Theses and Dissertations at Montana State University (MSU)
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Item Unusual isomerization behavior of organic solutes at the aqueous-silica interface(Montana State University - Bozeman, College of Letters & Science, 2019) Purnell, Grace Elizabeth; Chairperson, Graduate Committee: Robert Walker; Robert A. Walker was a co-author of the article, 'Hindered isomerization at the silica/aqueous interface: surface polarity or restricted solvation?' in the journal 'Langmuir' which is contained within this dissertation.; Robert A. Walker was a co-author of the article, 'Surface solvation and hindered isomerization at the water/silica interface explored with second harmonic generation' in the journal 'The journal of chemical physics' which is contained within this dissertation.; Marshall T. McNally, Patrik R. Callis and Robert A. Walker were co-authors of the article, 'Buried liquid interfaces as a form of chemistry in confinement: the case of 4-dimethylaminobenzonitrile at the silica-aqueous interface' submitted to the journal 'The journal of the American Chemical Society' which is contained within this dissertation.; Marshall T. McNally, and Robert A. Walker were co-authors of the article, 'Isomerization at aqueous-silica interfaces and the role of solute structure' submitted to the journal 'Chemical physics letters' which is contained within this dissertation.Experiments described in this thesis address the question of how strong association between water molecules and the silica surface alter the solvation and isomerization behavior of adsorbed organic molecules from bulk solution limits. The work was motivated by the hypothesis that the ice-like structure induced by strong hydrogen bonding with the surface silanol groups would restrict solute isomerization. This hypothesis was tested using 2 surface-specific spectroscopic techniques: second harmonic generation (SHG) and time-correlated single photon counting in a total internal reflection geometry (TIR-TCSPC). This work examined two different 7-aminocoumarin dyes (Coumarin 151 and Coumarin 152) and dimethylaminobenzonitrile (DMABN). Coumarin 152 and DMABN both isomerize to form a twisted intramolecular charge transfer (TICT) state upon photoexcitation, whereas Coumarin 151 forms a simple (planar) intramolecular charge transfer state. SHG studies characterized the local solvation environment surrounding adsorbed molecules by providing electronic excitation energies that were compared to bulk excitation energies in different representative solvents. TIR-TCSPC measured the time-resolved emission of adsorbed molecules and quantified a solute's tendency to form TICT (or ICT) isomers at the aqueous-silica interface. Together, SHG and TIR-TCSPC provide a cohesive description of the local polarity across an aqueous-silica interface and how restricted solvent dynamics change a solute's photophysical chemistry. TIR-TCSPC studies reported that both C152 and DMABN are unable to isomerize to TICT states at the aqueous-silica interface, acting as if they were solvated in a nonpolar solvent or in a confined geometry. SHG studies confirm that the aqueous-silica interface is, in fact, more polar than the bulk aqueous limit, strongly implying that the observed effects are dynamic in origin rather than polarity driven. In contrast, studies of C151 show that this solute is largely insensitive to anisotropic, restrictive surface effects. Together results from these three molecules lead us to conclude that adsorption to the strongly associating aqueous-silica interface restricts large amplitude isomerization in organic molecules. Adsorption to less strongly associating interfaces does not cause this restriction. In the event that photo-induced isomerization does not require large amplitude motion, interfacial solvation has little effect on adsorbed solute behavior.Item Organic enrichment at aqueous interfaces studied with non-linear spectroscopy: cooperative adsorption of soluble saccharides to lipid monolayers(Montana State University - Bozeman, College of Letters & Science, 2019) Link, Katie Ann; Chairperson, Graduate Committee: Robert Walker; Chia-Yun Hsieh, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang and Robert A. Walker were co-authors of the article, 'Vibrational studies of saccharide-induced lipid film reorganization at aqueous/vapor interfaces' in the journal 'Chemical physics' which is contained within this thesis.; Gabrielle N. Spurzem, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang and Robert A. Walker were co-authors of the article, 'Organic enrichment at aqueous interfaces: cooperative adsorption of glucuronic acid to DPPC monolayers studied with vibrational sum frequency generation' submitted to the journal 'Journal of physical chemistry B' which is contained within this thesis.; Gabrielle N. Spurzem, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang, and Robert A. Walker were co-authors of the article, 'Cooperative adsorption of trehalose to DPPC studied with vibrational sum frequency generation' which is contained within this thesis.Field measurements of sea spray aerosols have reported high concentrations of soluble organic material that are in excess of the concentration of soluble organics in the ocean. The studies described in this dissertation investigated a possible mechanism for this increase deemed cooperative adsorption. The cooperative adsorption mechanism describes an interaction between an insoluble Langmuir monolayer at the aqueous/vapor interface and soluble organic molecules that would not normally be enriched at the surface. In this model, the soluble