Browsing by Subject "Antimony"
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Item Archaea at the El Tatio Geyser Field : community composition, diversity, and distribution across hydrothermal features and geochemical gradients(2012-05) Franks, Megan A.; Bennett, Philip C. (Philip Charles), 1959-; Bell, Christopher J.; Cardenas, Meinhard B.; Engel, Annette S.; Hawkes, Christine V.Methanogenesis, a metabolic pathway unique to Archaea, is severely inhibited by the reduced form of arsenic (As). Despite this inhibition, methanogenic Archaea are present in some hydrothermal features at the El Tatio Geyser Field (ETGF), a high-arsenic site with 100+ hydrothermal features, including boiling pools, geyers, fumaroles, and springs. The ability of methanogenic Archaea and other microorganisms to withstand elevated arsenic concentrations, and a variety of other extreme environmental conditions at ETGF, may be due to unique adaptations or syntrophic relationships with other microorganisms. ETGF is situated in the Andes Mountains at an altitude of ~4300 meters. UV radiation is elevated in this region and air temperatures fluctuate widely. Most hydrothermal waters discharge at ~85˚C, the local boiling point, and rapidly evaporate due to the arid climate. This concentrates hydrothermal salts and metals, including arsenic (As) and antimony (Sb). Additionally, dissolved inorganic carbon (DIC) concentrations are extremely low in most features and may limit life. Water chemistry analyses done for this study show variability in dissolved constituents between features that are consistent over time. Variations may be due to the source or residence time of waters, and differences in chemistry could be responsible for the presence or absence of methanogenic Archaea at hydrothermal sites. The overlying control on microbial diversity and community composition may be water geochemistry, and potentially specific constituents. The goals of this study were to detect novel microbial taxa at ETGF, including novel methanogens, as well as to document microbial community composition at select hydrothermal features. The distribution and diversity of microorganisms at each feature was analyzed phylogenetically and within an ecological context in order to determine physicochemical and biological controls on community composition. Additionally, a model methanogen was used in laboratory analyses to determine how concentrations and oxidation states affected growth and methane production. This methanogen, Methanothermobacter thermautotrophicus, is found at ETGF, Yellowstone, and other hydrothermal fields, and thrives in high-temperature environments. MPN (most probable number) analyses show that culturable biomass from multiple sites contain metabolically active methanogens. These results support the biogenicity of dissolved methane detected in the field. 16S rRNA surveys of Archaea at four sites show that Archaea are diverse, and archaeal community composition varies across features. Phylogenetic tree construction indicates that Archaea from ETGF group together, suggesting that the isolation and broad environmental constrains on ETGF have some control on phylogenetic diversity. Laboratory analyses of As and Sb concentrations on M. thermautotrophicus suggest that Sb may decrease the inhibition of methanogenesis by As by preventing the formation of As(III) from As(V). Statistical analyses correlating microbial community composition and structure to physicochemical parameters show that archaeal and bacterial communities relate to different variables; with Bacteria correlating to water temperature, and Archaea correlating to dissolved constituents such as hydrogen gas and sulfate.Item Cationic Main Group Compounds as Water Compatible Small Anion Receptors(2013-05-06) Leamer, Lauren AnneThe fluoride anion plays an important role in dental health and as a result is added to drinking water at low concentrations. If the concentration of fluoride is too high however, skeletal fluorosis can occur. Because of this, there has been significant interest in the development of water compatible anion sensors that can sense fluoride at the ppm level. This is made difficult by the high hydration enthalpy of fluoride (?H0 = -504 KJ/mol) which significantly lowers the reactivity of this anion in water. For this reason it has become the goal of the Gabba? group, as well as other research groups to develop fluoride sensing small molecules. Such molecules should possess sufficient Lewis acidity to overcome the hydration enthalpy of the fluoride anion. A significant amount of research has been conducted on triarylboranes containing cationic moieties such as ammonium, phosphonium, and sulfonium groups. This thesis will describe additional examples of such species, including a series of ammonium boranes of the general formula [p-(Mes2B)C6H4(NMe2R)]+. As indicated by anion complexation studies, the R group present in these molecules has a notable effect on the anion affinity of the somewhat distant boron center. Another component of this thesis deals with the chemistry of newly synthesized stiboranes that are also decorated by peripheral ammonium groups. As observed for the ammonium boranes mentioned above, the ammonium groups present in these stiboranes drives anion capture, leading to zwitterionic ammonium antimonite formation.Item Development of antimony-based anode systems for lithium-ion batteries(2015-08) Allcorn, Eric Koederitz; Manthiram, Arumugam; Goodenough, John B; Ferreira, Paulo J; Yu, Guihua; Mullins, Charles BThe superior energy storage characteristics of lithium-ion batteries have made them the state-of-the-art battery technology for the past two decades where they have been integral to the proliferation of portable electronics. Efforts to expand their