Dynamics of Uranyl Peroxide Nanocapsules

Discrete aqueous metal oxide polyionic clusters that include aluminum polycations, transition-metal polyoxometalates, and the actinyl peroxide clusters have captivated the interest of scientists in the realm of both their fundamental and applied chemistries. Yet the counterions for these polycations or polyanions are often ignored, even though they are imperative for solubility, crystallization, purification, and even templating cluster formation. The actinyl peroxide clusters have counterions not only external, but internal to the hollow peroxide capsules. In this study, we reveal the dynamic behavior of these internal alkali counterions via solid-state and liquid NMR experiments. These studies on two select cluster geometries, those containing 24 and 28 uranyl polyhedra, respectively, show that the capsules-like clusters are not rigid entities. Rather, the internal alkalis both have mobility inside the capsules, as well as exchange with species in the media in which they are dissolved. The alkali mobilities are affected by both what is inside the clusters as well as the composition of the dissolving medium

A comprehensive comparison of transition-metal and actinyl polyoxometalates

While the d⁰ transition-metal POMs of Group V (V⁵⁺, Nb⁵⁺, Ta⁵⁺) and Group VI (Mo⁶⁺, W⁶⁺) have been known for more than a century, the actinyl peroxide POMs, specifically those built of uranyl triperoxide or uranyl dihydroxidediperoxide polyhedra, were only realized within the last decade. While virtually every metal on the Periodic Table can form discrete clusters of some type, the actinyls are the only—in addition to the transition-metal POMs– whose chemistry is dictated by the prevalence of the ‘yl’ oxygen ligand. Thus this emerging structural, solution, and computational chemistry of actinide POMs warrants comparison to the mature chemistry of transition-metal POMs. This assessment between the transition-metal POMs and actinyl POMs (uranyl peroxide POMs, specifically) has provided much insight to the similarities and differences between these two chemistries. We further break down the comparison between the alkaline POMs of Nb and Ta; and the acidic POMs of V, Mo and W. This more indepth literature review and discussion reveals that while an initial evaluation suggests the actinyl POMs are more akin to the alkaline transition-metal POMs, they actually share characteristics unique to the acidic POMs as well. This tutorial review is meant to provide fodder for deriving new POM chemistries of both the familiar transition-metals and the emerging actinides, as well as fostering communication and collaboration between the two scientific communities

Strategic Design and Optimization of Inorganic Sorbents for Cesium, Strontium and Actinides

The basic science goal in this project identifies structure/affinity relationships for selected radionuclides and existing sorbents. The task will apply this knowledge to the design and synthesis of new sorbents that will exhibit increased cesium, strontium and actinide removal. The target problem focuses on the treatment of high-level nuclear wastes. The general approach can likewise be applied to non-radioactive separations

Final Report for Environmental Management Science Program - Strategic Design and Optimization of Inorganic Sorbents for Cesium, Strontium and Actinides: Activities at the University of Notre Dame

The basic science goal in this project identifies structure/affinity relationships for selected radionuclides and existing sorbents. The task will apply this knowledge to the design and synthesis of new sorbents that will exhibit increased cesium, strontium and actinide removal. The target problem focuses on the treatment of high-level nuclear wastes. The general approach can likewise be applied to non-radioactive separations. The project involves a collaboration among four organizations, with each focused on a different aspect of the problem. This document is the final report on the three years of activities conducted at the University of Notre Dame, where the research focus was on the use of molecular modeling to understand ion exchange selectivity in titanosilicates and polyoxoniobate materials

Low density molecular gas in the galaxy

The distributions and physical conditions in molecular gas in the interstellar medium have been investigated in both the Galaxy and towards external galaxies. For example, Galactic plane surveys in the CO J =1-0 line with the Columbia 1.2-m telescope and with the Five College Radio Astronomy Observatory (FCRAO) 14-m telescopes have been able to trace spiral arms more clearly than HI surveys have been able to reveal, and indicate that most of molecular mass is contained in Giant Molecular Clouds (GMCs). Extensive maps of the whole Milky Way showed two prominent features, the 4-kpc molecular ring and the Galactic center. The physical conditions in the Galaxy have been studied by comparing the intensity of CO J =1-0 line with those of other lines, e.g., 13CO J =1-0, higher J transitions of CO, and dense gas tracers such as HCO+, CS, and HCN. Previous studies were however strongly biased towards regions where CO emission was known to be intense. The radial distribution of molecular hydrogen shows that most of the H2 gas which is indirectly traced by observations of its associated CO emission, originates from the inner Galaxy (Dame 1993). Extending outwards from a galacto-centric distance of ~7 kpc, the H2 mass surface density decreases dramatically, and HI dominates over H2 in the outer Galaxy. What are physical conditions of molecular gas where the CO emission is relatively weak, and can we really trace all of the molecular gas through obervations of CO? These kinds of problems have not been solved yet, but are addressed in our study

