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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The preparation and characterization of chemically deuterium incorporated cotton fibers

Preparation of deuterium incorporated cellulose is a vital tool to investigate cellulose internal structure and to expand the application fields of cellulose materials. In this study, cellulosic cotton fibers with anti-rehydration (exchange-resistant) deuterium incorporated in cellulose were prepared by chemical hydrogen–deuterium exchange treatment. The chemical hydrogen–deuterium exchange process, along with exchange time, were characterized by nuclear magnetic resonance hydrogen spectroscopy (1H-NMR). The anti-rehydration deuterium incorporation was determined by Fourier Transform infrared spectroscopy (FTIR) and Stable Isotope Ratio Mass Spectrometer (IRSM). Here, the effect of the deuterium hydroxyl substitution on cotton fiber’s spectral data, microstructure, crystalline information, degree of polymerization, as well as it’s thermogravimetric analysis (charcoalization and combustion) are explored. Analysis of the chemical exchange process indicated that the hydrogen–deuterium exchange occurred preferentially in the amorphous cellulose component over the first several minutes. Deuterium exchange in the anti-rehydration crystalline phase took several hours. Increasing the treatment time, enhanced exchange-resistant deuterium incorporation to as high as about 60% of the cotton fibers’ cellulose hydroxyl groups was achieved. The characterization of FTIR, Fourier transform Raman (FT-Raman), and near-infrared spectra (NIR) all exhibited the deuterium spectral isotope effect on cellulose hydroxl groups. While, apart from the effect of reaction temperature, deuterium incorporation isotope effect did not affect the cellulose microstructure, crystalline index and the degree of polymerization properties. Furthermore, the thermogravimetric analysis of deuterated cotton fibers under N 2 and air atmosphere were both altered due to the thermodynamic isotope effect. These observations revealed the hydrogen–deuterium exchange treatment process and impacts on cellulose fiber properties, which helped us to better understand the cellulose internal structure and may facilitate the potential utilization of deuterated cellulosic materials.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

A comparative study of silver- and palladium-exchanged zeolites in propylene and nitrogen oxide adsorption and desorption for cold-start applications

Here, silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a small amount of NO. The presence of H 2 O inhibited the adsorption of both C 3 H 6 and NO. Ion-exchanging BEA zeolites with Ag (1.2 and 5.1 wt.% Ag/BEA) attenuated the inhibiting effect of H 2 O on C 3 H 6 adsorption, while NO storage remained inhibited. Adsorption experiments indicated that C 3 H 6 and NO competed with each other for Pd sites with C 3 H 6 showing stronger adsorption compared to NO, whereas Ag sites preferentially adsorbed C 3 H 6 . DRIFTS data indicated the formation of nitrate, formate and acetate species on Ag and Pd, while C 3 H 6 and NO adsorption was also observed on the zeolite hydroxyl groups in the absence of H 2 O. However, the C 3 H 6 and NO adsorption on the zeolite hydroxyl groups was significantly inhibited in the presence of H 2 O. Additionally, nitrosyl, acrolein and carbonate species were formed over 1.0 wt.% Pd/BEA. The effluent analysis during the temperature-programmed desorption in the DRIFTS reactor revealed that adsorbed C 3 H 6 and NO reacted during the release to form oxidation reaction byproducts. The 1.0 wt.% Pd/BEA zeolite showed the greatest oxidation ability during desorption with the majority of stored C 3 H 6 converted to CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Double in-situ lignin modification in surfactant-assisted glycerol organosolv pretreatment of sugarcane bagasse towards efficient enzymatic hydrolysis

