Les métallodendrimères sont des macromolécules précises contenant des centres métalliques dont les propriétés sont exploitables pour la fabrication de nanodevices utiles en catalyse, reconnaissance moléculaire et en tant que précurseurs de nanoparticules. Pour leur contruction, de nouvelles réactions ont été mises au point à partir d’alcynes organométalliques électrophiles qui ont permis la formation de liaisons C-C, C-N et M=C, mettant en jeu des métallocènes du fer, du ruthénium et du cobalt. Cette ingéniérie moléculaire a conduit à de nouvelles métallo-étoiles, dendrimères et nanoparticules d’or aux propriéties rédox originales. / Metallodendrimers are precise macromolecules containing metallic centers with properties that are exploitable for nanodevice fabrication providing uses in catalysis, molecular recognition and as nanoparticle precursors. For their construction, new reactions have been disclosed from electrophilic organometallic alkynes leading to the formation of C-C, C-N and C=C bonds that involve iron, ruthenium and cobalt metallocenes. This molecular engineering has produced new metallo-stars, metallodendrimers and gold nanoparticles with original redox properties.

As commercially manufactured nanomaterials become more commonplace, they have the potential to enter ecological and biological environments sometime during their lifecycle of production, distribution, use or disposal. Despite rapid advances in the production and application of nanomaterials, little is known about how nanomaterials may interact with the environment or affect human health. This research investigates an environmental application of nanomaterials and characterizes the physicochemical properties of commonly manufactured nanomaterials in environmental health and safety studies. Characterization of nanomaterials for applications and environmental health and safety studies is essential in order to understand how physicochemical properties correlate with chemical, ecological, or biological response or lack of response. Full characterization includes determining the bulk and surface properties of nanomaterials. Bulk characterization methods examine the shape, size, phase, electronic structure and crystallinity, and surface characterization methods include surface area, arrangement of surface atoms, surface electronic structure, surface composition and functionality. This work investigates the selective catalytic reduction (SCR) of NO2 to N2 and O2 with ammonia on nanocrystalline NaY, Aldrich NaY and nanocrystalline CuY using in situ Fourier transform infrared (FTIR) spectroscopy. It was determined that the kinetics of SCR were 30% faster on nanocrystalline NaY compared to commercial NaY due to an increase in external surface area and external surface reactivity. Copper-cation exchanged nanocrystalline Y resulted in an additional increase in the rate of SCR as well as distinct NO2 and NH3 adsorption sites associated with the copper cation. These superior materials for reducing NOx could contribute to a cleaner environment. This work consists of characterization of commonly manufactured or synthesized nanomaterials and studies of nanomaterials in specific environmental conditions. Bulk and surface characterization techniques were used to examine carbon nanotubes, titanium dioxide nanoparticles, bare silver nanoparticles and polymer-coated silver nanoparticles, and copper nanoparticles. Lithium titanate nanomaterial was collected from a manufacturing facility was also characterized to identify occupational health risks. Particle size distribution measurements and chemical composition data showed the lithium titanate nanomaterial forms larger micrometer agglomerates, while the nanoparticles present were due to incidental processes. A unique approach was applied to study particle size during dissolution of nanoparticles in aqueous and acidic conditions. An electrospray coupled to a scanning mobility particle sizer (ES-SMPS) was used to determine the particle size distribution (PSD) of bare silver nanoparticles in nitric acid and copper nanoparticles in hydrochloric acid. The results show unique, size-dependent dissolution behavior for the nanoparticles relative to their micrometer sized counterparts. This research shows size-dependent properties of nanomaterials can influence how they will be transported and transformed in specific environments, and the behavior of larger sized materials cannot be used to predict nanomaterial behavior. The type of nanomaterial and the media it enters are important factors for determining the fate of the nanomaterial. These studies will be important when considering measures for exposure control and environmental remediation of nanomaterials.

