Browsing by Subject "FTIR"

Now showing 1 - 5 of 5
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    Adsorption of Freshwater Dissolved Organic Matter to Clay and Polyethylene Particles
    (2019-08) Burrows, Alvin
    Organic matter (OM), especially dissolved organic matter (DOM), plays several integral roles in aquatic systems. OM acts as a short-term sink of carbon and a food source for heterotrophs and shields biota from harmful UV radiation. It also facilitates the transport of nutrients, trace metals and pollutants in the environment. The uptake and transport of these compounds are related to the fate of the DOM to which they are bound. Suspended solids such as clays or microplastics can adsorb DOM into their interlayer spaces or onto their surfaces leading to: 1. Possible physical protection of OM that would have been mineralized or degraded by biota; 2. Increased transport of OM through the water column to the sediments (for sinking particles) or increased time for OM in the surface water (for less-dense microplastic particles); 3. Increased uptake by larger aquatic organisms. Increased particle-associated mobility (either by sinking through the water column or being transported at the surface via wind-driven processes) also increases associated nutrient, trace metal and pollutant transport, which in sufficient quantities, may perturb the aquatic system’s equilibrium and affect its chemistry. Microplastics, a new particle-type in aquatic systems, have been observed and documented in the world’s oceans since the 1970s, but their presence in the Laurentian Great Lakes was first recorded in 2013. The roles that microplastics and other particulates (both naturally occurring and anthropogenically impacted) play in aquatic environments need to be thoroughly studied so that a better understanding of their fate and environmental impact can be gained. The goal of this study was to qualitatively examine and compare the adsorption of open water Lake Superior DOM and DOM from a tributary stream to polyethylene microplastic spheres and to clays (kaolinite and montmorillonite). UV-VIS optical proxies were used to monitor changes in aromaticity (A254, SUVA) and molecular weight (E2:E3, S250-400, SR) within the remaining dissolved phase. Aromaticity proxies suggest that clays preferentially adsorbed aromatic species, while polyethylene had no significant effect on DOM composition. Changes in the amount of carbon remaining in the dissolved phase were measured using dissolved organic carbon (DOC) analysis while the amount adsorbed to the surface of the particulates was measured using elemental analysis (EA). DOC analysis did not show significant changes in the amount of dissolved organic carbon after sorption testing. EA was unable to provide a definitive answer for carbon adsorbed by polyethylene but suggests that kaolinite and montmorillonite adsorb similar amounts of carbon in both environments.
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    An ATR-FTIR study of semiconductor-semiconductor and semiconductor-dielectric interfaces in model organic electronic devices.
    (2009-08) Mills, Travis
    Organic electronics offer many benefits to inorganic electronics such as the promise of cheap, large-scale processing on flexible substrates and incorporation into many household devices. Organic photovoltaic (OPV) devices and organic field effect transistors (OFETs) offer low-cost implementation which might compete in some applications with their inorganic counterparts. However, fundamental work is necessary to uncover the physics governing the operation of OPVs and OFETs, in order to improve the efficiency of the devices. Much of the fundamental understanding developed in this work occurs at buried interfaces, such as the donor acceptor interface in OPVs or the semiconductor dielectric interface in OFETs. This thesis first introduces the reader to the device physics and state of the art in the development of OPVs and OFETs. After describing the experimental techniques used, a discussion of interfacial electric fields in bulk heterojunction polymer/small molecular solar cells will follow. It was found using the vibrational Stark effect, that donor acceptor interfacial electric fields could be measured and related to previous experiments. The interfacial field hinders the dissociation of excitons but also prevents geminate pair recombination. In OFET devices, the semiconductor dielectric interface was studied and the rate limiting steps to device performance in polymer electrolyte gated OFETs were determined. The interfaces studied provide insight into the fundamental operation of both OPVs and OFETs, which should help produce more efficient and controllable production of organic electronic devices.
