Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 362-371). Available also in a digital version from Dissertation Abstracts.

Symmetric nonaqueous redox flow batteries (RFBs) use negative and positive battery solutions of the same solution composition to operate at high cell voltages. This research effort targets these systems since they offer performance improvements derived from using nonaqueous systems and symmetric active species. Nonaqueous solutions permit significantly higher cell voltages than state-of-the-art aqueous RFBs and symmetric active species chemistries reduce the required complexity of cell reactors. Both performance advantages correspond to significant cost improvements beyond already commercially competitive aqueous RFB chemistries. This document focuses on two classes of symmetric nonaqueous RFB chemistries: coordination complexes such as vanadium acetylacetonate [V(acac)₃] or chromium acetylacetonate [Cr(acac)₃], and organic active species such as 9,10-diphenylanthracene (DPA). V(acac)₃ delivers reversible electrochemistry that supports a 2.2 V equilibrium cell potential, but there are some gaps in the understanding of its degradation mechanisms. Cr(acac)₃ supports redox reactions that suggest cell potentials above 4 V, but shows signs of irreversibility in voltammetry experiments and is not yet well understood. Finally, the DPA system could be interesting because it does not use metal active species, and its voltammetry promises cell potentials above 3 V. Yet DPA suffers from low solubility in nonaqueous solvents that limit its practicality. These three systems show promise for symmetric nonaqueous RFBs and offer avenues for further improvement. Voltammetry and spectroelectrochemical electrolysis experiments on the metal coordination complexes clarify the mechanisms behind the voltammetry on these symmetric chemistries. Ligand dissociation causes the irreversible behavior observed in voltammetry on Cr(acac)₃. The same experiments reaffirm the expected cyclability of V(acac)₃. Chemical functionalization of the DPA center is performed to investigate the solubility and reactivity of various derivatives. Functionalizing DPA with ethylene glycol chains to form 'DdPA' significantly increases solubility limits from 0.6 mM and 44 mM for DPA in acetonitrile and 1,2-dimethoxyethane, respectively, to 12 mM and 0.21 M for DdPA in the same solvents. At the same time, DdPA retains redox activity that promises 3 V cell potentials. Ultimately, a custom, nonaqueous-compatible redox flow reactor was designed and used to test the performance of V(acac)₃, DPA, and DdPA under various operating conditions. Contradicting previous reports, V(acac)₃ delivers stable cycling over the 21- cycle experimental protocol. Exploration over a range of flow rates and current densities give energy and power densities up to 1.09 WhL^-1 and 0.16 Wcm^-2, respectively, for the battery solution compositions examined. These experiments further predict values up to 28 WhL^-1 and at least 0.22 Wcm^-2 for optimized V(acac)₃ battery solutions. DPA and DdPA deliver the highest operating potential observed from organic nonaqueous RFBs, discharging at 3 V and 2.9 V, but require further work to understand degradation in the systems.

No description available.

This project concerns the effect of freeze-thaw cycles on the pore-scale structure of nonaqueous phase liquid (NAPL) contaminants in water-saturated porous media. This problem is of critical importance to the entrapment of such contaminants in cold temperate, polar and high altitude regions, and has not been examined in the literature to date. This research work is conducted in three stages: (i) two-dimensional nondestructive visualisation of residual light non-aqueous phase liquid (LNAPL), and dense non-aqueous phase liquid (DNAPL), in porous media subject to successive freeze-thaw cycles; (ii) three-dimensional experiments on LNAPL in porous media subject to freeze-thaw, with quantification of phase volumes by X-ray micro-computed tomography (micro-CT); and (iii) the explanation of results by several pore scale mathematical and conceptual models. The two-dimensional cell experiments (using a monolayer of 0.5 mm diameter glass beads held between two glass sheets), and three-dimensional X-ray micro-CT experiments reveal a substantial mobilisation and rupture of ganglia during successive freeze-thaw cycles; this includes the detachment of smaller ganglia from larger ganglia and the mobilisation of NAPL in the direction of freezing front. The experiments also reveal significant shedding of numerous single/sub-singlet ganglia along narrow pore corridors, their entrapment in growing polycrystalline ice, and the coalescence of such small ganglia during thawing to form larger singlets. These changes were more predominant where the freezing commenced. The results of the experimental studies were interpreted by developing several mathematical and conceptual models, including freezing-induced pressure model, Darcy's law model, multipore ganglia model (rupture coefficient) and ice-snap off model.