Colloidally synthesized silicon (Si) and germanium (Ge) were explored as high capacity anode materials in lithium ion batteries. a-Si:H particles were synthesized through the thermal decomposition of trisilane in supercritical n-hexane. Precise control over particle size and hydrogen content was demonstrated. Particles ranged in size from 240-1500 nm with hydrogen contents from 10-60 atomic%. Particles with low hydrogen content had some degree of local ordering and were easily crystallized during Raman spectroscopy. The as-synthesized particles did not perform well as an anode material due to low conductivity. Increasing surface conductivity led to enhanced lithiation potential. Cu nanoparticles were deposited on the surface of the a-Si:H particles through a hydrogen facilitated reduction of Cu salts. The resulting Cu coated particles had a lithiation capacity seven times that of pristine a-Si:H particles. Monophenylsilane (MPS) grown Si nanowire paper was annealed under forming gas to reduce a polyphenylsilane shell into conductive carbon. The resulting paper required no binder or carbon additive and achieved capacities of 804 mA h/g vs 8 mA h/g for unannealed wires. Si and Ge heterostructures were explored to take advantage of the higher inherent conductivity of Ge. Ge nanowires were successfully coated with a-Si by thermal decomposition of trisilane on their surface, forming Ge@a-Si core shell structures. The capacity increased with increasing Si loading. The peak lithiation capacity was 1850 mA h/g after 20 cycles – higher than the theoretical capacity of pure Ge. MPS additives created a thin amorphous shell on the wire surfaces. By incubating the wires after MPS addition the shell was partially reduced, conductivity increased, and a 75% increase in lithiation capacity was observed for the nanowire paper. The syntheses of Bi and Au nanoparticles were also explored. Highly monodisperse Bi nanocrystals were produced with size control from 6-18 nm. The Bi was utilized as seeds for the SLS synthesis of Ge nanorods and copper indium diselenide (CuInSe2) nanowires. Sub 2 nm Au nanocrystals were synthesized. A SQUID magnetometer probed their magnetic behavior. Though bulk Au is diamagnetic, the Au particles were paramagnetic. Magnetic susceptibility increased with decreasing particle diameter. / text

Trivalent rare earth cations (RE3+) activated nanometre-sized Y2O2S and Gd2O2S phosphors were prepared by converting hydroxycarbonate precursor powders during a firing process. The precursors were prepared using the urea homoprecipitation method. The choice of host crystal and dopant were optimised to meet the specific requirements for practical applications in the field of lighting, X-ray detection, and displays. Parameters that affect the luminescent properties of the resulting phosphors, such as doping concentration, excitation mechanism, firing temperature, and host lattice were investigated. Tb3+ and Er3+ co-doped Y2O2S and Gd2O2S were studied for their upconversion properties under 632.8 nm red laser excitation. The intensities of UC emission were affected by both doping concentration and host lattices. Tb3+ and Er3+ co-doped Y2O2S was found to show strong downconversion from Tb3+ and upconversion from Er3+. The presence of the Er3+ cations directly affects the Tb3+ down-converting properties by acting as centres for energy transfer. The possible energy transfer between Gd3+ and Er3+ should be responsible for the different trend of Er3+ upconversion intensity in Y2O2S and Gd2O2S. It has been established that the Tb3+ and Er3+ co-doped system is superior than the Yb3+ and Er3+ co-doped one. In the latter system the presence of Yb3+ reduces the efficiency of both upconversion and downconversion emission under red laser excitation. These phosphors show potential applications in the security and anti-fraud field. The novel ZnS:Mn QDs were prepared and successfully incorporated into GaN based photonic crystal (PC) holes to efficiently produce white light. The crystal structure and luminescent properties of the ZnS:Mn QDs were investigated as well as the factors affecting the filling rate. Zn1-xCdxS:Mn QDs were also investigated. The addition of Cd cations leads to a red shift in the PL excitation spectra of the Zn1-xCdxS:Mn QDs. The crystal structures and surface properties were also affected by the presence of Cd. Monodisperse PbS QDs with particle size of ~5 nm has been obtained using a similar aqueous reaction method.

