This dissertation presents experimental and computational study of thermal and electrical transport in one-dimensional nanostructures. Synthesizing materials into one-dimensional nanowire has been proved very effective for suppressing the phonon contribution due to scattering at the wire boundaries. Three one-dimensional nanostructured thermoelectric candidates - SiGe nanowires, SrTiO3 nanowires, and ZnO nanowires – were presented and discussed in this dissertation. SiGe nanowires are successfully synthesized on a cleaned n-type (100) Si substrate coated with gold thin film as a catalytic metal, via the vapor-liquid-solid (VLS) growth method. The thermoelectric properties of SiGe nanowires with different diameter, Ge concentration, and phosphorus doping concentration were measured using a MEMS micro-device consisting of two suspended silicon nitride membranes in the temperature range of 60 K ~450 K. The experimental results were obtained by “simultaneously” measuring thermal conductivity, electrical conductivity, and thermopower. The ZT improvement is attributed to remarkable thermal conductivity reductions, which are thought to derive from the effective scattering of a broad range of phonons by alloying Si with Ge as well as by limiting phonon transport within the nanowire diameters. An improved model based on Boltzmann transport equation with relaxation time approximation was introduced for estimating thermoelectric properties of phosphorus heavily doped SiGe nanowires from 300 to 1200 K. All the electron and phonon scatterings were comprehensively discussed and utilized to develop the new model for estimating electrical conductivity, thermopower, and thermal conductivity of SiGe nanowires. As thermoelectric materials, oxide nanowires have great advantages comparing to other semiconductors. Two nanostructured materials, SrTiO3 nanotubes and ZnO nanowires, are introduced and successfully synthesized by simple methods. Thermal conductivity of ZnO nanowires with different diameter were characterized from 60 K to 450 K. In order to measure thermoelectric properties of one-dimensional nanostructures at temperature up to 800 K, a new temperature vacuum system was carefully designed and built from scratch. The thermal conductivity of ZnO nanowires with different diameters at high temperature were measured from 300 K to 800 K.

<p>Proton exchange membrane fuel cells (PEMFCs) are considered as one of the most promising alternative clean and sustainable energy sources to fossil fuels. In general, PEMFC is consisted of anodic and cathodic electrode assembly, electrolyte, and proton-exchange membrane. While renewable fuels, such as hydrogen gas and formic acid, get oxidized at the anode to produce protons, oxygen molecules are reduced to form water at the cathode. Platinum has been widely used for both anodic and cathodic reactions due to its excellent catalytic reactivity.</p> <p><br></p> <p>Significant effort has been devoted to improving the reactivity and selectivity of Pt-based catalysts by alloying with a second metal. AuPt alloy nanoparticles have been studied extensively for electrochemical formic acid oxidation reaction, and isolated Pt species are recognized as the most active sites. While the majority body of literature focuses on structure-reactivity relationships</p> <p>based on as-synthesized materials, less attention is paid to the structural evolution during electrochemical catalysis. In this work, we develop a colloidal synthetic method to deposit Pt shell onto Au nanoparticles with variable thickness to study the microstructural evolution under electrocatalytic formic oxidation. We find that Pt atoms are submerged from the surface to form isolated Pt species in the first 100 cycles, which show enhanced FAO activity by shifting the reaction pathway. Additional CV scanning causes further depletion of Pt from the surface, resulting in the deactivation of the catalyst.</p> <p><br></p> <p>Despite the high activity of Pt-based catalysts, the use of these materials is limited by its high cost. Recently, transition metal sulfides such as cobalt sulfides have been found to show comparable activity to Pt-based catalysts in pH 7 ORR. However, it is challenging to isolate the role of coordination environment amidst multiple geometries and oxidation states that exist within any given phase. In this effort, we synthesize isolated Co atoms supported on colloidal WS₂nanosheets. By doing post synthetic treatment on these nanosheets, we are able to achieve a range of Co-S coordination number. Correlating Co-S CN to their ORR activities, we find the optimal active sites for ORR in neutral media possess a Co-S coordination number of 3-4.</p>