The objective of this Ph.D. study is to explore an important and fertile research topic on the methods for synthesis of nanomaterials by homogeneous nonaqueous solution phase reaction. Research in this work focuses on synthesizing several kinds of nanomaterials in different environments and structure, including spherical nanoparticles, nanowires and core-shell structure composites We first synthesized metallic nanomaterials in this system, such as ~10 nm Fe nanoparticles, ~6 nm Au nanoparticles, and ~100 nm Bi nanoparticles, this system are the preparation for the following studies. Secondly, we synthesized bimetallic nanomaterials in this system, such as Fe50Co50 alloy and Bi doped with Mn. For FeCo alloy, after annealing at 500 °C, a pure phase of Fe50Co50 was obtained. And we first synthesized the nanowires of bismuth doped with manganese. By studying intermediates at different temperatures during the growth process of nanowires, the evolution of the crystallization of metallic products and the mechanism of the formation of the nanowires are investigated. Thirdly, we synthesized core-shell structure nanocomposites, including either gold as the shell or polymer as the shell. 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. 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 Aucoated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And Poly (Vinyl Pyrolidone) (PVP) coated iron nanoparticles also have been successfully synthesized in a polar aprotic solvent, which shows the welldefined core-shell structures. In this approach, Poly (Vinyl Pyrolidone) (PVP) was employed as the coating polymer directly coated on metallic core (iron) nanoparticles. In this work, a combination of TEM (transmission electron microscopy), EDS (Energy disperse X-ray spectroscopy), XRD (X-ray powder diffractometry), ICP (inductively-coupled plasma spectrometer), TGA (Thermogravimetric analysis), UV-visible absorption spectroscopy, IR (infrared) spectroscopy and SQUID magnetometry (Superconducting Quantum Interference Device) were employed to characterize the morphology, structure, composition and magnetic properties of the products. In summary, this Ph.D. study successfully and systematically synthesized several kinds of nanocomposites in a system. The synthetic procedure is simple, economic and easily scaled-up for further applications. And many techniques were employed to characterize the products.

This study investigated the use of radon-222 as an in situ partitioning tracer for quantifying nonaqueous phase liquid (NAPL) saturations in the subsurface. Laboratory physical aquifer models (PAMs), field experiments, and numerical simulations were used to investigate radon partitioning in static (no-flow) experiments and in single-well, 'push-pull' tests conducted in non-contaminated and NAPL-contaminated aquifers. Laboratory push-pull tests in a wedge-shaped PAM and field push-pull tests in a NAPL-contaminated aquifer showed that radon was retarded in the presence of NAPL, with retardation manifested in increased dispersion of radon extraction phase breakthrough curves (BTCs). An approximate analytical solution to the governing transport equation and numerical simulations provided estimates of the radon retardation factor (R), which was used to calculate NAPL saturations (S[subscripts n]). Laboratory static and push-pull tests were conducted in a large-scale rectangular PAM before and after NAPL contamination, and after alcohol cosolvent flushing and pump-and-treat remediation. Radon concentrations in static tests were decreased due to partitioning after NAPL contamination and increased after remediation. Push-pull tests showed increased radon retardation after NAPL contamination; radon retardation generally decreased after remediation. Numerical simulations modeling radon as an injected or ex situ partitioning tracer were used to estimate retardation factors and resulted in overestimations of the likely S[subscripts n] in the PAM. Radon partitioning was sensitive to changes in S[subscripts n] in both static and push-pull tests. However, the test results were sensitive to test location, sample size, test design, and heterogeneity in S[subscripts n] distribution. Numerical simulations of hypothetical push-pull tests conducted in a NAPL-contaminated aquifer were used to investigate the influence of homogeneous and heterogeneous S[subscripts n] distributions and initial radon concentrations on radon BTCs and resulting S[subscripts n] calculations. Both of these factors were found to affect radon BTC behavior. A revised method of plotting and interpreting radon BTCs combined with numerical simulations modeling radon as an in situ partitioning tracer (incorporating initial radon concentrations into the model as a function of S[subscripts n]) were used to re-analyze laboratory and field push-pull test BTCs. This method reduced the overestimation of calculated S[subscripts n] values from laboratory tests. / Graduation date: 2003