Lithium-ion batteries have revolutionized the portable electronics market, and they are currently pursued intensively for vehicle applications and storage of renewable energies (solar and wind energy). Cost, safety, cycle life, and energy and power densities are the critical parameters for these applications. With this perspective, there has been immense interest to develop new cathode and anode materials as well as to develop novel synthesis and processing approaches. This dissertation explores the use of novel synthesis approaches to obtain high-performance, nanostructured phosphate and silicate cathodes and iron oxide nanowire anodes and investigates their structure-property relationships. First, a novel microwave-solvothermal (MW-ST) approach has been developed to synthesize phase-pure, highly crystalline LiFePO₄ nanorods within 5-15 minutes at low temperatures of < 300 °C, without requiring reducing gas atmospheres. The LiFePO₄ nanorods, after forming a nanocomposite with conducting polymer or multi-walled carbon nanotubes or coating with conductive carbon, offer excellent cycle life and rate performance when implemented as cathodes in lithium-ion cells. In addition, other LiMPO₄ (M = Mn, Co, and Ni) olivine nanorods have also been synthesized by the MW-ST approach and characterized. The MW-ST process has then been extended to prepare a new class of carbon-coated, nanostructured silicates of the formula Li₂MSiO₄ (M = Fe and Mn). These materials have two times higher theoretical capacities (~ 330 mAh/g) than olivine phosphates (~ 170 mAh/g). Li₂FeSiO₄ exhibits practical discharge capacities of 148 mAh/g at room temperature and 203 mAh/g at 55 °C, with good rate capability and stable cycle life. Li₂MnSiO₄, on the other hand, shows higher discharge capacities of 210 mAh/g at room temperature and 250 mAh/g at 55 °C, but it exhibits poor rate performance and rapid capacity fade during cycling. In addition, carbon-coated olivine solid solution nano-particles of the formula LiM[subscript 1-y]M[subscript y]PO₄ (M = Fe, Mn, Co, and Mg), synthesized by a facile, high-energy mechanical milling process (HMME), have also been investigated. The electrochemical data reveal a systematic shift in the redox potential (open-circuit voltage) of the M²⁺/³⁺ couples in the LiM[subscript 1-y]M[subscript y]PO₄ solid solutions compared to those of the pristine LiMPO₄. The shifts in the redox potentials have been explained by the changes in the M-O covalence (inductive effect), which are caused by changes in the electronegativity of M or the M-O bond length or M-O-M interactions. Finally, a two-step microwave-hydrothermal process has been developed to synthesize carbon-decorated, single-crystalline Fe₃O₄ nanowires. The resulting iron oxide nanowires exhibit capacity values > 800 mAh/g with stable cycle life and high rate performance as an anode in lithium-ion cells. / text

X-ray sensors are essential to many applications which are not limited to diagnostics and imaging technologies. Such sensors are extensively used in industry, medicine, research and space technology for applications such as safety, security, quality control, imaging and treatment. Depending on the effect of the radiation on the matter employed in the sensor, different types of X-ray sensors are fabricated. However, available techniques of X-ray detection have been under development due to specific shortcomings such as finite life time, low sensitivity, and post-processing requirements. This thesis is focused on design, fabrication and characterization of novel radiation sensors based on bio/nanomaterials. Bacteriorhodopsin (BR), a proton pump protein in the cell membrane of Halobacterium Salinarum, has been used to fabricate a sensor to measure dose and dose rate of X-ray beam in the kilovoltage and megavoltage energy range. The mass attenuation coefficients, effective atomic numbers and electron densities of BR and its comprising amino acids have been calculated for 1 keV-100 GeV photons to better understand the interaction of BR with X-ray photons. A theoretical formulation for calculating the change in the conductivity of nanoparticles under radiation is also provided. In particular, the dependence of radiation induced conductivity to irradiated particle size is given. In addition to that, an X-ray sensor based on thin film of bismuth sulfide has been fabricated using laser micromachining and chemical deposition techniques. This sensor has been characterized under a diagnostic X-ray machine with kilovoltage energy beam.

