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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Hydrogen‐Bonded Polyimide/Metal‐Organic Framework Hybrid Membranes for Ultrafast Separations of Multiple Gas Pairs

Abstract Membranes have seen a growing role in mitigating the extensive energy used for gas separations. Further expanding their effectiveness in reducing the energy penalty requires a fast separation process via a facile technique readily integrated with industrial membrane formation platforms, which has remained a challenge. Here, an ultrapermeable polyimide/metal‐organic framework (MOF) hybrid membrane is reported, enabling ultrafast gas separations for multiple applications (e.g., CO 2 capture and hydrogen regeneration) while offering synthetic enhanced compatibility with the current membrane manufacturing processes. The membranes demonstrate a CO 2 and H 2 permeability of 2494 and 2932 Barrers, respectively, with a CO 2 /CH 4 , H 2 /CH 4 , and H 2 /N 2 selectivity of 29.3, 34.4, and 23.8, respectively, considerably surpassing the current Robeson permeability–selectivity upper bounds. At a MOF loading of 55 wt%, the membranes display a record‐high 16‐fold enhancement of H 2 permeability comparing with the neat polymer. With mild membrane processing conditions (e.g., a heating temperature less than 80 °C) and a performance continuously exceeding Robeson upper bounds for over 5300 h, the membranes exhibit enhanced compatibility with state‐of‐the‐art membrane manufacturing processes. This performance results from intimate interactions between the polymer and MOFs via extensive, direct hydrogen bonding. This design approach offers a new route to ultraproductive membrane materials for energy‐efficient gas separations.

Ma, Canghai↗
DOE OSTI2019

Defect‐Tailoring Mediated Electron–Hole Separation in Single‐Unit‐Cell Bi 3 O 4 Br Nanosheets for Boosting Photocatalytic Hydrogen Evolution and Nitrogen Fixation

Abstract Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron–hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron–hole separation is not always clear. A model atomically thin structure of single‐unit‐cell Bi 3 O 4 Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk‐ and surface‐charge separation. Defect‐rich single‐unit‐cell Bi 3 O 4 Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi 3 O 4 Br. After the preparation of single‐unit‐cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single‐unit‐cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next‐generation photocatalysts.

Di, Jun↗
DOE OSTI2023

Palladium-Percolated Networks Enabled by Low Loadings of Branched Nanorods for Enhanced H 2 Separations

Nanoparticles (NPs) at high loadings are often used in mixed matrix membranes (MMMs) to improve gas separation properties, but they can lead to defects and poor processability that impede membrane fabrication. Herein, it is demonstrated that branched nanorods (NRs) with controlled aspect ratios can significantly reduce the required loading to achieve superior gas separation properties while maintaining excellent processability, as demonstrated by the dispersion of palladium (Pd) NRs in polybenzimidazole for H 2 /CO 2 separation. Increasing the aspect ratio from 1 for NPs to 40 for NRs decreases the percolation threshold volume fraction by a factor of 30, from 0.35 to 0.011. An MMM with percolated networks formed by Pd NRs at a volume fraction of 0.039 exhibits H 2 permeability of 110 Barrer and H 2 /CO 2 selectivity of 31 when challenged with simulated syngas at 200 °C, surpassing Robeson's upper bound. In conclusion, this work highlights the advantage of NRs over NPs and nanowires and shows that right-sizing nanofillers in MMMs is critical to construct highly sieving pathways at minimal loadings. In conclusion, this work paves the way for this general feature to be applied across materials systems for a variety of chemical separations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hybrid Ultra‐Microporous Materials for Selective Xenon Adsorption and Separation

Abstract The demand for Xe/Kr separation continues to grow due to the industrial significance of high‐purity Xe gas. Current separation processes rely on energy intensive cryogenic distillation. Therefore, less energy intensive alternatives, such as physisorptive separation, using porous materials, are required. Herein we show that an underexplored class of porous materials called hybrid ultra‐microporous materials (HUMs) affords new benchmark selectivity for Xe separation from Xe/Kr mixtures. The isostructural materials, CROFOUR‐1‐Ni and CROFOUR‐2‐Ni, are coordination networks that have coordinatively saturated metal centers and two distinct types of micropores, one of which is lined by CrO 4 2− (CROFOUR) anions and the other is decorated by the functionalized organic linker. These nets offer unprecedented selectivity towards Xe. Modelling indicates that the selectivity of these nets is tailored by synergy between the pore size and the strong electrostatics afforded by the CrO 4 2− anions.

