Kinetics and Reactions Related User Projects

• The Role of Interfacial Processes on Mineral Transformations in Wet Supercritical CO2
  Project Lead: Andrew Felmy
  Project Lead Institution: Environmental Molecular Sciences Laboratory
  Abstract
  We propose a comprehensive experimental and theoretical investigation of the role of interfacial water and CO2 on the energies, mechanisms, and rates of reactivity of a series of orthosilicate and phyllosilicate minerals in contact with supercritical-CO2 (scCO2) containing variable H2O. The molecular mechanisms for carbonation reactions, as well as the distribution of H2O between scCO2 and mineral surfaces, will be followed using molecular simulations and surface spectroscopy as a function of T, P, mineral composition and structure, and aH2O. The dynamics of water reactivity will be simulated using newly developed molecular dynamics models and reaction barriers will be calculated using density functional and molecular orbital theory electronic structure methods. The theoretical studies will be coupled with high-resolution spectroscopic measurements (e.g., IR/FTIR, NMR) to investigate the formation and structure of water layers at mineral surfaces and in the interlayer region of phyllosilicates, and identify potential interfacial carbonate and silicate species. The macroscopic reactivity of the orthosilicates and the changes in interlayer water structure and reactivity of the phyllosilicates will be determined experimentally using high pressure cells. The proposed research will provide new insights into mineral transformations under extreme conditions and help establish a basis for assessing the effectiveness of CO2 sequestration in geologic disposal sites.
• The role of U(V) during heterogeneous reduction of aqueous U(VI) to U(IV).
  Project Lead: Eugene Ilton
  Project Lead Institution: Pacific Northwest National Laboratory
  Abstract
  This proposal is being submitted in response to the Science theme call: Biogeochemistry and Subsurface Science, understanding the chemistry of radionuclides in the subsurface. It directly relates to the EMSL mission to provide resources for discovery and technological innovation in the environmental molecular sciences. The results of the proposed work will support the needs of the DOE and nation in managing uranium waste resulting from weapons production and the nuclear fuel cycle. We request standard access and the work is non-proprietary. We are proposing to study the role of the intermediate pentavalent oxidation state of uranium during heterogeneous reduction of U6+ to U4+ on mineral surfaces exposed to uranyl-bearing aqueous solutions. We will build on our previous work that showed that U5+ had measurable residence times on annite surfaces. The primary question is whether U4+ is formed by two sequential one electron transfers from the mineral to sorbed uranyl, or by disproportionation of sorbed U5+. We intend to probe the redox mechanism by monitoring the residence time of sorbed U5+ after the surface has been rendered redox inert and by varying the free energy of the reduction reaction, Gr. We will vary Gr by working with different minerals that span geochemically relevant redox potentials and by tuning the chemical potential of aqueous uranium (e.g., introduce carbonate). We also plan to investigate U5+ surface speciation. We will use a variety of microscopic and spectroscopic methods to interrogate our samples, including HRTEM (+EELS) and high resolution cryogenic XPS that are available at the EMSL. Additional characterization with XANES and EXAFS will be performed at the APS. We also propose to develop a quick and accessible method to quantify sorbed U5+ concentrations that only involves wet chemistry and optical spectroscopy. This method would make it possible for most geochemistry programs to identify U5+ without traveling to a synchrotron or having a high energy resolution XPS. We note that U5+ has significance for contaminated DOE sites in three primary ways: 1.) the U5+ to U4+ transformation is likely the rate determining step for reduction of uranyl to UO2; consequently U5+ could provide critical information on reduction rates and mechanisms, 2.) U5+ is easily mistaken for either U6+ or U4+ without careful analysis which could lead to false estimates of U transport behavior in the subsurface, and 3.) identifying and eventually quantifying U5+ will provide more accurate estimates for total energy balance during bioreduction of uranyl.
• In-Situ/Liquid Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) for Environmental Interfaces
  Project Lead: James Cowin
  Project Lead Institution: Pacific Northwest National Laboratory
  Abstract
  Chemistry of liquid interfaces is extremely important in environmental and industrial processes but is poorly understood. Liquid layers coat nearly all real-world systems from the oceans to atmospheric particles, and include surface "brines" that coat rocks and soils, and ice, selective membranes for energy storage and production, important industrial catalysts, and even us. New tools are needed to study these inherently inhomogeneous systems, under realistic conditions of humidity and in the presence of trace and reactive gases. We propose an In-Situ/Liquids Time-of-Flight Secondary Ion Mass Spectrometer (ISL-TOFSIMS) system, that will for the first time allow a comprehensive molecular-specific understanding of chemistry at liquid and liquid/solid interfaces. Major recent developments in TOFSIMS (cluster beams) and novel micro-scale chemistry methods make this revolutionary advance possible and timely. The proposed system can measure molecular and ion concentrations, microsecond reaction kinetics with high spatial resolution (120 nm laterally, 1 nm vertically) and 3D mapping capability, and has a unique "in operation" sensitivity calibration. These features will enable exploring pressing issues in interface-specific photochemistry, surface segregation and transport at liquid, brine, ice and mineral surfaces, and transport across aqueous-based membranes and adherent films, all under relevant gaseous conditions.
