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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Mechanistic mass transfer in hollow fiber membrane solvent extraction for bio-based isobutanol

Membrane solvent extraction (MSE) has emerged as a promising method for selectively recovering bioproducts from complex aqueous streams. Bio-isobutanol, a next-generation feedstock for biofuel, remains challenging to recover because of its low concentration and the presence of inhibitory substances. This study explores the potential of hollow fiber (HF) MSE for bio-isobutanol recovery and systematically examines the coupled effects of fiber packing, shell-side flow dynamics, and aqueous chemistry on performance. A resistance-in-series model is applied to understand mass transfer in the HF MSE modules, quantify local resistances, and validate overall performance. The results show that increasing the fiber packing provides a larger interfacial area but induces poor flow distribution and channeling, hindering effective isobutanol transport. Meanwhile, increasing the shell-side velocity improves isobutanol recovery due to reductions in the boundary layer thickness. The presence of salts, added to mimic fermentation broth, increases the partition coefficient through salting-out effects, further improving isobutanol flux. A modified correlation for the shell-side mass transfer coefficient (k s,ϕ+v ), integrating geometric and hydrodynamic effects, was developed and validated. The proposed model achieves highly predictive accuracy (r 2 = 0.9808) across a wide range of conditions, outperforming previous models. The findings provide mechanistic insight into the interaction of geometric packing, hydrodynamics, and chemistry in governing mass transfer in HF MSE. Overall, this work demonstrates the potential of HF MSE for efficient bio-isobutanol recovery and also provides practical guidelines on critical factors (packing fraction, partition coefficient, and shell-side velocity), aiding in the design and scaling of MSE systems for resource recovery.

Aqueous chemistry↗
DOE OSTI2021

Experimental and computational kinetics study of the liquid-phase hydrogenation of C=C and C=O bonds

Solvent effects on adsorption equilibrium and reaction kinetics are evaluated for hydrogenation reactions catalyzed by Pd/alumina in a series of different solvents. Three reactants – cyclohexene, benzene and benzaldehyde – and three solvents – n-heptane (HEP), methylcyclohexane (MCHA), decalin (DL) – have been investigated. Kinetic analysis of hydrogenation of cyclohexene reveals that hydrogen adsorbs on different sites from those where cyclohexene and the solvents adsorb; however, the presence of hydrogen on these separate sites affects the heats of adsorption of the hydrocarbons. When the solvent is a weakly interacting linear alkane (HEP), the rate determining step of the reaction is the first hydrogenation of adsorbed cyclohexene. Furthermore, this conclusion is supported by DFT calculations that show a higher enthalpy barrier for the first hydrogenation than for the second, while statistical thermodynamics analysis validates the physical significance of the entropy of adsorption parameters derived from the kinetic fitting of experimental data. By contrast, with solvents such as MCHA and DL, which interact more strongly with the metal surface and compete for active sites with the reactant and the surface intermediate, the rate limiting step seems to shift to the second hydrogenation step.

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

Exploring the Unusual Reactivity of the Hydrated Electron with CO 2

Many questions remain about the reactions of the hydrated electron despite decades of study. Of particular note is the fact that they do not appear to follow the Marcus theory of electron transfer reactions, a feature that has yet to be explained. To investigate these issues, we use ab initio molecular dynamics (AIMD) simulations to investigate a one of the better studied reactions, the hydrated electron reduction of CO 2 . The rate constant for the hydrated electron-CO 2 reaction complex to react to form CO 2 - is, for the first time, estimated from AIMD simulations. Results at 298 and 373 K show the rate constant is insensitive to temperature, consistent with the low measured activation energy for the reaction, and the implications of this behavior are examined. The sampling provided by the simulations yields insight into the reaction mechanism. The reaction is found to involve both solvent reorganization and changes in the carbon dioxide structure. The latter lead to significant vibrational excitation of the bending and symmetric stretch vibrations in the CO 2 - product, indicating the reaction is vibrationally nonadiabatic. The former is estimated from calculation of an approximate collective solvent coordinate and the free energy in this coordinate is determined. Furthermore, these results indicate that AIMD simulations can reasonably estimate hydrated electron reaction activation energies and provide new insight into the mechanism that can help illuminate the features of this unusual chemistry.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Sub-picosecond Production of Solute Radical Cations in Tetrahydrofuran after Radiolysis