Insight into Hydrogen Bonding of Uranyl Hydroxide Layers and Capsules by Use of ¹H Magic-Angle Spinning NMR Spectroscopy

Solid-state ¹H magic-angle spinning (MAS) NMR was used to investigate local proton environments in anhydrous [UO₂(OH)₂] (α-UOH) and hydrated uranyl hydroxide [(UO₂)₄O(OH₆ 6·5H₂O (metaschoepite). For the metaschoepite material, proton resonances of the μ₂-OH hydroxyl and interlayer waters were resolved, with two-dimensional (2D) double-quantum (DQ) ¹H–¹H NMR correlation experiments revealing strong dipolar interactions between these different proton species. The experimental NMR results were combined with first-principles CASTEP GIPAW (gauge including projector-augmented wave) chemical shift calculations to develop correlations between hydrogen-bond strength and observed ¹H NMR chemical shifts. These NMR correlations allowed characterization of local hydrogen-bond environments in uranyl U₂₄ capsules and of changes in hydrogen bonding that occurred during thermal dehydration of metaschoepite.This is the publisher’s final pdf. The published article is copyrighted by the American Chemical Society and can be found at: http://pubs.acs.org/journal/jpccck/about.htm

A Comprehensive Study of the Solubility, Thermochemistry, Ion Exchange, and Precipitation Kinetics of NO3 Cancrinite and NO3 Sodalite

NO3 cancrinite and NO3 sodalite haves been found as a common sodium alumino-silicate forming in strongly caustic alkaline aqueous solutions associated with radioactive High Level Waste (HLW) stored in many underground tanks and also in nuclear waste treatment facilities such as the Savannah River Site (SRS). The appearance of these phases have created very expensive problems in waste treatment plants by fouling process evaporators in the SRS waste processing facility. Therefore, in order to prevent their formation an assessment of the relative stability, formation kinetics, and the ion-exchange characteristics of these two phases in HLW solutions needs to be investigated. The goals of this project are to: (1) Develop a robust equilibrium thermodynamic framework to accurately describe and predict the formation of NO3 cancrinite and NO3 sodalite. (2) Provide a comprehensive characterization of the solid precipitation rates and mechanisms using novel spectroscopic (e.g., NMR) and thermochemical techniques in conditions encountered in HLW waste solutions. (3) Investigate the ion exchange capacity of these zeolitic phases with respect to radionuclides and RCRA metal species

Nanostructured polyoxometalate arrays with unprecedented properties and functions.

Polyoxometalates (POMs) are ionic (usually anionic) metal -oxo clusters that are both functional entities for a variety of applications, as well as structural units that can be used as building blocks if reacted under appropriate conditions. This is a powerful combination in that functionality can be built into materials, or doped into matrices. Additionally, by assembling functional POMs in ordered materials, new collective behaviors may be realized. Further, the vast variety of POM geometries, compositions and charges that are achievable gives this system a high degree of tunability. Processing conditions to link together POMs to build materials offer another vector of control, thus providing infinite possibilities of materials that can he nano-engineered through POM building blocks. POM applications that can be built into POM-based materials include catalysis, electro-optic and electro-chromic, anti-viral, metal binding, and protein binding. We have begun to explore three approaches in developing this field of functional, nano-engineered POM-based materials; and this report summarizes the work carried out for these approaches to date. The three strategies are: (1) doping POMs into silica matrices using sol-gel science, (2) forming POM-surfactant arrays and metal-POM-surfactant arrays, (3) using aerosol-spray pyrolysis of the POM-surfactant arrays to superimpose hierarchical architecture by self-assembly during aerosol-processing. Doping POMs into silica matrices was successful, but the POMs were partially degraded upon attempts to remove the structure-directing templates. The POM-surfactant and metal-POM-surfactant arrays approach was highly successful and holds much promise as a novel approach to nano-engineering new materials from structural and functional POM building blocks, as well as forming metastable or unusual POM geometries that may not be obtained by other synthetic methods. The aerosol-assisted self assembly approach is in very preliminary state of investigation, but also shows promise in that structured materials were formed; where the structure was altered by aerosol processing. We will be seeking alternative funding to continue investigating the second synthetic strategy that we have begun to develop during this 1-year project