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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Laser Vaporization Controlled Condensation and Laser Irradiation in Solution for the Synthesis of Supported Nanoparticle Catalysts

Kisurin, Vitaly, Mr. 01 January 2016 (has links)
Solid catalyst supports of SiOx-RGO (Reduced Graphene Oxide) and UiO-67 (Universitet i Oslo) have been successfully synthesized and were loaded with palladium nanoparticles to test for a series of heterogeneous reactions. The SiOx/RGO catalysts were synthesized through laser ablation of silicon and graphite oxide micron powder and UiO-67 metal-organic framework (MOF) was synthesized through mixing of precursors with DMF/HCl solution and washing the resultant powder from impurities. The SiOx/RGO supports were later impregnated with palladium precursors which were then subject to Microwave Irradiation (MWI). The UiO-67 framework was impregnated with palladium precursors and was irradiated with pulsed Nd:YAG 532 nm laser and was purified through washing and centrifugation. The resulting catalyst supports were characterized with UV-Vis, FTIR, Raman, XRD and XPS techniques and the UiO-67 framework was subject to Brunauer-Emmet-Teller (BET) surface area measurements before and after the catalytic reactions. The catalytic activity of palladium nanoparticles supported on SiOx/RGO and UiO-67 framework was tested in carbon cross-coupling reactions of Suzuki-Miyaura, Sonogashira reactions and oxidation of benzyl alcohol respectively. The catalysts have demonstrated excellent performance and have yielded a promising future for the catalytic supports in the previously stated reactions.
52

Controlled Attachment of Nanoparticles to Layered Oxides

Yao, Yuan 18 May 2012 (has links)
A series of oxide materials were modified with different nanoparticles (NPs). Novel cobalt@H4Nb6O17 nanopeapod structures were fabricated and magnetic NPs modified oxide nanosheets and nanoscrolls were prepared. Both aqueous method and two-phase method were applied to prepare gold NPs onto oxide nanosheets, nanoscrolls and other nanocrystals. The combination of H4Nb6O17 nanoscrolls and cobalt NPs generate a novel method to fabricate nanopeapod structures. Cobalt NPs were synthesized in the presence of exfoliated H4Nb6O17 nanosheets and the resulting magnetic chain structures, formed due to the dipole-dipole interaction, were captured within scrolled lamella. The yield of peapod structures can be improved by using proper reagents and reaction temperatures. As similar method with iron oxide NPs also produced peapod-like structures in a low yield. Exfoliated Dion-Jacobson phase layered perovskite HLaNb2O7 (HLN), its organic derivate propoxyl-HLaNb2O7 (pHLN), Ruddlesden-Popper phase perovskite H2SrTa2O7 (HSTO) and Aurivillius phase perovskite H2W2O7 (HWO) were synthesized and functionalized with gold NPs by in-situ methods. Gold NPs were prepared by both an aqueous method and two-phase method. The size of NPs can be adjusted by different reaction times. Overall, the latter method shows a narrower size distribution and better dispersion. In addition, most gold NPs prepared by the two-phase method were attached on the surface of nanosheets and almost no free gold NPs were observed in solution. This approach should be applicable to most layered perovskites. The aqueous and two-phase methods were also applied on the preparation of gold NPs onto H4Nb6O17 nanosheets and nanoscrolls. H4Nb6O17 nanosheets were prepared by two approaches and showed similar gold NPs attachment. LiNbO3 nanocrystals can be also modified with gold NPs by the two-phase method though free gold NPs were observed. Further studies involved the functionalization of layered perovskites and related compounds with magnetic NPs. Iron oxide and cobalt NPs were synthesized in the presence of layered perovskite and modified perovskite nanosheets were obtained.
53

Microstructure and Magnetic Properties for Mn-Al based Permanent Magnet Materials

