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Yang, Ping

Publications and source records attributed to Yang, Ping.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A Pseudotetrahedral Uranium(V) Complex

A series of uranium amides were synthesized from N,N,N-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy] and uranium tetrachloride to give U(NCySiMe 3 ) x (Cl) 4–x , where x = 2, 3, or 4. The diamide was then isolated as a bimetallic, bridging lithium chloride adduct ((UCl 2 (NCyTMS) 2 ) 2 -LiCl(THF) 2 ), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS) 3 -LiCl(THF) 2 ). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron. Cyclic voltammetry revealed an easily accessible reversible oxidation wave, and upon chemical oxidation, the U V amido cation was isolated in near-quantitative yields. The synthesis of this family of compounds allows a direct comparison of the electronic structure and properties of isostructural U IV and U V tetraamide complexes. Spectroscopic investigations consisting of UV–vis, NIR, MCD, EPR, and U L 3 -edge XANES, along with density functional and wave function calculations, of the four-coordinate U IV and U V complexes have been used to understand the electronic structure of these pseudotetrahedral complexes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Towards photocathodes with elongated lifetimes and high quantum efficiency by passivating with two dimensional materials

Photocathodes are key components of electron injectors for X-ray free electron laser and X-ray energy recovery linacs, which generate brilliant, ultrafast, and coherent X-rays for the exploration of matter with ultrahigh resolutions in both space and time. Whereas alkali-based semiconducting photocathodes display a higher quantum efficiency (QE) in the visible light spectrum than their metallic counterparts, their lifetimes are much shorter due to the high reactivity of alkali-based surfaces to the residual gases in the vacuum chamber. Overcoming the tradeoff between QE and lifetimes has been a great challenge in the accelerator community. Here in this paper, based on ab initio density functional calculations, we propose an approach to overcome this tradeoff by coating with atomically thin two-dimensional (2D) nanomaterials. On one hand, the 2D coating layers can enhance the lifetimes of photocathodes by preventing the chemical reactions with the residual gases. On the other hand, the 2D coating layers can effectively engineer the work function of photocathodes, thus controlling their QE. A monolayer of insulating BN reduces the work function, whereas a monolayer of semi-metallic graphene or semiconducting molybdenum disulfide (MoS 2 ) increases the work function. This phenomenon originates from the induced interfacial dipoles. The reduction of work function by BN implies that it is capable of maintaining the high QE of semiconducting photocathodes in addition to enhance their lifetimes. This study advances our understandings on the surface chemistry of coated photocathodes and opens new technological avenues to fabricate photocathodes with high QE and longer lifetimes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models

Abstract Cloud longwave scattering is generally neglected in general circulation models (GCMs), but it plays a significant and highly uncertain role in the atmospheric energy budget as demonstrated in recent studies. To reduce the errors caused by neglecting cloud longwave scattering, two new radiance adjustment methods are developed that retain the computational efficiency of broadband radiative transfer simulations. In particular, two existing scaling methods and the two new adjustment methods are implemented in the Rapid Radiative Transfer Model (RRTM). The results are then compared with those based on the Discrete Ordinate Radiative Transfer model (DISORT) that explicitly accounts for multiple scattering by clouds. The two scaling methods are shown to improve the accuracy of radiative transfer simulations for optically thin clouds but not effectively for optically thick clouds. However, the adjustment methods reduce computational errors over a wide range, from optically thin to thick clouds. With the adjustment methods, the errors resulting from neglecting cloud longwave scattering are reduced to less than 2 W m−2 for the upward irradiance at the top of the atmosphere and less than 0.5 W m−2 for the surface downward irradiance. The adjustment schemes prove to be more accurate and efficient than a four-stream approximation that explicitly accounts for multiple scattering. The neglect of cloud longwave scattering results in an underestimate of the surface downward irradiance (cooling effect), but the errors are almost eliminated by the adjustment methods (warming effect).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Photocatalytic activities and chemically-bonded mechanism of SiO2@ TiO2 nanocomposites coated cement-based materials

