Browsing by Subject "CO2"
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Item Carbon dioxide sequestration and heterotrophy in shallow lakes.(2009-10) Kenning, Jon M.Research has recently begun to show the importance of lakes in controlling global CO2 budgets, but this work has only been done on a few large lakes. Small, shallow lakes and wetlands are the most plentiful lake ecosystems in world, but the most ignored. Here, I explore their ability to sequester CO2 and in some cases release the greenhouse gas to atmosphere. I found that pristine shallow lakes where macrophytes (aquatic vegetation) dominated, the lakes sequestered much more CO2 than disturbed lakes where phytoplankton dominated. Furthermore, I found that heterotrophs in shallow lakes respired tremendous amounts of carbon of terrestrial origin, thus calling into question the net ability of terrestrial ecosystems to sequester carbon. Finally, I found that some of the underlying mechanisms, including the productivity of different autotrophs and growth efficiencies of bacteria, favor greater carbon sequestration by macrophyte-rich shallow lakes. All of my observations form a basis for future work into the ability of shallow lakes to sequester CO2 and stresses the importance of not only saving shallow lakes and wetlands, but preserving them in a macrophyte-rich state.Item Computationally Driven Characterization of Magnetism, Adsorption, and Reactivity in Metal-Organic Frameworks(2016-06) Borycz, JoshuaMetal-organic frameworks (MOFs) are a class of nanoporous materials that are composed of metal-containing nodes connected by organic linkers. The study of MOFs has grown in importance due to the wide range of possible node and linker combinations, which allow tailoring towards specific applications. This work demonstrates that theory can complement experiment in a way that advances the chemical understanding of MOFs. This thesis contains the results of several investigations on three different areas of MOF research: 1) magnetism, 2) CO2 adsorption, and 3) catalysis. The calculation of magnetic properties within MOFs is quite problematic due to the weak nature of the interactions between the metal centers. The metal atoms in MOFs can be far apart due to the organic linkers and are often in unique chemical environments that are diffcult to characterize. These weak interactions mean that the computational methods must be carefully selected and tested to attain adequate precision. The objective of the work in this thesis was to determine the single-ion anisotropy and magnetic ordering of Fe-MOF-74 before and after oxidation. MOFs have desirable properties for CO2 adsorption such as large pores and high surface areas. Accurate force fields are required in order to make predictions for adsorption interactions with the internal surface of MOFs. Therefore it is important to have computational protocols that enable the derivation of reliable interaction parameters in order to study the trends of adsorption for different metal centers. In the research herein we used ab initio calculations to compute parameters for classical force fields for members of the IRMOF-10 and the MOF-74 series. MOFs have been considered for catalysis due to their thermal stability, reactive metal sites, and large diameter pores. In this thesis we report a series of studies that advance the understanding of the reactivity of MOFs containing Zr6 and Hf6 polyoxometalate nodes. In the first study the proton topology of the nodes within NU-1000 was determined. Several other studies that make use of these MOFs as supports for single-site metal catalysts are also reported. Finally, research where NU-1000 serves as a template for a thermally stable nanocasted material used for high temperature Lewis acid catalysis is also discussed.Item The role of C-O-H volatiles in the martian mantle and the production of the martian atmosphere.(2012-08) Stanley, Benjamin DanforthEvidence suggests that liquid water was once eroding the martian surface at rates comparable to many climates on present-day Earth. However, the thin modern martian atmosphere does not support liquid water. The fundamental variable in the evolution of the martian atmosphere is the storage of C-O-H volatiles in the interior, and the processes and fluxes leading to ventilation of those volatiles to the atmosphere. A key constraint on the likely CO2 fluxes accompanying martian magmatism is that much of the martian mantle is thought to be sufficiently reduced, between the iron-wüstite buffer (IW) and one log unit above IW (IW+1), such that carbon resides principally as graphite. In a reduced, graphite-saturated mantle there is a simple relationship between CO2 solubility and oxygen fugacity (fO2) which shows that an order of magnitude increase in oxygen fugacity changes the amount of CO2 dissolved in the melt by one order of magnitude. This thesis presents experimental investigations of the solubility of CO2, and other C-O-H species, in martian basalts and the implications for martian atmospheric evolution through three sets of laboratory-based experiments. In Chapter 2, experimental carbonate solubility is determined in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa, and 1400-1650 ºC. Experimentally determined CO2 solubilities are used to model the production of an early martian greenhouse. For the Humphrey source region, constrained by phase equilibria to be near 1350 ºC and 1.2 GPa, the resulting CO2 contents are 51 ppm at the IW, and 510 ppm at IW+1. However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459) which are investigated in Chapter 3. Similar experiments are performed on a synthetic starting material based on Y 980459. Despite large differences in FeO* (Fe2O3+FeO) and MgO contents, the CO2 solubilities in Y 980459 are