Mohamed, Mona H.↗
DOE OSTI2025

Aqueous Zr/Hf IV ‐Oxo Cluster Speciation and Separation

Abstract Many industrial separations of chemically‐similar elements are achieved by solvent extraction, exploiting differences in speciation and solubility across aqueous‐organic interfaces. We recently identified [OM 4 (OH) 6 (SCN) 12 ] 4− (OM 4 , M=Zr/Hf IV ) tetrahedral oxoclusters as the main species in industrial processes that produce nuclear‐grade Zr and Hf from crude ore. However, isostructural/isoelectronic OM 4 ‐oxoclusters do not explain selective extraction of Hf into the organic phase. Here we have characterized heterometal Hf−Zr clusters in solution and the solid‐state yielding key information about their fundamentally different chemistry that engenders separation. Clusters prepared with both ammonium (industrial process) and tetramethylammonium counter cations revealed that 1) heterometal clusters (instead of a mixture of homometal clusters) assemble, and 2) Hf‐rich OM 4 selectively precipitates over Zr‐rich OM 4 , providing a separation process that does not require an organic extractant. Mass spectrometry, small‐angle X‐ray scattering, solution‐state 1 H nuclear magnetic resonance (NMR) spectroscopy, and solid‐state 17 O NMR evidence both mixed‐metal speciation and selective Hf‐precipitation. Raman spectroscopy suggests greater Zr‐ligand lability than Hf‐ligand lability, consistent with higher aqueous solubility of Zr‐rich clusters, enabling both extraction and precipitation‐based separation. Fundamentally, we also identify a key difference between these chemically similar elements that has enabled diversification of Zr‐polyoxocation chemistry over the last decade, while Hf‐polyoxocation chemistry lags.

Roseborough, Alexander [Department of Chemistry Or↗
DOE OSTI2024

Directly Fused Porphyrin‐Tetracyanopentacenequinone Conjugates: Role of the Cross‐Conjugated, Powerful Electron Acceptor in Promoting Highly Efficient Charge Separation

Tetracyanopentacenequinone, a powerful electron acceptor, is fused directly to the porphyrin π-system to create a new class of donor-acceptor conjugates. Owing to the direct fusion and electron-deficient property of tetracyanopentacenequinone, strong intramolecular charge transfer both in the ground and excited states was witnessed. As a control, porphyrin fused with pentacenequinone was also investigated. Upon complete spectral and electrochemical characterization, the excited state properties were initially probed by time-dependent DFT studies, and the occurrence of electron transfer from different excited states was established. Free-energy calculations revealed higher exothermic electron transfer (>600 mV) than the control pentacenequinone-porphyrin systems. Pump-probe studies covering broad spatial and temporal regions revealed efficient excited state charge separation. This was unlike the control pentacenequinone-porphyrin system, where slow charge separation was witnessed only in the case of the zinc derivatives but not the free-base ones, followed by the populating of the triplet excited state. The lifetimes of the charge-separated states ranged between 30–500 ps depending on the solvent and metal ion in the porphyrin cavity. Nanosecond transient absorption studies established the charge recombination path to populate the triplet state of porphyrin or directly to the ground state as a function of solvent polarity and the nature of the conjugate. Furthermore, the significance of cross-conjugated tetracyanopentacenequinone fused directly to the porphyrin π system in promoting highly exothermic and efficient charge separation, irrespective of its cross conjugation, is borne out from this study.

Cross conjugation↗
DOE OSTI2024

Emerging Rare Earth Element Separation Technologies

Rare earth elements are essential for numerous clean energy applications, yet their mining, separation, and processing pose significant environmental challenges. Traditional separation processes often result in ecological damage, highlighting the critical need for innovative techniques that reduce environmental impacts. This article reviews recent advancements in rare earth separation technologies, with a particular focus on the role of neutral organic compounds. It explores how these compounds change selectivity across the rare earth series, offering promising strategies for designing more effective rare earth element separation systems. Furthermore, the article points out research areas requiring additional investigation to improve the sustainability of these critical processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Evaluating the impact of functional groups on membrane‐mediated CO 2 / N 2 gas separations using a common polymer backbone

