• Characterizing Heterogeneously Charged Mineral Oxide Surfaces Using Nonlinear Spectroscopy

      Borguet, Eric; Levis, Robert J.; Voelz, Vincent; Yeganeh, Mohsen S. (Temple University. Libraries, 2019)
      Mineral oxide/aqueous interfaces play an important role in the transport of water through aquafers and streams, erosion, the formation of beaches and river deltas, nuclear waste storage, the sequestration and filtration of small ions, and are widely used in industrial scale catalysis. Unlike metal or semiconductor electrodes, the surface charge resulting from the protonation or deprotonation of insulating mineral oxides is highly localized and heterogeneous in nature. While the unique acid/base chemistry associated with different mineral oxide surfaces leads to their wide variety of applications, the extent to which surface groups found on mineral oxides partake in acid/base chemistry is still controversial due to the difficulty associated with experimentally probing them. Surface specific spectroscopic techniques, such as vibrational Sum Frequency Generation (vSFG), provide an opportunity to investigate how the surface architecture and corresponding chemical nature of various mineral oxide surfaces orient the interfacial solvent at a variety of solvent compositions and surface charges. Although vSFG has been used as a tool to measure the orientation and composition of interfacial O-H species originating from the surface and solvent for many mineral oxide/aqueous interfaces since the late 1990’s, controversy still exists in the assignment of vSFG spectra in the O-H stretching region of SiO2, Al2O3, CaF2, and TiO2/aqueous interfaces. The first section of this dissertation focuses on how the nonlinear optics and computational community’s understanding of the structure associated with mineral oxide/aqueous interfaces has evolved and where it stands now. Of particular interest is how the addition of electrolyte and variation of bulk pH allow modulation of the depth of the interfacial region and surface charge. Electrolyte solutions can vary the length of the interface by screening interfacial charges through non-specific adsorption at the interface, or generating surface charge if accumulation is facilitated by specific adsorption. The specific interaction of small ions with mineral oxide surfaces is relevant in geochemistry and filtration technology, and can also aid in prediction of contaminant mobility in ground water systems. Chapters two and three discuss the theory and application of vSFG, and the experimental setup used to capture vSFG spectra in this work, respectively. The fourth chapter investigates how monovalent or divalent cations accumulate at alpha-Al2O3(0001)/H2O interfaces and reorganize the interfacial solvent structure. The reactivity of these interfaces is strongly impacted by the presence of ions. Thus, it is critical to understand how ions alter the interfacial environment. This is achieved by measuring the changes in the structure and vibrational dynamics of interfacial water induced by the presence of ions in close vicinity to the mineral surface. The alpha-Al2O3(0001) surface represents a flexible platform to study the effect of ions on interfacial aqueous environments at positive, neutral and negative surface charge. Using vibrational sum frequency generation (vSFG) in the frequency and time domain, we investigate how monovalent and divalent cations affect the hydrogen bonding environment of the first few layers of interfacial water next to an alpha-Al2O3(0001) surface. Our results indicate that monovalent cations, such as Li+, Na+, K+, and Cs+, appear to have lower adsorption affinities for the interface compared to Ca2+, Sr2+, and Ba2+. This leads to an interfacial region that is structured in a cation valence dependent manner. Time resolved vSFG measurements reveal that the O-H vibrational lifetime (T1) of interfacial species at pH 10 conditions in the presence of NaCl and BaCl2 remains similar, but restructuring of the surface seen in steady state vSFG is manifested in the degree to which strongly hydrogen bonded species recover to their original populations post excitation. By tracking the accumulation of ions at the interface via the vSFG response, we can characterize the unique surface arrangements of interfacial water molecules induced by a range of monovalent and divalent cations at the alpha-Al2O3(0001)/water interface. In the fifth chapter the Stark active C ≡ N stretch of potassium thiocyanate is used as a molecular probe of interfacial electrostatic potential at the alpha-Al2O3(0001)/H2O interface. We confirm the presence of the thiocyanate ion in the interfacial region via reorganization of surface waters in the O-H stretching region. Changes in electrostatic potential are then tracked via Stark shifts of the vibrational frequency of the C ≡ N stretch. Our vSFG measurements show that we can simultaneously measure the SFG response of SCN- ions experiencing charged and neutral surface sites and assign a local potential of + 308 mV and -154 mV to positively and negatively charged aluminol groups, respectively. Thiocyanate anions at charged surface sites adopt similar relative orientations independent of surface charge, but adopt an opposite orientation at neutral surface sites. MD-DFT simulations of SCN- near the neutral alpha-Al2O3(0001)//H2O interface show that the vSFG response in the C ≡ N stretch region originates from a