Nyberg, Axel January 2017 (has links)
Manganese-Aluminium is an alloy with attractive ferromagnetic propertieswhenL10-structured ( -phase). If sucient permanent magnetic propertiescan be achieved at a low cost, it has potential to be a new permanentmagnet material on the market. In this thesis, drop synthesized ingots ofMn55Al45C2 were crushed and examined as solid pieces and as powders.The goal was to better understand how the material behaves magneticallyafter synthesis in relation to its chemical composition and cooling rate. Representativecross-sections of solid ingot pieces were created by mounting thepieces in polyfast followed by polishing. The surfaces were studied withScanning Electron Microscopy and Energy-dispersive X-ray spectroscopy tomap the chemical composition and then by Magnetic Force Microscopy andMagneto-optic Kerr eect to see how the chemical composition inuencesthe magnetic properties. It was found that areas richer in aluminium (Al),compared with the rest of the surface, behaved non-magnetically. The resultsfrom X-ray diraction on the powders suggests that the Al-rich areasconsists of the non-magnetic- and 2-phases.The powder that was extracted from the top of one of the drop synthesizedingots was nearly pure -phase but did not have an impressive magnetization.A complementary magnetic measurement was done on a solid piece from thetop part. This piece was found to reach a higher magnetization at a lowereld. The result indicates that crushing the material, even just by hand witha mortar and pestle, greatly reduces the magnetization.
54

Transparent conductive oxides deposited by magnetron sputtering: synthesis and characterization / Transparanta ledande oxider deponerade via magnetronsputtering: syntes och karaktärisering

Axelsson, Mathias January 2019 (has links)
The thesis has dealt with transparent conducting oxide (TCO) materials, with a focus on Al:ZnO and with studies on Sn:In2O3 and ZnO. TCOs are a material group that is used for its properties of being conductive and at the same time transparent. In solar cells, a top layer of TCO is often used to allow light to transmit into the cell and then conduct the resulting current.   A set of growth parameters was chosen and optimized through a literature study and experiments. The depositied thin films were characterized by optical and electrical characterization methods. Rf-magnetron-sputtering was used as the deposition method, where the influence of O2, argon and substrate temperature were the parameters to be studied. As a part of the characterization a model for spectroscopic ellipsometry on Al:ZnO was made, enabling faster measurement of transport properties. The main parameter affecting the TCO properties was found to be oxygen flow and the optimum flow value for each material has been determined. Substrate heating did not show any significant improvement on the resistivity of Al:ZnO with a minimum value of ~5.0*10-4 Ωcm while no heating resulted in a value of ~6.0*10-4  Ωcm. These values are comparable to the state-of-the-art from the literature.   As a demonstration of application, the developed AZO and ZnO were applied to CIGS solar cells and these were compared to a reference. The newly developed AZO and ZnO was comparable to the reference but a lower mean fill factor indicates that improvements can be made.
55

SYNTHESIS, AND STRUCTURAL, ELECTROCHEMICAL, AND MAGNETIC PROPERTY CHARACTERIZATION OF PROMISING ELECTRODE MATERIALS FOR LITHIUM-ION BATTERIES AND SODIUM-ION BATTERIES

Han, Ruixin 01 January 2018 (has links)
Iron oxides, have been widely studied as promising anode materials in lithium-ion batteries (LIBs) for their high capacity (≈ 1000 mA h g-1 for Fe2O3 and Fe3O4,), non-toxicity, and low cost. In this work, β-FeOOH has been evaluated within a LIB half-cell showing an excellent capacity of ≈ 1500 mA h g-1 , superior to Fe2O3 or Fe3O4. Reaction mechanism has been proposed with the assistance of X-ray photoelectron spectroscopy (XPS). Various magnetic properties have been suggested for β-FeOOH such as superparamagnetism, antiferromagnetism and complex magnetism, for which, size of the material is believed to play a critical role. Here, we present a size-controlled synthesis of β-FeOOH nanorods. Co-existing superparamagnetism and antiferromagnetism have been revealed in β-FeOOH by using a Physical Property Measurement System (PPMS). Compared with the high price of lithium in LIBs, sodium-ion batteries (SIBs) have attracted increasing attentions for lower cost. Recent studies have reported Na0.44MnO2 to be a promising candidate for cathode material of SIBs. This thesis has approached a novel solid-state synthesis of Na0.44MnO2 whiskers and a nano-scaled open cell for in situ TEM study. Preliminary results show the first-stage fabrication of the cell on a biasing protochip.
56

