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Physical Sciences

Frontiers in Geochemistry

2016

"Ions and the ultrafast spectroscopy and dynamics at aqueous interfaces"

Eric Borguet
Professor
Temple University
EMSL/1077
Thursday, October 27, 2016
9:00 am

Interfacial water structure, which can be probed by vibrational sum-frequency generation (vSFG) spectroscopy, is key to many processes. Time-resolved vSFG shows that in the absence of surface charge (pH 2), water at silica surfaces exhibits significantly slower OH stretch vibrational relaxation (~600 fs) compared to bulk. However, at charged silica surfaces (e.g., pH 6), bulk-like fast dynamics (~200 fs) are observed at low ionic strength. This decelerates to ~600 fs, with the addition of NaCl. In parallel, vSFG results demonstrated that silica interfacial water structure is most sensitive to cations at pH=6-8. Consequently, it is unclear whether the observed slowing of the vibrational dynamics is due to the reduction in Debye length, or because of changes in the local hydrogen bonding environment caused by the electrolyte and how this might depend on the identity of the ions. Our results shed light on the ongoing debate on the role of ions in interfacial water structure and whether the observed behavior is specific to silica/water interfaces or can be generalized to other systems.

2015

"The scientific publishing sea change"

Dr. Nicholas Wigginton
Senior Editor
Science
EMSL Auditorium
Wednesday, June 3, 2015
9:00 AM

The publishing world is in the midst of a sea change. Scientific publishing is no exception, yet has its own set of emerging issues (e.g., data sharing, new publication models, changing demographics). The peer-reviewed scientific literature, however, continues to be the primary means of scientific communication within the community, to the press, and to policymakers, and ultimately to the public. Many of these issues are unfortunately overlooked, even during early career training. Based on my experience as a research editor at Science, I will discuss how researchers can better prepare for these changes in their various roles as authors, reviewers, and readers.

2014

"Tip induced crystallization lithography"

Dr. Xin Zhang
Texas Tech University
Department of Chemical Engineering
CSF Darwin Room
Tuesday, July 8, 2014
9:00 AM

The preparation of uniform large-area organic crystal arrays on substrates and controlling their shapes, morphologies, sizes, and densities plays an important role in material sciences and physics chemistry, such as producing high-quality organic thin film based semiconductors, solar cells, field-effect transistors, light-emitting diodes and promoting the sensitivity of chemical and biological sensors. It also aids in providing an environment to understand the thermodynamics, kinetics, sensitivity, and detonics of energetic materials in micro- or nano-scale. We developed a new atomic force microscopy (AFM) based technique, tip induced crystallization lithography (TICL), for efficiently fabricating large-area organic crystal arrays on various substrates. This technique depends on coating an amorphous organic thin film on a substrate and then inducing crystallization of the thin film using AFM tips. After removing the noncrystalline materials from the substrate by heating or solvent washing, the organic crystal arrays are obtained on the substrate. By adjusting the scanning features, crystal growth time, thin film thickness, size and density of noncrystalline particles in the original amorphous thin film, and substrate surface energy, the shape, morphology, size, and density of the patterned organic crystal arrays can be controlled. The size of the smallest feature made using TICL technique is less than 1 Ám.

2012

"Sum frequency vibrational spectroscopy studies of hydroxyl functional groups and hydrogen bonding on corundum surfaces: Challenges and future applications"

Dr. Glenn Waychunas
Lawrence Berkeley National Laboratory, Earth Sciences Division, Senior Staff Scientist
Principal Investigator, BES Geochemistry Program
ETB Columbia River Room
Wednesday, February 15, 2012
9:00 AM

Sum frequency optical techniques can be used to characterize reactive functional groups (hydroxyls, amines, carboxylates) on mineral surfaces with certain caveats. In the best cases direct comparisons can be made with surface x-ray scattering structural information, and acid-base protonation reactions can be explored in situ on a molecular basis. Applications to strongly colored or fluorescent minerals present problems, but there are strategies that can be used to work around these issues. Studies of organic molecule sorption and interfacial reactions appear very promising and are being developed. The talk will discuss how we hope to effectively merge information from surface x-ray scattering, sum frequency vibrational spectroscopy , and computational approaches to develop an improved picture of solid surface terminations, inorganic and organic sorbate binding, hydrogen bonding and local water structure.


2010

Eric H Oelkers
Eric H Oelkers

"The Kinetics of Carbon Storage"

Highlight: The Chemistry of Carbon Sequestration

Eric H Oelkers
Research Director/CNRS, Toulouse, France
EMSL Auditorium
Thursday, October 28, 2010
9:00 AM

Thermodynamic calculations suggest that the ultimate fate of CO2 injected into the subsurface is its incorporation into carbonate rocks. The degree to which this actually happens depends greatly on the rates of both dissolution reactions, which release divalent metal cations into solution and precipitation reactions that combine injected CO2 with divalent cations to form stable carbonate minerals. Although it is commonly believed that the overall rate of this process will be limited by the slow dissolution rates of silicate minerals, recent work shows that other than Ca-carbonates, such as calcite, few carbonate minerals precipitate readily at low temperatures; laboratory studies show that magnesite (MgCO3) and dawsonite (NaAlCO3(OH2)) fail to precipitate at temperatures of ~100 and ~160° C, respectively. At such conditions, metals that could transform into carbonates are preferentially precipitated into clay minerals such as smectite. The key, therefore to creating stable carbon storage in carbonate minerals may be the identification of those catalysts that favor low temperature formation of these minerals and/or inhibit formation of secondary silicate minerals. Although these catalysts have yet to be identified insights can be obtained from mineral precipitation mechanisms which suggest that the rate timing step for these reactions is the breaking of the metal hydration shells in solution. Nevertheless, even in the absence of carbonate precipitation, silicate dissolution alone can stabilize injected CO2 in the aqueous phase through addition of alkalinity and/or complexing agents.