• Role of Microenvironments and Transition Zones in Subsurface Reactive Contaminant Transport
  Project Lead: James Mckinley
  Project Lead Institution: Pacific Northwest National Laboratory
  Abstract
  The PNNL Scientific Focus Area (SFA) will resolve critical Hanford and basic subsurface science issues through integrated, multi-disciplinary, science-theme focused research on the role of microenvironments and transition zones in the reactive transport of technetium (Tc), uranium (U), and plutonium (Pu). Microenvironments are small domains within larger ones that exert a disproportionate influence on subsurface contaminant migration. They may be internal fractures or microbiologic niches within porous media lithic fragments; grain coatings, bio-films, or micro-colonies on larger mineral particles; or compact silt/clay stringers in gravel-dominated subsurface sediments. Transition zones are field scale features where chemical, physical, or microbiologic properties change dramatically over relatively short distances (e.g., 1 m). They exhibit steep, transport-controlled gradients of system controlling chemical species such as O2, H+, or organic carbon. Microenvironments and transition zones frequently dominate subsurface contaminant reactivity, with strong effects resulting from the coupling of chemical reaction, physical transport (advection, diffusion), and microbiologic processes. Past EMSP and NABIR research has documented the importance of these zones at the Hanford site. The overall ten-year goals of the SFA are to develop: i.) an integrated conceptual model for microbial ecology in the Hanford subsurface and its influence on contaminant migration, ii.) a fundamental understanding of chemical reaction, biotransformation, and physical transport processes in microenvironments and transition zones, and iii.) quantitative biogeochemical reactive transport models for Tc, U, and Pu that integrate multi-process coupling at different spatial scales for field-scale application. Targeted contaminant chemical reaction and biotransformation processes include heterogeneous/biologic electron transfer, precipitation and dissolution, and surface complexation. The SFA will emphasize lab-based, coupled computational and experimental research using relevant physical/biologic models, and sediments and microbial isolates from various Hanford settings to explore molecular, microscopic, and macroscopic processes underlying field-scale contaminant migration. It will also pursue the refinement of geophysical techniques to define, characterize, and map spatial structures and reactive transport properties of microenvironments and transition zones in the field. The SFA will partner with the PNNL Environmental Molecular Sciences Laboratory (EMSL) to develop molecular understandings of key processes, and the Hanford Integrated Field Challenge (IFC) for access to, and samples from subsurface environments where these zones exist and are important.
• Microscopic Mass Transfer of U and Tc in Subsurface Sediments
  Project Lead: Chongxuan Liu
  Project Lead Institution: Pacific Northwest National Laboratory
  Abstract
  This project will investigate microscopic mass transfer process and its influence on and coupling with geochemical and biogeochemical reactions in subsurface sediments. The research will focus on the reactive diffusion at pore and sub-pore scales that are relevant to U/Tc residence in Hanford sediment microenvironments. These include intragrain fractures, aggregates, cements, and coating materials with mass flux dominated by abiotic processes, and intra-aggregates and biofilms of microbial agents and minerals with activity/concentration gradients dictated by biological reactions. Molecular dynamic simulations of ions with different size and charge will be performed to determine self-diffusion coefficients in porous media with variable pore sizes and pore surface charges, and provide insights into charge- and species- coupled ion diffusion. Percolation-based analysis will be performed to investigate the influence of intragrain pore or fracture connectivity on the apparent diffusion coefficients by integrating molecular self-diffusion coefficients and statistical percolation threshold. Microscopic and spectroscopic measurements of diffusion systems that are representative of Hanford U/Tc microenvironments will be performed to measure diffusion properties and validate theoretical calculations. Batch, stirred-flow cell, and short column experiments will be used to evaluate the influence of coupled diffusion and geochemical/biogeochemical reactions in controlling the reactive diffusion rates at pore-scale (Fendorf). Multi-component, pore-scale reactive diffusion models will be developed to integrate self-diffusion coefficients, charge and species coupling, and pore connectivity effect; and to describe and be validated by the results from the wet-lab experiments. The project will collaborate with the Fredrickson pore scale and Zachara reactive transport projects. The geochemical and biogeochemical reactions from these projects will be used for experimental design and data interpretation of microscopic reactive diffusion. This project will benefit pore-scale modeling efforts (Scheibe) by providing sub-pore reactive diffusion models. The pore-scale simulations will in turn benefit this project by providing insights for developing scaling approaches to model pore-scale reactive diffusion processes in the mineralogically complex Hanford sediments. The research will incrementally increase the number of controlling factors and will focus on the following three scenarios: 1) saturated, microporous environments dominated by abiotic processes, 2) saturated microenvironments with mass flux dictated by biological reactions, and 3) unsaturated microenvironments with mass flux affected by water content and percolation.
