Understanding Trace Iron and Chromium Incorporation During Gibbsite Crystallization and Effects on Mineral Dissolution.

Incorporation of pollutants, e.g., heavy metals, or critical elements, e.

Systematic Study of Solid-State U(VI) Photoreactivity: Long-Lived Radicalization and Electron Transfer in Uranyl Tetrachloride.

Reported are the syntheses, structural characterizations, and luminescence properties of three novel [UOCl] bearing compounds containing substituted 1,1'-dialkyl-4,4'-bipyridinum dications (i.e., viologens).

Photolysis of Dissolved Organic Matter over Hematite Nanoplatelets.

Solar photoexcitation of chromophoric groups in dissolved organic matter (DOM), when coupled to photoreduction of ubiquitous Fe(III)-oxide nanoparticles, can significantly accelerate DOM degradation in near-surface terrestrial systems, but the mechanisms of these reactions remain elusive. We examined the photolysis of chromophoric soil DOM coated onto hematite nanoplatelets featuring (001) exposed facets using a combination of molecular spectroscopies and density functional theory (DFT) computations. Reactive oxygen species (ROS) probed by electron paramagnetic resonance (EPR) spectroscopy revealed that both singlet oxygen and superoxide are the predominant ROS responsible for DOM degradation.

Tracking nitrite's deviation from Stokes-Einstein predictions with pulsed field gradient N NMR spectroscopy.

Predicting the behavior of oxyanions in radioactive waste stored at the Department of Energy legacy nuclear sites requires the development of novel analytical methods. This work demonstrates N pulsed field gradient nuclear magnetic resonance spectroscopy to quantify the diffusivity of nitrite. Experimental results, supported by molecular dynamics simulations, indicate that the diffusivity of free hydrated nitrite exceeds that of free hydrated sodium despite the greater hydrodynamic radius of nitrite.

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal-Ligand Covalency in Actinide Complexes: Cl in CsUOCl.

We report a study of the temperature dependence of Cl nuclear quadrupole resonance (NQR) transition energies and spin-lattice relaxation times () for U-depleted dicesium uranyl tetrachloride (CsUOCl) aimed at elucidating electronic interactions between the uranium center and atoms in the equatorial plane of the UO ion. The transition frequency decreases slowly with temperature below 75 K and with a more rapid linear dependence above this temperature. The spin-lattice relaxation time becomes shorter with temperature, and as temperatures increase, the decrease becomes nearly quadratic.

Increased Crystal Field Drives Intermediate Coupling and Minimizes Decoherence in Tetravalent Praseodymium Qubits.

Crystal field (CF) control of rare-earth (RE) ions has been employed to minimize decoherence in qubits and to enhance the effective barrier of single-molecule magnets. The CF approach has been focused on the effects of symmetry on dynamic magnetic properties. Herein, the magnitude of the CF is increased via control of the RE oxidation state.

Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions.

Ultraviolet (UV) photolysis of nitrite ions (NO2-) in aqueous solutions produces a suite of radicals, viz., NO·, O-, ·OH, and ·NO2. The O- and NO· radicals are initially formed from the dissociation of photoexcited NO2-.

Enhancing CO Transport Across a PEEK-Ionene Membrane and Water-Lean Solvent Interface.

Efficient direct air capture (DAC) of CO will require strategies to deal with the relatively low concentration in the atmosphere. One such strategy is to employ the combination of a CO -selective membrane coupled with a CO capture solvent acting as a draw solution. Here, the interactions between a leading water-lean carbon-capture solvent, a polyether ether ketone (PEEK)-ionene membrane, CO , and combinations were probed using advanced NMR techniques coupled with advanced simulations.

Interplay between copper redox and transfer and support acidity and topology in low temperature NH-SCR.

Low-temperature standard NH-SCR over copper-exchanged zeolite catalysts occurs on NH-solvated Cu-ion active sites in a quasi-homogeneous manner. As key kinetically relevant reaction steps, the reaction intermediate Cu(NH) ion hydrolyzes to Cu(OH)(NH) ion to gain redox activity. The Cu(OH)(NH) ion also transfers between neighboring zeolite cages to form highly reactive reaction intermediates.

Elucidating the Reaction Pathways of Veratrylglycero-β-Guaiacyl Ether Degradation over Metal-Free Solid Acid Catalyst with Hydrogen.