Highlights: • Two samples have different deposited density of TiO{sub 2} nanoparticles on each SiO{sub 2} nanosphere, which depend on the difference of the water dosage. • When the curing time is 28 days, water adsorption rates of mortar-2 at 270 min have decreased by 17.8%, which may be attributed to pozzolanic reactivity of SiO{sub 2} on cement-based materials. • The formation of C-S-H gels via pozzolanic reaction of SiO{sub 2} on cement-based materials has been demonstrated by XPS and NMR spectra. • Cem-1 and cem-2 show excellent photocatalytic property. - Abstract: Photocatalytic technology has been studied in building materials, especially for the surface. However, the drawback of surface-treatment application is weak adhesion between coatings and the substrates resulting poor durability in outdoor environments. In the study, two SiO{sub 2}@TiO{sub 2} core-shell nanocomposites were synthetized and coated cement-based materials, and the photocatalytic activity (rhodamine B removal efficiency) and surface modification/densification performances of coated cement-based materials were studied. The two samples have different deposited densities of TiO{sub 2} nanoparticles on each SiO{sub 2} nanosphere. Water adsorption rates of coated mortar measured at 270 min decreased by 17.8% when curing time was 28 days. Reaction experiments of SiO{sub 2}@TiO{sub 2} nanocomposites and Ca(OH){sub 2} with different dosages were carried out to investigate the reaction mechanism. The formation of C-S-H gel was confirmed due to the pozzolanic reaction of samples and Ca(OH){sub 2}. The coated cement pastes show excellent photocatalytic activity for rhodamine B removal.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Substituents on the Electronic Structure of Mono- and Bis(phosphido) Thorium(IV) Complexes

Here, a series of metallocene thorium complexes with mono- and bis(phosphido) ligands have been investigated with varying hues: (C 5 Me 5 ) 2 Th(Cl)[P(Mes) 2 ] (Mes = mesityl = 2,4,6-(CH 3 ) 3 C 6 H 2 ; dark red-purple), (C 5 Me 5 ) 2 Th[P(Mes)(CH 3 )] 2 (dark red-purple), (C 5 Me 5 ) 2 Th(CH 3 )[P(Mes) 2 ] (dark red-purple), (C 5 Me 5 ) 2 Th(CH 3 )[P(Mes)(SiMe 3 )] (orange), (C 5 Me 5 ) 2 Th(Cl)[P(Mes)(SiMe 3 )] (orange), (C 5 Me 5 ) 2 Th[P(Mes)(SiMe 3 )] 2 (orange), and (C 5 Me 5 ) 2 Th[PH(Mes)] 2 (pale yellow). While all of these complexes bear a mesityl group on phosphorus, the electronic structure observed differs depending on the other substituent (mesityl, methyl, trimethylsilyl, or hydrogen). This sparked an investigation of the electronic structure of these complexes using 31 P NMR and electronic absorption spectroscopy in concert with time-dependent density functional theory calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Identification of the Formal +2 Oxidation State of Neptunium: Synthesis and Structural Characterization of {Np II [C 5 H 3 (SiMe 3 ) 2 ] 3 } 1–

Here in this paper, we report a new formal oxidation state for neptunium in a crystallographically characterizable molecular complex, namely Np 2+ in [K(crypt)][Np II Cp" 3 ] [crypt = 2.2.2-cryptand, Cp" = C 5 H 3 (SiMe 3 ) 2 ]. Density functional theory calculations indicate that the ground state electronic configuration of the Np 2+ ion in the complex is 5f 4 6d 1 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Improved Representation of Surface Spectral Emissivity in a Global Climate Model and Its Impact on Simulated Climate

Surface longwave emissivity can be less than unity and vary significantly with frequency. However, most climate models still assume a blackbody surface in the longwave (LW) radiation scheme of their atmosphere models. This study incorporates realistic surface spectral emissivity into the atmospheric component of the Community Earth System Model (CESM), version 1.1.1, and evaluates its impact on simulated climate. By ensuring consistency of the broadband surface longwave flux across different components of the CESM, the top-of-the-atmosphere (TOA) energy balance in the modified model can be attained without retuning the model. Inclusion of surface spectral emissivity, however, leads to a decrease of net upward longwave flux at the surface and a comparable increase of latent heat flux. Global-mean surface temperature difference between the modified and standard CESM simulation is 0.20 K for the fully coupled run and 0.45 K for the slab-ocean run. Noticeable surface temperature differences between the modified and standard CESM simulations are seen over the Sahara Desert and polar regions. Accordingly, the climatological mean sea ice fraction in the modified CESM simulation can be less than that in the standard CESM simulation by as much as 0.1 in some regions. When spectral emissivities of sea ice and open ocean surfaces are considered, the broadband LW sea ice emissivity feedback is estimated to be −0.003 W m −2 K −1 , assuming flat ice emissivity as sea ice emissivity, and 0.002 W m −2 K −1 , assuming coarse snow emissivity as sea ice emissivity, which are two orders of magnitude smaller than the surface albedo feedback.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Ligand induced shape transformation of thorium dioxide nanocrystals