application into the realms of transportation and stationary storage require additional performance enhancements, though. These enhancements will be achieved through the application of advanced new materials such as alloy anodes like antimony. Alloy anodes offer the potential for dramatic enhancement of cell capacity both gravimetrically and volumetrically due to the high lithium content in their lithiated phases. Additionally, their higher operating voltage means that their incorporation should increase cell safety, a key parameter in large-scale applications, by reducing the risk of lithium plating. The primary factor inhibiting the adoption of alloy anodes is their short cycle life brought about by the large volume change they undergo during cycling that leads to crumbling of the active material and drastic capacity loss. To overcome this issue the following mitigation techniques are applied to antimony active materials: (i) use of active-material intermetallics of M[subscript x]Sb (where M = Ni or Fe) instead of pure antimony; (ii) incorporation of active material into reinforcing active/inactive composites with Al₂O₃, TiC, and/or carbon black; (iii) reduction of active material particles to nano-scale. In addition, the use of high-energy mechanical milling allows these methods to be applied with a simple and potentially scalable synthesis procedure and yields high-density final products. The actual safety performance of antimony anodes are also analyzed due to the importance of such parameters in large-battery applications. Because antimony alone without other components is an impractical anode material, the effects on safety and thermal stability of incorporating it into intermetallic and composite structures are also investigated. The advanced nanocomposites developed in this work demonstrate excellent cycle life with good all-around performance parameters that make them viable, safer candidates to replace graphite in next generation lithium-ion batteries. Pure antimony is also shown to offer enhancement in cell safety performance relative to graphite as well, and nanocomposites based upon its use as an active material are able to retain these favorable safety characteristics.Item Fate and transport of arsenic and antimony in the El Tatio Geyser Field, Chile(2007-05) Landrum, Jeffrey Thomas, 1979-; Bennett, Philip C. (Philip Charles), 1959-El Tatio Geyser Field (ETGF), northern Chile, hosts widespread geothermal activity, with very high aqueous concentrations of arsenic and antimony, higher than any other known geothermal system. Boiling springs (86°C) discharge circum-neutral pH, Na-Cl type waters with low organic carbon. Net discharge of a stream draining the ETGF basin is approximately 10 cfs. As(III), the dominant As species in discharge waters, rapidly oxidizes to As(V) at an estimated first order rate of 0.35 min-1, determined in the field by first arrival of a tracer. As and Sb concentrations and speciation in hydrothermal waters, deposits, and microbial biomass are evaluated as a product of microbial metabolism, sorption to metal-oxyhydroxides, and co-precipitation. Mechanisms controlling these reactions ( i.e. cooling, evaporation, changes in redox and pH) are evaluated and modeled. Sequential extractions reveal that As, sorbs to Fe and Mn oxy-hydroxide complexes. In contrast, Sb solid phase partitioning is influenced primarily by the co-precipitation of Sb-oxide minerals with siliceous sinter (up to 2% wt. Sb). Diurnal variations occur in spring water chemistry and may cause Sb-rich laminations in siliceous hydrothermal deposits. Microbial energetics calculations and enrichment experiments suggest that microbial activity influences the mobility of As, and probably Sb in the ETGF basin by altering redox speciation and sorption to microbial biomass.Item Synthesis and characterization of nanocomposite alloy anodes for lithium-ion batteries(2012-05) Applestone, Danielle Salina; Manthiram, Arumugam; Goodenough, John; Mullins, Charles; Stevenson, Keith; Meyers, JeremyLithium-ion batteries are most commonly employed as power sources for portable electronic devices. Limited capacity, high cost, and safety problems associated with the commercially used graphite anode materials are hampering the use of lithium-ion batteries in larger-scale applications such as the electric vehicle. Nanocomposite alloys have shown promise as new anode materials because of their better safety due to higher operating potential, increased energy density, low cost, and straightforward synthesis as compared to graphite. The purpose of this dissertation is to investigate and understand the electrochemical properties of several types of nanocomposite alloys and to assess their viability as replacement anode materials for lithium-ion batteries. Tin and antimony are two elements that are active toward lithium. Accordingly, this dissertation is focused on tin-based and antimony-based nanocomposite alloy materials. Tin and antimony each have larger theoretical capacities than commercially available anodes, but the capacity fades dramatically in the first few cycles when metallic tin or antimony is used as the anode in a lithium-ion battery. This capacity fade is largely due to the agglomeration of particles in the anode material and the formation of a barrier layer between the surface of the anode and the electrolyte. In order to suppress agglomeration, the active anode material can be constrained by an inactive matrix of material that makes up the nanocomposite. By controlling the surface of the particles in the nanocomposite via methods such as the addition of additives to the electrolyte, the detrimental effects of the solid-electrolyte interphase layer (SEI) can be minimized, and the capacity of the material can be