Lynda Soderholm
Lynda Soderholm

"Metal Complexes: Their Free Energies and Their Reactivities in Solution"

Highlight: Pushing the Envelope on Actinide Speciation

Dr. Lynda (Lynne) Soderholm
Argonne National Laboratory
Chemical Sciences & Engineering Division
EMSL 1077
Wednesday, July 14, 2010
2:00 PM

A metal ion dissolved in solution experiences correlations with solvent molecules and other dissolved ions, the strengths and numbers of which determine its solubility and stability. Aided by a number of analytical techniques, notably UV/visible and XAFS spectroscopies, a picture has emerged over the last several decades in which a dissolved metal ion is understood to have a near-neighbor ligation sphere that is relatively strongly bound and is the primary contributor to the reactivity and energetics of the ion. Indeed much of the theoretical modeling done to provide a framework for predicting metal-ion behavior in solution includes a detailed description of this first coordination sphere. Although it has been recognized that there can been second and more distant ligation spheres, they have been largely ignored, in part because of the lack of metrical information about their structure, and in part because it is thought that their contribution is minimal to the overall energetics of the dissolved metal ion.


"Isotopic molecular geochemistry: Using isotopes to probe nanoscale processes at mineral surfaces"

Professor Donald J. DePaolo
Director, Center for Isotope Geochemistry
Class of 1951 Professor of Geochemistry
Director, Earth Sciences Division, Lawrence Berkeley National Laboratory
EMSL Auditorium
Tuesday, May 25, 2010
9:00 AM

Recent work on mid-mass "non-traditional" stable isotope systems like Ca, Mg, Fe, Cr, and Mo suggests that minerals like calcite that form by precipitation from aqueous solution do not do so at isotopic equilibrium. In most instances the precipitated solid phase is enriched in the light isotope species relative to the solution phase, and the magnitude of the enrichment varies with precipitation rate. Non-equilibrium isotopic effects are especially apparent for mid-mass elements because the equilibrium fractionations are very small; the effects are of broad interest because isotopic fractionation can be a measure of the molecular exchange fluxes at mineral-solution interfaces, and calcite and other carbonates and sulfates are widely used as monitors of paleo-environment. Molecular exchange fluxes are difficult to measure with other approaches, and are likely to be sensitive to the presence of trace metals and organic molecules in solution and on the mineral surface.

Recent experimental results on Ca and O isotopes will be reviewed, and a macroscopic kinetic theory for isotopic fractionation and trace element incorporation into calcite presented. Examples of kinetic isotopic effects that are important in nature will be illustrated using Ca isotopes, O isotopes and Sr/Ca in calcite, and O and H isotopes in precipitation.


"Size-induced Shifts in Oxidation-Reduction Phase Equilibria in Nanophase Transition Metal Oxides"

Highlight: Small Particles, Big Impact

Professor Alexandra Navrotsky
NEAT ORU & Thermochemistry Facility
Chemistry Annex
University of California at Davis
EMSL Auditorium
Tuesday, May 18, 2010
9:00 AM

It is now well established that difference in surface energies can alter the relative free energies of different polymorphs, causing size driven thermodynamic crossovers in phase stability at the nanoscale. It has also been shown that, because oxyhydroxides generally have smaller surface energies than oxides, dehydration equilibria, e.g. goethite to hematite plus water, can shift to higher temperature by as much as 100 K at the nanoscale. A general formulation of the effect of particle size on chemical equilibria among solid phases is that increasing surface area will favor the phase assemblage of lower surface energy.


"Surface Potentials and Equilibrium at Mineral-Water Interfaces"

Highlight: Understanding the Potential of a Single Crystal

Professor Nikola Kallay
Department of Chemistry
Faculty of Science, University of Zagreb
EMSL/1077
Wednesday, March 17, 2010
10:00 AM

Knowledge of the electrostatic potential distribution across mineral-water interfaces is important for understanding processes such as metal adsorption and dissolution and growth. Most present day information in this regard is based on measurements of colloidal mineral particles. However, model accuracy requires a more fundamental understanding of the relationship between the potential distribution and the arrangements of atoms at the surface. This talk centers on electrostatic potential measurements for single crystallographic terminations of single crystal minerals. The electrostatic potential at the inner surface plane within the electrical interfacial layer (surface potential ψ0) at these interfaces affects the state of charged surface species formed by interactions with potential determining ions (p.d.i) and is one of the main parameters characterizing the interface.

2009

"Biogeochemical Factors Governing the Speciation and Reactivity of Reduced Uranium: Implications for Bioremediation and Natural Attenuation"

Highlight: Class-ing Up Uranium

Dr. John Bargar
Stanford Synchrotron Radiation Lightsource
SLAC National Accelerator Laboratory
Friday, September 18, 2009

Primitive: that's how Dr. John Bargar describes the state of knowledge of the reactivity of biogenic uranite in ground water. Biogenic uranite is a form of uranium, produced by bacteria, that is fairly immobile in groundwater. Bargar discussed his work to turn this primitive knowledge into a sophisticated understanding at Pacific Northwest National Laboratory's Frontiers in Biogeochemistry Seminar Series. The series features scientists who discuss novel ideas and advancements in geochemical research and development.

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