• QMP Based Tunable IR Wavelength Conversion Devices For Dental Applications
  Project Lead: Fumio Ohuchi
  Project Lead Institution: University of Washington
  Abstract
  This Partner Proposal is to develop a new capability at EMSL with potentially wide application - a tunable IR wavelength conversion device using quasi-phase-matched optical parametric (QPM) generation. Anticipated outcome of this proposal is to develop a simple, compact, robust and maintenance-free module for tunable IR wavelength conversion for biological, atmospheric, and materials research. In this proposal, a particular emphasis will be placed on the development of tunable IR sources with wavelength around 2.78μm, equivalent to those produced by an Er, Cr:YSCC laser that is currently applied for pulpotomy, bony spicule or tori removal in dentistry. There are strong needs for tunable IR wavelength laser systems that are physically compact and mechanically robust, and are easy to operate. In particular, such systems are needed now for both biological research on both soft and hard tissue samples and for real-time atmospheric field studies where analysis of particulate/water vapor mixtures are required. Current laser systems that are utilized in these fields are not fully optimized for specific needs. Rather, what is used are existing laser systems that require modification, either during production or by the individual user. Essentially, no optimization of the wavelength for specific applications is made in existing systems. In addition, the size of these systems tends to be excessively large, operation tends to be overly sensitive to environmental conditions, and routine maintenance is still required. T-Ch Aw from the UW Dental School, expressed his concerns about the inadequate nature of current IR laser systems utilized for clinical research and operations. In general, clinical researchers are less active to the development of laser systems, even though they realized their specific needs, simply because development of the instrumentation is not their first priority. Our view to this problem is for us to develop a proper tunable IR laser system capability at EMSL that is specifically designed to meet the needs of a new group of potential EMSL users. Specifically, as part of this project, researchers from the University of Washingtonâ??s School of Dentistry will be involved from the beginning in the design and application of this new capability. At EMSL, oral surgeons, UW post-docs, and NIMS specialists will team with EMSL scientists throughout the project. This integrated approach is a reflection of the projectâ??s scientific strength and innovative capacity. Successful outcome of this research will lead to further advancement of the laser system for both fundamental and clinical research, and lay a foundation for possible efforts towards technology transfer. In this project, Dr. Kenneth Beck from EMSL will play a role in developing and testing proposed tunable IR wavelength conversion modules in collaboration with Prof. Kenji Kitamura from NIMS, who originally demonstrated QPM using single crystal materials of Mg doped lithium tantalate (LiTaO3) that were developed in NIMS. Development for a clinical laser will be lead by Prof. Tâ??Ch Aw from UW-Dentistry. Prof. Fumio Ohuchi from UW-MSE will assess the damage created by laser and structural characterization for further improvement of the materials systems.
• Electron valence characteristics of rare-earth ions in wide bandgap semiconductor nanowires
  Project Lead: Yi Gu
  Project Lead Institution: Washington State University
  Abstract
  The proposed research aims to probe and understand electron valence characteristics of rare-earth ions embedded in wide bandgap semiconductor nanowires, specifically zinc oxide (ZnO) and gallium nitride (GaN) nanowires, using X-ray photoelectron spectroscopy (XPS) techniques. As the electron valence state of rare-earth ions play a critical role in determining optical and magnetic properties of these ions, this project will contribute significantly to the on-going efforts by the PI to achieve a fundamental understanding of optical and magnetic properties of rare-earth doped ZnO and GaN nanowires and how these properties can be controlled by the material dimension, surface conditions, electronic doping, and external electric fields. For the proposed study, in this general user proposal (open call), the access to the Physical Electronics Instruments Quantum 2000 X-ray photoelectron spectrometer at the Environmental Molecular Sciences Laboratory (EMSL), with one two-day slots of the XPS time for every month, is requested. The high energy resolution capabilities of this facility are ideal for proposed studies to resolve photoelectron peaks from rare-earth ions with different electron valence states. The information obtained by XPS studies will provide the basis for understanding the optical and magnetic properties of rare-earth doped ZnO and GaN nanowires. With semiconductor nanowires emerging as one of the most powerful and versatile building blocks for future devices, this proposed research will contribute significantly to the realization of ultra-high-density and low energy-loss integrated electronic and photonic technologies as well as highly sensitive biological/chemical sensing applications.