Organosolv pretreatment effectively fractionates lignocellulosic biomass for efficient enzymatic hydrolysis, yielding fermentable sugars. However, substantial lignin redeposition on the substrate surface and residual lignin content exacerbate lignin’s inhibitory effects on subsequent enzymatic hydrolysis. Here, an in-situ lignin modification is proposed to address this challenge by incorporating polyethylene glycol (PEG) series into glycerol organosolv (GO) pretreatment. According to the results obtained, PEG-assisted GO pretreated substrate exhibited significantly increased sugar yield during enzymatic hydrolysis, particularly with PEG 4000, showing 35.4% higher glucose yield over 72 h. The improved glucose yield with PEG could be attributed to changes in the physicochemical structure and properties of residual lignin, mitigating its non-productive interaction with cellulase enzymes. PEG's presence in GO pretreatment also increased β-O-4 linkages preservation by 55% and reduced phenolic hydroxyl groups by 28% in lignin fragments versus no surfactants. This outcome resulted from introducing glycerol and PEG hydroxyl tails into the lignin structure, forming α-etherified lignin and rendering it more hydrophilic. Simulations confirmed strong Van Der Waals and hydrogen bonding interactions between lignin units and PEG, hindering lignin fragments repolymerization. Incorporating PEG in the organosolv pretreatment proves highly beneficial for cellulase-mediated lignocellulosic biorefinery, resembling a lignin-first strategy. The optimized process enables efficient biomass utilization for sustainable fuels and chemicals production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Influence of CaO/FeO ratio on the formation mechanism and properties of alkali-activated Fe-rich slags

Highlights: • Effect of the CaO/FeO molar ratio in alkali-activated Fe-rich slags is unraveled. • Low CaO/FeO molar ratios enhance the early kinetics and compressive strength. • Reaction extent and strength further increase with higher CaO/FeO ratio after 7 days. • Fe{sup 2+}-trioctahedral layers of the binder are hydroxylated and in a silicate phase. • The final strength is determined by the influence of Ca on the reaction products. In the search for CO{sub 2} mitigating cement technologies, alkali-activated Fe-rich slags present a possible alternative. The influence of the chemical composition of the synthetic Fe-silicate slag on the reaction mechanisms is assessed by varying the CaO/FeO molar ratio. The alkali-activated Fe-rich slags consist of trioctahedral layers that are shown to be hydroxylated and in contact with silicates, in a similar way to phyllosilicate minerals. The formation of this phyllosilicate-like structure is hindered during the first days for samples with high CaO/FeO ratios, because of the partial incorporation of Ca in the trioctahedral layers. At later ages, the samples with higher CaO/FeO ratios gain in reaction extent, to exceed the reaction extent of low CaO/FeO ratios at 28 days and beyond. The increase in compressive strength is even more pronounced than the effect on the reaction extent, which underlines the importance of Ca on the inherent strength of the binding phases.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optimized thermodynamic properties of REE aqueous species (REE 3+ and REEOH 2+ ) and experimental database for modeling the solubility of REE phosphate minerals (monazite, xenotime, and rhabdophane) from 25 to 300 °C

Rare earth elements (REE) are critical elements found in monazite, xenotime, and hydrated REE phosphates which typically form in hydrothermal mineral deposits. Accurate predictions of the solubility of these REE phosphates and the speciation of REE in aqueous fluids are both key to understanding the controls on the transport, fractionation, and deposition of REE in natural systems. Previous monazite and xenotime solubility experiments indicate the presence of large discrepancies between experimentally derived solubility constants versus calculated solubilities by combining different data sources for the thermodynamic properties of minerals and aqueous species at hydrothermal conditions. In this study, these discrepancies were resolved by using the program GEMSFITS to optimize the standard partial molal Gibbs energy of formation (Δ f G° 298 ) of REE aqueous species (REE 3+ and REE hydroxyl complexes) at 298.15 K and 1 bar while keeping the thermodynamic properties fixed for the REE phosphates. A comprehensive experimental database was compiled using solubility data available between 25 and 300 °C. The latter permits conducting thermodynamic parameter optimization of Δ f G° 298 for REE aqueous species. Optimal matching of the rhabdophane solubility data between 25 and 100 °C requires modifying the Δ f G° 298 values of REE 3+ by 1–6 kJ/mol, whereas matching of the monazite solubility data between 100 and 300 °C requires modifying the Δ f G° 298 values of both REE 3+ and REEOH 2+ by ~15–31 kJ/mol and ~2–10 kJ/mol, respectively. For xenotime, adjustments of Δ f G° 298 values by 1–26 kJ/mol are only necessary for the REE 3+ species. The optimizations indicate that the solubility of monazite in acidic solutions is controlled by the light (L)REE 3+ species at <150 °C and the LREEOH 2+ species at >150 °C, whereas the solubility of xenotime is controlled by the heavy (H)REE 3+ species between 25 and 300 °C. Based on the optimization results, we conclude that the revised Helgeson-Kirkham-Flowers equation of state does not reliably predict the thermodynamic properties of REE 3+ , REEOH 2+ , and likely other REE hydroxyl species at hydrothermal conditions. We therefore provide an experimental database (ThermoExp_REE) as a basic framework for future updates, extensions with other ligands, and optimizations as new experimental REE data become available. As a result, the optimized thermodynamic properties of aqueous species and minerals are available open access to accurately predict the solubility of REE phosphates in fluid-rock systems.