The optical properties of GaN nanocolumn structures containing InGaN quantum disks are investigated by optical microphotoluminescence spectroscopy using pulsed lasers, and cathodo- luminescence. The results are analyzed in the context of current theories regarding an inho- mogeneous strain distribution in the disk which has been theorized to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. Simulations of the strain distribution for the relevant materials and structures are also performed, and the results analysed. It is concluded from ex- perimental measurements that no extreme lateral separation of carriers occurs in the quantum disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Microphotoluminescence studies are also carried out on a single GaN nanocolumn struc- ture that has been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system. Additional, albeit early-stage, work on novel structures based on the production of GaN nanocolumns, namely nanotubes and nanopyramids, is also presented.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / A series of nanoparticle synthesis methods were devised with the aim of controlling shape. CuO nanorods were synthesized by a hydrothermal treatment with different chemical combinations. Physical parameters: concentration, temperature, and aging time greatly affected the size, morphology and the composition of nanorods. These CuO nanomaterials were reduced to metallic copper at elevated temperature by 4% H[subscript]2 diluted in helium while preserving the morphology. The CuO and Cu nanomaterials were employed for near infra-red (NIR) diffuse reflectance. Among them, CuO nanorods were found to be the best NIR diffuse reflectors, indicating potential application as NIR obscurants. Cu[subscript]2O and its composite samples with different morphologies, some with unique morphologies, were synthesized by reducing Cu[superscript]2[superscript]+ precursors without using any surfactant. The effects of change of Cu-precursors, reducing agents, and other physical conditions such as temperature and pressure were investigated. Since Cu[subscript]2O is a semiconductor (E[subscript]g ~ 2.1 eV), these samples were used as photocatalyst for the degradation of methyl violet B solution under UV-vis light and as dark catalysts for decomposition of H[subscript]2O[subscript]2 to investigate the effect of morphology. The photocatalytic activity was found to be morphology dependent and the dark catalytic activity was found to be dependent on both surface area and morphology. Mixed oxides of MgO and TiO[subscript]2 with different ratios, and pure TiO[subscript]2 were synthesized by two methods—flame synthesis and aerogel. These mixed oxides were employed as photo-catalysts under UV-vis light to oxidize acetaldehyde. The mixed oxides with low content of MgO (~ 2 mole %) were found to be more UV active photo-catalysts for the degradation of acetaldehyde than the degradation by TiO[subscript]2. The mixed oxides prepared by the aerogel method were found to be superior photo-catalysts than the mixed oxides of equal ratio prepared by flame synthesis. Silica aerosol gels were prepared by two methods: detonation and flame synthesis. Hexamethyldisiloxane (HMDSO) was used as a precursor during the detonation at different conditions. Interestingly, spherical silica nanoparticles were found to be formed by the detonation. Relatively smaller silica nanoparticles with larger volume fraction were found to be favorable for the formation of silica aerosol gels. During the flame synthesis, the silicon precursors, dimethoxydimethylsilane (DMDMS) and HMDSO, were used. Different shapes—spherical, oval, and non-spherical—and sizes of silica particles were formed. These silica nanomaterials were almost amorphous, and they might have many potential applications.

"Carbon is one of the most abundant non-metal elements in the world. The unique arrangement of electrons enables diverse properties and applications of carbon. Long before the discovery of C60 in 1985, which is now considered a milestone in the vibrant field of carbon nanotechnology, carbon has been a vital part of human history. It has been a key enabling material in many fields including aerospace, transportation, energy storage, electric devices, infrared sensors, etc. The report of fullerene triggered a feverish surge of interest and effort in the study of nanostructured carbon. Along with the discovery of carbon nanotubes (CNTs) and graphene nanosheets (GNS), the nanocarbon family has been extensively studied. However, controlled production of carbon nanomaterials with low cost and high efficiency and incorporation of nanocarbons to maximize their contribution in advanced applications still faces a lot of technical difficulties. The objective of this work is to study and optimize processes to synthesize multiwall carbon nanotubes (MWCNTs) and GNS, and to apply GNS in nanocomposite anode materials for Lithium ion batteries (LIBs). Therefore, in this thesis, there are three main parts: (1) development of the post-processing method to obtain free-standing CNT arrays by the template-assisted chemical vapor deposition (CVD) method; (2) development of a synthesis protocol to obtain GNS by oxidation of natural graphite flakes and reduction of the resulted graphene oxides; and (3) fabrication of TiO2/GNS in core-shell structure by a static electric assembling method to improve anode performance for LIB applications."