Efficient cleavage of β-O-4 bonds in lignin to high-yield aromatic compounds for the potential production of fuels and chemicals is vital for the economics of the modern biorefinery industry. This work is distinct in that a detailed mechanistic analysis of the reaction pathways of veratrylglycero-β-guaiacyl ether (VGE) catalyzed by transition-metal-free solid acid zeolite in aqueous conditions at high hydrogen pressure has been performed. VGE degradation produced high monomers yields (≈87 %), including guaiacol (48.

Interlayer Cation Polarizability Affects Supercritical Carbon Dioxide Adsorption by Swelling Clays.

Several strategies for mitigating the build-up of atmospheric carbon dioxide (CO) bring wet supercritical CO (scCO) in contact with phyllosilicates such as illites and smectites. While some work has examined the role of the charge-balancing cation and smectite framework features on CO/smectite interactions, to our knowledge no one has examined how the polarizability of the charge-balancing cation influences these behaviors. In this paper, the scCO adsorption properties of Pb, Rb, and NH saturated smectite clays at variable relative humidity are studied by integrating in situ high-pressure X-ray diffraction (XRD), infrared spectroscopic titrations, and magic angle spinning nuclear magnetic resonance (MAS NMR) methods.

Rate Controlling in Low-Temperature Standard NH-SCR: Implications from EPR Spectroscopy and Reaction Kinetics.

A series of seven Cu/SSZ-13 catalysts with Si/Al = 6.7 are used to elucidate key rate-controlling factors during low-temperature standard ammonia-selective catalytic reduction (NH-SCR), via a combination of SCR kinetics and electron paramagnetic resonance (EPR) spectroscopy. Strong Cu-loading-dependent kinetics, with Cu atomic efficiency increasing nearly by an order of magnitude, is found when per chabazite cage occupancy for Cu ion increases from ∼0.

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure Xe NMR Techniques.

Microsized pore parameters, such as pore size and distance between pores in a series of model EPDM rubbers, were determined under the pressure of 500 psi using Xe nuclear magnetic resonance (NMR) techniques: spin-lattice () and spin-spin () relaxation measurements, pulsed-field gradient (PFG) NMR, and two-dimensional exchange spectroscopy (2D EXSY). The / (≫1) ratio for the xenon confined in the pores is larger than that for nonconfined free xenon. This suggests that almost the entire pore surface interacts with xenon atoms like a closed pore.

Equatorial Electronic Structure in the Uranyl Ion: CsUOCl and CsUOBr.

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn-Sham methods with and without environment embedding for CsUOCl and CsUOBr. This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U-O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U-X bond (X = Cl, Br), and the second is parallel to the UO ion; in CsUOCl, the components are nearly equal in magnitude, whereas in CsUOBr, due to short-range bromide-cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair.

Palladium/Ferrierite versus Palladium/SSZ-13 Passive NOx Adsorbers: Adsorbate-Controlled Location of Atomically Dispersed Palladium(II) in Ferrierite Determines High Activity and Stability.

Pd-loaded FER and SSZ-13 zeolites as low-temperature passive NOx adsorbers (PNA) are compared under practical conditions. Vehicle cold start exposes the material to CO under a range of concentrations, necessitating a systematic exploration of the effect of CO on the performance of isolated Pd ions in PNA. The NO release temperature of both adsorbers decreases gradually with an increase in CO concentration from a few hundred to a few thousand ppm.

Integrated Capture and Conversion of CO to Methane Using a Water-lean, Post-Combustion CO Capture Solvent.

Integrated carbon capture and conversion of CO into materials (IC M) is an attractive solution to meet global energy demand, reduce our dependence on fossil fuels, and lower CO emissions. Herein, using a water-lean post-combustion capture solvent, [N-(2-ethoxyethyl)-3-morpholinopropan-1-amine] (2-EEMPA), >90 % conversion of captured CO to hydrocarbons, mostly methane, is achieved in the presence of a heterogenous Ru catalyst under relatively mild reaction conditions (170 °C and <15 bar H pressure). The catalytic performance was better in 2-EEMPA than in aqueous 5 m monoethanol amine (MEA).

Measurement of local magnetic fields in actinide tetrafluorides.