Synthesis and Characterization of Magnetic Cabides and Oxides Nanomaterials

Tsui, Hei Man 01 January 2018 (has links)
The design and development of nanoparticles is of great interest in the current energy and electronic industry. However, based on the current materials available the production cost can be high with insignificant magnetic and mechanical properties. Specifically, rare-earth magnetic materials composed of neodymium and samarium are known for their high magnetic performance, however, due to the cost of development there is a need to develop a versatile and cost effective material. Alternatively, cobalt carbide nanomaterials have shown to be a promising alternative for rare-earth free magnets as they exhibit comparable properties as hexaferrite magnetic materials. The primary goal of this dissertation focuses on the development of nanoparticles for permeant magnetic, and magnetic refrigeration applications. The first part of this work focuses on the synthesis of cobalt carbide (CoxC, x=2,3) nanoparticles using a novel polyol synthesis method by introducing a small amount of Ru, Cu, or Au as nucleating agent. It was found that the morphology and magnetic properties of the as-synthesized CoxC nanoparticles change as a result of directional growth of nanoparticles using nucleating agents. Needle-like particle morphology ranges from 20-50 nm in width and as long as 1 µm in length were synthesized using Ru as nucleating agent. These particles exhibit magnetization saturation of 33.5 emu/g with a coercivity of 2870 Oe and a maximum energy product 1.92 MGOe (BHmax) observed. Particle morphology is a critical aspect in the development of magnetic nanoparticles as anisotropic particles have shown increased coercivity and magnetic properties. These CoxC nanomaterials have a higher maximum energy product compared to previous work providing further insight into the development of non-rare earth magnetic material. The second part of this dissertation work focuses on the sol-gel synthesis of perovskite LaCaMnO3 (LCMO) nanomaterials. In this process, various chain lengths of polyethylene glycol (PEG) was added into a solution consisting of La, Ca, and Mn salts. The solution was left for the gelation process, and high temperature sintering to obtain the final product. By varying the polymer chain of the PEG, the size of the as synthesized LaCaMnO3 nanomaterials were altered. The as-synthesized LCMO nanomaterials have shown a maximum change in magnetic entropy (-ΔSM) was found to be 19.3 Jkg-1K-1 at 278 K for a field change of 0-3 T and 8.7 Jkg-1K-1 for a field change of 0-1 T. This is a significant improvement in comparison to current literature of the material suggesting that this is a promising alternative to Gd materials that is prone to oxidation. With additional development, LCMO or related maganites could lead to application in commercial technologies.
57

Biosensing and Catalysis Applications of Nanoporous Gold (NPG) and Platinum-Speckled Nanoporous Gold (NPG-Pt) Electrodes

Freeman, Christopher J 01 January 2018 (has links)
The importance of porous materials has risen substantially in the last few decades due to their ability to reduce the size and cost of bioanalytical devices and fuel cells. First, this work aims to describe the fabrication of nanoporous gold (NPG) electrodes that are resistant to electrode passivation due to fibrinogen biofouling in redox solutions. The effect on potentiometric and voltammetric experiments was seen as a deviation from ideal behavior on planar gold electrodes, whereas NPG electrodes were consistently behaving in a Nernstian fashion at low concentrations of ferri-ferrocyanide (£100 mM). An improvement in electrode behavior on NPG electrodes versus planar gold was seen in solutions containing ascorbic acid as well as blood plasma. Second, cost effective NPG electrodes were fabricated using a glass substrate to test the response in the presence of a variety of redox molecules. The optical transparency of these electrodes allowed for microdroplet measurements to be made using an inverted microscope in several redox solutions for validation and subsequent biological applicability. Nernstian behavior was demonstrated for all one- and two-electron transfer systems in both poised and unpoised solutions. All experiments were conducted using volumes between 280 and 1400 pL producing rapid results in less than one minute. Third, in order to decrease the requirement for complex instrumentation, microdroplet fabrication technique was used to create mini-nanoporous gold (mNPG) electrodes on glass capillary tubes. The cylindrical shape of the electrodes allowed for testing in sample volumes of 100 mL. The response to ferri-ferrocyanide, ascorbic acid, cysteine, and uric acid was then investigated with Nernstian behavior shown. However, the mNPG electrodes were insensitive to glucose and hydrogen peroxide. In order to increase the sensitivity of the electrodes, a minimal amount of platinum was electrodeposited onto the NPG surface using a low concentration of platinum salt (0.75 mM) for a short deposition time (2 seconds) producing a Nernstian response to both glucose and hydrogen peroxide. Lastly, to test the viability of crossover applications, the platinum incorporated NPG electrode was employed as a fuel cell anode material, testing their oxidation capability with methanol, ethanol, and formic acid.
58