Radon-222 gas has unique properties allowing it to be used as an indicator for the presence of organic phase liquids in the saturated zone. It naturally occurs in soils. It is radioactive, making quantitative detection straight forward. A noble gas, it is chemically inert and does not react with aquifer media. Finally, radon has an affinity to concentrate in nonaqueous phase liquids. A proposed linear equilibrium partitioning model was tested by batch equilibration with the pore fluid to establish the deficit in aqueous radon concentrations that results from its partitioning into the residual saturation of the organic phase (Soltrol-220). Five sets of experiments were run on columns with 0.0, 1.0, 2.5, 5.0, and 8.0 percent residual soltrol fractions. The model was found to accurately represent the partitioning process. A one-dimensional physical model was run to see if the data from the partitioning experiments could be successfully applied to predict the aqueous radon concentrations in a more complex situation. The results indicate that radon-222 has great potential to be used as a means of detecting and quantifying the presence of residual organic phase liquids in the saturated zone. / Graduation date: 1995

Nanostructured materials are materials consisting of nanoparticulate building blocks on the scale of nanometers (i.e. 10-9 m). Composition, crystallinity and morphology can enhance or even induce new properties of the materials, which are desirable for todays and future technological applications. In this work, we have shown new strategies to synthesise metal oxide and metal nitride nanomaterials. The first part of the work deals with the study of nonaqueous synthesis of metal oxide nanoparticles. We succeeded in the synthesis of In2O3 nanopartcles where we could clearly influence the morphology by varying the type of the precursors and the solvents; of ZnO mesocrystals by using acetonitrile as a solvent; of transition metal oxides (Nb2O5, Ta2O5 and HfO2) that are particularly hard to obtain on the nanoscale and other technologically important materials. Solvothermal synthesis however is not restricted to formation of oxide materials only. In the second part we show examples of nonaqueous, solvothermal reactions of metal nitrides, but the main focus lies on the investigation of the influence of different morphologies of metal oxide precursors on the formation of the metal nitride nanoparticles. In spite of various reports, the number and variety of nanocrystalline metal nitrides is marginally small by comparison to metal oxides; hence preformed metal oxides as precursors for the preparation of metal nitrides are a logical choice. By reacting oxide nanoparticles with cyanamide, urea or melamine, at temperatures of 800 to 900 °C under nitrogen flow metal nitrides could be obtained. We studied in detail the influence of the starting material and realized that size, crystallinity, type of nitrogen source and temperature play the most important role. We have managed to propose and verify a dissolution-recrystallisation model as the formation mechanism. Furthermore we could show that the initial morphology of the oxides could be retained when ammonia flow was used instead. / Nanostrukturierte Materialien sind Materialien, die aus nanopartikulären Baueinheiten in der Größenordnung von Nanonmetern (d.h. 10-9 m) bestehen. Zusammensetzung, Kristallinität und Morphologie können die natürlichen Eigenschaften dieser Materialien verbessern oder zusätzliche Eigenschaften erzeugen, die für heutige und zukünftige Anwendungen und Verfahren wünschenswert sind. In dieser Arbeit präsentieren wir neue Strategien zur Synthese von Nanopartikeln der Metaloxide und Metalnitride. Im einführenden Teil wird die nichtwässrige Synthese von Metaloxidnanopartikeln beschrieben. Uns gelang die Darstellung von In2O3 Nanopartikeln, deren Größe und Form wir durch die Wahl des Prekursors und des Lösemittels deutlich beeinflussen konnten; von ZnO Mesokristallen durch den Einsatz von Acetonitril als Lösemittel; von Übergangsmetalloxiden (Nb2O5, Ta2O5 and HfO2), die besonders schwer im Nanomaßstab zu erhalten sind und von anderen, technisch relevanten Materialien. Die Möglichkeiten der solvothermalen Synthese sind nicht mit der Darstellung von Oxidmaterialen erschöpft. Im zweiten Teil zeigen wir einige Beispiele nichtwässriger, solvothermaler Synthese von Metalnitriden auf; das Hauptaugenmerk liegt aber auf einer Betrachtung der Einflüsse der Morphologie von Metaloxidnanopartikelprekursoren auf die Bildung der Metalnitridnanopartikel. Die Anzahl und Vielfalt bekannter nanokristalliner Metalnitride ist verschwindend klein im Vergleich zu den Metaloxiden, die in der Fachliteratur etabliert sind und demzufolge einen reichen Baukasten an Prekursoren zur Darstellung von Metalnitriden liefern. Durch die Reaktion von Metaloxidnanopartikeln mit Cyanamid, Urea oder Melamine bei Temperaturen von 800 bis 900 °C unter Stickstofffluss konnten Metalnitride erhalten werden. Eine detaillierte Studie der Reaktionsbedingungen und des Reaktionsablaufs zeigte auf, dass Größe und Kristallinität der Metaloxide, die Art der Stickstoffquelle und die Temperatur die entscheidenden Faktoren sind und legte eine Auflösungs-Rekristallisation als Modelmechanismus dieser Art Reaktion nahe. Darüber hinaus konnte gezeigt worden, dass die anfängliche Morphologie des Oxids unter einem Ammoniafluss beibehalten werden konnte.