The work presented herein describes efforts to synthesize and characterize new types of cyanide-bridged molecular materials encompassing both discrete clusters and extended solids. This investigation focused on the incorporation of anisotropic 4d and 5d transition metal ion building blocks into such materials. In this vein, systematic studies on the magnetic properties of families of these cyano-bridges species were conducted and these new materials represent a new addition to the field of cyanide chemistry incorporating for the first time the hexacyanometallates of [Ru(CN)6]3- and [Os(CN)6]3- into discrete molecules and extended networks. These compounds will serve as models for new theoretical studies in understanding the role of magnetic exchange interactions, both isotropic and anisotropic, in the study of nanomagnetic materials. Results were obtained from using the well known octacyanometallates of MoV and WV as building blocks for the synthesis and the magnetic investigation of both trigonal bipyramidal and pentadecanuclear clusters including the discovery of a new SMM. By expanding the research to previously unused hexacyanometallates, the synthesis and characterization of the first known examples of clusters based on hexacyanoosmate(III) and hexacyanoruthenate(III) building blocks and their use in preparing new theoretical models of magnetic species. A novel pair of clusters is further detailed in the study of the trigonal bipyramidal clusters of [Fe(tmphen)2]3[Os(CN)6]2 and [Fe(tmphen)2]3[Ru(CN)6]2 and an in depth study of the CTIST behavior of these clusters using Mossbauer spectroscopy, variable temperature crystallography, epr, and variable temperature IR measurements. Finally, this work discusses new magnetic Prussian Blue analogs prepared from the hexacyanoosmate(III) and hexacyanoruthenate(III) anions with a comparison to the trigonal bipyramidal clusters presented based on these hexacyanoosmate(III) and hexacyanoruthenate(III) building blocks.

The use of spontaneous self-assembly as a lithography free means to construct well-ordered, often intriguing structures has received much attention for its ease of producing complex, centimeter-scale structures with small feature sizes. These self-organized structures promise new opportunities for developing miniaturized optical, electronic, optoelectronic, and magnetic devices. One extremely simple route to intriguing structures is the evaporative self-assembly of nonvolatile solutes from a sessile droplet on a solid substrate. However, flow instabilities during the evaporation process often result in non-equilibrium and irregular dissipative structures (e.g., randomly organized convection patterns, stochastically distributed multi-rings, etc.). Therefore, in order to fully control the evaporative self-assembly of solutes, two strategies, namely, controlled evaporative self-assembly (CESA) and flow-enabled evaporative-induced self-assembly (FESA) were developed to create ordered structures of various nanomaterials. First, hierarchical assemblies of amphiphilic diblock copolymer (i.e., polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP)) micelles were crafted by FESA. The periodic threads comprising a monolayer or a bilayer of PS-b-P4VP micelles were precisely positioned and patterned over large areas. Second, highly aligned parallel DNA nanowires in the forms of nanostructured spokes over a macroscopic area were created via evaporative self-assembly (CESA) by subjecting DNA aqueous solution to evaporate in a curve-on-flat geometry composed of a spherical on a flat substrate. Third, large-scale aligned metallic nanowires templated by highly oriented DNA were produced by flow-enabled self-assembly (FESA). A simple yet robust swelling-induced transfer printing (SIT-Printing) technique was developed to transfer ultralong DNA nanowires onto the desirable substrate. Subsequently, the resulting DNA nanowires were exploited as templates to form metallic nanowires by exposing DNA nanowires preloaded with metal salts under oxygen plasma. Moreover, DNA nanowires were also employed as scaffold for aligning metal nanoparticles and nanorods. Fourth, colloidal microchannels (i.e., cracks) on a large scale were yielded by fully controlling the drying process of colloidal suspensions via flow-enabled self-assembly (FESA). The influence of chemically patterned substrate (i.e., hydrophobic stripes on a hydrophilic