In this thesis, high temperature vapor deposition method has been extensively used to synthesize nanomaterials. One of the as-synthesized nanostructures is superlattice-structured nanohelix, which is made of two types of alternating and periodically distributed long crystal strips. The manipulation of the nanohelix showed super-elasticity and special fracture mechanism. The other widely studied nanomaterial is vertically aligned ZnO nanowire array, which is epitaxially grown on GaN and SiC substrates. Several manipulation methods such as e-beam lithography (EBL), dielectrophoresis, and in situ direct manipulation, have been developed, so that the mechanical and electrical properties of a single nanowire can be characterized, which provide essential references for fabricating bridged nanowire based devices. Specifically, an improved atomic force microscope (AFM) based method has been developed to accurately measure the elastic modulus of bridged ZnO nanowires. Bridged nanostructure is an extremely important configuration in planar MEMS/NEMS devices and this new approach provides insights to the importance of boundary conditions. Novel physical and statistical models have been firstly developed to obtain better estimate of elastic modulus. For electrical properties of bridged nanowires, it is found that the direct contact of ZnO nanowire and Au electrodes displays a back-to-back Schottky behavior. Self-assembled monolayer (SAM) can improve the mechanical contact and increase the conductance. These devices with Schottky contacts show much better UV sensing performance than the ones with Ohmic contacts. Barrier height change is believed to play an important role in a lot of sensors. A thermionic emission-diffusion model is deduced to successfully explain the current change in a strain sensor. This thesis clearly exhibits the unique properties of ZnO nanomaterials and provides deeper understanding to methodologies as well as the phenomena. With further exploration, ZnO nanomaterials should be able to better understood and utilized, and come close to the next step of commercialization.

Understanding the toxicity of carbon nanomaterials, such as carbon nanotubes and graphenes, is important for the development of nanotechnology. Studies have shown that surface redox capability is an important factor for toxicity of carbon nanomaterials. We have measured the surface reductive capacity for a number of carbon nanomaterials in previous studies, but the effects of various engineering processes on surface redox capability have not been investigated until this study. In this study, commercially available carbon black, carbon nanotubes, standard reference materials, fullerenes, graphenes and acetylene soot generated in the lab were used. The carbon nanomaterials were subjected to heating at various temperatures in various atmospheres up to 500 ˚C, and soaking in water at room temperature under various atmospheres, and weathering in the powder form at room temperature under various atmospheres. The redox capability of the carbon nanomaterials was quantified in terms of the reductive capacity towards Fe3+ ions (RCFI). The RCFI values of the asreceived nanomaterials and that of the nanomaterials after various treatments were compared. The carbon nanomaterials were also characterized using x-ray photoelectron spectroscopy (XPS), for understanding the surface chemistry mechanisms of RCFI and the effects of various treatments. In general, heating induced a significant increase in RCFI, regardless of the atmosphere under which the nanomaterials were heated. On the other hand, aging in O2- containing atmospheres brought about significant decrease in RCFI, either in water suspension or in the powder form. Water vapor enhanced the aging effect of O2. CO2 was found to affect the RCFI and the aging of carbon nanomaterials. The extent of RCFI change due to heating or aging was dependent on the type of material. According to the XPS results, the RCFI of some carbon nanomaterials such as carbon black may be correlated with the C-O surface functional groups. However, the definitive correlation between the oxygen-containing surface functional group and RCFI for all carbon nanomaterials couldn’t be determined by the XPS result. This indicates that the RCFI changes of carbon nanomaterials after treatments mainly derived from the factors such as the active sites of edges other than the oxygen-containing surface functional group changes as other studies show. This suggests that the RCFI measurement cannot be replaced by XPS analysis. The effects of heating and aging on RCFI, and more generally the surface redox capability of carbon nanomaterials, reveals that various engineering and environmental processes may significantly change the toxicity of carbon nanomaterials. The findings of this study suggest that it is important to take into account the effects of engineering and environmental processes when assessing the toxicity of carbon nanomaterials.