SCN-H-O-Al complex, suggesting the surface site specificity of these experiments. By tracking how this molecular probe responds to local surface charges we offer insight into the local electrostatic potential at neutral and charged surface aluminol groups. Chapter six investigates the vibrational dynamics of potassium thiocyanate at the alumina/water interface. Here, we leverage the sensitivity of the C ≡ N stretch vibrational lifetime of potassium thiocyanate to measure the local electrostatic potential at the alpha-Al2O3(0001)/H2O interface. To accomplish this, KSCN was investigated using free induction decay vSFG (FID-vSFG) and time resolved pump probe (TR-vSFG) measurements, which measure the total dephasing time and vibrational lifetime of the excited C ≡ N stretch, respectively. Our FID-vSFG spectra suggest that at all surface charges the total dephasing time of SCN- is on the order of ~300-600 fs. TR-vSFG characterizations of potassium thiocyanate report the vibrational lifetime of the excited C ≡ N stretch between ~0.5-2 ps. TR-vSFG measurements show two distinct vibrational relaxation rates, which are assigned the CN stretch and the HOH bend plus libration combination band of interfacial water. The variation in the T1 lifetime of the CN stretch with bulk pH show that changes in the SCN- net orientation measured using steady-state vSFG can be correlated to the vibrational dynamics in the interfacial region. The energy transfer to the bend plus libration combination band of water is also sensitive to the surface charge, as the lifetime of this species becomes shorter as the bulk pH is increased. Lastly, in chapter seven this thesis is summarized, and future directions of the experiments presented here are discussed.
    • Damming the American Imagination

      Orvell, Miles; Wells, Susan, 1947-; Lee, Sue-Im, 1969-; Bruggeman, Seth C., 1975- (Temple University. Libraries, 2019)
      This work intervenes in the complex relationship between the large-scale management and exploitation of water in the United States and its impact on the bioregional literary imagination in the Tennessee Valley between 1933-1963. It shows through site-based environmental criticism and literary analysis that the “dam” becomes a material and symbolic place of convergence where one can examine the relationship between humans and their biospheres. As interdisciplinary rhetorical, literary, historical, archival and cultural analysis, this work engages writers such as David E. Lilienthal, William Bradford Huie, Robert Penn Warren, and Madison Jones in order to reveal the inherently conflicted realities of environmental conservation, individual identity, and displaced regional imaginations in American literature.
    • Fresh Water Scenes in Minoan Art

      Betancourt, Philip P., 1936-; Evans, Jane DeRose, 1956-; Bolman, Elizabeth S., 1960-; Myer, George H. (Temple University. Libraries, 2017)
      The goal of this dissertation is to provide a comprehensive study of scenes of fresh water in Minoan art from the Middle Minoan II (MM II) through the Late Minoan I (LM I) periods. This dissertation addresses and fills the gap in the scholarship regarding the depiction of riparian environments and the special place of these depictions in Aegean art. It also attempts to clarify the use and function of riverscapes across chronological periods. Rivers, marshes, streams, and springs, appear on a variety of media and fulfil multiple functions from MM II onward. Images of fresh water were used as topographical markers, ornamentation and decoration, and for religious purposes. Moreover, several images suggest that the Minoans may have believed that the realm for the goddess (or one of the goddesses) was a lush, riverscape. A second goal of this dissertation is to clarify and dispose of the term “Nilotic” as a label for images of fresh water in the Aegean. Since its introduction into the literature of Aegean studies in the beginning of the 20th century, the term “Nilotic” has been used inconsistently to describe Aegean scenes of fresh water that may or may not contain Egyptian elements. This assumption has led some scholars to state that Aegean riverscapes are ultimately derived from Egyptian scenes of fishing and fowling because they share similar iconographic elements. Unfortunately, the process of synthesis is important to the understanding of Aegean riverscapes, and iconographic similarities are somewhat superficial. Furthermore, the term has been used without regard for a long-standing tradition of the depiction of riparian environments in Bronze Age Aegean art. To fully address both goals of this project, the origin of individual iconographic elements has been traced through various media, including glyptic art, pottery, and wall painting. Wall paintings from the Cyclades and some Late Helladic IA scenes have been included when appropriate. Whenever possible, categories of riverscapes have been grouped together, but each wall painting, has been examined and interpreted individually. Some unique, highly pictorial, and detailed images in other media have also been addressed separately. Parallels in Egyptian and, in some cases, Near Eastern art have been sought to determine the validity of the term “Nilotic,” and a special study of Egyptian scenes of hunting in the marshes has been conducted in comparison to Aegean scenes. Iconography, synthesis, and context have all been taken into consideration.