Abstract Polymeric membranes have shown tremendous promise for the separation of CO 2 from flue gas streams. However, few systematic studies have been conducted to better understand the impact that chemical functionalities have on membrane‐based gas separation performance. To address this gap, we herein describe the synthesis and gas separation performance of a series of vinyl‐addition polynorbornenes bearing various CO 2 ‐philic functional groups. To facilitate direct comparison between functional groups, each material was designed to maintain a common polymer backbone. Though the incorporation of CO 2 ‐philic moieties within a dense polymeric membrane is frequently hypothesized to enhance CO 2 solubility, and thereby increase CO 2 /N 2 selectivity, our results demonstrate that the incorporation of CO 2 ‐philic groups onto a common polymer backbone do not necessarily result in increased gas separation performance. Experimental and computational results demonstrate that the incorporation of amidoxime groups onto a polynorbornene backbone increase CO 2 /N 2 selectivity, whereas commonly employed ethereal side chains only increased permeability.

Higgins, Morgan A.↗
DOE OSTI2021

A Comprehensive Review of Selected Major Categories of Lithium Isotope Separation Techniques

The ability to generate materials with an enriched isotopic abundance, that is one that differs from natural abundance, is critical in terms of technology. Isotopes are used in a wide range of applications, including radioactive tracers, nondestructive tests, radiotherapy in human medicine, nuclear fuels, and isotope‐substituted compounds for chemistry and biology research, as well as environmental geochemical signature tracers. A commonly discussed research topic is the isotopic separation of various elements—uranium, hydrogen, lithium, and iodine, among many others. Among these isotopes, lithium isotopes are especially important in various applications including strategic areas. These isotopes are light and hence their separation techniques are not very obvious. Herein, all the main categories of Li isotope separation are reviewed in depth with a focus on electrochemical technologies for stable lithium isotope separation.

Murali, Arun↗
DOE OSTI2024

Twice upon a time: timelike-separated quantum extremal surfaces

The Python’s Lunch conjecture for the complexity of bulk reconstruction involves two types of nonminimal quantum extremal surfaces (QESs): bulges and throats, which differ by their local properties. The conjecture relies on the connection between bulk spatial geometry and quantum codes: a constricting geometry from bulge to throat encodes the bulk state nonisometrically, and so requires an exponentially complex Grover search to decode. However, thus far, the Python’s Lunch conjecture is only defined for spacetimes where all QESs are spacelike-separated from one another. Here we explicitly construct (time-reflection symmetric) spacetimes featuring both timelike-separated bulges and timelike-separated throats. Interestingly, all our examples also feature a third type of QES, locally resembling a de Sitter bifurcation surface, which we name a bounce. By analyzing the Hessian of generalized entropy at a QES, we argue that this classification into throats, bulges and bounces is exhaustive. We then propose an updated Python’s Lunch conjecture that can accommodate general timelike-separated QESs and bounces. Notably, our proposal suggests that the gravitational analogue of a tensor network is not necessarily the time-reflection symmetric slice, even when one exists.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Effects of urban debris material on the extraction chromatographic separation of strontium—part I: steel

An incident involving a radiation dispersal device (RDD) would most likely occur in an urban or metropolitan area. However, the majority of radiochemical separation schemes available have been developed for environmental samples that are not necessarily representative of those found in an urban environment. 90 Sr is one of the possible radioisotopes that could be used in an RDD. It is therefore important to find efficient and accurate ways to separate it from debris in the area of deployment. Finally, this research demonstrates that the presence of steel in dissolved samples shows no appreciable interference with extraction chromatographic separations. Instead, it indicates that the separation could actually be improved by the presence of the steel constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Improving the separation of strontium and barium with Sr Resin using chelating eluent solutions

