Matching Items (6)

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Trade-offs in utilizing of zero-valent iron for synergistic biotic and abiotic reduction of trichloroethene and perchlorate in soil and groundwater

Description

The advantages and challenges of combining zero-valent iron (ZVI) and microbial reduction of trichloroethene (TCE) and perchlorate (ClO4-) in contaminated soil and groundwater are not well understood. The objective of

The advantages and challenges of combining zero-valent iron (ZVI) and microbial reduction of trichloroethene (TCE) and perchlorate (ClO4-) in contaminated soil and groundwater are not well understood. The objective of this work was to identify the benefits and limitations of simultaneous application of ZVI and bioaugmentation for detoxification of TCE and ClO4- using conditions relevant to a specific contaminated site. We studied conditions representing a ZVI-injection zone and a downstream zone influenced Fe (II) produced, for simultaneous ZVI and microbial reductive dechlorination applications using bench scale semi-batch microcosm experiments. 16.5 g L-1 ZVI effectively reduced TCE to ethene and ethane but ClO4- was barely reduced. Microbial reductive dechlorination was limited by both ZVI as well as Fe (II) derived from oxidation of ZVI. In the case of TCE, rapid abiotic TCE reduction made the TCE unavailable for the dechlorinating bacteria. In the case of perchlorate, ZVI inhibited the indigenous perchlorate-reducing bacteria present in the soil and groundwater. Further, H2 generated by ZVI reactions stimulated competing microbial processes like sulfate reduction and methanogenesis. In the microcosms representing the ZVI downstream zone (Fe (II) only), we detected accumulation of cis-dichloroethene (cis-DCE) and vinyl chloride (VC) after 56 days. Some ethene also formed under these conditions. In the absence of ZVI or Fe (II), we detected complete TCE dechlorination to ethene and faster rates of ClO4- reduction. The results illustrate potential limitations of combining ZVI with microbial reduction of chlorinated compounds and show the potential that each technology has when applied separately.

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Created

Date Created
  • 2017

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Role of defects interactions with embrittlement species in iron: a multiscale perspective

Description

Hydrogen embrittlement (HE) is a phenomenon that affects both the physical and chemical properties of several intrinsically ductile metals. Consequently, understanding the mechanisms behind HE has been of particular interest

Hydrogen embrittlement (HE) is a phenomenon that affects both the physical and chemical properties of several intrinsically ductile metals. Consequently, understanding the mechanisms behind HE has been of particular interest in both experimental and modeling research. Discrepancies between experimental observations and modeling results have led to various proposals for HE mechanisms. Therefore, to gain insights into HE mechanisms in iron, this dissertation aims to investigate several key issues involving HE such as: a) the incipient crack tip events; b) the cohesive strength of grain boundaries (GBs); c) the dislocation-GB interactions and d) the dislocation mobility.

The crack tip, which presents a preferential trap site for hydrogen segregation, was examined using atomistic methods and the continuum based Rice-Thompson criterion as sufficient concentration of hydrogen can alter the crack tip deformation mechanism. Results suggest that there is a plausible co-existence of the adsorption induced dislocation emission and hydrogen enhanced decohesion mechanisms. In the case of GB-hydrogen interaction, we observed that the segregation of hydrogen along the interface leads to a reduction in cohesive strength resulting in intergranular failure. A methodology was further developed to quantify the role of the GB structure on this behavior.

GBs play a fundamental role in determining the strengthening mechanisms acting as an impediment to the dislocation motion; however, the presence of an unsurmountable barrier for a dislocation can generate slip localization that could further lead to intergranular crack initiation. It was found that the presence of hydrogen increases the strain energy stored within the GB which could lead to a transition in failure mode. Finally, in the case of body centered cubic metals, understanding the complex screw dislocation motion is critical to the development of an accurate continuum description of the plastic behavior. Further, the presence of hydrogen has been shown to drastically alter the plastic deformation, but the precise role of hydrogen is still unclear. Thus, the role of hydrogen on the dislocation mobility was examined using density functional theory and atomistic simulations. Overall, this dissertation provides a novel atomic-scale understanding of the HE mechanism and development of multiscale tools for future endeavors.

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Created

Date Created
  • 2015

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Experimental constraints on Fe concentrations in biomass burning aerosols

Description

Atmospheric deposition of iron (Fe) can limit primary productivity and carbon dioxide uptake in some marine ecosystems. Recent modeling studies suggest that biomass burning aerosols may contribute a significant amount

Atmospheric deposition of iron (Fe) can limit primary productivity and carbon dioxide uptake in some marine ecosystems. Recent modeling studies suggest that biomass burning aerosols may contribute a significant amount of soluble Fe to the surface ocean. Existing studies of burn-induced trace element mobilization have often collected both entrained soil particles along with material from biomass burning, making it difficult to determine the actual source of aerosolized trace metals.

In order to better constrain the importance of biomass versus entrained soil as a source of trace metals in burn aerosols, small-scale burn experiments were conducted using soil-free foliage representative of a variety of fire-impacted ecosystems. The resulting burn aerosols were collected in two stages (PM > 2.5 μm and PM < 2.5 μm) on cellulose filters using a high-volume air sampler equipped with an all-Teflon impactor. Unburned foliage and burn aerosols were analyzed for Fe and other trace metals using inductively coupled plasma mass spectrometry (ICP-MS).

