A5047775545- Radioactive element chemistry and processing
- Crystallization and Solubility Studies
- Bauxite Residue and Utilization
- X-ray Diffraction in Crystallography
- Lanthanide and Transition Metal Complexes
- Chemical Synthesis and Characterization
- Polyoxometalates: Synthesis and Applications
- Clay minerals and soil interactions
- Zeolite Catalysis and Synthesis
- Chromatography in Natural Products
- Advanced NMR Techniques and Applications
- Vanadium and Halogenation Chemistry
- Seismic Waves and Analysis
- Catalysis and Oxidation Reactions
- Concrete and Cement Materials Research
- Ionosphere and magnetosphere dynamics
- Earthquake Detection and Analysis
- Geochemistry and Elemental Analysis
- Crystal Structures and Properties
- Geochemistry and Geologic Mapping
- Magnesium Oxide Properties and Applications
- Phosphorus and nutrient management
- Mesoporous Materials and Catalysis
- Analytical Chemistry and Chromatography
- Iron oxide chemistry and applications
Los Alamos National Laboratory
2020-2024
Government of the United States of America
2023-2024
University of Notre Dame
2016-2023
Pacific Northwest National Laboratory
2018-2021
Physical Sciences (United States)
2021
Richland College
2019-2020
Hunter College
2019
City University of New York
2019
Planetary Science Institute
2017
University of California, Davis
2017
Boehmite (γ-AlOOH) and gibbsite (α-Al(OH)3) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora industrial applications. Developing the ability to understand predict properties characteristics these materials, on basis their natural growth or synthesis pathways, is an fundamental science enterprise with wide-ranging impacts. The present study describes bulk surface novel materials comprehensive detail, using collectively sophisticated...
Gibbsite (α-Al(OH)3) transformation into layered double hydroxides, such as lithium aluminum hydroxide dihydrate (LiAl-LDH), is generally thought to occur by solid-state intercalation of Li+, in part because the intrinsic structural similarities quasi-2D octahedral Al3+ frameworks these two materials. However, caustic environments where gibbsite solubility high relative LiAl-LDH, a dissolution-reprecipitation pathway conceptually enabled, proceeding via precipitation tetrahedral (Td)...
Combination of uranium, peroxide, and mono- (Na, K) or divalent (Mg, Ca, Sr) cations under alkaline aqueous conditions results in the rapid formation anionic uranyl triperoxide monomers (UTs), (UO2(O2)3)4–, exhibiting unique Raman signatures. Electronic structure calculations were decisive for interpretation spectra assignment unexpected signals associated with vibrations peroxide ions. Assignments verified by 18O isotopic labeling ions supporting computational-based experimentally observed...
Aluminum hydroxide (Al(OH)3, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role aluminum refining nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to lack of situ probes capable isolating incipient ion pairs. At molecular level Al is cycling between tetrahedral (Td) coordination solution octahedral (Oh) the solid. We explored Al(OH)3 that was used produce variably...
The first neutron diffraction study of a single crystal containing uranyl peroxide nanoclusters is reported for pyrophosphate-functionalized Na44K6[(UO2)24(O2)24(P2O7)12][IO3]2·140H2O (1). Relative to earlier X-ray studies, provides superior information concerning the positions H atoms and lighter counterions. Hydrogen have been assigned reveal an extensive network H-bonds; notably, most O present in anionic cluster accept H-bonds from surrounding H2O molecules, none surface-bound are...
The characterization of prenucleation species is essential to understand crystallization mechanisms across many chemical systems and often involves the use vibrational spectroscopy. Nowhere this more evident than in development "green" aluminum processing technologies, where detailed understanding speciation its polynuclear analogues highly alkaline, low water solutions elusive. aluminate anion Al(OH)4– predominates alkaline conditions, yet equilibrium with dimeric species, either μ-oxo...
Solid UO2 dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, with a focus on the role alkali metals. powders were dissolved containing XOH (X = Li, Na, K) 30% H2O2. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed linear trends versus concentration resulting from oxidative UO2, X:U molar ratios 1.0, showing availability determines U concentrations solution. The maximum solution...
Uranium concentrations as high 2.94 × 105 parts per million (1.82 mol of U/1 kg H2O) occur in water containing nanoscale uranyl cage clusters. The anionic clusters, with diameters 1.5–2.5 nm, are charge-balanced by encapsulated cations, well cations within their electrical double layer solution. concentration uranium these systems is impacted the countercations (K, Li, Na), and molecular dynamics simulations have predicted distributions selected cases. Formation cages prevents hydrolysis...
Combining reactants in water under ambient conditions results the assembly and crystallization of 2.6 nm diameter cage clusters designated U48V6P48 within 3 weeks. These consist 24 uranyl hexagonal bipyramids, pentagonal six vanadyl square pyramids, 48 phosphate tetrahedra. Peroxide-bridged dimers bipyramids are linked directly to vanadyl-stabilized tetramers form cage, with tetrahedra providing additional linkages between these two units. Time-resolved small-angle X-ray scattering Raman...
Addition of NaNO<sub>2</sub> and/or NaNO<sub>3</sub> to the α-Al(OH)<sub>3</sub>–NaOH–H<sub>2</sub>O system leads significant enhancement α-Al(OH)<sub>3</sub> solubility.
Herein, we report a new salt of pyrophosphate-functionalized uranyl peroxide nanocluster {U24Pp12} (1) exhibiting Oh molecular symmetry both in the solid and solution. Study system yielding 1 across wide range pH by single-crystal X-ray diffraction, small-angle scattering, combination traditional 31P diffusion-ordered spectroscopy (DOSY) NMR affords unprecedented insight into amphoteric chemistry this system. Key results include formation rare binary {U24}·{U24Pp12} (3) observed under...