similar to those in a less primitive Humphrey rock and a Hawaiian tholeiite. The small sensitivity of CO2 solubility to compositional variations among martian and tholeiitic basalts means that the experimentally determined solubilities may be applicable to a wide spectrum of martian magmatic products. In Chapter 4, the extraction of C-O-H volatiles from the Martian mantle is determined using the dissolved concentrations of C-O-H volatiles as a function of oxygen fugacity in synthetic martian magmas coexisting with graphite. CO2 solubilities change by one order of magnitude with an order of magnitude change in oxygen fugacity, as predicted by previous work. Other reduced species, such as Fe-carbonyls and amides, are detected in reduced graphite-saturated martian basalts. An atmosphere produced by degassing of magmas similar to this study would be richer in C-O-H species than previously modeled using only CO2 and could create a much warmer climate that stabilizes liquid water on the ancient martian surface.Item Time Resolved Vibrational Spectroscopies as a Tool for Exploring Dynamics of Confined Systems(2022-01) Pyles, CynthiaThis thesis examines a variety of vibrational probe-containing molecules such as triphenyl hydrides, CO2, and metal carbonyls with the goal of better understanding the dynamics for each system. Particular emphasis is placed on understanding how the behavior of a restricted probe, such as one dissolved in a rigid polymer or confined to a nanopore, may differ from the same probe placed in bulk solvent or a more rubbery polymer. The first study described herein scrutinized the vibrational heavy atom effect and its impact on ultrafast vibrational dynamics. A series of three triphenyl hydride compounds was investigated in a range of solvents by Fourier transform infrared (FTIR), infrared (IR) pump-probe, and two-dimensional infrared (2D-IR) spectroscopies. The mass of the central atom in the three compounds was varied systematically down the group 14 elements of silicon, germanium, and tin while keeping the rest of the molecule unaltered. Interestingly, frequency-frequency correlation functions obtained from 2D-IR spectra indicated that an increasingly large central atom produces small, but measurable changes in the dynamics of the solvation shell surrounding each compound. Next, CO2 (g) was examined via 2D-IR spectroscopy as a precursory study to understanding its behavior inside polymers. Processes which lead to dephasing of the vibrational echo such as collisions were largely circumvented by using CO2 diluted in N2 under ambient pressure and temperature. Off diagonal features in the 2D-IR spectra were observed which correspond to population and coherence exchange between rovibrational transitions. Then, CO2 (g) was dissolved inside polymers such as poly(methyl methacrylate), poly (methyl acrylate), and poly(dimethylsiloxane). These polymers with differing properties were chosen to study the impact of the glass transition on the dynamics of the dissolved CO2 probe. Interactions between the polymeric backbone and probe also impacted the dynamics. The parameters obtained from 2D-IR studies directly correlated with the diffusivity of CO2 through the polymer matrices. Next, I inspected CO2 (g) adsorbed to microporous systems such as MIL-53(Al) and ZIF-8. Preliminary FTIR studies suggest that these samples could possess a wealth of dynamic information despite narrow FTIR peaks, much like CO2 dissolved in polymers. Experimental limitations regarding these novel systems are briefly discussed. Lastly, I compared the dynamics of three ruthenium-bound carbonyl complexes: Ru3CO12 in bulk THF, [HRu3(CO)11]- entrapped in an aluminum sol-gel, and [NEt4][HRu3(CO)11] in bulk THF. Ru3CO12 is catalytically inactive but becomes active upon incorporation into an alumina sol-gel matrix. Pump probe and 2D-IR studies indicated that the changed dynamics are primarily due to an altered solvent shell which most likely exhibits long-range ordering. Though it is uncertain whether the increased catalytic activity of [HRu3(CO)11]- is due to the presence of the hydride or this newly ordered solvent shell, the results nonetheless showcase 2D-IR’s efficacy in sensing dynamics of confined environments.Item Tracing the flow of carbon through ecosystems using stable isotope techniques(2010-03) Fassbinder, Joel J.The stable isotope 13C has become a popular tool for tracing carbon exchange between atmospheric and terrestrial reservoirs. Stable isotope techniques have been applied in a variety of ecosystems to partition the component fluxes of net CO2 exchange (FN) and have been incorporated into several atmospheric inversion models that estimate the ter- restrial carbon sink on the regional and global scales. While the use of stable isotope theory has helped provide valuable insight into the temporal and spatial variability of car- bon exchange, there has been some concern about the theory’s dependence on several key assumptions that have gone unverified due to limiting sampling techniques. Specific concerns regard the temporal variability of the isotopic composition of ecosystem respi- ration (δR) and its potential influence on ecosystem flux partitioning. In this thesis, an automated chamber system was combined with stable isotope techniques to evaluate and apply isotopic partitioning theory both in an agricultural ecosystem and in a climate con- trolled experiment using corn and soybean plants. Further, this new automated sampling technique was combined with isotopic flux-gradient measurements to examine the main factors controlling variability in ecosystem respiration and its isotopic composition. The findings from this thesis research may benefit land surface schemes that simulate isotopic fluxes for input to atmospheric inversion models.