organics are drawn to the surface through non-covalent interactions with the lipid surfactant. This mechanism was investigated with the surface specific nonlinear optical technique, vibrational sum frequency generation spectroscopy. These optical measurements were coupled with surface tension measurements and differential scanning calorimetry measurements. To study cooperative adsorption, model systems were used; these were composed of a phosphatidylcholine lipid surfactant, DPPC, and soluble saccharides including glucosamine, glucuronic acid, and trehalose. Glucosamine, in both a positive and neutral state, induced ordering in both expanded and condensed DPPC monolayers, supporting cooperative adsorption as a mechanism. Glucuronic acid, an anion, ordered lipid monolayers in the limits that the lipid DPPC was moderately packed and there were no competing ions in solution. Trehalose, a larger, uncharged saccharide showed, through ordering the DPPC monolayer, indications of cooperative adsorption in moderately packed DPPC when the trehalose concentration was sufficiently high. These results support cooperative adsorption as a mechanism for the accumulation of soluble organics in sea spray aerosols with some limitations.Item The role of adsorbed phase volume on the thermodynamics of supercritical methane adsorption on microporous carbon(Montana State University - Bozeman, College of Engineering, 2019) Remington, Emily Lynn; Chairperson, Graduate Committee: Sarah L. Codd; Nicholas P. Stadie (co-chair)Experimental determination of the isosteric heat of adsorption at the fluidsolid interface is an important undertaking in the chemical sciences since this fundamental thermodynamic quantity is closely related to the binding energy of the adsorbate on the adsorbent surface. The usual methods employed to calculate the isosteric heat from measured gas adsorption equilibria, however, are unsuited to the treatment of adsorption under a high-pressure adsorptive fluid (where the difference in molar volume between the two phases becomes small and depends significantly on that of the adsorbed phase). Herein we employ a methodological approach to the thermodynamic analysis of adsorption up to high pressures in the supercritical regime, with a specific focus on methane adsorption on microporous carbonaceous materials at T/T c between 1.25-2.75 and P/P c up to 2. The aim is to achieve a meritorious description of the thermodynamics of the adsorbed phase with as few independent parameters as possible. We compare several simple approaches to estimating the molar volume of the adsorbed phase, and demonstrate that among the several well-known sources of error involved in the isosteric approach, that attributed to molar volume estimations is not itself prohibitive to achieving meritorious results. We contrast the isosteric approach with that of the so-called 'isoexcess' methodology, and thereby shed new insights into the key role of the finite adsorbed phase volume in assessments of adsorption thermodynamics.Item Spectroscopic studies of noncovalent interactions at interfaces and their effects on interfacial structure, organization, and association(Montana State University - Bozeman, College of Letters & Science, 2015) Gobrogge, Eric Andrew; Chairperson, Graduate Committee: Robert Walker; B. Lauren Woods was an author and Robert A. Walker was a co-author of the article, 'Liquid organization at polar solid/liquid interfaces' in the journal 'Faraday discussions' which is contained within this thesis.; Jessica H. Ennist was an author and Kristian H. Schlick, Robert A. Walker and Mary J. Cloninger were co-authors of the article, 'Cyclodextrin-functionalized chromatographic materials tailored for reversible adsorption' in the journal 'ACS applied materials & interfaces' which is contained within this thesis.; Robert A. Walker was a co-author of the article, 'Partitioning of binary solvents at solid/liquid and solid/vapor interfaces' in the journal 'Journal of physical chemistry letters' which is contained within this thesis.Studies described in this dissertation used linear and nonlinear optical methods to examine the effects of noncovalent forces on molecular structure, organization and reactivity at solid/liquid, solid/vapor and liquid/vapor interfaces. These studies address three general questions: 1) Solvent structure at solid/liquid interfaces; 2) Solute adsorption to chemically tailored solid and liquid interfaces; and 3) Partitioning of binary solvents at solid/liquid and solid/vapor interfaces. 1) Solvent structure at solid/liquid interfaces. Vibrational sum frequency spectroscopy (VSFS) was used to study the interfacial organization of different alkanes and alcohols at the silica/liquid interface. Results showed that solvent organization depended sensitively on both interactions with the interface and on the solvent's molecular structure. Silica/methanol and silica/ethanol interfaces were also compared in order to determine why ethanol gives a VSFG spectrum but methanol does not. 2) Solute adsorption to chemically tailored interfaces. VSFS and fluorescence spectroscopy were used to characterize and analyze the effectiveness of silica substrates functionalized specifically to promote adsorption of organic analytes in aqueous solutions through catch and release chemistry. VSFS has also been used to study cooperative adsorption at aqueous/vapor interfaces to explore how insoluble surfactants can increase near-surface concentrations of soluble species. 