Ultrafast hole transfer from solvent radical cations produced by radiolysis with ~10 ps, 9 MeV electron pulses to solutes was investigated in tetrahydrofuran (THF). Because of rapid fragmentation of initially produced THF +• , solute radical cations are not expected and have not previously been reported. Using 9,9-Dihexyl-2,7-dibromofluorene (Br 2 F) at 5 to 1000 mM, Br 2 F +• was observed with radiation chemical yields up to G = 2.23 / 100 eV absorbed. While more than half of this was the result of direct solute ionization, the results highlight the importance of capture of holes from THF +• prior to solvation and fragmentation. The observed data show a time-resolution limited (15 ps) rise in transient absorption of Br 2 F +• , identical in form to reports of pre-solvated or dry electron capture in water and a few organic liquids, including THF. The results were thus interpreted with a similar formalism, finding C 37 = 1.7 M, the concentration at which 37% of holes escape capture. The yield of solvent hole capture can be accounted for by the formation of solvent holes adjacent to solute molecules reacting faster than they can fragment, however mechanisms such as delocalized holes or rapid hopping may play a role. Finally, low temperature results find over two times more capture, supporting the speculation that if THF +• was longer lived, the yield of capture in under 15 ps would have been at least 2x larger at 1 M Br 2 F, possibly capturing nearly all available holes from the solvent.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Reactivity of Zn + aq in high-temperature water radiolysis

For this work, reactivity of transients involving Zn + in high-temperature water radiolysis has been studied in the temperature range of 25–300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn 2+ ions using pulse radiolysis. The Zn + species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, H 2 O 2 and ˙H. We find that the absorption of monovalent zinc is very sensitive to the pH of the medium. An absorption maximum at 306–311 nm is most pronounced at pH 7 and the signal then decreases in acidic media where the reducing electrons are competitively captured by protons. At pH values higher than 7, hydroxo-forms of Zn 2+ are created and the maximum of the absorption signal begins to shift to the red spectral region. We find that the optical spectrum of Zn + aq cannot be fully explained in terms of a charge-transfer to solvent (CTTS) process, which was previously proposed. Reaction rates of most of the recombination reactions investigated follow the empirical Arrhenius relationship at temperatures up to 200 °C and have been determined at higher temperatures for the first time. A bimolecular disproportionation reaction of Zn + aq is not observed under the conditions investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

On the mechanisms of ion adsorption to aqueous interfaces: air-water vs. oil-water

The adsorption of ions to water-hydrophobe interfaces influences a wide range of phenomena, including chemical reaction rates, ion transport across biological membranes, and electrochemical and many catalytic processes; hence, developing a detailed understanding of the behavior of ions at water-hydrophobe interfaces is of central interest. Here, we characterize the adsorption of the chaotropic thiocyanate anion (SCN − ) to two prototypical liquid hydrophobic surfaces, water-toluene and water-decane, by surface-sensitive nonlinear spectroscopy and compare the results against our previous studies of SCN − adsorption to the air-water interface. For these systems, we observe no spectral shift in the charge transfer to solvent spectrum of SCN − , and the Gibb’s free energies of adsorption for these three different interfaces all agree within error. We employed molecular dynamics simulations to develop a molecular-level understanding of the adsorption mechanism and found that the adsorption for SCN − to both water-toluene and water-decane interfaces is driven by an increase in entropy, with very little enthalpic contribution. This is a qualitatively different mechanism than reported for SCN − adsorption to the air-water and graphene-water interfaces, wherein a favorable enthalpy change was the main driving force, against an unfavorable entropy change.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Scalar rate correlation at a turbulent liquid free surface - A two-regime correlation for high Schmidt numbers

An experimental correlation is derived for gas absorption at a turbulent, shear-free liquid interface. The correlation is expressed in terms of the liquid-side turbulence intensity, liquid-side macroscale, and the properties of the diffusing gas and solvent. The transfer coefficient increases linearly with rms velocity up to a point where the eddy Reynolds number reaches a critical (Schmidt number dependent) value. At higher velocities, there is a more rapid linear rise. The slope of the lower Reynolds number region is proportional to the square root of the diffusivity; at Reynolds numbers much higher than that of the break point, the slope becomes independent of diffusivity.