Doctor of Philosophy / Department of Chemistry / Daniel A. Higgins / This dissertation describes the application of fluorescence microscopy techniques to investigations of mass transport phenomena in self-assembled nanomaterials. The microscopic morphologies of the materials and the mass-transport dynamics of probe molecules dispersed within them were assessed with high temporal and spatial resolution by single molecule imaging and spectroscopic methods. Three distinct sets of experiments were performed in completing the work for this dissertation. In the first study, single molecule imaging was employed to explore the interactions and field-induced migration of double-stranded DNA (ds-DNA) molecules with nanostructured Pluronic F127 gels. While DNA interactions with nanostructured gels have been explored in the past, none had apparently looked at these interactions in gels comprising hexagonally ordered arrays of cylindrical micelles. Therefore, these studies focused on materials DNA dispersed in flow aligned hexagonal F127. DNA molecules were found to be strongly confined in the hexagonal mesophase structures from their elongation, alignment, and exclusively occurred electrophoretic migration in the direction parallel to the cylinder long axis. These observations will lead to a better understanding of macromolecular interactions with nanostructured gels like those now being investigated for use in drug delivery and chemical separations. In the second study, imaging-fluorescence correlation spectroscopy (imaging-FCS) was used to study the rate and mechanism of sulforhodamine B (SRB) dye within novel bolaamphiphile-based self-assembled nanotubes. These nanotubes were only recently developed and their mass transport properties remain largely unexplored. The nanotubes employed here are unique because they incorporate amine groups and glucose groups on their inner and outer surfaces, respectively. Wide-field fluorescence video microscopy was first applied to locate and image dye-doped nanotubes dispersed on a glass surface. Imaging-FCS was employed as it allows for the dynamics to be recorded simultaneously from a large sample region, thus the SRB mass transport within nanotubes can be spatially resolved. The coulombic interactions between cationic ammonium ions on the inner nanotube surface and the anionic SRB molecules was shown to play a critical role in governing dye dynamics under varied pH and ionic strength conditions. Mass transport of SRB within the nanotubes is concluded to occur by a desorption-mediated Fickian diffusion mechanism. In the third set of experiments, solvatochromic dye molecules were employed in novel imaging-FCS studies of the role played by partitioning in governing mass transport phenomena within the same organic nanotubes used above. Two forms of the solvatochromic dye Nile Red (NR) were employed: the commercial hydrophobic form of NR, and a more polar derivative 2-hydroxybenzophenoxazinone (named NR-OH). The partitioning of dye molecules within the nanotubes was investigated assessing the diffusion rate for each dye. The preliminary results suggested NR and NR-OH preferentially partitioned into the tube walls and the ethanol phase filling the tubes, respectively. The diffusion coefficient data indicated NR-OH diffused faster than NR, consistent with the presence of NR-OH in a relatively less viscous environment (e.g., the ethanol phase filling the tubes). The results of these studies afford information essential to the use of organic nanotubes in controlled drug release and possibly in catalysis applications.

“Nanomaterials” is a generic term used to describe nano-sized crystals and bulk homogenous materials with a structural disorder at the nanoscale. Ancient (and modern) ceramics and glasses derive some of their properties (eg. pliability and low sintering temperature) from the fact that their raw material namely natural clay is nanosized. Furthermore the pigments used to colour ceramics and glasses need to have particle sizes <500 nm for the object to appear homogenously coloured to the human eye. Raman spectroscopy intrinsically probes chemical bonds and is therefore one of the few techniques that has been proven useful to provide information at the nanoscale. It is an excellent tool to study ceramics and glasses as a Raman spectrum can be used to identify phases, analyse amorphous domains in the silicate network and identify pigments on a nano-scale. The characteristics of a glass, ceramic or ceramic glaze derived through its Raman spectrum can then be linked to the technology used to produce an artefact and in this way provide information about its relative age and provenance. Likewise, the identification of pigments and binders in San rock art might provide information about production techniques and assist in the developement of conservation procedures. In this thesis micro-Raman spectroscopy (with X-ray fluorescence, X-ray powder diffraction, electronmicroscopy and photoluminescence as supportive techniques) was utilised to study archaeological artefacts from the Mapungubwe Collection and San rock art. It was possible to re-date celadon shards excavated on Mapungubwe hill in 1934 to the Yuan or even later Ming dynasty in stead of its original classification as Song. A profile of the glass technology used to produce the Mapungubwe oblates, small trade beads from the “royal burials” on Mapungubwe hill was determined and quite a few unique characteristics of the beads may eventually help to establish their provenance. The possible influence of the presence of rock hyraces at rock art sites on the deterioration of rock art were investigated and during the study very rare polymorphs of CaCO3 (vaterite and monohydrocalcite) were discovered in rock hyrax urine. This study was extended to analyse a San rock art fragment and another first was the identification of animal fat on the fragment, but the exact origin of the fat has to be verified by similar experiments. / Thesis (PhD)--University of Pretoria, 2009. / Physics / unrestricted