Nanocrystals (NCs) with size and shape dependent properties are a thriving research field. Significant progress has been made in the controlled synthesis of NCs of stable elements in the past two decades; however, the knowledge of the NCs of actinide compounds has been considerably limited due the difficulties in handling them both experimentally and theoretically. Actinide compounds, especially actinide oxides, play a critical role in many stages of the nuclear fuel cycle. Recently, a non-aqueous surfactant assisted approach has been developed for the synthesis of actinide oxide NCs with different morphologies, but an understanding of its control factors is still missing to date. Herein we present a comprehensive study on the low index surfaces of thorium dioxide (ThO 2 ) and their interactions with relevant surfactant ligands using density functional calculations. A systematic picture on the thermodynamic stability of ThO 2 NCs of different sizes and shapes is obtained employing empirical models based on the calculated surface energies. It is found that bare ThO 2 NCs prefer the octahedral shape terminated by (111) surfaces. Oleic acid displays selective adsorption on the (110) surface, leading to the shape transformation from octahedrons to nanorods. Other ligands such as acetylacetone, oleylamine, and trioctylphosphine oxide do not modify the equilibrium shape of ThO 2 NCs. This research provides atomic level insights into the anisotropic growth of ThO2 NCs that was recently observed in experiments, and thus may contribute to the controlled synthesis of actinide oxide NCs with well-defined size and shape for future applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Bond Covalency and Oxidation State of Actinide Ions Complexed with Therapeutic Chelating Agent 3,4,3-LI(1,2-HOPO)

The hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) is a promising agent for biological decorporation of radionuclides, and allows spectroscopic detection of many lanthanide (Ln) and actinide (An) species via sensitized luminescence. Despite the manifest uses of this ligand, the structural and thermodynamic properties of its complexes across the An series remain understudied. Theoretical investigations of the binding of An(III) and An(IV) ions, from actinium to einsteinium, by the 3,4,3-LI(1,2-HOPO) ligand, as well as experimental extended X-ray absorption fine structure (EXAFS) studies on the trivalent americium, curium, and californium complexes were employed in this paper to address the resulting structures, thermodynamic parameters, redox properties, and corresponding electronic configurations. An(IV) ions were found to form much stronger complexes than An(III) ions, consistent with experimental measurements. Complexation of both An(III) and An(IV) ions generally becomes more favorable for heavier actinides, reflecting increased energy degeneracy driven covalency and concomitant orbital mixing between the 5f orbitals of the An ions and the π orbitals of the ligand. Finally and notably, the ability of this ligand to either accept or donate electron density as needed from its pyridine rings is found to be key to its extraordinary stability across the actinide series.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

In-situ neutron diffraction investigation on twinning/detwinning activities during tension-compression load reversal in a twinning induced plasticity steel

The tension-compression type of load reversal produces an asymmetric cyclic tension-compression behavior and varied yielding stresses in the subsequent monotonic tension and compression in a twinning induced plasticity steel. The micromechanical behavior was elucidated via the evolutions of the stacking fault probability and the grain orientation density captured by in-situ neutron diffraction. The latter indicates more profound detwinning activities in a reversal from tension to compression than those from compression to tension and more twinning involves in monotonic tension than in compression. In conclusion, this is confirmed by the calculated twinning activities in monotonic tension and compression using the visco-plastic self-consistent model.