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    Berkovich nanoindentation and FTIR data describing the effect of water on olivine plasticity
    (2023-08-28) Kumamoto, Kathryn, M; Breithaupt, Thomas, P; Hansen, Lars, N; Wallis, David; Li, Bo-Shiuan; Armstrong, David, EJ; Goldsby, David, L; Li, Yang; Warren, Jessica, M; Wilkinson, Angus, J; lnhansen@umn.edu; Hansen, Lars, N; Rock and Mineral Physics Lab
    This data set contains data collected as part of a study to determine the influence of dissolved hydrogen on the mechanical properties of olivine. Nanoindentation experiments were conducted to measure the hardness of both pristine olivine crystals and olivine crystals predoped with hydrogen. The hydrogen content of samples was assessed with Fourier-transform infrared spectroscopy (FTIR). This data set includes mechanical data from indentation experiments as well as spectra from FTIR measurements.
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    Effects of nanocrystalline silicon inclusions in doped and undoped thin films of hydrogenated amorphous silicon.
    (2009-12) Blackwell, Charlie Pearman
    Hydrogenated amorphous silicon has attracted considerable interest as a low-cost material for various large-area electronic devices, such as scanners, thin film transistors employed in flat panel displays, and photovoltaic devices. A major limitation of amorphous silicon is a light-induced degradation of the photoconductivity and dark conductivity, associated with the creation of metastable dangling bond defects. Recent reports that mixed phase thin films, consisting of silicon nanocrystallites embedded within a hydrogenated amorphous silicon matrix, display a resistance to this light-induced degradation have motivated the development of a novel deposition system to synthesize such materials. Conventional techniques to generate such amorphous/nanocrystalline mixed phase films involve running a Plasma Enhanced Chemical Vapor Deposition system very far from those conditions that yield high quality amorphous silicon. A dual-plasma co-deposition system has thus been constructed, whereby the silicon nanoparticles can be fabricated in one chamber, and then injected into a second plasma reactor, in which the surrounding amorphous silicon is deposited. The deposition process, as well as structural, optical, and electronic characterization of these films, including the dark conductivity, photoconductivity, infra-red absorption spectra, micro-RAMAN spectra, and the optical absorption spectra, will be discussed for these films.
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    Microplastics in the surface water and sediments of western Lake Superior as determined via microscopy, Pyr-GC/MS, and FTIR.
    (2017-09) Hendrickson, Erik
    While the presence of plastic pollution is well known in the world’s oceans and is beginning to be documented in the world’s freshwater systems, there is not yet an in-depth understanding of the distributions, chemical compositions, fates and ecological impacts of plastic particles in most aquatic systems. Microplastic particles are of particular concern due to their direct biological effects (such as false satiation), their roles as sorbents of other chemical compounds, and as vectors for invasive species. In this study, we evaluate the magnitude, distribution, and common polymers of microplastic pollution in surface waters and sediments in western Lake Superior, the deepest and most pristine of the Laurentian Great Lakes. Microscopy, Pyrolysis-Gas Chromatography/Mass spectrometry (Pyr-GC/MS), and Fourier Transform Infrared spectroscopy (FTIR) were used to quantify and identify microplastic particles. Despite the low human population density in Lake Superior’s watershed, microplastic particles (particularly fibers, fragments, and films) were identified in western-lake surface waters at levels significantly greater than those previously reported in Lake Superior’s eastern basin (p-value < 0.05). Microplastic concentrations in western-lake surface waters were found to range from 0 to 110,000 particles•km-2 (n=15, mean: 39,000 particles•km-2, standard deviation: 28,000 particles•km-2, and 95% confidence interval: ±14,000 particles•km-2). Fibers were the most frequently observed morphology in lake surface waters and sediments. The most common polymer in surface waters and sediments was PVC; for surface waters, PP and PE were the next most frequently observed, and PET was the only other polymer observed in sediments. Our ability to evaluate microplastic abundances in Lake Superior’s waters and sediments was in part determined by the need to correct for ambient contamination from atmospheric deposition of microplastics during sampling and sample processing. The effects of this contamination, coupled with the small sample area of sediment obtainable by multi-corer, made determining microplastic concentrations in surface sediments problematic. Results presented here provide quantitative and qualitative data on microplastic pollution in western Lake Superior using improved analytical methodology, including polymer characterization by two different techniques. This study also provides insights into possible sources of microplastic pollution in Lake Superior, and ways to improve future microplastics studies in aquatic systems.