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This thesis focuses on the development of method to the photochemical synthesis of niobium nanoparticles (NbNP) using Irgacure 907 (I-907) photoinitiator. This investigation is composed of two parts; whereas the mechanistic study of formation of particles was investigated first, and then followed by particles property characterization. By studying the mechanism of formation we were able to obtain knowledge on how to control the size of NbNP. This knowledge provided us with ability to generate a library of nanoparticles with the varying sizes. Furthermore, the study of I-907 photoproducts has given insight for an alternative method for the synthesis of NbNP using a milder reducing agent, 4-(methylthio)benzaldehyde (MSBA). Exposure of NbNP to air causes their oxidation leading to the formation of niobium oxide nanoparticles (NbONP). The oxidation of NbONP was characterized with variety of techniques (XPS, EDS and HRTEM) that demonstrated the core-shell structure of the nanoparticles. These methods indicated that the core is metallic Nb0 and the shell is the niobium oxide, Nb2O5. Since Nb2O5 is known be a strong Brønsted acid, we tested the Brønsted activity of NbONP with pH sensitive dye coumarin-6 (C6) (monitored using fluorescence and UV-vis). The results of these spectroscopic experiments indicated that NbONP can protonate C6, thus serving as confirmation for the acidity of NbONP. Furthermore, particles with varying sizes were tested with C6 to check if the difference in size affects the acidity. It was observed that the particles with the larger sizes have the strongest acidity and the particles of smaller sizes are less acidic.

Slow photon, or light with reduced group velocity, is a unique phenomenon found in photonic crystals that theoreticians have long suggested to be invaluable for increasing the efficiency of light-driven processes. This thesis demonstrates experimentally the feasibility of using slow photons to optically amplify photochemistry of both organic and inorganic systems. The effect of photonic properties on organic photochemistry was investigated by tracing out the wavelength-dependent rate of photoisomerization of azobenzene anchored on silica opals. The application of slow photons to inorganic photochemical processes was realized by molding nanocrystalline titania into an inverse opal structure and investigating its photodegradation efficiency in relation to the photonic properties. Changes in the photodegradation efficiency were directly linked to modifications of the electronic band gap absorption as a result of the photonic properties. The highest enhancement of twofold was achieved when the energy of the slow photons overlaps with the electronic band gap absorption, such that the loss of light due to photonic stop-band reflection was significantly reduced. In addition, the strength of slow-photon amplification with respect to the macroscopic structural order was studied by introducing controlled disorder via the incorporation of guest spheres into the opal templates. For the first time, a correlation between structural order, photonic properties and a photochemical process was established. The ability to combine slow-photon optical amplification with chemical enhancement was further achieved by incorporating platinum nanoparticles in inverse titania opals where the platinum nanoparticles increased the lifetimes of the higher population of electron-hole pairs arising from slow photon. Overall, various important factors governing the slow photon enhancement were investigated in detail, including the energy of the photonic stop band, angle dependence, thickness of the film, degree of structural order, filling fraction of the dielectric material and diffusion of a second medium if present. Theoretical calculations based on scalar-wave approximation in support of the experimental findings were provided wherever possible. The findings provide a blueprint for achieving optical amplification using slow photons in the broad range of photochemical or photophysical processes.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1970. / Includes bibliographies. / 2 pt. in 1 v illus., tables

Glyphosate (N-(phosphonomethyl)glycine) is the phytotoxic reagent in the widely used Roundup® herbicide. Its mode of action in plants is the disruption of the Shikimate pathway, part of an important route to the biosynthesis of essential aromatic amino acids. It is well documented that glyphosate can be degraded by soil microorganisms after contact of the herbicide solution with the soil. It is also accepted that glyphosate, an excellent ligand, is readily absorbed to metal ions, such as Fe(III), that can be abundant in soils. There have been many accounts on the microbial degradation of glyphosate, and several metal-glyphosate complexes have been synthesised and characterised. Surprisingly, given the degree of adsorption to metal ions in the soil, there have not, to date, been any reports in the literature on the reactivity of metal-glyphosate complexes. The behaviour of these types of complexes under various reaction conditions may give us an insight into the mechanisms present when glyphosate degrades. In order to explore the behaviour of metal-glyphosate adducts, we have prepared several new cobalt-PMG complexes in the lab. These complexes have been characterised by NMR, mass spectrometry, elemental analysis, and in some cases X-ray crystal structure determination. We chose to synthesise complexes where the PMG ligand is bidentate or tridentate, filling the remaining four or three (respectively) coordination sites with an ancillary, nitrogen-containing ligand. We have subjected the complexes to photolytic and basic conditions, as we are interested in ascertaining how coordinated PMG might behave when irradiated with UV light, and when it is C-deprotonated. Metal-glyphosate complexes in nature may be exposed to UV light, so we are concerned with how the coordinated ligand might react under these circumstances. We have found that the prepared cobalt-PMG complexes are reactive when exposed to UV light, and that this appears to result in the degradation of the complex, and in some cases, the PMG ligand itself. The reactivity of C-deprotonated PMG is also an area of interest to us. It is possible that elevations in soil pH can lead to C-deprotonation of glyphosate, then further reactivity that may contribute to the degradation of the compound. Furthermore, when the herbicide is held in the active site of an enzyme within a microbe, it may become deprotonated, and this may aid in its microbial degradation. We have found that, under basic conditions, the reactivity of the prepared PMG complexes depends on the ancillary ligand attached - π-acidic, pyridine-containing ancillary ligands appear to increase the reactivity of coordinated PMG. It seems that amine-containing ligands hinder the reactivity of the coordinated PMG such that the complex remains intact. It is hoped that the results of the research described in this thesis will assist in the future investigations into the reactivity of the herbicide glyphosate.

Thesis (M.S.)--Wake Forest University. Dept. of Chemistry, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2007.

Thesis (Ph. D.)--University of Washington, 2006. / Includes bibliographical references (leaves 157-161).