58 GEOSCIENCES↗
DOE OSTI2025

NdPO 4 solubility and aqueous Neodymium speciation in supercritical fluids: An experimental study at 500–700 °C and 1.7 kbar

A key aspect in the formation of rare earth elements (REE) deposits is the role of REE transport as aqueous REE complexes in supercritical hydrothermal solutions, where the nature of the aqueous complex is controlled by solution composition, temperature and pressure. Despite chloride being considered as one of the most abundant transporting ligands in magmatic-hydrothermal fluids, experimental investigations on the stability of aqueous REE chloride complexes are scarce above 300 °C. In this study, synthetic NdPO 4 crystals were reacted with non-saline and saline (0, 0.05 and 0.5 mNaCl), acidic (0.01 mHCl) aqueous solutions in a series of solubility experiments conducted at 500–700 °C and 1.7 kbar, where the solubilities were determined using a stable Nd isotope ( 145 Nd isotope spike) dilution technique. NdPO 4 solubility ranges between 28 ppm and 10,858 ppm, where solubility increases with both temperature and salinity. At 500 °C, log mNdPO 4 increases from –3.93 to –1.60 and there is a strong correlation between NdPO 4 solubility and NaCl concentrations (slope of 1.2 ± 0.3), indicating stabilization of the Nd chloride aqueous complexes with a stoichiometry corresponding to NdCl 2+ . At 600 °C, this correlation is weaker (slope of 0.4, log mNdPO 4 increases from –2.63 to –1.88) indicating the stabilization of both Nd chloride and hydroxyl species controlling solubility. At 700 °C, NdPO 4 solubility is largely independent of NaCl concentration indicating that solubility is controlled by Nd hydroxyl complexes, where stoichiometry suggests the neutral Nd(OH) 3 0 species is dominant. The solubility product (Ksp) of NdPO4 is derived from experimental data with the relation: log K sp = -41.81 – 0.057T – 20987/T, with T temperature in Kelvin. Comparison of the measured Nd phosphate solubility to thermodynamic predictions using the available Helgeson-Kirkham-Flowers equation of state parameters for aqueous Nd complexes indicate that predictions are up to three orders of magnitude lower compared to experimental observations. This discrepancy is most pronounced in saline solutions, suggesting that thermodynamic properties of the REE chloride species in supercritical fluids require revision. Numerical simulations of fluid-rock interaction between acidic, saline fluids and a Strange Lake felsic mineral assemblage demonstrates that NdPO 4 solubility predictions from models are four to six orders of magnitude lower than those calculated based on empirical fits from experiments, which suggests that acidic, saline fluids may play an important role in mobilizing large amounts of light REE from 450 to 700 °C.

58 GEOSCIENCES↗
DOE OSTI2022

From acetone fractionation to lignin-based phenolic and polyurethane resins

In this paper, acetone fractionation was used to increase the homogeneity of softwood kraft lignin for product development. The acetone soluble and insoluble fractions were analyzed in terms of elemental composition, chemical structure, and thermal properties. The phenolic hydroxyl content of the acetone soluble fraction increased by 24%. The acetone soluble fraction of kraft lignin was used to fully substitute phenol in phenolic resin formulation. The resulting formulated lignin-formaldehyde adhesive showed higher adhesion strength (4.3 MPa) compared to a lab formulated phenol-formaldehyde resin (3.4 MPa) with 100% wood failure after lap shear test. On the other hand, the acetone insoluble lignin fraction, which had 23% higher aliphatic hydroxyl content compared to the starting lignin, was used to entirely replace petroleum-based polyol in polyurethane resin formulation. Then a bio-derived solvent (dihydrolevoglucosenone, Cyrene) was used to dissolve the acetone insoluble lignin fraction to synthesize lignin-based polyurethane resin. Tailoring the structure of kraft lignin through solvent fractionation resulted in two fractions, which were used to replace 100% of two major petrochemicals (phenol and polyol) in the formulations of phenolic and PU resins, that would otherwise be challenging due to the heterogeneity of softwood kraft lignin.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structure-performance relationships in lignin-based transesterification vitrimers: The role of lignin structural features