Khoo, Boo-Cheong↗
NASA NTRS1982

Coal desulfurization

A method for enhancing solubilizing mass transport of reactive agents into and out of carbonaceous materials, such as coal. Solubility parameters of mass transfer and solvent media are matched to individual peaks in the solubility parameter spectrum of coals to enhance swelling and/or dissolution. Methanol containing reactive agent carriers are found particularly effective for removing organic sulfur from coals by chlorinolysis.

Corcoran, William H.↗
NASA NTRS2016

Correlation of Spectral and Electrochemical Properties of a Series of Ferrocene Derivatives

Charge-transfer-to-solvent (CTTS) bands are observed in the UV/VIS spectra of a series of ferrocene derivatives (ferrocene; 1,1’-dimethyl; 1,2,3,4,5-pentamethyl; 1,2,3,4,l’,2’,3’,4’-octamethyl; and decamethyl) by the addition of increasing amounts of CCl4 to ethanol solutions. A linear correlation (slope = 8540 per cm/V) was found between the redox potential and the energy of the CTTS band, consistent with electrochemical and photochemical oxidation by removal of an electron from the same molecular orbital. Inclusion of literature data for ruthenocene and [(η^(5)-C5H5)Fe(CO)]4 results in a line with a slope of 8140 per cm/V, within 1 percent of the wavenumber to electron volt conversion factor. Calculation of association constants (K) shows a slight decrease (1.2 to 0.7 per mole fraction) as the bulkiness of the cyclopentadienyl ring increases, consistent with either a steric or a repulsive electronic effect. The extinction coefficient of the CTTS absorption was constant at approximately 1700 per Mcm .

ultraviolet spectroscopy↗
DOE OSTI2020

CO2 mass transfer enhancement of aqueous amine solvents by particle additives

The present invention relates to methods for improving carbon capture by providing particles within an amine solvent. The particles provide for increased turbulence at the interface between the counter-flowing gas and solvent, which allows for increased amine and carbamate salt diffusion between the liquid film and bulk.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Polymer nanoparticle photocatalysts realized in non-aqueous solvents

Colloidal organic nanoparticles (oNPs) have emerged as a promising category of photocatalyst, thanks to their long-lived surface-bound charges, electronic tunability, and strong absorption in the visible spectrum. Our previous research has established a direct correlation between charge generation in oNPs and their photocatalytic activity, highlighting their effectiveness as a framework for stable, long-lived free carriers. However, oNPs have been restricted to use only in aqueous environments as a result of being synthesized via either nano-emulsion or nano-precipitation procedures. Herein, we present a method for transferring oNP photocatalysts from water into polar non-aqueous solvents while retaining their long-term colloidal stability. We observed that the polymer chains in the solvent-transferred oNPs rearrange from a predominantly H-aggregate structure in water to a combination of H- and J-aggregate characteristics in N,N-dimethylformamide, suggesting a dynamic rearrangement in response to the new solvent environment. Importantly, transient absorption and time-resolved microwave conductivity measurements confirm that the solvent-transferred oNPs maintain their ability to generate free charges at an internal heterojunction. This development opens unique opportunities for eventually leveraging light-generated, long-lived electrons and holes in synthetic redox chemistry across diverse solvent environments, a direction that will be explored in future studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

Santos, Javier↗
DOE OSTI2025

A Theory of Ultrafast Charge Transfer Relaxation with Non-Innocent Solvent Molecules