substrate) on the formation of colloidal microchannels was explored. In addition, such colloidal microchannels with tunable center-to-center distance between the adjacent cracks, λ_(c-c) was exploited as template for aligning inorganic nanoparticles. Importantly, theoretical study of the formation mechanism of parallel stripes of solutes by FESA was conducted. The relationship between the characteristic spacing of adjacent stripes λ_(c-c) and other experimental parameters such as the stripe width, the stop time and the moving speed of lower substrate were scrutinized. Such theoretical modeling would provide guidance for the precise design and crafting of ordered structures composed of nanomaterials by FESA in the future study. Interestingly, during the preparation of Au nanorods, the formation of ultrathin gold nanowires were unexpectedly observed. Based on conventional synthetic route to Au nanorods using CTAB as soft-templates, we discovered that the addition of a small amount of hydrophobic solvent (e.g., toluene or chloroform) to the Au growth solution entailed the formation of ultrathin Au nanowire, rather than Au nanorods. The growth mechanism of such intriguing water-soluble ultrathin Au nanowires, differed from those formed by using oleylamine (i.e., non-water-soluble Au nanowires), was explored. In general, the ability to craft ordered structures comprising nanomaterials by FESA and CESA provides new opportunities for organizing nanomaterials for use in electronics, optics, optoelectronics, sensors, nanotechnology and biotechnology.

Solution-grown silicon and germanium nanowires were produced using various solvents and nanocrystalline seed materials. Silicon nanowires grown using monophenylsilane as the silicon source and gold catalyst seeds were made into a freestanding, lightweight, mechanically robust fabric and tested as a negative electrode material in lithium ion batteries. Annealing the fabric under reducing atmosphere converts the intrinsic poly(phenylsilane) shell into a highly conductive carbonaceous coating, improving Li storage behavior. Reduced graphite oxide (graphene) was studied as a freestanding support for gold-seeded germanium and silicon nanowires, the latter grown using trisilane. Graphene improves capacity retention for germanium nanowires but shows little improvement for silicon. Slurry-cast films of nanowires were also tested as negative electrodes in lithium ion batteries using a variety of electrolyte solvent / binder combinations. Gold is detrimental to performance of silicon nanowires grown using trisilane. Removing gold through a simple wet etching procedure dramatically improves capacity retention. Silicon nanowires were also synthesized using in-situ formed tin seeds. Tin-seeded nanowires are easier to produce and outperform gold-seeded wires in lithium ion batteries. Germanium nanowires perform exceptionally well under high current loads when cycled using electrolyte solutions that contain fluoroethylene carbonate and show promise for high- power applications. Controlled synthesis of solution-grown germanium nanorods is demonstrated using nanocrystalline bismuth seeds. The addition of poly(vinylpyrrolidinone) / hexadecene copolymer leads to branched nanorods. Absorbance spectra were calculated using the discrete dipole approximation to compare against spectra obtained experimentally. The absorbance spectra and electric field internal to the nanorods depend highly on nanorod orientation. The presence of bismuth or gold at the tip of the nanorods also significantly alters the spectra and electric fields. Ligand and surface chemistry of solution grown indium phosphide nanowires is also examined. Octylphosphonic acid and hexadecylamine are both essential for the growth of single crystalline indium phosphide nanowires. Potential solution synthesis routes to indium (III) oxide nanowires and indium phosphide nanowires with twinning superlattice structure are presented. Various phosphoric acid derivatives were tested in place of octylphosphonic acid and the efficacy of each is discussed. / text