      Borguet, Eric; Klein, Michael Leslie; Levis, Robert J.; Lester, Marsha I. (Temple University. Libraries, 2015)
      The distinct structure and dynamics of interfacial water are due to a break in the extended hydrogen bonding network present in bulk water. At solid-aqueous interfaces, the presence of surface charge, which induces a static electric field, and the electrolytes, which are present in most naturally relevant systems, can additionally perturb the hydrogen bonding environment due to polarization. The interplay between the surface-charge-induced electric field and the ions in changing the structure of interfacial water has important consequences in the chemistry of processes ranging from protein-water interactions to mineral-water reactivity in oil recovery. Accessing information about the first few layers of water at buried interfaces is challenging. Vibrational sum-frequency generation (vSFG) spectroscopy is a powerful technique to study exclusively the interfacial region and is used here to investigate the role of interfacial solvent structure on surface reactivity. It is known that the rate of quartz dissolution increases on addition of salt at neat water pH. The reason for this enhancement was hypothesized to be a consequence of perturbations in interfacial water structure. The vSFG spectra, which is a measure of ordering in the interfacial water structure, shows an enhanced effect of salt (NaCl) at neat pH 6~8. The trend in the effect of salt on vSFG spectra versus the bulk pH is remarkably consistent with the enhancement of rate of quartz dissolution, providing the first experimental correlation between interfacial water structure and silica dissolution. If salt alters the structure of interfacial water, it must affect the vibrational energy transfer pathways of water, which is extremely fast in bulk water (~130 fs). Thus far, the role of ions on the vibrational dynamics of water at charged surfaces has been limited to the screening effects and reduction in the depth of the region that contributes to vSFG. Here, we measure the ultrafast vibrational relaxation of the O-H stretch of water at silica at different bulk pH, using time-resolved (TR-vSFG). The fast vibrational dynamics of water (~200 fs) observed at charged silica surfaces (pH 6 and pH 12), slows down (~600 fs) on addition of NaCl only at pH 6 and not at pH 12. On the other hand at pH 2 (neutral surface), the vibrational relaxation shows an acceleration at high ionic strengths (0.5 M NaCl). The TR-vSFG results suggest that there is a surface-charge dependence on the sensitivity of the interfacial dynamics to ions and that reduction in the probe depth of vSFG alone cannot explain the changes in the vibrational lifetime of interfacial O-H. This is further supported by the cation specific effects observed in the TR-vSFG of the silica/water interface. While the vibrational relaxation of O-H stretch slows on addition of all salts (LiCl, NaCl, RbCl, and CsCl), the degree of slowing down is sensitive to the cation identity. The vibrational lifetime of O-H stretch in the presence of different cations follows the order: Li+ < Na+ < Rb+, consistent with previous Hofmeister effect reported in vSFG spectroscopy as well as AFM measurements at silica/water interface. To provide molecular insight on the effect of surface charge density and ionic strength on the changes in interfacial water structure, Molecular Dynamics (MD) simulations were performed on water at different types of surfaces. It was shown that the properties of water near the interface, e.g., a net orientation and the depth to which this persists, depend on the degree of specific adsorption of the counter ions. Our vSFG results, along with the insights from MD simulations, highlight the importance of considering the role of ions on the solvent structure within the electric double layer region, beyond the screening effects predicted by classical electrochemical models.