maintained. Moreover, the nanocomposite alloys described in this dissertation can be used above the voltage where lithium plating occurs, thereby enhancing the safety of lithium-ion batteries. The alloy anodes in this study are synthesized by high-energy mechanical milling and furnace heating. The materials are characterized by X-ray diffraction, scanning and transmission electron microscopies, and X-ray photoelectron spectroscopy. Electrochemical performances are assessed at various temperatures, potential ranges, and charge rates. The lithiation/delithiation reaction mechanisms for these nanocomposite materials are explored with ex-situ X-ray diffraction. Specifically, three different nanocomposite alloy anode materials have been developed: Mo3Sb7-C, Cu2Sb-Al2O3-C, and Cu6Sn5-TiC-C. Mo3Sb7-C has high gravimetric capacity and involves a reaction mechanism whereby crystalline Mo3Sb7 disappears and is reformed during each cycle. Cu2Sb-Al2O3-C with small particles (2 - 10 nm) of Cu2Sb dispersed in the Al2O3-C matrix is made by a single-step ball milling process. It exhibits long cycle life (+ 500 cycles), and the reversibility of the reaction of Cu2Sb-Al2O3-C with lithium is improved when longer milling times are used for synthesis. The reaction mechanism for Cu2Sb-Al2O3-C appears to be dependent upon the size of the crystalline Cu2Sb particles. The coulombic efficiency of Cu2Sb-Al2O3-C is improved through the addition of 2 % vinylethylene carbonate to the electrolyte. With a high tap density of 2.2 g/cm3, Cu6Sn5-TiC-C exhibits high volumetric capacity. The reversibility of the reaction of Cu6Sn5-TiC-C with lithium is improved when the material is cycled above 0.2 V vs. Li/Li+.Item The Asiatic clam (Corbicula fluminea) as a bio-monitor for determining the distribution of antimony, arsenic and thallium in the water column and sediments of Manadas Creek, Laredo, Texas(Texas A&M International University, 2016-02) Garcia, Natasha; Vaughan, TomManadas Creek is an urban tributary of the Rio Grande that flows past a decommissioned antimony smelter. This smelter is associated with the heavy metal contamination in the creek and still poses a threat to the surrounding aquatic environment. With concerns on the rise of metal pollution, the biomonitor, the Asiatic clam (Corbicula fluminea) was used to determine bioaccumulation from the water column and sediments in Manadas Creek. The metals arsenic (As), antimony (Sb) and thallium (Tl) were analyzed in the water, sediments, gills, mantle, foot, digestive (DI) tract, gonads and shell of clams collected from sites between March to August 2013. Metal analysis of arsenic, antimony and thallium was performed by ICP-OES. High levels of antimony, arsenic and thallium in the water (13.45±6.65; 10.33±3.4; 7.47±1.73) and sediments (75.77±1.59; 6.41±1.19) at the site downstream from the smelter were observed. Additionally, tissue samples from this site had the highest concentrations, however there was no direct correlation between the metal concentrations in the water column and sediments with the tissues. There were no detectable concentrations of arsenic, antimony and thallium in shell samples. Site 3 had the highest thallium concentration in the sediments (3.00±0.68). No detectable thallium concentrations were detected in the tissues. Based on the results, the organotropism for arsenic is DI tract > gills > gonads > foot > mantle > shell and the organotropism for antimony is gills > DI tract > gonads > mantle > foot > shell. The Asiatic clam (Corbicula fluminea) is a useful biomonitor to provide data on the status of metal pollution in Manadas Creek, Laredo, Texas.Item Tin, Antimony, Bismuth, and Tellurium Lewis Acids in sigma-Accepting Ligands for Transition Metals(2012-10-19) Lin, Tzu-PinThe interactions between ligands and transition metals have been an essential subject in inorganic chemistry. Other than the commonly known L-type (two-electron donors) and X-type ligands (one-electron donors), Z-type ligands (two-electron acceptors) have begun to surface in the past decade. Capable of drawing a pair of d-electrons away from a metal, Z-ligands affect the electronic structures of transition metals leading to fascinating properties as well as reactivity. In particular, recent advance in Z-ligand chemistry have resulted in the discovery of transition metal borane complexes featuring metal ? boron interactions. Owing to the presence of a metal ? boron interaction which stabilizes the low valent state, these complexes have been shown to activate small molecules such as H2, CO2, and CHCl3. Further, the concept of Z-ligand has been extended to s- and d-block Lewis acids. In spite of these achievements, Z-ligands that contain Group 14-16 elements as Lewis acids remain scarce and relatively unexplored. For this reason, we have launched a series of investigations targeting complexes with transition metal ? Group 14-16 interactions. These investigations have allowed us to synthesize a series of novel complexes with palladium, platinum, or gold as metallobasic late transition metals and tin, antimony, bismuth, and tellurium as Lewis acids. The transition metal ? Lewis acid interactions of these complexes, which are supported by o-phosphinophenylene, 1,8-naphthalenediyl or 8-quinolinyl buttresses, have been established experimentally and theoretically. Further, the reactivity of these complexes toward anions and oxidants has also been explored. These experiments have led to the discovery of tellurium-platinum complexes that sustain reversible two-electron redox processes including the photo-reductive elimination of chlorine. Other noteworthy outcomes of this research include the isolation of the first telluroxanyl-metal complex as well as the discovery of complexes with HgII ? SbV interactions.