Tetrachloroethene (PCE) is a major groundwater contaminant that often persists as dense, nonaqueous phase liquids (DNAPLs) in subsurface environments. Dissolved-phase PCE plumes emanate from DNAPL source zones, which act as continuous sources of contamination for decades. Removal of DNAPL source zones is crucial to achieve lasting remedy of contaminated aquifers. This research explored the contributions of the microbial reductive dechlorination process (i.e., anaerobic bioremediation) to PCE-DNAPL source zone remediation, either in isolation or as a polishing step for the removal of residual DNAPL remaining after application of surfactant enhanced aquifer remediation (SEAR), an emerging physical-chemical source zone treatment. Specific objectives of this research were to: (1) evaluate the ability of microorganisms to dechlorinate in the presence of PCE-DNAPL and at high dissolved-phase PCE concentrations expected near/in DNAPL source zones, (2) assess the distribution and activity of key dechlorinating populations during bioenhanced PCE-DNAPL dissolution in continuous-flow column experiments, (3) determine the influence of Tween 80, a biodegradable surfactant commonly used in SEAR, on the microbial reductive dechlorination process, (4) design and optimize quantitative real-time PCR (qPCR) protocols to detect and enumerate key dechlorinating populations (e.g., Geobacter lovleyi, Sulfurospirillum multivorans), and (5) explore the effects of oxygen on Dehalococcoides viability and biomarker quantification. This research demonstrated that microbial dechlorinating activity within DNAPL source zones promotes bioenhanced dissolution although many dechlorinating isolates cannot tolerate saturated PCE concentrations. Application of newly designed qPCR protocols established a direct link between dissolution enhancement and the distribution of relevant dechlorinating populations in the vicinity of PCE-DNAPL. The limited and reversible impact of Tween 80 on key dechlorinators supported the feasibility of a treatment train approach of SEAR followed by microbial reductive dechlorination to remediate PCE-DNAPL source zones. Finally, experiments with oxygen-exposed, Dehalococcoides-containing cultures suggested limitations of using Dehalococcoides DNA and RNA biomarkers for monitoring bioremediation at field sites. These findings advance the scientific understanding of the microbial reductive dechlorination process and are relevant to environmental remediation practitioners. The advantages and current shortcomings of PCE-DNAPL source zone bioremediation, as well as recommendations for future research, are discussed.