A5039662881- Iron oxide chemistry and applications
- Calcium Carbonate Crystallization and Inhibition
- Mine drainage and remediation techniques
- X-ray Diffraction in Crystallography
- Geochemistry and Elemental Analysis
- Radioactive element chemistry and processing
- High-pressure geophysics and materials
- Geochemistry and Geologic Mapping
- Arsenic contamination and mitigation
- Nanoparticles: synthesis and applications
- Paleontology and Stratigraphy of Fossils
- Heavy metals in environment
- Quantum Dots Synthesis And Properties
- Clay minerals and soil interactions
- Electrocatalysts for Energy Conversion
- Catalytic Processes in Materials Science
- Geological and Geochemical Analysis
- Bone Tissue Engineering Materials
- Magnetic Properties and Applications
- Corrosion Behavior and Inhibition
- Minerals Flotation and Separation Techniques
- Crystal Structures and Properties
- Gold and Silver Nanoparticles Synthesis and Applications
- Mineralogy and Gemology Studies
- Magnetic properties of thin films
Virginia Tech
2015-2024
Stanford University
2010-2016
Stanford Synchrotron Radiation Lightsource
2010-2016
SLAC National Accelerator Laboratory
2010-2016
Duke University
2011-2013
Menlo School
2012
Stony Brook University
2005-2010
Interface (United States)
2010
Argonne National Laboratory
2005-2009
State University of New York
2005-2008
Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, nanocrystallinity this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered atomic arrangement real-space modeling pair distribution function (PDF) derived from direct Fourier transformation total x-ray scattering. The PDF for synthesized with use different routes is consistent a single phase (hexagonal space...
Despite the increasing use of silver nanoparticles (Ag-NPs) in nanotechnology and their toxicity to invertebrates, transformations fate Ag-NPs environment are poorly understood. This work focuses on sulfidation processes PVP-coated Ag-NPs, one most likely corrosion phenomena that may happen environment. The sulfur ratio was varied order control extent transformation sulfide (Ag2S). A combination synchrotron-based X-ray Diffraction (XRD) Extended Absorption Fine Structure spectroscopy shows...
The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, with different organic polymer coatings including poly(vinylpyrrolidone) gum arabic. size morphology characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy synchrotron-based total scattering pair...
The natural nanomineral ferrihydrite is an important component of many environmental and soil systems has been implicated as the inorganic core ferritin in biological systems. Knowledge its basic structure, composition, extent structural disorder essential for understanding reactivity, stability, magnetic behavior, well changes these properties during aging. Here we investigate compositional, structural, that occur upon aging “2-line” presence adsorbed citrate at elevated temperature....
Amorphous calcium carbonate (ACC) is an important phase involved in calcification by a wide variety of invertebrate organisms and technological interest the development functional materials. Despite widespread scientific this full characterization structure lacking. This mainly due to its metastability difficulties evaluating using conventional determination methods. Here we present new findings from application two techniques, pair distribution function analysis nuclear magnetic resonance...
We adopt a reverse Monte Carlo refinement approach, using experimental X-ray total scattering data, to develop structure model for synthetic, hydrated amorphous calcium carbonate (ACC). The ACC is revealed consist of porous calcium-rich framework that supports interconnected channels containing water and molecules. existence previously unrecognized nanometer-scale channel network suggests mechanisms how additives can be accommodated within the provide temporary stabilization, as well...
Environmental transformations of nanoparticles (NPs) affect their properties and toxicity potential. Sulfidation is an important transformation process affecting the fate NPs containing metal cations with affinity for sulfide. Here, extent mechanism sulfidation ZnO were investigated, resulting products carefully characterized. Synchrotron X-ray absorption spectroscopy diffraction analysis reveal that to ZnS occurs readily at ambient temperature in presence inorganic The depends on sulfide...
