Unraveling pH-Dependent Changes in Adsorption Structure of Uranyl on Alumina (012).

Mitigating uranium transport in groundwater is imperative for ensuring access to clean water across the globe. Here, resonant anomalous X-ray reflectivity is used to investigate the adsorption of uranyl on alumina (012) in acidic aqueous solutions, representing typical U concentrations of contaminated water near mining sites. The analyses reveal that U adsorbs at two distinct heights of 2.

Solvent effects on extractant conformational energetics in liquid-liquid extraction: a simulation study of molecular solvents and ionic liquids.

Extractant design in liquid-liquid extraction (LLE) is a research frontier of metal ion separations that typically focuses on the direct extractant-metal interactions. However, a more detailed understanding of energetic drivers of separations beyond primary metal coordination is often lacking, including the role of solvent in the extractant phase. In this work, we propose a new mechanism for enhancing metal-complexant energetics with nanostructured solvents.

Advancing Chemical Separations: Unraveling the Structure and Dynamics of Phase Splitting in Liquid-Liquid Extraction.

Liquid-liquid extraction (LLE), the go-to process for a variety of chemical separations, is limited by spontaneous organic phase splitting upon sufficient solute loading, called third phase formation. In this study we explore the applicability of critical phenomena theory to gain insight into this deleterious phase behavior with the goal of improving separations efficiency and minimizing waste. A series of samples representative of rare earth purification were constructed to include each of one light and one heavy lanthanide (cerium and lutetium) paired with one of two common malonamide extractants (DMDOHEMA and DMDBTDMA).

Impact of Water Extraction on Malonamide Aggregation: A Molecular Dynamics and Graph Theoretic Approach.

Solution structure in liquid-liquid extraction affects the efficacy of separation; however, even for simplified organic phases, structural characterization and attribution of aggregation to intermolecular interactions are fundamental challenges. We investigate water uptake into organic phases for two malonamides commonly applied to actinide and lanthanide separations. Extracted water induces reorganization of the amphiphilic extractant molecules, although we find this rearrangement is not strongly manifested in small-angle X-ray scattering making it challenging to probe without methods such as atomistic simulation.

Molecular-scale origins of solution nanostructure and excess thermodynamic properties in a water/amphiphile mixture.

The molecular and nanoscale origins of nonideality in excess thermodynamic properties are essential to understanding cosolvent mixtures, yet they remain challenging to determine. Here, we consider a binary mixture of water and an amphiphile, N,N,N',N'-tetramethylmalonamide (TMMA), which is characterized by strong hydrogen bonding between the two components and no hydrogen bonding between amphiphiles. Using molecular dynamics simulation, validated with excess volume measurements and X-ray scattering, we identify three distinct solution regimes across the composition range of the binary mixture and find that the transition between two of these regimes, marked by the water percolation threshold, is closely correlated with minima in the excess volume and excess enthalpy.

Amphiphile Organization in Organic Solutions: An Alternative Explanation for Small-Angle X-ray Scattering Features in Malonamide/Alkane Mixtures.

The role of different intermolecular interactions in the aggregation of amphiphiles in an organic solvent is studied for systems of relevance to liquid-liquid extraction (LLE), a chemical process used to selectively recover metals from complex mixtures. Of specific interest is the role, or lack thereof, of hydrogen bonding, which is often assumed to be a main driver of the organic phase structural organization that has been linked to separation efficacy. Toward that end, a series of malonamide extractants in -dodecane have been studied in the absence of any extracted aqueous solutes, including water.

Nanoscale Critical Phenomena in a Complex Fluid Studied by X-Ray Photon Correlation Spectroscopy.

The advent of high-speed x-ray photon correlation spectroscopy now allows the study of critical phenomena in fluids to much smaller length scales and over a wider range of temperatures than is possible with dynamic light scattering. We present an x-ray photon correlation spectroscopy study of critical fluctuation dynamics in a complex fluid typical of those used in liquid-liquid extraction (LLE) of ions, dodecane-DMDBTDMA with extracted aqueous Ce(NO_{3})_{3}. We observe good agreement with both static and dynamic scaling without the need for significant noncritical background corrections.

Leveraging Actinide Hydrolysis Chemistry for Targeted Th and U Separations using Amidoxime-Functionalized Poly(HIPE)s.

Polymerized high internal phase emulsions (poly(HIPE)s) are porous polymer monoliths whose synthesis can easily be tailored to allow incorporation of functional units. In this work, nitrile containing poly(HIPE)s have been prepared with either acrylonitrile (AN) or 4-cyanostyrene (4CS) comonomers. Post-synthetic modification of these nitrile-containing poly(HIPE)s yields their corresponding amidoximated analogues, which were studied for actinide uptake.

NpSe : a Binary Chalcogenide Containing Modulated Selenide Chains and Ambiguous-Valent Metal.

A new binary compound, NpSe possesses metal-chalcogen and chalcogen-chalcogen interactions different from those reported for other metal dichalcogenides. Its structure is incommensurately modulated and features linear Se chains and valence-ambiguous Np cations.

Functional electrical stimulation following nerve injury in a large animal model.

Introduction: Controversy exists over the effects of functional electrical stimulation (FES) on reinnervation. We hypothesized that intramuscular FES would not delay reinnervation after recurrent laryngeal nerve (RLn) axonotmesis.

Methods: RLn cryo-injury and electrode implantation in ipsilateral posterior cricoarytenoid muscle (PCA) were performed in horses.

Insight into selectivity: uptake studies of radionuclides Sr, Cs, and UO with bis-amidoxime polymers.