Lignin has been hailed as an ideal renewable alternative for petrochemical-based prepolymers in material synthesis for a sustainable and circular economy, due to its abundant aromatic network and high carbon content. However, the properties and performance of lignin-derived macromolecules are strongly influenced by the lignin itself. While numerous studies have explored the impact of lignin content on the thermomechanical performance of lignin-based vitrimers, literature on how the inherent structural features of lignin affect these properties is scanty. In this study, hardwood organosolv lignin was fractionated in ethyl acetate, ethanol, and acetone to obtain lignin fractions with varying structural characteristics. These fractions were then modified through carboxylation and crosslinked with epoxidized soybean oil (ESO) at a hydroxyl to epoxy group ratio of 1:1 to produce lignin-based transesterification vitrimers (LVs). The thermal properties (i.e. glass transition temperature and thermal stability), tensile strength, storage modulus, and stress relaxation behavior of the LVs were studied and carefully related to the structural features of lignin. The results revealed a positive relationship between strong hydroxyl content in modified lignin and the tensile strength (5.10–9.71 MPa), storage modulus (1099.4 – 1372.8 MPa), crosslinking density, and stress relaxation of the LVs. Additionally, both the storage modulus and tensile strength exhibited a positive relationship with the ratio of rigid linkages in modified lignin, while lignin molecular weight was found to significantly impact the thermal properties of LVs (i.e Tg and thermal stability). This study not only highlights the valorization of lignin in vitrimer synthesis but also provide insights for designing lignin-based materials with tailored properties for specific applications.

Bio-based polymer↗
DOE OSTI2020

Activation and surface reactions of CO and H 2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions

Here, activation and surface reactions of CO and H 2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions were (quasi) in situ studied using temperature programmed surface reaction spectra, diffuse reflectance Fourier transform infrared spectroscopy, inelastic neutron scattering spectroscopy and electron paramagnetic resonance. CO undergoes disproportion reaction to produce gaseous CO 2 and surface carbon adatoms, and adsorbs to form surface formate species. H 2 adsorption forms dominant irreversibly-adsorbed surface hydroxyl groups and interstitial H species and very minor surface Zn-H species. Surface formate species and hydroxyl groups react to produce CO 2 and H 2 , while surface carbon adatoms are hydrogenated by surface Zn-H species sequentially to produce CH(a), CH 2 (a), CH 3 (a) and eventually gaseous CH 4 . The ZnO nanoplates, exposing a higher fraction of Zn-ZnO(0001) and O-ZnO(000–1) polar facets, are more active than the ZnO powders to catalyze CO hydrogenation to CH 4 . These results provide fundamental understanding of the reaction mechanisms and structural effects of CO hydrogenation reaction catalyzed by ZnO-based catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Exfoliation of surfactant swollen layered MWW zeolites into two-dimensional zeolite nanosheets using telechelic liquid polybutadiene

We report two-dimensional (2D) zeolites have the potential to enhance mass transport by reducing diffusion lengths and thus find applications in catalysis and separation. High aspect ratio 2D zeolite nanosheets are required for fabrication of thin, high-flux zeolite membranes. Preparation of 2D zeolite nanosheets can be achieved by exfoliation of layered zeolite precursors, which usually requires multiple steps including swelling with cationic surfactants, exfoliation by applying a mechanical force such as shearing or sonication, purification and removal of the surfactants. The exfoliation of surfactant swollen layered zeolite precursors has been studied using molten polystyrene and telechelic liquid polybutadiene, but still requires extensive shearing force. Recently, a novel one-step exfoliation method has been developed for nonswollen MWW zeolite precursors using tetrabutylammonium hydroxide (TBAOH) solution. In this work, we study the exfoliation of surfactant swollen MWW layered precursors (with and without aluminum) in commercially available liquid hydroxyl-terminated polybutadiene (HTPB) with the aim to provide fundamental understanding of the interaction between the liquid polybutadiene and the surfactant swollen layered zeolite precursors. It was found that surfactant swollen ITQ-1, (ITQ-1(S)), a pure silica layered precursor with MWW framework after being swollen with a cationic surfactant, can be exfoliated in liquid HTPB at room temperature without applying any additional shearing force. The aluminum containing surfactant swollen MWW precursors can be also exfoliated in HTPB at room temperature, but require additional shearing forces. The exfoliation process was monitored using rheology experiments and studied by tuning the composition of the zeolite precursors. The interaction between the layered zeolite precursor and the hydroxyl group of the liquid polybutadiene allows the polymer to intercalate the precursor and exfoliate it into nanosheets. The presence of framework aluminum and the nature of the organic structure directing agents (OSDAs) are key parameters affecting the exfoliation process. Framework Al is unfavorable for the exfoliation possibly due to the surface charges introduced by the aluminum. Bulky OSDA, trimethyladamantammonium (TMAda + ), in the interlayer spacing may facilitate the exfoliation.