3) Binary solvent partitioning at solid/liquid and solid/vapor interfaces. VSFS was used to study molecular organization at silica/binary solvent interfaces where the binary solvent consisted of acetonitrile and methanol in varying mole fractions. The vibrational spectra indicated that while methanol adsorbed ideally at the silica/vapor interface, acetonitrile accumulated in excess relative to the vapor phase composition. At the silica/liquid interface, methanol appeared to remain strongly associated with the surface until an acetonitrile mole fraction of 0.85 was reached. At higher mole fractions, interfacial acetonitrile adopts an antiparallel bilayer organization. This binary mixture was also compared to various other binary mixtures at the silica/vapor and silica/liquid interfaces.Item Adsorption capacity of SAPO-34 and ZSM-5 zeolites determined by breakthrough experiments(Montana State University - Bozeman, College of Engineering, 2016) Ilic, Boris; Chairperson, Graduate Committee: Stephanie WettsteinAlthough it has been known for over 50 years that zeolite frameworks are flexible, it has been only of recent that a systematic investigation into this phenomenon has begun. An area that has not been significantly explored is the affect that zeolite flexibility may have on adsorption capacities. In order to explore this, a flow system was built and assembled, and the system performance was verified by replicating literature ZSM-5/isobutane, ZSM-5/n-hexane, and SAPO-34/methanol adsorption isotherms. Different packing schemes (powders, mixtures, pellets) were studied and corresponding adsorption capacities were evaluated for accuracy and precision. It was found that zeolite powder pressed into pellets led to the lowest deviation from literature values and that larger crystal sizes may also lead to more accurate values. While further investigation into packing methods is recommended, the relatively accurate adsorption capacities that were acquired suggests that the established flow system has been built and calibrated correctly, and that further adsorption experiments probing the flexibility of the zeolite structure can begin.Item Adsorption of chloroform by soils in a continuous flow reactor(Montana State University - Bozeman, 1984) Karlsen, Barbara HeckmanItem Adsorption of chloroform on soils(Montana State University - Bozeman, 1983) Liltved, HelgeItem Linear and nonlinear optical studies of molecular adsorption to silica/liquid interfaces(Montana State University - Bozeman, College of Letters & Science, 2015) Woods, Brittany Lauren Gray; Chairperson, Graduate Committee: Robert Walker; Rob Walker was a co-author of the article, 'pH effects on molecular adsorption and solvation of p-nitrophenol at silica/aqueous interfaces' in the journal 'Journal of physical chemistry A' which is contained within this thesis.; Jenna K. George, Alex M. Sherman, Patrik R. Callis and Robert A. Walker were co-authors of the article, 'Adsorption and aggregation at silica/methanol interface: the role of solute structure' submitted to the journal 'Journal of physical chemistry C' which is contained within this thesis.; Jenna K. George and Robert Walker were co-authors of the article, 'Spectroscopic solvation mechanisms at silica/acetonitrile interfaces' submitted to the journal 'Physical chemistry and chemical physics' which is contained within this thesis.Adsorption mechanisms at buried interfaces are difficult to predict a priori, with many interactions to consider including those between the substrate and solvent, the substrate and adsorbate, and the solvent and adsorbate. Studies described in this thesis examine the roles these variables have on controlling interfacial behavior, including molecular adsorption and aggregation at solid/liquid interfaces. Specifically, second harmonic generation (SHG) was employed to characterize adsorption environments and adsorption energies at different silica/liquid interfaces, due to the technique's surface specificity. Additionally, time resolved fluorescence was used to quantify emission lifetimes within these same interfacial regions. By systematically changing the substrate, solvent identity, and adsorbate functionality, the impact of each contribution was identified and quantified. Initial studies examined the role played by interfacial pH in controlling adsorption. Above pH 5, silica surfaces become negatively charged and promote two distinct adsorption mechanisms. Adsorption due to these mechanisms requires very long equilibration times (>3hrs). Subsequent experiments studied the role played by solvent identity on interfacial solvation. At a methanol/silica interface a non-polar interfacial environment was produced, independent of solute choice. Non-polar solvents conversely create polar interfacial solvation environments. At these different solid/liquid interfaces, similarly structured coumarin dyes, C151 and C152, were examined. Slight changes in structure lead to differing behaviors at the surface, C151 terminates at monolayer coverage while C152 shows clear signs of multilayer formation. This observation is explained by the difference in hydrogen bonding opportunities for each adsorbate: C151 can accept and donate H-bonds while C152 can only accept H-bonds, resulting in more degrees of freedom for C152 at an interface and thus the possibility of aggregation.Item Adsorption of complexed Cd(II) species by aluminum oxide(Montana State University - Bozeman, College of Letters & Science, 1986) Sharpsten, Michael RichardItem Experimental studies of the defect structure of the TIO 2(110) surface before and after the exposure to oxygen, hydrogen and carbon monoxide(Montana State University - Bozeman, College of Letters & Science, 1985) Rocker, Gerd Heinrich
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