Age dating radioactive 137 Cs and 90 Sr sources, which are a potential concern in radiation dispersal devices, can provide evidence for attribution in a nuclear forensic investigation. Precise measurement of the 137 Cs– 137 Ba or 90 Sr– 90 Zr isotope ratio by ICP-MS in tandem with non-linearity and mass-bias data manipulation dramatically increases precision and decreases uncertainty, leaving inadequate chemical separation efficiencies as a major contributor—and in some cases the lead contributor—to uncertainty in age determination. To improve the separation of these isobars before ICP-MS analysis, we evaluated eluents containing EDTA and DTPA chelating agents against previously studied eluents for their ability to achieve complete removal of Sr and Ba from Eichrom Technologies’ Sr Resin. Barium separation efficiencies using 0.05 M EDTA, pH-adjusted 0.05 M EDTA, and pH-adjusted 0.05 M DTPA were found to be 100.9 ± 2.2%, 99.4 ± 0.8%, and 99.3 ± 1.2%, respectively. Strontium separation efficiencies using 0.05 M disodium EDTA and 0.05 M potassium EDTA were determined to be 100.14 ± 0.53% and 100.19 ± 0.97% respectively. Furthermore, these results demonstrate that eluents containing chelating agents out-perform previously studied eluent solutions at removing barium and strontium from Sr Resin.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Laboratory Enrichment of Radioactive Assemblages and Estimation of Thorium and Uranium Radioactivity in Fractions Separated from Placer Sands in Southeast Bangladesh

The present study reports the likely first attempt of separating radioactive minerals for estimation of activity concentration in the beach placer sands of Bangladesh. Several sand samples from heavy mineral deposits located at the south-eastern coastal belt of Bangladesh were processed to physically upgrade their radioactivity concentrations using plant and laboratory equipment. Following some modified flow procedure, individual fractions were separated and investigated using gamma-ray spectrometry and powder-XRD analysis. The radioactivity measurements indicated contributions of the thorium and uranium radioactive series and of {sup 40}K. The maximum values of {sup 232}Th and {sup 238}U, estimated from the radioactivity of {sup 208}Tl and {sup 234}Th in secular equilibrium, were found to be 152,000 and 63,300 Bq/kg, respectively. The fraction of the moderately conductive part in electric separation contained thorium predominantly, while that of the non-conductive part was found to be uranium rich. The present arrangement of the pilot plant cascade and the fine tuning of setting parameters were found to be effective and economic separation process of the radioactive minerals from placer sands in Bangladesh. Probable radiological impacts and extraction potentiality of such radioactive materials are also discussed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

A Limit to Accelerated Free-Sintering: Nano-Phase Separation Interferes With Organic Debinding

Nano-phase separating Ni–12 at. pct Ag powders are processed via high-energy ball milling and brought into a supersaturated state with a reduction of the grain size to the nanocrystalline scale, a combination that is designed to encourage rapid densification by phase separation upon heating. This unstable powder is then characterized by dilatometry, in-situ x-ray diffraction, thermogravimetry and microstructure analysis for sintering cycles up to 940 °C. However, these powder compacts exhibit excessive pore evolution and significant macroscopic swelling caused by removal of the organic process additives. This competition of organic removal with densification is known in nanocrystalline metals, but the present study adds an additional dimension of phase separation, which shifts the dominant swelling mechanism as the formation of the second phase traps the volatilizing organics and hinders the debinding process. The creep swelling and overall loss in relative density is then dominated by the creep deformation of the second Ag phase. The interference between organic removal and low-temperature onset of consolidation represents a new challenge to efforts aimed at rapid free sintering and should guide the design of rapidly sintering alloys; specifically, the present work emphasizes the need to select alloys that have their sintering-accelerating phase separation temperature above the range where gases are evolved.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Influence of Lactic Acid Concentration on the Separation of Light Rare Earth Elements by Continuous Liquid–Liquid Extraction with 2-Ethylhexyl Phosphonic Acid Mono-2-ethylhexyl Ester

The separation of rare earth elements (REEs) using solvent extraction adding complexing agents appears to be an alternative to saponification of the extractant. We evaluated the effect of lactic acid concentration on didymium (praseodymium and neodymium) and lanthanum extraction with 2-ethylhexyl phosphonic acid mono-2-ethyl hexyl ester [HEH(EHP)] as extractant. First, we investigated in batch experiments the separation of lanthanum (La) and didymium (Pr and Nd) using McCabe–Thiele diagrams to estimate the number of extraction stages when the feed solution was or was not conditioned with lactic acid. Additionally, we conducted continuous liquid–liquid extraction experiments and evaluated the influence of lactic acid concentration on the REE extraction and separation. The tests showed that the extraction percentage of REEs and the separation factor Pr/La increased when the lactic acid concentration increased, but the didymium purity decreased. Lanthanum, praseodymium, and neodymium extraction rate were 23.0, 89.7, and 99.2 pct, respectively, with 1:1 aqueous/organic volume flow rate and feed solution doped with 0.52 mol L{sup −1} lactic acid. The highest didymium purity reached was 92.0 pct with 0.26 mol L{sup −1} lactic acid concentration.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Efficient Separation and Extraction of Vanadium and Chromium in High Chromium Vanadium Slag by Selective Two-Stage Roasting–Leaching

