A5051053578- Iron oxide chemistry and applications
- Minerals Flotation and Separation Techniques
- Quantum Dots Synthesis And Properties
- Catalytic Processes in Materials Science
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Environmental remediation with nanomaterials
- Zeolite Catalysis and Synthesis
- nanoparticles nucleation surface interactions
- Metal-Organic Frameworks: Synthesis and Applications
- Mine drainage and remediation techniques
- Mesoporous Materials and Catalysis
- Arsenic contamination and mitigation
- Copper-based nanomaterials and applications
- Nanomaterials for catalytic reactions
- Clay minerals and soil interactions
- Calcium Carbonate Crystallization and Inhibition
- Nanoparticles: synthesis and applications
- Radioactive element chemistry and processing
- Geomagnetism and Paleomagnetism Studies
- Gold and Silver Nanoparticles Synthesis and Applications
- Advanced Photocatalysis Techniques
- Chalcogenide Semiconductor Thin Films
- Geochemistry and Elemental Analysis
- Metal Extraction and Bioleaching
University of Minnesota
2016-2025
Twin Cities Orthopedics
2007-2025
University of Minnesota System
2006-2017
Minneapolis Institute of Arts
2014-2017
Pacific Northwest National Laboratory
2004-2015
Sandia National Laboratories
2015
Washington University in St. Louis
2015
Georgia Institute of Technology
2015
Land Stewardship Project
2014
Environmental Molecular Sciences Laboratory
2011
Dislocations are common defects in solids, yet all crystals begin as dislocation-free nuclei. The mechanisms by which dislocations form during early growth poorly understood. When nanocrystalline materials grow oriented attachment at crystallographically specific surfaces and there is a small misorientation the interface, result. Spiral two or more closely spaced screw provides mechanism for generating complex polytypic polymorphic structures. These results of fundamental importance to...
Crystals are generally considered to grow by attachment of ions inorganic surfaces or organic templates. High-resolution transmission electron microscopy biomineralization products iron-oxidizing bacteria revealed an alternative coarsening mechanism in which adjacent 2- 3-nanometer particles aggregate and rotate so their structures adopt parallel orientations three dimensions. Crystal growth is accomplished eliminating water molecules at interfaces forming iron-oxygen bonds. Self-assembly...
There are reports that nano-sized zero-valent iron (Fe0) exhibits greater reactivity than micro-sized particles of Fe0, and it has been suggested the higher nano-Fe0 may impart advantages for groundwater remediation or other environmental applications. However, most these preliminary in they leave a host potentially significant (and often challenging) material process variables either uncontrolled unresolved. In an effort to better understand nano-Fe0, we have used variety complementary...
The extensive use of titanium dioxide nanoparticles (nano-TiO2) in many consumer products has raised concerns about possible risks to the environment magnitude threat may depend on whether nano-TiO2 remains dispersed environment, or forms much larger-sized aggregates clusters. Currently, limited information is available issue. In this context, purpose present article report initial measurements morphology and rate formation aqueous suspensions as a function ionic strength nature electrolyte...
Atomic-resolution transmission electron micrographs show that nanocrystalline TiO 2 coarsens by oriented attachment and growth under hydrothermal conditions.In addition to forming homogeneous single crystals, at anatase surfaces leads twinning on {112} intergrowths (001) {001}.Brookite, a polytype of anatase, occurs some twin surfaces.Alternating two octahedra-wide structural slabs in brookite are shared with the adjacent domains.Because interfaces contain one unit cell brookite, we propose...
Oriented aggregation is a special case of that provides an important route by which nanocrystals grow, defects are formed, and unique, often symmetry-defying, crystal morphologies produced. This growth mechanism involves the irreversible crystallographically specific self-assembly primary results in formation new single crystals, twins, intergrowths. paper presents molecular model for oriented aggregation. rapid equilibrium association dissociation conversion associated producing aggregates.
Fluorinated anionic surfactants have drawn considerable attention due to recent work showing significant concentrations in surface waters and biota from around the globe. A detailed understanding of transport fate fluorinated through soil like media must include an elucidation mineral chemistry. Five materials were equilibrated with solutions perfluorooctane sulfonate (PFOS) characterize adsorption: kaolinite, Ottawa sand standard, synthetic goethite, Lake Michigan sediment, iron-coated...
Oriented aggregation is a special case of in which nanocrystals self-assemble and form new secondary single crystals. This process has been suggested to proceed via an intermediate state known as the mesocrystal, have parallel crystallographic alignment but are spatially separated. We present first direct observations mesocrystals with size shape similar product oriented aggregates by employing cryo-TEM directly image particles aqueous suspension. The images reveal that not only also...
