Browsing by Subject "Carbon Dioxide"

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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.
Coupling geothermal energy capture with carbon dioxide sequestration in naturally permeable, porous geologic formations -- a novel approach for expanding geothermal energy utilization.
(2011-08) Randolph, Jimmy Bryan
This thesis research presents a new method to harness geothermal energy by combining it with geologic carbon dioxide (CO2) sequestration. CO2 is injected into deep, naturally porous and permeable geologic formations. The geothermally heated CO2 is piped to the surface, used to produce electricity, and then returned to the subsurface. This new approach represents a radical shift in electric/heat power generation as it not only utilizes a renewable energy source but has a negative carbon footprint. This research explores the potential and applicability of the approach and related aspects of geologic fluid and heat flow.
An Investigation into the Seasonal Economic and Energy Performance of CO2 Plume Geothermal (CPG) Power Plants
(2015-08) Peterson, Margaret
CO2 Plume Geothermal (CPG) energy production is a renewable form of energy that combines geothermal technology with CO2 sequestration, using the CO2 as the working fluid in naturally permeable thermal reservoirs. In this thesis, we compare the energy and economic performance of an electricity production only CPG plant, as well as CPG plants with that of a combined heat and power (CHP) and district heating cooling (DHC). Initially, the monthly economic parameters of electricity-only CPG power plants are modeled for six cities: Williston, ND, Dallas, TX, New Orleans, LA, Houston, TX, Sacramento, CA, and Williamsport, PA. Meteorological data for each city are used to determine energy production and electric power is assumed to be sold in a competitive market. The monthly economic performance of each plant is compiled over 20 years, the assumed lifetime of a CPG plant, and used to determine each plant's potential for profit. It is found that it is crucial to consider location when determining the economic potential of CPG plants. Cool climates tend to result in higher electricity production as a result of a higher thermodynamic plant efficiency; however, it is also necessary to consider the economic environment, as electricity prices can have just as much of an impact, if not more, on a plant's financial performance. CPG power plants are also found to be economically competitive with other renewable energy options at the same capacity level and current CO2 sequestration and tax incentives can make unfavorable CPG power plants profitable. Next, CPG CHP DHC plants are considered, and three cases of heat production are investigated. Case 1 assumes the system meets peak winter heat demand, Case 2 assumes that some form of thermal storage is available and the system meets average monthly heat demand, and Case 3 assumes that all possible heat produced during winter months is sold. Electricity and heat are assumed to be sold in a competitive market. Six cities are considered, Williston, ND, Dallas, TX, New Orleans, LA, Houston, TX, Sacramento, CA, and Williamsport, PA, spanning 4 of the 5 US climate zones (Zones 1, 2, 3, and 5). Meteorological data are used to estimate energy production and heat demand. CPG is found to produce CO2 at high enough temperatures to be used in a district heating system. Case 1 most closely matches actual demand ratios for power vs heat in the various cities. CPG CHP/DHC plants in cities located in Zone 1 and Zone 2 climates have a higher net present value (NPV) than electricity-only plants. Case 2 and Case 3 CPG CHP/DHC plants in Zone 3 and Zone 5 can have a higher NPV than electricity only, but more consideration must be given to heat demand to ensure profit is increased. In all cities considered, tax credits and CO2 sequestration benefits can increase financial performance of CPG CHP/DHC plants.
Optical properties of Iridium(III) cyclometalates:excited state interaction with small molecules and dynamics of light-harvesting materials.
(2012-08) Schwartz, Kyle Robert
The research presented in this thesis concerns the use and understanding of luminescent Ir(III) cyclometalates. Areas of research involve the design, synthesis, and characterization of novel luminescent Ir(III) cyclometalates, including photophysical investigation of their phosphorescent excited states using steady-state and time resolved absorption/luminescence spectroscopies. This broad research description may be further separated into two subareas: study of excited state interaction with small molecules and excited-state dynamics of metal-organic light harvesting dyads. The first chapter of this thesis examines the interaction of Ir(III) cyclometalates with the small molecule carbon dioxide (CO2). It has been the goal of investigators to develop methods for direct optical detection of CO2. This has been difficult as CO2 is considered chemically inert and there are few luminescent probes directly sensitive to CO2. Most optical detection schemes previously developed for CO2 use indirect detection methods, which rely upon measuring changes in pH brought about by hydrolysis of CO2. Research efforts to design a reliable method for the direct optical detection of CO2 were accomplished through development of a system where hydrazine, a simple amino ligand, when coupled into the coordination sphere of an Ir(III) cyclometalate reacts with CO2. The result of this reaction provides a significant shift in the luminescence λmax of the phosphorescent probe, a previously unobserved optical response for the direct detection of CO2. The second chapter investigates phosphorescent excited states and their ability to function as triplet sensitizers for the generation of singlet oxygen (1O2) and luminescent probes for molecular oxygen (O2) concentration. Interaction of phosphorescent excited states with O2 results in energy transfer from the luminescent probe to O2, quenching the phosphorescent excited state. Energy transfer also generates the reactive oxygen species (ROS) 1O2. We have used this duality to develop an analytical methodology to follow the serendipitously discovered photoreactivity of 1O2 with common organic solvent dimethyl sulfoxide (DMSO) using the luminescence profile of Ir(III) and Ru(II) phosphors. Reaction of the triplet sensitized 1O2 with a photooxygenation substrate results in the consumption of O2 from the system and an increase in the observed luminescence intensity. Detailed kinetic investigations of the luminescence recovery and O2 depletion were preformed on air-saturated closed cell systems. Determinations of the quantum efficiencies for the photooxygenation system were performed and differences in choice of triplet sensitizer discussed. Study of 1O2 reactivity with substrates of biological and environmental relevance using this methodology should provide an additional tool to understand better oxidative damage induced by 1O2 within these systems. In chapter three a detailed study involving the design, synthesis, and characterization of the electrochemical and phototophysical properties of Ir(III) cyclometalates with pendant terthiophenes as secondary organic chromophores is presented. The interplay of the excited states between each chromophore represents an interesting photoredox active system for energy-to-light or light-to-energy devices. Greater knowledge of the primary photophysical events within these complexes will provide a better understanding of how energy moves in these hybrid systems after light absorption, leading to increased device efficiency.