TWIP↗
DOE OSTI2018

Coordination Chemistry of a Strongly-Donating Hydroxylamine with Early Actinides: An Investigation of Redox Properties and Electronic Structure

Separations of f-block elements are a critical aspect of nuclear waste processing. Redox-based separations offer promise, but challenges remain in stabilizing and differentiating actinides in high oxidation states. The investigation of new ligand types that provide thermodynamic stabilization to high-valent actinides is essential for expanding their fundamental chemistry and to elaborate new separation techniques and storage methods. We report herein the preparation and characterization of Th and U complexes of the pyridyl-hydroxylamine ligand, N-tert-butyl-N-(pyridin-2-yl)hydroxylamine (pyNO–). Electrochemical studies performed on the homoleptic complexes [M(pyNO) 4 ] (M = Th, U) revealed significant stabilization of the U complex upon one-electron oxidation. The salt [U(pyNO) 4 ] + was isolated by chemical oxidation of [U(pyNO) 4 ]; spectroscopic and computational data support assignment as a U V cation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series

Abstract The chemistry of trivalent transplutonium ions (Am 3+ , Cm 3+ , Bk 3+ , Cf 3+ , Es 3+ …) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. Herein, we present the first extended X‐ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal–oxygen nearest‐neighbor bond lengths in the case of Cf 3+ . Corroborating those results, density functional theory calculations, extended to Es 3+ , suggest that the shorter Cf−O and Es−O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [M III DTPA(H 2 O)] 2− (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.

Deblonde, Gauthier J. ‐P.↗
DOE OSTI2018

Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series

The chemistry of trivalent transplutonium ions (Am 3+ , Cm 3+ , Bk 3+ , Cf 3+ , Es 3+ …) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. We present the first extended X-ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal–oxygen nearest-neighbor bond lengths in the case of Cf 3+ . Corroborating those results, density functional theory calculations, extended to Es 3+ , suggest that the shorter Cf-O and Es-O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [M III DTPA(H 2 O)] 2- (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Major improvements on the longwave radiative interactions between surface and clouds in the Polar Regions in atmospheric global circulation model (GCM). Final Project Report

1. Summary of Work and Accomplishments in Year 1 (01/15/2015-01/14/2016). We developed new ice cloud parameterizations based on state-of-the-art MODIS Collection 6 (MC6) ice particle model. Features of the model include the consideration of surface roughness of ice crystals and spectral consistency in cloud property retrievals. Using more than 14,000 particle size distributions (PSDs) from in-situ measurements and the latest ice particle single-scattering property library, our parameterizations provide band-averaged bulk-scattering properties. According to statistics of fittings, the parameterization schemes represent the band-averaged bulk-scattering properties very well. Compared to the ice particle model developed by Fu (1998), flux simulations with the MC6 particle model result in larger upward flux at the top of the atmosphere (TOA) and smaller at the surface for typical cirrus clouds. In the assessment of the effect of longwave light scattering, our results also support the conclusions of previous studies. The error in flux calculations reaches about 10 W/m 2 when a cirrus cloud is thin and its particle size is small. 2. Summary of Work and Accomplishments in Year 2 (01/15/2016-01/14/2017) Clouds are a major modulator of the global radiation budgets. However, representations of clouds in general circulation models (GCMs) neglect many important processes, particularly those related to ice clouds. One major uncertainty source is the radiative transfer scheme in GCMs. To reduce the computational burden in most GCMs, absorption is the only radiative transfer process considered in longwave spectral bands. Recently, a state-of-the-art MC6 ice model has been available, which provides spectral consistency in ice cloud retrievals. With an advanced light scattering library for ice particles, we performed sensitivity studies of the potential impacts on the climate including light scattering for MC6 model and other 11 ice cloud models. Specifically, we modified RRTMG_LW (the GCM version of Longwave Rapid Radiative Transfer Model), a radiative transfer module widely used in GCMs and numerical prediction models, to identify flux simulation differences with and without considering light scattering processes. The simulations with light scattering come from a rigorous radiative solver, DISORT (Discrete Ordinates Radiative Transfer Program for a Multi-Layered Plane-Parallel Medium), are used as benchmarks. The results show that the weighted annual mean biases of RRTMG_LW for the upward flux at the top of the atmosphere, the downward flux at the surface, and the net flux into the atmosphere are about 0.8 ± 0.3, -0.1 ± 0.05, and -0.7 ± 0.3 W m-2, respectively. According to the different the ice crystal shapes, the weighted annual mean bias for heating rate is about -0.006 ± 0.02 to 0.04 K/day. 3. Summary of Work and Accomplishments in Year 3 (01/15/2017-01/14/2018) Since absorption dominates optical properties of clouds in the longwave (LW) spectrum, most of general circulation models (GCMs) only take absorption properties of clouds into account in the radiative transfer modules in order to reduce computational costs. To quantify the biases of excluding LW scattering when clouds exist, we simulated fluxes and heating rates by using satellite data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, Clouds and the Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectrometer (MODIS) merged products (CCCM) in 2010. In annual global average, neglecting LW scattering causes overestimation by 2.6 W/m 2 for the top-of-atmosphere (TOA) upward fluxes and underestimation by 1.2 W/m 2 for surface downward fluxes. In particular, regional extreme biases are approximately 12 W/m 2 for TOA upward fluxes and are approximately -3.6 W/m 2 for surface downward fluxes, or are approximately 5% of the global averaged outgoing longwave radiation (OLR) and 1% of the global averaged surface downward fluxes, respectively. In terms of heating rates, on average, LW scattering heats the whole atmosphere column by 0.0045 K/day, heats the cloud layers by 0.0420 K/day, heats the surface by 0.028 K/day, and cools the tropopause by 0.018 K/day.