Single-crystal time-of-flight neutron diffraction has provided atomic resolution of H atoms H2O molecules and hydroxyl groups, as well Li cations in the uranyl peroxide nanocluster U60. Solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to confirm dynamics these constituents, revealing transportation through cluster walls. units that are located on surface involved transfer from inside outside vice versa. This exchange occurs a concerted motion...
Understanding the stability fields and decomposition products of various metal- actinide-oxide nanoclusters is essential for their development into useful materials industrial processes. Herein, we explore spontaneous transformation sulfate-centered, phosphate functionalized uranyl peroxide nanocluster {U20P6} to {U24} under aqueous ambient conditions using time-resolved small-angle X-ray scattering, Raman, 31P NMR spectroscopy. We show that unusual μ-η1:η2 bridging mode between ions...
Uranyl-peroxide capsules are the newest family of polyoxometalates. Although discovered 13 years previously with over 70 topologies reported, there is a lack in fundamental understanding assembly mechanisms, particularly role alkali counterions. Herein, reaction pathway and uranyl peroxide reported by tracking conversion from K+ triperoxide monomer to uranyl-peroxide U28 capsule means small-angle X-ray scattering Raman spectroscopy. For first time, pentamer face isolated structurally...
Two novel hybrid uranyl peroxide phosphate cage clusters, designated U20P6 and U20P12, contain bridges between in an unusual μ–η1:η2 configuration, as well the common μ–η2:η2 configuration. These appear to be only high-nuclearity metal complexes containing bridges, they are unique among cages. Both clusters 20 polyhedra, U20P12 6 12 tetrahedra, respectively. The polyhedra both cages arranged on vertices of distorted topological dodecahedrons (20 vertex fullerenes). Each is completed by...
Pulsed field gradient nuclear magnetic resonance (PFG-NMR) measurements were successfully applied to the 27Al ( I = 5/2) nucleus in concentrated electrolytes investigate diffusion of aluminate ions [Al(OH)4-] simulant high-level waste (3 M NaOH) between 25 and 85 °C. The temperature-dependent coefficients obtained from 1H, 23Na, PFG-NMR well fit by a Vogel-Fulcher-Tammann model power law equation. Comparison 0.1 Al(OH)4- ∼3 MOH (where Na+, K+, (CH3)4N+) at room temperature varied agreement...
The molecular speciation of aluminum (Al3+) in alkaline solutions is fundamental to its precipitation chemistry within a number industrial applications that include ore refinement and processing Al wastes. Under these conditions, Al3+ predominantly Al(OH)4–, while at high [Al3+] dimeric species are also known form. To date, the mechanism dimer formation remains unclear likely influenced by complex ion···ion interactions. In present work, we investigate suite potential dimerization pathways...
Crystallization of Al3+-bearing solid phases from highly alkaline Na2O:Al2O3:H2O solutions commonly necessitates an Al3+ coordination change tetrahedral to octahedral, but intermediate states are often difficult isolate. Here, a similar process is examined during the solid-state recrystallization monosodium aluminate hydrate (MSA) nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While MSA structure contains solely oxolated Al3+, NSA molecular salt...
In highly alkaline "water-in-salt" Na2O/Al2O3/H2O solutions where the monomeric Al(OH)4– anion dominates, isolation of transitional species that seed crystallization sodium aluminate salt hydrates has been challenging. For example, discrimination dimeric [for Al2O(OH)62–] via 27Al nuclear magnetic resonance (NMR) spectroscopy is limited fast interconversion through hydrolysis and condensation reactions. Despite this, using magic-angle spinning NMR (27Al MAS NMR) at high field strengths (14.1...
The uranyl triperoxide anionic monomer is a fundamental building block for peroxide polyoxometalate capsules. reaction pathway from the to capsule can be greatly altered by counterion: both rate and resulting structure. We synthesized characterized triperoxides Mg2UO2(O2)3·13H2O (MgUT), Ca2UO2(O2)3·9H2O (CaUT), Sr2UO2(O2)3·9H2O (SrUT), K4UO2(O2)3·3H2O (KUT) compared their thermodynamic stabilities. enthalpies of formation oxides elements these compounds were calculated thermochemical cycles...
Tetrahedrally coordinated Al(OH)<sub>4</sub><sup>−</sup> and Al<sub>2</sub>O(OH)<sub>6</sub><sup>2−</sup> have been isolated in the solid-state interrogated using XRD, NMR, XAS, IR, Raman.
The role of oligomeric aluminate species in the precipitation aluminum (Al) phases such as gibbsite (α-Al(OH)3) from aqueous hydroxide solutions remains unclear and difficult to probe directly, despite its importance for developing accurate predictions Al solubility highly alkaline systems. Precipitation this system entails a transition predominantly tetrahedrally coordinated (Al(OH)4-) solution octahedrally gibbsite. Here we report quantitative study dissolved Al-KOH-H2O using combination...
The solubility and spectroscopy of sodium nitrite in hydroxide solutions are detailed to provide insight into processes underlying solubility.
Little is known about the crystal chemistry of neptunyl peroxide compounds compared to uranyl compounds, for which dozens structures have been described. Uranyl peroxides are formed over a broad range pH and solution conditions, but complicated by ability H2O2 act as an oxidizing or reducing agent Np, depending on conditions present. The combination Np(V) in 1 M HCl, H2O2, CaCl2 under alkaline leads immediate crystallization triperoxide monomer, Ca2[NpO2(O2)3]·9H2O, first Np(VI)-based...