The role of photodegradation in plant litter decomposition in grassland ecosystems
(2009-08) Brandt, Leslie Alyson
Decomposition of plant litter is the primary process by which carbon and nutrients are returned from plants to the soil and atmosphere. Although plant litter decomposition is primarily driven by plant litter chemistry, temperature, and precipitation these factors have failed to fully explain decomposition patterns in arid and semiarid grassland ecosystems. In my dissertation, I tested the hypothesis that solar radiation, particularly in the UV range (280-400 nm) contributes to the decomposition process in these systems via the process of photodegradation. In a three-year field study in the semiarid shortgrass steppe in Colorado, I examined whether photodegradation by UV radiation played a role in plant litter decomposition and whether the role of photodegradation in the decomposition process was affected by plant litter chemistry and precipitation. In a series of laboratory experiments, I examined the pathways by which mass is lost via photodegradation. In a two-year cross-site field experiment, I examined whether photodegradation may explain the difference in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems. The combined results of this research show that photodegradation is an important process in plant litter decomposition in mesic grassland ecosystems as well as arid and semiarid grassland ecosystems, accounting for up to 50% of litter mass loss. Results also show that litter mass loss via photodegradation is the result of photochemical production of carbon dioxide, which can be up to 4 g C m-2 y-1 in arid ecosystems. This research has important implications for future basic research in biogeochemical modeling, photochemistry of natural compounds, and plant litter decomposition in arid ecosystems.
Small Size, Huge Impact: Disproportionate Effects of Ponds on Aquatic Carbon Cycling and Atmospheric Greenhouse Gases
(2023-05) Rabaey, Joseph
The carbon cycle is essential for all life and is a major driver of Earth’s climate. Freshwater ecosystems (such as lakes, ponds, rivers, wetlands, etc.) play an outsized role in the global carbon cycle, acting in the transport, storage, and emission of carbon to the atmosphere. Freshwaters are significant sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4) to the atmosphere despite only covering 1% of Earth’s surface area, and they have become critical a piece in global greenhouse gas models. Surprisingly, the freshwater ecosystems that may contribute the most to global emissions are small ponds, though causes of emissions and variation across ponds are not well understood. My dissertation aims to more fully understand carbon cycling in ponds and identify key factors that influence greenhouse gas emissions. Through measurements of ecosystem metabolism (i.e., the balance of photosynthesis and aerobic respiration), I found that production and respiration rates in ponds are some of the highest across all freshwater ecosystems, with shallow depths influencing many factors that lead to high rates. By measuring greenhouse gas emissions from a wide range of ponds, I found that the absence of oxygen and high phosphorus concentrations can combine to lead to elevated CH4 emissions. In addition, duckweed on the surface of ponds can exacerbate these conditions and is potentially a target for management strategies. Finally, I monitored greenhouse gas emissions in four ponds throughout an entire year and found that water column mixing and stratification greatly impacts the seasonal timing and magnitude of greenhouse gas emissions. Overall, this work emphasizes that ponds are dynamic ecosystems with high rates of carbon cycling and greenhouse gas emissions, with implications for management and global greenhouse gas dynamics.
A Study of Post-Combustion Carbon Capture
(2021-06) Luedtke, Zachary
The Systematic Design of Nickel Complexes Toward Energy-Relevant Bond Activations
(2022-07) Prat, Jacob
The production of catalysts capable of the efficient and selective reactivity of CO2, H2, and CO toward useful products is required to lower global energy costs and allow for a sustainable carbon neutral future. To this end the design and synthesis of metal complexes capable of controlling the reactivity of these small molecules is highly desired. Bimetallic complexes allow for a greater chemical space allowing for high tailorability of metal catalyst properties presenting a new strategy for solving these issues. The tuning of a Z-type nickel-support bond toward small molecule reactivity unifies the chemistry described herein. In the introductory chapter the environmental and energy considerations motivating this work is made explicit. Inspired by enzymatic catalysis, a nickel-iron bimetallic complex for CO2 reduction to CO was studied in depth by NMR, Mössbauer, and electrochemical studies is detailed in Chapter 2. In Chapter 3 the role of a group 13 support on H2 binding and hydride transfer reactivity was investigated with the synthesis and characterization of a set of nickel-boron complexes. In Chapter 3 the combination of open ligand choice and metal support for the modulation of CO and CO2 binding was explored with iron and tin bimetallic nickel complexes.

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