58 GEOSCIENCES↗
DOE OSTI2018

Formation, Stability, and Chemistry of Tetravalent Actinide Nanocrystals

First database with almost 4000 stable structures for thorium dioxide (ThO 2 ) n (n≤8) calculated with density functional theory. The figure shows the lowest energy minima for different units of ThO 2 and the energy landscape generated by the found stable structures for Th 8 O 16 . This highlights the structural richness of the ThO interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Design of State-of-the-art Flow Cells for Energy Applications

The worldwide energy demand is increasing every day and it necessitates rational and efficient usage of renewable energy. Undoubtedly, utilization of renewable energy can address various environmental challenges. However, all current renewable energy resources (wind, solar, and hydroelectric power) are intermittent and fluctuating in their nature that raises an important question of introducing effective energy storage solutions. Utilization of redox flow cells (RFCs) has recently been recognized as a viable technology for large-scale energy storage and, hence, is well suited for integrating renewable energy and balancing electricity grids. In brief, RFC is an electrochemical storage device where energy is stored in chemical bonds, similar to a battery, but with reactants external to the cell. The state-of-the-art in flow cell technology uses an aqueous acidic electrolyte and simple metal redox couples. Thus, there is an urgent call to develop efficient (high-energy density) and low-cost RFCs to meet the efflorescent energy storage demands. To address the first challenge of achieving high-energy density, we plan to design and further modify complexes composed of bifunctional multidentate ligands and specific metal centers, capable of storing as many electrons as possible. In order to address the second challenge of reducing cost of the RFCs, we plan to use iron (Fe) metal as it regularly occupies multiple oxidation states and is the second most abundant metal in the earth’s crust that makes it an ideal metal for improved energy densities, higher potentials, and numbers of electrons per molecule while maintaining potential cost competitiveness. Density functional theory calculations considering solvation effects will be performed to yield accurate predictions of redox potentials.

25 ENERGY STORAGE↗
DOE OSTI2018

Design of State-of-the-art Flow Cells for Energy Applications

The worldwide energy demand is increasing every day and it necessitates rational and efficient usage of renewable energy. Undoubtedly, utilization of renewable energy can address various environmental challenges. However, all current renewable energy resources (wind, solar, and hydroelectric power) are intermittent and fluctuating in their nature that raises an important question of introducing effective energy storage solutions. Utilization of redox flow cells (RFCs) has recently been recognized as a viable technology for large-scale energy storage and, hence, is well suited for integrating renewable energy and balancing electricity grids. In brief, RFC is an electrochemical storage device (Fig. 1), where energy is stored in chemical bonds, similar to a battery, but with reactants external to the cell. The state-of-the-art in flow cell technology uses an aqueous acidic electrolyte and simple metal redox couples. Several of these systems have been commercialized although current technologies, such as vanadium (V) and zinc-bromine (Zn-Br 2 ) RFCs, for grid level energy storage, suffer from a number of drawbacks, i.e. expensive and resource-limited active materials (vanadium RFCc), and low current performance (Zn-Br 2 RFCs due to Zn dendrite formation). Thus, there is an urgent call to develop efficient (high-energy density) and low-cost RFCs to meet the efflorescent energy storage demands. Approach: To address the first challenge of achieving high-energy density, we plan to design and further modify complexes composed of bifunctional multidentate ligands and specific metal centers, capable of storing as many electrons as possible.

25 ENERGY STORAGE↗