engineering. In this thesis, we have evaluated the possibility of electron confinement in strained Si-Si1-xGex core-shell nanowire heterostructures. Cylindrical strain distribution was calculated analytically for structures of various dimensions and shell compositions. The strain-induced conduction band edge shift of each region was found using k•p theory coupled with a coordinate system shift to account for strain. A positive conduction band offset of up to 200 meV was found for a Si-Si0.2Ge0.8 structure. We have also designed and characterized a modulation doping scheme for p-type, Ge-SiGe core-shell NWFETs. Finite element simulations of hole density versus radial position were done for different combinations of dopant position and concentration. Three modulation doped nanowire samples, each with a different boron doping density in the shell, were grown using a combined vapor-liquid-solid and chemical vapor deposition process. Low temperature current-voltage measurements of bottom- and top-gate samples indicate that hole mobility is limited by the proximity of charged impurities. / text