2D nanosheets↗
DOE OSTI2020

Boosting electrosynthesis of ammonia on surface-engineered MXene Ti 3 C 2

Seeking a breakthrough in the development of efficient nitrogen fixation catalysts has become the frontier of energy and chemical conversion schemes. In this work, we report that the MXene Ti 3 C 2 can serve as a promising catalyst for the electrochemical N 2 reduction reaction (NRR) under ambient conditions. The electrocatalytic performance of Ti 3 C 2 can be further optimized through surface engineering. Specifically, Ti 3 C 2 with the increased surface hydroxyl moieties demonstrates enhanced production of NH 3 with a yield rate of 1.71 μg h -1 cm -2 , a Faradaic efficiency of 7.01% at -0.2 V vs. RHE at 20 °C and an even higher yield rate of 12.46 μg h -1 cm -2 together with a Faradaic efficiency of 9.03% at -0.2 V vs. RHE at 60 °C. The detailed electrochemical analysis suggests that the surface hydroxyl modification can effectively facilitate the electron transfer, surface adsorption and activation of dinitrogen. Our work sheds light on the development of efficient NRR catalysts based on earth-abundant elements.

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

A comparative reactivity study of 1-alkene fuels from ethylene to 1-heptene

In this work, a comparative reactivity study of 1-alkene fuels from ethylene to 1-heptene has been performed using ignition delay time (IDT) measurements from both a high-pressure shock tube and a rapid compression machine, at an equivalence ratio of 1.0 in ‘air’, at a pressure of 30 atm in the temperature range of 600–1300 K. At low temperatures (< 950 K), the results show that 1-alkenes with longer carbon chains show higher fuel reactivity, with 1-pentene being the first fuel to show negative temperature coefficient (NTC) behavior followed by 1-hexene and 1-heptene. At high temperatures (> 950 K), the experimental results show that all of the fuels except propene show very similar fuel reactivity, with the IDTs of propene being approximately four times longer than for all of the other 1-alkenes. To analyze the experimental results, a chemistry mechanism has been developed using consistent rate constants for these alkenes. At 650 K, flux analyses show that hydroxyl radicals add to the double bond, followed by addition to molecular oxygen producing hydroxy-alkylperoxy radicals, which can proceed via the Waddington mechanism or alternate internal H-atom isomerizations in chain branching similar to those for alkanes. We have found that the major chain propagation reaction pathways that compete with chain branching pathyways mainly produce hydroxyl rather than hydroperoxyl radicals, which explains the less pronounced NTC behavior for larger 1-alkenes compared to their corresponding alkanes. At 1200 K, flux analyses show that the accumulation of hydroperoxyl radicals is important for the auto-ignition of 1-alkenes from propene to 1-heptene. The rate of production of hydroperoxyl radicals for 1-alkenes from 1-butene to 1-heptene is higher than that for propene, which is due to the longer carbon chain facilitating hydroperoxyl radical formation via more efficient reaction pathways. This is the major reason that propene presents lower fuel reactivity than the other 1-alkenes at high temperatures.