Iron(III) hydroxides are abundant in near-surface natural environments and play an important role geochemical processes the fate of contaminants. The issue structure common nanophase material ferrihydrite (ferric hydroxide) is controversial has been debated literature for many years without definitive resolution. At least two types ferrihydrite, 2-line 6-line forms, conventionally recognized. It suggested that these forms possess different structures built up by mixtures distinct components....
Fe(III) (oxyhydr)oxides affect the mobility of contaminants in environment by providing reactive surfaces for sorption. This includes toxic metal cadmium (Cd), which prevails agricultural soils and is taken up crops. Fe(III)-reducing bacteria can mobilize such mineral dissolution or immobilize them sorption to coprecipitation with secondary Fe minerals. To date, not much known about fate mineral-associated Cd during microbial reduction. Here, we describe isolation a new Geobacter sp. strain...
The decomposition of H2O2 to H2O and O2 catalyzed by platinum nanocatalysts controls the energy yield several conversion technologies, such as hydrogen fuel cells. However, reaction mechanism rate-limiting step this have been unsolved for more than 100 years. We determined both studying effect different conditions, nanoparticle size, surface composition on rates three with average particle sizes 3, 11, 22 nm. Rate models indicate that pathway is similar all nanocatalysts. Larger size...
The presence of oxyanions, such as nitrate (NO3–) and phosphate (PO43–), regulates the nucleation growth goethite (Gt) hematite (Hm) during transformation ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control rate pathway Fh to Gt Hm. However, how mechanism Hm is still unclear. We used synchrotron scattering methods cryogenic transmission electron microscopy investigate effects NO3– outer-sphere PO43– inner-sphere on formation from Fh. TEM results indicated...
Extensive mats of Fe oxyhydroxides and associated Fe-oxidizing microbial organisms form in diverse geochemical settings – freshwater seeps to deep-sea vents where ever opposing Fe(II)-oxygen gradients prevail. The mineralogy, reactivity, structural transformations precipitated from submarine hydrothermal fluids within remains elusive active fossil systems. In response, a study mat formation at the Loihi Seamount was conducted describe physical chemical characteristics Fe-phases using...
Nickel-rich layered cathode materials have the potential to enable cheaper and higher energy lithium ion batteries. However, these face major challenges (e.g., surface reconstruction, microcracking, oxygen evolution) that can hinder safety cycle life of Many studies nickel-rich focused on ways improve performance. Understanding effects temperature cycling chemical structural transformations is essential assess performance suitability for practical battery applications. The present study...
The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, the presence other ions in system such as nitrate (NO3–), sulfate (SO42–), arsenate (AsO43–). Although mechanism Fh oxyanion complexation have been separately studied, effect surface complex type strength on remains only partly understood. We developed a kinetic model that describes effects goethite (Gt) hematite (Hm). Two sets oxyanion-adsorbed...
Abstract Amorphous calcium carbonate is an important precursor for biomineralization in marine organisms. Key outstanding problems include understanding the structure of amorphous and rationalizing its metastability as phase. Here we report high-quality atomistic models generated using state-of-the-art interatomic potentials to help guide fits X-ray total scattering data. Exploiting a recently developed inversion approach, extract from these effective Ca⋯Ca interaction potential governing...
Fe oxidation processes may have occurred during groundwater‐mediated diagenesis in Meridiani Planum sediments. To address this question, melanterite experiments were conducted at epsomite saturation as a function of pH. Results show that schwertmannite is initially formed from acidic and its formation aging to mixtures jarosite nanocrystalline goethite strongly controlled by pH over the range ∼2.0–4.0. The turn 3+ hydrolysis. In one 77‐d experiment, hematite was tentatively identified...
Chromium(III) (oxy)hydroxide and mixed Cr(III)−Fe(III) (oxy)hydroxides are environmentally important compounds for controlling chromium speciation bioaccessibility in soils aquatic systems also industrially as precursors materials catalyst synthesis. However, direct characterization of the atomic arrangements these is complicated because their amorphous X-ray properties. This study involves synthesis complete compositional series, use complementary thermal, microscopic, spectroscopic,...