Use of Surface Enhanced Raman Spectroscopy for the Detection of Bioactive Lipids

Ohlhaver, Christopher M 01 January 2018 (has links)
The detection and analysis of lipids in biological matrices for clinical applications poses many challenges, but rapid and reliable detection will prove invaluable for clinical diagnosis. Herein, we report the application of drop-casted Ag nanoplatelets as surface enhanced Raman scattering (SERS) substrates for qualitative detection of 20-hydroxyeicosatetraenoic acid (20-HETE), which is a potential biomarker for diagnosis of hypertensive disorders. Biomarker peaks of 20-HETE can be reliably detected and differentiated from those of the structurally similar lipids (arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid) commonly found in human blood, even 1 pM concentrations. Additionally, one study mixed 20-HETE with three structurally similar lipids at concentrations several orders of magnitude greater than the target lipid and 20-HETE could still be detected under these conditions. These experiments demonstrate the viability of SERS for the rapid and reliable detection of endogenous bioactive lipids, which has significant clinical impact in enabling point of care diagnostics.
59

Metal-Organic Frameworks and Graphene-Based Support Materials for Heterogeneous Catalysis

Lin, Andrew 01 January 2018 (has links)
Nanoparticles are involved in a broad range of applications, including heterogeneous catalysis. Nanoparticles tend to quickly lose their well-defined shapes and facets due to aggregation under duress such as heat. A series of highly studied materials are explored as support materials for nanoparticle supports. These supports include metal-organic frameworks (MOF), graphene oxide (GO), and a MOF-PRGO (partially reduced graphene oxide) hybrid. The inclusion of a support with the palladium increased lifespan of the catalyst by separation of nanoparticles. The choice of support material not only allowed for supporting of palladium nanoparticles, but allowed for rational catalyst synthesis in order to design catalysts with improved catalytic activity. CO oxidation, vanillin hydrogenation, and Suzuki cross coupling were studied. For the CO oxidation reaction, a cerium-based MOF, Ce-MOF, is shown to increase activity of palladium nanoparticles by capturing reactant gases and acting as an oxygen reservoir that cycles between (III) and (IV) states while transferring oxygen to palladium nanoparticles at the Pd/Ce-MOF interface. A hybrid Ce-MOF-PRGO was synthesized to increase the surface area and acidity of Ce-MOF materials and was shown to be active for vanillin hydrogenation. Smaller rod-like Ce-MOF crystals were observed, indicating intercalation of crystals on GO. Zirconium-based MOF UiO-66-NH2 was acidified via incorporation of tungstophosphoric acid (HPW), which increased the selectivity of products by adjusting the mechanistic pathway. GO was partially functionalized with aromatic amines to improve the coupling of bromobenzene and phenylboronic acid. Small amounts of aromatic amines increased the Pd(0) content and decreased nanoparticle size.
60

Single-Step Biofriendly Synthesis of Surface Modifiable, Near-Spherical Gold Nanoparticles for Applications in Biological Detection and Catalysis

Badwaik, Vivek D. 01 August 2011 (has links)
There is an increased interest in understanding the toxicity and rational design of gold nanoparticles (GNPs) for biomedical applications in recent years. Such efforts warrant reliable, viable, and biofriendly synthetic methodology for GNPs with homogeneous sizes and shapes, particularly sizes above 30 nm, which is currently challenging. In the present study, an environmentally benign, biofriendly, singlestep/ single-phase synthetic method using dextrose as a reducing and capping agent in a buffered aqueous solution at moderate temperature is introduced. The resulting GNPs are near-spherical, stable, catalytically active, place exchangeable, and water-soluble within the size range of 10-120 nm. The added advantage of the biologically friendly reaction medium employed in this new synthetic approach provides a method for the direct embedment/integration of GNPs into biological systems such as the E. coli bacterium without additional capping ligand or surface modification processes.

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