1-Alkene↗
DOE OSTI2024

The evolution of model Rh/Fe 3 O 4 (001) catalysts in hydrogen environments

Single metal atoms dispersed on oxides are a new emerging class of catalysts owing to their unique electronic and chemical properties. Here, in this study, we have prepared a series of model single-atom catalysts possessing well-characterized Rh sites that include Rh adatoms (Rh ad ), mixed surface layers with octahedrally-coordinated Rh (Rh oct ), as well as metallic Rh clusters and nanoparticles (Rh met ) on Fe 3 O 4 (001). Using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we investigated the activity of such model systems towards H2 and their stability in reducing environments. Our results show that the atomically dispersed Rhad and Rhoct species do not activate H 2 , which would result in the formation of surface hydroxyls on Fe 3 O 4 (001). In contrast, the presence of Rh met in H 2 results in the formation of hydroxyls and subsequent etching of the Fe 3 O 4 (001) at higher temperatures (≥ 500 K) due to water formation via the Mars-van Krevelen mechanism. Additionally, such surface etching leads to the release of the Rh oct from the surface lattice and their sintering to Rh met . To bridge the material gap between the surface science models and high surface area catalysts, we perform parallel studies on powder Rh/Fe 3 O 4 catalysts. The XPS characterization shows remarkable similarities between these systems. Further, our surface science studies provide an atomistic picture of the behavior of high surface area catalysts in the H 2 atmosphere.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Crystal structure of brimonidine hydrogen tartrate, (C 11 H 11 BrN 5 )(HC 4 H 4 O 6 )

The crystal structure of brimonidine hydrogen tartrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Brimonidine hydrogen tartrate crystallizes in space groupP2 1 (#4) witha= 7.56032(2),b= 7.35278(2),c= 30.10149(9) Å,β= 90.1992(2)°,V= 1673.312(10) Å 3 , andZ= 4 at 295 K. The crystal structure consists of alternating layers of cations and anions parallel to theab-plane. Each of the hydrogen tartrate anions is linked to itself by very strong charge-assisted O–H⋯O hydrogen bonds into chains along thea-axis. Each hydroxyl group of each tartrate acts as a donor in an O–H⋯O or O–H⋯N hydrogen bond. One of these is intramolecular, but the other three are intermolecular. These hydrogen bonds link the hydrogen tartrate anions into layers parallel to theab-plane and also link the anion–cation layers. The protonated N atoms act as donors in N–H⋯O or N–H⋯N hydrogen bonds to the carboxyl groups of the tartrates and to a ring nitrogen atom. These link the cations and anions, as well as providing cation–cation links. The amino N atoms of the cations form N–H⋯O hydrogen bonds to hydroxyl groups of the anions. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®)

Materials Science↗
DOE OSTI2025

Carbonation of MgO Single Crystals: Implications for Direct Air Capture of CO 2

Direct air capture (DAC) may be feasible to remove carbon dioxide (CO 2 ) from the atmosphere at the gigaton scale, holding promise to become a major contributor to climate change mitigation. Mineral looping using magnesium oxide (MgO) is potentially an economical, efficient, and sustainable pathway to gigaton-scale DAC. The hydroxylation and carbonation of MgO determine the efficiency of the looping process, but their rates and mechanisms remain uncertain. Here, in this work, MgO single crystals were reacted in air or CO 2 at varying humidities and characterized by X-ray scattering, microscopy, and vibrational spectroscopy. Results show that the hydroxylation formed a brucite (Mg(OH) 2 )-like layer immediately after crystal cleaving. Concurrently, the carbonation formed hydrated magnesium carbonate phases, including barringtonite (MgCO 3 ·2H 2 O) and nesquehonite (MgCO 3 ·2H 2 O), in the layer. Rapid initial growth of the layer is also manifested in short-range bending/warping of nanocrystallites, resulting in multiple orientations of the same phases on the surface. The layer growth slowed down over time, indicating surface passivation. The formation of barringtonite and nesquehonite with 1:1 CO 3 /Mg ratio indicates an efficient carbonation when compared to other magnesium carbonate phases of lower ratio. Our results are essential for understanding surface passivation mechanisms and tackling the passivation issue of mineral looping DAC technology.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Coupling of Lipid Peroxidation and Criegee Intermediate Mediated Autoxidation in the Heterogeneous Oxidation of Linoleic Acid Aerosols