    • Modeling of liquid water and ionic solutions by first-principles simulations

      Wu, Xifan; Ruzsinszky, Adrienn; Yan, Qimin; Carnevale, Vincenzo (Temple University. Libraries, 2020)
      Water is one of the most important materials and has enormous impacts on life. Due to its delicate Hydrogen bond (H-bond) network, water shows various anomalous properties which has not been fully illuminated. Advanced experimental methods, such as scattering experiments and various spectroscopy techniques, have been developed and applied to study the nature of H-bond in liquid water. On the other hand, ab initio molecular dynamics (AIMD) have been widely adopted as an important theoretical tool to provide microscopic information of water on a sub-picosecond timescale. Recent AIMD studies based on the strongly constrained and appropriately normed (SCAN) exchange correlation functional yield an excellent description of the structural, electronic, and dynamic properties of liquid water. In this dissertation, we will focus on studying the structural, electronic and dynamic properties of liquid water as well as the modeling of the hydration structures of ions in aqueous solutions, using AIMD with potential energy surface provided by the novel SCAN functional. In the first work we represent an accurately predicted infrared spectrum of liquid water and show how the improvements are connected to the description of the underlying H-bond network. The second work mainly focusing on modeling the nuclear quantum effects (NQEs) and isotope effect of liquid water with a force field model based on artificial neural network, where qualitative agreements with experimental observations are achieved. In the third work, we study the isotope effect on the x-ray absorption spectra of liquid and attribute observed differences to the structural distinctions between light and heavy water as mentioned in the previous work. And in the last two projects, we systematically show the necessity of including NQEs of the hydrogen atom when modeling chloride ionic solution. Prominent changes in the hydration structure as well as electronic structure can be identified when NQEs are taken into consideration.

      Wayland, Bradford B.; Zdilla, Michael J., 1978-; Wunder, Stephanie L.; Cannon, Kevin C. (Temple University. Libraries, 2012)
      Environmental and energy issues have stimulated renewed interest in utilizing both water and methanol as reagents and reaction mediums. Our current interest is to evaluate the scope of group nine organometallics and establish thermodynamic parameters for their reactivity in aqueous solvent. A comprehensive thermodynamic database for a wide scope of organo-rhodium transformations in a range of reaction media including benzene, water, and methanol has been well established by our group. Aqueous solutions of rhodium porphyrin have been determined to manifest an exceptional range of substrate reactions with carbon monoxide, dihydrogen, olefins, methanol and aldehydes. This study will focus on expansion of the thermodynamic database to all the group nine metals, particularly the iridium porphyrin systems in both water and methanol. Substrate reactivity and development of new mechanistic strategies for the conversion of carbon monoxide, alkanes, and alkenes to organic oxygenates are central objectives. Water/Methanol soluble porphyrin iridium complexes including iridium tetrakis(p-sulfonatophenyl)porphyrin ((TSPP)Ir) and iridium tetrakis(3,5-sulfonatomesityl)porphyrin ((TMPS)Ir) derivatives can be prepared by sulfonation of tetra phenyl porphyrin (H2TPP) and tetra mesityl porphyrin (H2TMP). The reactivity of dihydrogen with aqueous solutions of iridium(III) tetrakis(p-sulfonatophenyl)porphyrin ((TSPP)Ir(III)) complexes produce equilibrium distributions between six iridium species including iridium hydride ([(TSPP)Ir-D(D2O)]-4), iridium(I) ([(TSPP)IrI(D2O)]-5), and iridium (II) dimer ([(TSPP)IrII(D2O)]2-8) complexes. Each of these types of iridium porphyrin species including Ir(I), Ir(II), Ir(III), Ir-H, and Ir-OH function as precursors for a range of organometallic substrate reactions. A primary objective is to define the quantitative relationships pertaining to the distribution of species in aqueous solution as a function of the dihydrogen and hydrogen ion concentrations through direct measurement of five equilibrium constants along with free energy changes of coordinated water and free energy changes of reactions of dihydrogen in water. Reactivity, kinetics and evaluation of equilibrium thermodynamics, including the reactions of iridium hydroxide and methoxide with olefins to produce beta-hydroxyalkyl and beta-methoxyalkyl complexes, reactions of iridium hydride and olefins to produce iridium alkyl complexes, and reactions of iridium hydride with carbon monoxide to produce iridium formyl [Ir-CHO] complexes are also objectives of this research. Another research goal is the design and synthesis of diporphyrin ligands that form dimetal complexes capable of preorganizing transition states for substrate reactions that involve two metal centers. Dirhodium dimetalloradical complexes are observed to manifest large rate increases over mono-metalloradical activation reactions of hydrogen, methane, and other small molecule substrates. In this study, synthesis of diporphyrin (bisporphyrin) ligands and other ligands which will permit dimetallo complexes like anti-aromatic [14]annulene and low steric porphine ligands will be also be examined.