Fluorine-19 magnetic shielding tensors have been measured in a series of actinide tetrafluorides (AnF) by solid state nuclear magnetic resonance spectroscopy. Tetravalent actinide centers with 0-8 valence electrons can form tetrafluorides with the same monoclinic structure type, making these compounds an attractive choice for a systematic study of the variation in the electronic structure across the 5f row of the Periodic Table. Pronounced deviations from predictions based on localized valence electron models have been detected by these experiments, which suggests that this approach may be used as a quantitative probe of electronic correlations.

Quasi- quantification of Cu(II) ions in Cu-SSZ-13 catalyst by an NH temperature-programmed reduction method.

A quasi-operando NH3 temperature-programmed reduction method (NH3-TPR), with N2:Cu = 1:1, is developed to quantify total Cu(ii) ions in Cu-SSZ-13 quenched from SCR-relevant reactions, and its accuracy is confirmed by in situ EPR. [Cu(OH)]+-Z and Cu2+-2Z can be further distinguished by NH3 reduction temperatures, and their different reducibility in SCR is revealed.

Identification and Quantification of Technetium Species in Hanford Waste Tank AN-102.

Technetium-99 (Tc), a high yield fission product generated in nuclear reactors, is one of the most difficult contaminants to address at the U.S. Department of Energy Hanford, Savannah River, and other sites.

The role of surface hydroxyls on the radiolysis of gibbsite and boehmite nanoplatelets.

Understanding mechanistic pathways to radiolytic hydrogen generation by metal oxyhydroxide nanomaterials is challenging because of the difficulties of distinguishing key locations of OH bond scission, from structural interiors to hydroxylated surfaces to physi-sorbed water molecules. Here we exploited the interface-selectivity of vibrational sum frequency generation (VSFG) to isolate surface versus bulk hydroxyl groups for gibbsite and boehmite nanoplatelets before and after Co irradiation at dose levels of approximately 7.0 and 29.

Evolution of Radicals from the Photolysis of High Ionic Strength Alkaline Nitrite Solutions.

Reactive nitrogen species (RNS), along with reactive oxygen species (ROS), are significant products from radiolysis in solution. While much research has been focused on biological systems, these species are also important products in the autoradiolysis that occurs in nuclear waste. Here, we determine the correlation between solution constituents, particularly nitrite, and radical products in highly alkaline solutions relevant to liquid waste.

Redox-Based Electrochemical Affinity Sensor for Detection of Aqueous Pertechnetate Anion.

Rapid, selective, and in situ detection of pertechnetate (TcO) in multicomponent matrices consisting of interfering anions such as the ubiquitous NO and Cl or the isostructural CrO is challenging. Present sensors lack the selectivities to exclude these interferences or the sensitivities to meet detection limits that are lower than the drinking water standards across the globe. This work presents an affinity-based electrochemical sensor for TcO detection that relies on selective reductive precipitation of aqueous TcO induced by a 1,4-benzenedimethanethiol capture probe immobilized on an electrode platform.

IRMOF-74()-Mg: a novel catalyst series for hydrogen activation and hydrogenolysis of C-O bonds.

Metal-Organic Frameworks (MOFs) that catalyze hydrogenolysis reactions are rare and there is little understanding of how the MOF, hydrogen, and substrate molecules interact. In this regard, the isoreticular IRMOF-74 series, two of which are known catalysts for hydrogenolysis of aromatic C-O bonds, provides an unusual opportunity for systematic probing of these reactions. The diameter of the 1D open channels can be varied within a common topology owing to the common secondary building unit (SBU) and controllable length of the hydroxy-carboxylate struts.

Synthesis and spin trapping properties of polystyrene supported trifluoromethylated cyclic nitrones.

Polystyrene supported fluorinated cyclic nitrone spin-traps: Resin-2-HFDMPO (2-hydroxymethyl-2-methyl-5-(trifluoromethyl)-3,4-dihydro-2H-pyrrole-1-oxide) and Resin-2-PFDMPO (2-(3-hydroxypropyl)-2-methyl-5-(trifluoromethyl)-3,4-dihydro-2H-pyrrole 1-oxide) containing a trifluoromethyl pyrroline-N-oxide core were developed to detect free radicals under flow conditions. A continuous flow EPR technique was used to evaluate the spin trapping properties of these tethered nitrones. While both resins trapped radicals, polymer supported nitrone Resin-2-PFDMPO with a longer and more flexible linker showed a more information rich spectrum than Resin-2-HFDMPO.