Autoxidation is an established mechanism for the degradation of organic molecules, which is relevant in the atmosphere, combustion processes, the environment, and the rancidification of lipids (commonly known as lipid peroxidation). Autoxidation proceeds via radical chain reactions involving hydroxyl (•OH), peroxy (RO2•), and alkoxy radicals, which are also prominent oxidants in the atmosphere. Recent reports have provided evidence for an alternative autoxidation mechanism driven instead by Criegee intermediates (CIs), which are produced from the reaction of β-hydroxy peroxy radicals (β-OH-RO2•). This work evaluates the contributions of these two mechanisms in the •OH initiated heterogeneous oxidation of linoleic acid (LA) aerosols. Reaction kinetics and product distributions are monitored using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. To explain the observed kinetics, a kinetic model is developed that incorporates both the conventional peroxidation and alternative CI-mediated autoxidation mechanisms. We observe that the CI-mediated autoxidation pathways enhance the heterogeneous autoxidation rate, while the peroxidation reactions, although present, contributes less to the overall oxidation rate. α-Acyloxyalkyl hydroperoxides (AAHPs) are identified as key indicators for bimolecular reactions of CI with LA, highlighting the role of LA as a CI scavenger. Moreover, the measured functionalized LA products with hydroxyl or carbonyl group(s), serve as markers for the peroxidation reactions. In summary, this work presents a quantitative framework to understand the coupled reaction network of •OH, RO2•, β-OH-RO2• radicals, and CI in driving heterogeneous autoxidation, which is crucial for understanding degradation mechanisms of organic molecules in the environment and atmosphere.

Criegee intermediate↗
DOE OSTI2020

Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes.

Superconcentrated aqueous electrolytes ("water-in-salt" electrolytes, or WiSEs) enable various aqueous battery chemistries beyond the voltage limits imposed by the Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored and could be better understood through added studies. Here, we report on our observations of strong acidity (pH 2.4) induced by lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at superconcentration (at 20 mol/kg). Multiple nuclear magnetic resonance (NMR) and pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations reveal that such acidity originates from the formation of nanometric ion-rich structures. The experimental and simulation results indicate the separation of water-rich and ion-rich domains at salt concentrations >= 5 m and the acidity arising therefrom is due to deprotonation of water molecules in the ion-rich domains. As such, the ion-rich domain is composed of hydrophobic -CF3 (of TFSI-) and hydrophilic hydroxyl (OH-) groups. At 20 m concentration, the tortuosity and radius of water diffusion channels are estimated to be similar to 10 and similar to 1 nm, respectively, which are close to values obtained from hydrated Nafion membranes that also have hydrophobic polytetrafluoroethylene (PTFE) backbones and hydrophilic channels consisting of SO3- ion cluster networks providing for the transport of ions and water. Thus, we have discovered the structural similarity between WiSE and hydrated Nafion membranes on the nanometer scale.

Han, Kee Sung↗
DOE OSTI2026

Insights into Rotational and Translational Dynamics in Mixtures of Ethylene Glycol and Choline Chloride Using Nuclear Magnetic Resonance Techniques

This work examines molecular dynamics and interactions in ethylene glycol–choline chloride (EG–ChCl) mixtures across 0–33 mol % ChCl, spanning the true eutectic region near 17–20 mol % and the commonly used 1:2 formulation. We combine pulsed-field-gradient (PFG) diffusion, fast-field-cycling (FFC) relaxometry, temperature-dependent 13 C T 1 , and nuclear Overhauser effect spectroscopy (NOESY) to disentangle local from macroscopic dynamics. PFG and FFC show that both translational and average rotational motions largely track the strong increase in viscosity with ChCl content, with ethylene glycol consistently diffusing faster than the choline cation and no global dynamical anomaly at the eutectic composition. More subtle, site-specific composition effects nevertheless emerge. The ratio of the diffusion coefficient of the hydroxyl group of choline to the diffusion coefficient of the methyl group of choline displays a shallow minimum in the 17–25 mol % region, indicating a modest change in how the hydroxyl-bearing end of choline samples the underlying translational motion relative to the methyl groups. 13 C T 1 analysis shows that rotational correlation times at 25 °C generally increase with ChCl, reflecting viscosity-coupled slowing, while the CH 2 –N α site exhibits a small but reproducible deviation from this monotonic trend near the eutectic. NOESY spectra at similar compositions reveal enhanced cross-relaxation between EG and choline protons, consistent with increased headgroup–solvent contact density rather than a wholesale structural rearrangement. Overall, our multitechnique study demonstrates that EG–ChCl dynamics are predominantly viscosity-dominated, with the eutectic region acting as a subtle dynamical crossover where specific choline segments become maximally coupled to the hydrogen-bond network. These insights refine the structure–dynamics picture of choline-chloride DESs and provide practical guidance for tuning composition in electrochemical, separation, and catalytic applications.

diffusion↗