Vanadium and chromium are important rare metals, leading to a focus on high chromium vanadium slag (HCVS) as a potential raw material to extract vanadium and chromium in China. In this work, a novel method based on selective two-stage roasting–leaching was proposed to separate and extract vanadium and chromium efficiently in HCVS. XRD, FT-IR, and SEM were utilized to analyze the phase evolutions and microstructure during the whole process. Calcification roasting, which can calcify vanadium selectively using thermodynamics, was carried out in the first roasting stage to transfer vanadium into acid-soluble vanadate and leave chromium in the leaching residue as (Fe{sub 0.6}Cr{sub 0.4}){sub 2}O{sub 3} after H{sub 2}SO{sub 4} leaching. When HCVS and CaO were mixed in the molar ratio CaO/V{sub 2}O{sub 3} (n(CaO)/n(V{sub 2}O{sub 3})) of 0.5 to 1.25, around 90 pct vanadium and less than 1 pct chromium were extracted in the first leaching liquid, thus achieving the separation of vanadium and chromium. In the second roasting stage, sodium salt, which combines with chromium easily, was added to the first leaching residue to extract chromium and 95.16 pct chromium was extracted under the optimal conditions. The total vanadium and chromium leaching rates were above 95 pct, achieving the efficient separation and extraction of vanadium and chromium. The established method provides a new technique to separate vanadium and chromium during roasting rather than in the liquid form, which is useful for the comprehensive application of HCVS.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Separation of conditions as a prerequisite for quantum theory

We introduce the notion of “separation of conditions” meaning that a description of statistical data obtained from experiments, performed under a set of different conditions, allows for a decomposition such that each partial description depends on mutually exclusive subsets of these conditions. Descriptions that allow a separation of conditions are shown to entail the basic mathematical framework of quantum theory. The Stern–Gerlach and the Einstein–Podolsky–Rosen–Bohm experiment with three, respectively nine possible outcomes are used to illustrate how the separation of conditions can be used to construct their quantum theoretical descriptions. It is shown that the mathematical structure of separated descriptions implies that, under certain restrictions, the time evolution of the data can be described by the von Neumann/Schrödinger equation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Sulfur-functionalized solid-phase materials for the selective separation of arsenic and selenium

Radioactive arsenic (As) isotopes are of growing interest for applications in nuclear medicine, national security, and environmental research. Recent efforts at the Facility for Rare Isotope Beams (FRIB) have focused on aqueous harvesting of selenium-72,73 ( 72,73 Se) and their daughter isotopes, arsenic-72,73 ( 72,73 As), which are particularly valuable for medical applications and nuclear data studies, respectively. Both conventional isotope production and harvesting methods require chemical separations to purify radioactive As from parent and co-produced Se radioisotopes. While several solid-phase separation methods for As and Se exist, many depend on complex oxidation state control or highly acidic conditions. This study presents results for sulfur-based solid-phase materials selected to enable uptake at lower acidity and eliminate the need for intricate redox chemistry. Specifically, the performance of three covalently bound sulfur-based ligands were evaluated: (1) thiophenol-polystyrene, (2) propanethiol-silica, and (3) thiourea-silica. Uptake characteristics—including distribution coefficients (Dw), kinetics, and column separation behavior—were assessed using 75 Se and 73 As in hydrochloric (HCl) acid and nitric (HNO 3 ) solutions. The resins demonstrated high-yield (>95%) and high-purity As recovery across a range of HCl concentrations. Comparable results in HNO 3 were achieved when combined with anion exchange chromatography. Furthermore, the potential application of these materials for medical isotope generators was also investigated through ligand stability and repeated elution studies. Overall, sulfur leaching from the resins was negligible at the concentrations relevant for these separations but increased with higher acid concentrations.

Arsenic↗