In this work we revisit the photodynamics of tetracyanoethylene-hexamethylbenzene (TCNE- HMB), the molecular complex studied by Hochstrasser et al. [J. Chem. Phys. 100, 4797–4810, 1994] that has long challenged the applicability of Marcus’s theory of elec- tron transfer for predicting photochemical reactions. Using a novel black-box electronic structure algorithm (time-dependent density functional theory with one double, TD- DFT-1D) to efficiently run molecular dynamics that can treat charge recombination, we run ab initio surface hopping molecular dynamics and confirm that, for a polar solvent, charge recombination rates can be incredibly fast (indeed faster than the sol- vent relaxation time); for non-polar solvents, the rate is much slower. We demonstrate that, although Marcus theory cannot be directly applied, these nonequilibrium (and sometimes incredibly fast) photoexcited dynamics can be effectively explained within a two-state model without any evidence of a transition through a conical intersection. Most importantly, for this paradigmatic model system, we are able to identify two nuclear coordinates of interest (rather than the single coordinate predicted by Marcus or a full set of internal quantum modes studied by Bixon and Jortner): the solvent relaxation in the first shell (that strongly modulates the energies of the charge trans- fer state and differentiates time scales for relaxation) and a nuclear displacement in the TCNE-HMB complex arising from a handful of vibrations that induces non-Born Oppenheimer motion and eventually facilitates an abrupt electronic transition to the ground state. Altogether, these findings suggest a tractable generalization of Marcus theory for future simulations of photochemistry with non-innocent solvent environ- ments in the spirit of a Hamiltonian suggested by Stuchebrukhov (J. Chem. Phys. 107, 3821, 1997).

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

Isoenergetic two-photon excitation enhances solvent-to-solute excited-state proton transfer

Two-photon excitation (TPE) is an attractive means for controlling chemistry in both space and time. Since isoenergetic one- and twophoton excitations (OPE and TPE) in non-centrosymmetric molecules are allowed to reach the same excited state, it is usually assumed that they produce similar excited-state reactivity. We compare the solvent-to-solute excited-state proton transfer of the super photobase FR0-SB following isoenergetic OPE and TPE. We find up to 62% increased reactivity following TPE compared to OPE. From steady-state spectroscopy, we rule out the involvement of different excited states and find that OPE and TPE spectra are identical in non-polar solvents but not in polar ones. We propose that differences in the matrix elements that contribute to the two-photon absorption cross sections lead to the observed enhanced isoenergetic reactivity, consistent with the predictions of our high-level coupledcluster-based computational protocol. We find that polar solvent configurations favor greater dipole moment change between ground and excited states, which enters the probability for TPE as the absolute value squared. This, in turn, causes a difference in the Franck– Condon region reached via TPE compared to OPE. We conclude that a new method has been found for controlling chemical reactivity via the matrix elements that affect two-photon cross sections, which may be of great utility for spatial and temporal precision chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanisms and Energetics of CO 2 Chemisorption in Choline-Based Eutectic Solvents

Understanding the influences of proton sharing and hydrogen transfer in amine and hydroxyl functionalized eutectic solvents is important for tuning CO 2 binding as they relate to the chemisorption capacity and energetics of solvent regeneration in carbon capture. In this study, we examine how the CO 2 binding mechanism and energetics vary in eutectic solvents composed of choline-based hydrogen-bond acceptors (HBAs) with amine and hydroxyl moieties and ethylene glycol (EG), propylene glycol (PG), 1,2-butanediol (BD), and monoethanolamine (MEA)-type hydrogen-bond donors (HBDs), through absorption–desorption experiments and spectral analysis, supported with density functional theory (DFT) calculations. While the HBD-CO 2 complex is the major and the thermodynamically more favored product of absorption in all of the examined eutectic solvents, this complexation is only possible proceeding a proton transfer from HBD to the HBA in diol-based systems (EG, PG, BD). The interplay between HBA-CO 2 and HBD-CO 2 speciation is governed by the HBD concentration, basicity, and steric effects, with increased HBD-CO 2 interactions in the presence of smaller HBDs (size: BD > PG > EG). On the other hand, in MEA-based systems, CO 2 readily binds to the amine followed by a proton transfer from the amine to the HBA as confirmed by DFT calculations. In this way, the MEA-CO 2 chemisorption capacities exceeded that of the conventional amine (up to 0.93 mol of CO 2 per mol of MEA versus 0.5). Furthermore, the increase in CO 2 capacities and enhanced binding in eutectics including MEA or the more basic HBAs also resulted in regeneration temperatures of 70 to 60 °C with calculated reaction energies of −82 to −57 kJ/mol, compared to 50 °C for others with weaker binding, following CO 2 absorption at 25 °C.

absorption↗