Results of this analysis show that less than 2% of Fe in plant biomass is likely mobilized as atmospheric aerosols during biomass burning events. The results of this study and estimates of annual global wildfire area were used to estimate the impact of biomass burning aerosols on total atmospheric Fe flux to the ocean. I estimate that foliage-derived Fe contributes 114 ± 57 Gg annually. Prior studies, which implicitly include both biomass and soil-derived Fe, concluded that biomass burning contributes approximately 690 Gg of Fe. Together, these studies suggest that fire-entrained soil particles contribute 83% (576 Gg) of Fe in biomass burning emissions, while plant derived iron only accounts for at most 17%.

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Created

Date Created
  • 2019

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Development of homogeneous first row metal catalysts (Fe, Mn, Co) for organic transformations and bond activation

Description

ABSTRACT

Transition metals have been extensively employed to address various challenges

related to catalytic organic transformations, small molecule activation, and energy storage

over the last few decades. Inspired by recent catalytic advances mediated

ABSTRACT

Transition metals have been extensively employed to address various challenges

related to catalytic organic transformations, small molecule activation, and energy storage

over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent

pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals,

our group has designed new PDI and DI ligands by modifying the imine substituents to

feature donor atoms. My doctoral research is focused on the development of PDI and DI

ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application

in bond activation reactions and the hydrofunctionalization of unsaturated bonds.

First two chapters of this dissertation are centered on the synthesis and

application of redox non-innocent ligand supported low valent iron complexes. Notably,

reduction of a DI-based iron dibromide led to the formation of a low valent iron

dinitrogen compound. This compound was found to undergo a sequential C-H and C-P

bond activation processes upon heating to form a dimeric compound. The plausible

mechanism for dimer formation is also described here.

Inspired by the excellent carbonyl hydrosilylation activity of our previously

reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation

Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2

furnished a deprotonated backbone methyl group containing Mn compound

[(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound,

[(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD

analysis. Hydrosilylation of aldehydes and ketones have been studied using

[(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different

ii

formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst.

Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we

sought to develop a cobalt catalyst that is active for hydroboration under mild conditions,

which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH

furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine

functionality. Having this compound characterized, a broad substrate scope for both

nitriles and imines have been investigated. The operative mechanism for nitrile

dihydroboration has been investigated based on the outcomes of a series of stoichiometric

reactions using NMR spectroscopy.

Contributors

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Created

Date Created
  • 2018

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Iron depletion therapy and chromium supplementation for improving insulin

Description

The effects of iron and chromium blood concentrations have been linked to blood glucose control in diabetics. It is suggested that iron causes oxidative stress in the beta cells

The effects of iron and chromium blood concentrations have been linked to blood glucose control in diabetics. It is suggested that iron causes oxidative stress in the beta cells of the pancreas and adipocytes creating insulin insufficiency and resistance. Chromium is believed to increase the action of insulin through its biologically active molecule chromodulin. Both of these mechanisms are not clear. This 20 week case study tests the feasibility of combining iron depletion therapy followed by chromium supplementation to improve insulin sensitivity. This single case study followed a protocol of two blood donations separated by eight weeks followed by chromium supplementation of 250 µg of chromium picolinate once a day four weeks after the second blood donation. Fasting blood draws were taken at baseline, post blood draws and pre and post chromium supplementation. Results were not promising for the first hypothesis of lowering HbA1c, but the results were promising for the second hypothesis of improving insulin sensitivity by lowering the HOMA score.

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Created

Date Created
  • 2015

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Non-traditional stable isotope variations: applications for biomedicine

Description

Applications of non-traditional stable isotope variations are moving beyond geosciences to biomedicine, made possible by advances in multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) technology. Mass-dependent isotope variation can

Applications of non-traditional stable isotope variations are moving beyond geosciences to biomedicine, made possible by advances in multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) technology. Mass-dependent isotope variation can provide information about the sources of elements and the chemical reactions that they undergo. Iron and calcium isotope systematics in biomedicine are relatively unexplored but have great potential scientific interest due to their essential nature in metabolism. Iron, a crucial element in biology, fractionates during biochemically relevant reactions. To test the extent of this fractionation in an important reaction process, equilibrium iron isotope fractionation during organic ligand exchange was determined. The results show that iron fractionates during organic ligand exchange, and that isotope enrichment increases as a function of the difference in binding constants between ligands. Additionally, to create a mass balance model for iron in a whole organism, iron isotope compositions in a whole mouse and in individual mouse organs were measured. The results indicate that fractionation occurs during transfer between individual organs, and that the whole organism was isotopically light compared with food. These two experiments advance our ability to interpret stable iron isotopes in biomedicine. Previous research demonstrated that calcium isotope variations in urine can be used as an indicator of changes in net bone mineral balance. In order to measure calcium isotopes by MC-ICP-MS, a chemical purification method was developed to quantitatively separate calcium from other elements in a biological matrix. Subsequently, this method was used to evaluate if calcium isotopes respond when organisms are subjected to conditions known to induce bone loss: 1) Rhesus monkeys were given an estrogen-suppressing drug; 2) Human patients underwent extended bed rest. In both studies, there were rapid, detectable changes in calcium isotope compositions from baseline - verifying that calcium isotopes can be used to rapidly detect changes in bone mineral balance. By characterizing iron isotope fractionation in biologically relevant processes and by demonstrating that calcium isotopes vary rapidly in response to bone loss, this thesis represents an important step in utilizing these isotope systems as a diagnostic and mechanistic tool to study the metabolism of these elements in vivo.

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Agent

Created

Date Created
  • 2011