Uptake characteristics of a bis-amidoximated polymer are presented for 90Sr2+, 137Cs+, and 233UO22+ to assess rational ligand design and polymer engineering efforts applied to selective uranium extraction. Functionalized with the bis-amidoxime diaryl ether ligand at a loading of 1.98 mmol per gram of polymer, the polymer was found to sorb uranium from a pH 6 solution with a separation factor (α) over cesium of 1.

Comparative CHARMM and AMOEBA Simulations of Lanthanide Hydration Energetics and Experimental Aqueous-Solution Structures.

The accurate understanding of metal ion hydration in solutions is a prerequisite for predicting stability, reactivity, and solubility. Herein, additive CHARMM force field parameters were developed to enable molecular dynamics simulations of lanthanide (Ln) speciation in water. Quantitatively similar to the much more resource-intensive polarizable AMOEBA potential, the CHARMM simulations reproduce the experimental hydration free energies and correlations in the first shell (Ln-oxygen distance and hydration number).

Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium-Nitrate Example.

The influence of countercations (A) in directing the composition of monomeric metal-ligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A counterions. Analyses of their chemical composition and solid-state structures demonstrate that A not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves.

Linking Solution Structures and Energetics: Thorium Nitrate Complexes.

Seeking predictive insights into how metal-ion speciation impacts solution chemistry as well as the composition and structure of solid-precipitates, thorium correlations, with both solvent and other solute ions, were quantitatively probed in a series of acidic, nitrate/perchlorate solutions held at constant ionic strength. Difference pair-distribution functions (dPDF), obtained from high-energy X-ray scattering (HEXS) data, provide unprecedented structural information on the number of Th ligating ions in solution and how they change with increasing nitrate concentration. A fit of the end member solution, Th (4 m perchloric acid and no nitrate), reveals a homoleptic Th aqua ion with 10 waters in its first coordination shell.

Subtle Effects of Aliphatic Alcohol Structure on Water Extraction and Solute Aggregation in Biphasic Water/n-Dodecane.

Organic phase aggregation behavior of 1-octanol and its structural isomer, 2-ethylhexanol, in a biphasic n-dodecane-water system is studied with a combination of physical measurement, small-angle X-ray scattering (SAXS), and atomistic molecular dynamic simulations. Physical properties of the organic phases are probed following their mixing and equilibration with immiscible water phases. Studies reveal that the interfacial tension decreases as a function of increasing alcohol concentration over the solubility range of the alcohol with no evidence for a critical aggregate concentration (cac).

A Comparison of Adsorption, Reduction, and Polymerization of the Plutonyl(VI) and Uranyl(VI) Ions from Solution onto the Muscovite Basal Plane.

X-ray scattering techniques [in situ resonant anomalous X-ray reflectivity (RAXR) and specular crystal truncation rods (CTR)] were used to compare muscovite (001) surfaces in contact with solutions containing either 0.1 mM plutonyl(VI) or 1 mM uranyl(VI) at pH = 3.2 ± 0.

Two Dihydroxo-Bridged Plutonium(IV) Nitrate Dimers and Their Relevance to Trends in Tetravalent Ion Hydrolysis and Condensation.

We report the room temperature synthesis and structural characterization of a μ2-hydroxo-bridged Pu(IV) dimer obtained from an acidic nitric acid solution. The discrete Pu2(OH)2(NO3)6(H2O)4 moiety crystallized with two distinct crystal structures, [Pu2(OH)2(NO3)6(H2O)4]2·11H2O (1) and Pu2(OH)2(NO3)6(H2O)4·2H2O (2), which differ primarily in the number of incorporated water molecules. High-energy X-ray scattering (HEXS) data obtained from the mother liquor showed evidence of a correlation at 3.

Erbium(III) Coordination at the Surface of an Aqueous Electrolyte.

Grazing-incidence (GI) X-ray absorption spectroscopy (XAS) under conditions of total external reflection is used to explore the coordination environment of the trivalent erbium ion, Er(3+), at an electrolyte-vapor interface. A parallel study of the bulk aqueous electrolyte (1 M ErCl3 in HCl at pH = 1.54) shows that the Er(3+) ions have a simple hydration shell with an average Er-OH2 bond distance of 2.

Aqueous hafnium sulfate chemistry: structures of crystalline precipitates.

Crystalline precipitates resulting from the hydrolysis and subsequent condensation of Hf(IV) aqueous acidic solutions at 60-95 °C are examined and compared. By varying the concentrations of the acid and sulfate source, a variety of complex hafnium-oxo-hydroxo-sulfate clusters are isolated and structures accessed. Four novel compounds were discovered, while the structures of two known compounds, an 18-mer and a planar hexamer, were updated.

X-ray studies of interfacial strontium-extractant complexes in a model solvent extraction system.

The interfacial behavior of a model solvent extraction liquid-liquid system, consisting of solutions of dihexadecyl phosphate (DHDP) in dodecane and SrCl2 in water, was studied to determine the structure of the interfacial ion-extractant complex and its variation with pH. Previous experiments on a similar extraction system with ErCl3 demonstrated that the kinetics of the extraction process could be greatly retarded by cooling through an adsorption transition, thus providing a method to immobilize ion-extractant complexes at the interface and further characterize them with X-ray interface-sensitive techniques. Here, we use this same method to study the SrCl2 system.

Observation of a rare earth ion-extractant complex arrested at the oil-water interface during solvent extraction.

Selective extraction of metal ions from a complex aqueous mixture into an organic phase is used to separate toxic or radioactive metals from polluted environments and nuclear waste, as well as to produce industrially relevant metals, such as rare earth ions. Selectivity arises from the choice of an extractant amphiphile, dissolved in the organic phase, which interacts preferentially with the target metal ion. The extractant-mediated process of ion transport from an aqueous to an organic phase takes place at the aqueous-organic interface; nevertheless, little is known about the molecular mechanism of this process despite its importance.