The International Agency for Research on Cancer (IARC) stated that chromium in the form of Cr(VI) has been deemed to be a class-A human carcinogen. It has been a major contaminant associated with wastewater. Moreover, the existence of heavy metals in aquatic systems is a critical concern for the environment as well as industries that manufacture or consume these particular elements. In order to remove these particular toxic metals, several well-known conventional methods including ion-exchange, filtration and adsorption are used. Amongst these methods, adsorption offers significant advantages such as the low-cost materials, ease of operation and efficiency in comparison to the other conventional methods. The aim of this work was to develop nanomaterials (particles and fibers) to address some critical issues for the treatment of heavy metals, especially chromium in aqueous systems. Furthermore, the use of nanomaterials and how they relate to nanoscale operations at the biological level has generated considerable concerns in spite of their novel properties. The first part of this thesis deals with the synthesis and characterizations of Fe3O4, magnetite, as nanoparticles which were further coated with surfactants bis(2,4,4-trimethylpentyl)dithiophosphinic acid, Cyanex-301, and 3-Mercaptopropionic acid with the active compound being the thiol (SH) groups, that will suffice as a viable material for Cr(VI) removal from aqueous solutions. The proposed mechanism was the complexation between the thiol group on Cyanex-301 and 3-Mercaptopropionic acid, respectively. The effect of different parameters on the adsorption including contact time, initial and final Cr(VI) ion concentration and solution pH was investigated. The second part of this thesis encompassed the fabrication of flexible nanocomposite materials, with a large surface area and architecture for the removal of Cr(VI) in batch and continuous flow mode. A technique known as electrospinning was used to produce the nanofibers. The flexible yet functional materials architecture has been achieved by growing ZnO nanorod arrays through chemical bath deposition on synthesized electrospun poly-L-lactide nanofibers. Moreover, polyacrylonitrile nanofibers (PAN) were synthesized and adapted by the addition of hydroxylamine hydrochloride to produce amidoxime polyacrylonitrile nanofibers (A-PAN). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the morphologies and particle sizes whereas Fourier-Transform Infrared spectroscopy (FT-IR) was used to identify either the presence or absence of functional groups for the formation of PAN and A-PAN nanofibers. The optimization of functionalized nanoadsorbents to adsorb Cr(VI) was also carried out to investigate the effect of experimental parameters: contact time, solution pH, initial, final and other metal ion concentration. Commercially manufactured pristine engineered (TiO2, ZnO and SiO2) nanoparticles and lab-made functionalized (Fe3O4 and CeO2) nanoparticles were studied while the powders were suspended in appropriate media by Dynamic Light Scattering (DLS) to identify their cytotoxicity effects. / <p>QC 20160111</p>

Nanomaterial’s applications have expanded greatly in the last few decades due to their interesting properties. Example of nanomaterials are metal nanoparticles NP. NP have interesting physical and optical properties that make them different and more useful than their bulk counterpart. Some of these properties are the large surface area to mass ratio and their ability to absorb light. NP have been applied in the health, environment, and catalysis fields The main focus of this thesis will be on the applications of nanomaterials in medicine and catalysis. In the first part of the thesis, coated polydispersed and polymorphic silver nanostructures AgNS were synthesized using seed mediated method. The synthesized AgNS were characterized using SEM, TEM, and UV-VIS. The stability of these AgNS were determined by measuring the shift in the plasmon band over time and by measuring their zeta potential. Moreover, the bactericidal properties of coated AgNS were tested on gram negative bacteria such as Escherichia coli and Pseudomonas aeruginosa and gram positive bacteria such as Methicillin- Resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus. The second part of the thesis discusses the field of nanocatalysis where different supported metal nanoparticles on TiO2 were synthesized and characterized by TEM, diffuse reflectance DR, XPS and ICP. The activity of the synthesized catalysts was tested for Ullmann C-C cross coupling reaction. The use of the photoresponisve Pd@TiO2 under the combination of UVA 368 and visible light 465nm irradiation offered the highest selectivity toward the cross coupling product.