Mononuclear and dinuclear copper species were synthesized at the nodes of an NU-1000 metal–organic framework (MOF) via cation exchange subsequent oxidation 200 °C in oxygen. Copper-exchanged MOFs are active for selectively converting methane to methanol 150–200 °C. At 150 1 bar methane, approximately a third centers involved methanol. Methanol productivity increased by 3–4-fold selectivity from 70% 90% increasing pressure 40 bar. Density functional theory showed that reaction pathways on...
Once nucleation is established, mineral growth the process by which crystals increase in size, either through addition of individual ions (monomers) or attachment more complex species that range from oligomers to nanoparticles. The relative contribution these two mechanisms, may occur separately simultaneously, varies with fluid properties such as supersaturation well crystallographic characteristics wherein nonclassical mechanisms involving particle are often prevalent at early stages...
We report on the growth kinetics of TiO2 nanoparticles synthesized from aqueous solution using titanium(IV) isopropoxide as precursor. The radius primary particles was found to be between 1.5 and 8 nm, average particle cubed is shown increase linearly with time in agreement Lifshitz-Slyozov-Wagner model for coarsening. rate constant coarsening increases temperature due dependence viscosity equilibrium solubility TiO2. At longer times higher temperatures, secondary formed by epitaxial...
Room-temperature volume measurements of the complete set calcite-structure carbonates in pressure range 0-8.1 GPa revealed systematic differences compressibilities that depend on cation type, resulting significant deviations from empirical relations an inverse linear correlation between K0 and V0. The bulk modulus for MgCO3 lies approximately 18 below trend 3d transition metal carbonates, which show expected correlation modulus with ambient cell (and M-O bond length). CdCO3, whose length...
MCM-22(P), the precursor to zeolite MCM-22, consists of stacks layers that can be swollen and exfoliated produce catalytically active materials. However, current swelling procedures result in significant degradation crystal morphology along with partial loss crystallinity dissolution crystalline phase. Fabrication polymer nanocomposites coatings MCM-22 for separation, barrier, other applications requires a method does not alter drastically layer structure preserves high aspect ratio layers....
Quantitative measurements of adsorption from solution show up to a 70-fold increase in the coefficient when variety organic acids are adsorbed onto 6 nm compared 16 nanocrystalline titania particles. A Langmuir model modified include dependence interfacial tension (interfacial free energy) on particle size predicts an constant (Kads) as crystallite decreases, agreement with experimental results. The Kads arises predominantly increased molar surface energy rapid decreases has important...
Self-assembly of nanoparticles is an important mechanism particle growth in the solution-phase synthesis oxides and oxyhydroxides. In this work, aqueous colloidal suspensions anatase (TiO2), hematite (Fe2O3), feroxyhite (FeOOH), heterogenite (CoOOH) was observed to occur by two primary mechanisms: coarsening topotactic assembly. Coarsening governed larger particles at expense smaller particles, assembly results single crystals unique morphology. The nanocrystals are nominally equidimensional...
Aging (or longevity) is one of the most important and potentially limiting factors in use nano-Fe0 to reduce groundwater contaminants. We investigated aging FeH2 (Toda RNIP-10DS) water with a focus on changes (i) composition structure particles (by XRD, TEM, XPS, bulk Fe0 content) (ii) reactivity carbon tetrachloride reaction kinetics, electrochemical corrosion potentials, H2 production rates). Our results show that becomes more reactive between 0 ∼2 days exposure then gradually loses over...
Nanoscale zerovalent iron (NZVI) that was aged in simulated groundwater evaluated for alterations composition and speciation over 6 months to understand the possible transformations NZVI could undergo natural waters. exposed 10 mN of various common anions (Cl−, NO3−, SO42−, HPO42−, HCO3−) or dissolved oxygen (saturated, ∼9 mg/L). Fresh samples, along with Fe-oxide model compounds, were then analyzed using synchrotron radiation X-ray absorption spectroscopy (XAS) yield both relative oxidation...
Goethite (α-FeOOH) is an antiferromagnetic iron oxyhydroxide that often synthesized by precipitation from homogeneous, aqueous solution followed aging. This paper addresses goethite growth phase transformation of six-line ferrihydrite nanoparticles to oriented aggregation the primary particles. Data tracking nanocrystal as a function pH, temperature, and time presented. In general, faster at higher pH temperature even coarsening becomes increasingly important increases. addition, particle...
Crystal growth mechanism, kinetics, and microstructure development play fundamental roles in tailoring materials with controllable sizes morphologies. Oriented attachment (OA) involves the spontaneous self-organization of adjacent nanocrystals, resulting crystal by addition solid particles that share a common crystallographic orientation. It is for to occur more than one mechanism simultaneously, such as OA coarsening. This complexity leads difficulty studying mechanism. Here, we briefly...