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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Synthesis and Electrochemical Behavior of Electron-Rich s-Tetrazine and Triazolo-tetrazine Nitrate Esters

Here, we have prepared energetic nitrate ester derivatives of 1,2,4,5-tetrazine and 1,2,4-triazolo[4,3-b]-[1,2,4,5]-tetrazine ring systems as model compounds to study the electrochemical behavior of tetrazines in the presence of explosive groups. The model compounds showed lower thermal stabilities relative to PETN (pentaerythritol tetranitrate), but slightly improved mechanical sensitivities. The presence of electron-rich amine donors leads to a cathodic shift of the tetrazine redox potentials relative to those of previously reported tetrazine explosives. At these potentials, electron-rich tetrazines with either covalently bound or co-dissolved nitrate ester groups are irreversibly reduced. Effectively, changes in the electronic structure of tetrazines affect their electrochemical response to the presence of nitrate ester groups. Thus, it may be possible to develop tetrazine-based electrochemical sensors for the detection of specific explosives and electrocatalysts for their disposal.

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

The Behavior of the Ru-bda Water Oxidation Catalysts at Low Oxidation States

The Ru complex [Ru II (bda-κ-N 2 O 2 )(N-NH 2 ) 2 ], 1, (bda 2- = (2,2'-bipyridine)-6,6'-dicarboxylate; N-NH 2 = 4-(pyridin-4-yl)aniline) is used as a synthetic intermediate to prepare Ru-bda complexes that contain the NO + , acetonitrile (MeCN) or H 2 O ligands at oxidation states II and III. Complex 1 reacts with excess NO + to form a Ru complex where the aryl amine ligands N-NH 2 in 1 are transformed into diazonium salts (N-N 2 + = 4-(pyridin-4-yl)benzenediazonium)) together with the formation of a new Ru-NO group at the equatorial zone, to generate [Ru II (bda-κ-N 2 O)(NO)(N-N 2 ) 2 ] 3+ , 2 3+ . Similarly, complex 1 can also react with a coordinating solvent, such as MeCN, at room temperature leading to complex [Ru II (bda-κ-N 2 O)(MeCN)(N-NH 2 ) 2 ], 3. Finally in acidic aqueous solutions solvent water coordinates the Ru center forming {[Ru II (bda-κ-(NO) 3 )(H 2 O)(N-NH 3 ) 2 ](H 2 O) n } 2+ , 4 2+ , that is strongly hydrogen bonded with additional water molecules at the second coordination sphere. We have additionally characterized the one electron oxidized complex {[Ru III (bda-κ-(NO) 3.5 )(H 2 O)(N-NH 3 ) 2 ](H 2 O) n } 3+ , 5 3+ . The coordination mode of the complexes has been studied both in the solid state and in solution through single-crystal XRD, X-ray absorption spectroscopy, variable-temperature NMR and DFT calculations. While the κ-N 2 O is the main coordination mode for 2 3+ and 3, an equilibrium that involves isomers with κ-N 2 O and κ-NO 2 coordination modes and neighboring hydrogen bonded water molecules is observed for 4 2+ and 5 3+ .

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

Reversible Photoswitching in Poly(2-oxazoline) Nanoreactors

This contribution reports light responsive catalytic nanoreactors based on poly(2-oxazoline) diblock copolymers. The hydrophobic block of the copolymer is a random copolymer consisting of a spiropyran functionalized 2-oxazoline (SPOx) and 2-(but-3-yn-1-yl)-4,5-dihydrooxazole (ButynOx), while the hydrophilic block is based on 2-methyl-2-oxazoline (MeOx). The block copolymer is terminated with tris(2-aminoethyl) amine (TREN) that serves as catalyst in a Knoevenagel condensation. Four block copolymers with different ButynOx/SPOx and hydrophilic/hydrophobic ratios are synthesized and self-assembled through solvent exchange. Micelles and vesicles of various sizes are observed by TEM, which undergo morphological and size changes in response to irradiation with UV light. We hypothesize that these transformations in the nanostructures are caused by increases in the hydrophilicity of the hydrophobic block when spiropyran (SP) isomerizes to merocyanine (MC) in the presence of UV light. The reversible transition from micellar to vesicular nanoreactors resulted in increased reaction kinetics through improved substrate accessibility to the catalytic site, or termination of the catalytic reaction due to polymer precipitation. Furthermore, these nanoreactors present a promising platform towards photoregulating reaction outcomes based on changes in nanostructure morphology.

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

Hydrazone-Linked Heptazine Polymeric Carbon Nitrides for Synergistic Visible-Light-Driven Catalysis

Heptazine-based conjugated polymeric carbon nitrides (PCNs) are promising metal-free photocatalysts, yet their synthesis is challenging due to the electron-deficiency and insolubility of heptazine units. Indeed, heptazine-containing polymers have only been prepared through nucleophilic substitution with amines by using toxic cyameluric chloride as the starting material. Herein, we report the novel and environmentally friendly method for preparing heptazine-based mesoporous PCNs with hydrazone links formed through a simple Schiff base condensation of melem-NH 2 and aldehydes. Unlike cyameluric chloride, melem-NH 2 is non-toxic, stable, and can be readily obtained from melem and hydrazine in solution. We demonstrate that the hydrazone linkages and the heptazine units synergistically enhance the photocatalytic activity of PCNs in visible-light-driven aerobic oxidation of benzyl alcohol to benzaldehyde. In particular, the polymer constructed from melem-NH2 and p-phthalaldehyde shows 17 times more activity than graphitic carbon nitride (g-C 3 N 4 ).

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

In Silico Screening of CO 2 –Dipeptide Interactions for Bioinspired Carbon Capture

Carbon capture, sequestration and utilization offers a viable solution for reducing the total amount of atmospheric CO 2 concentrations. On an industrial scale, amine-based solvents are extensively employed for CO 2 capture through chemisorption. Nevertheless, this method is marked by the high cost associated with solvent regeneration, high vapor pressure, and the corrosive and toxic attributes of by-products, such as nitrosamines. An alternative approach is the biomimicry of sustainable materials that have strong affinity and selectivity for CO 2 . Bioinspired approaches, such as those based on naturally occurring amino acids, have been proposed for direct air capture methodologies. In this study, we present a database consisting of 960 dipeptide molecular structures, composed of the 20 naturally occurring amino acids. Furthermore, those structures were analyzed with a novel computational workflow presented in this work that considers certain interaction sites that determine CO 2 affinity. Density functional theory (DFT) and symmetry-adapted perturbation theory (SAPT) computations were performed for the calculation of CO 2 interaction energies, which allowed to limit our search space to 400 unique dipeptide structures. Using this computational workflow, we provide statistical insights into dipeptides and their affinity for CO 2 binding, as well as design principles that can further enhance CO 2 capture through cooperative binding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Reinventing Design Principles for Developing Low-Viscosity Carbon Dioxide-Binding Organic Liquids for Flue Gas Clean Up

Anthropogenic carbon dioxide (CO 2 ) emission from point sources, such as coal fired-power plants, account for the majority of the green houses gasses in the atmosphere. Capture, storage and utilization are required to mitigate adverse environmental effects. Aqueous amine-based CO 2 capture solvents are currently considered the industry standard, but deployment to market is limited by their high regeneration energy demand. In that context, energy efficient and less-viscous water-lean transformational solvent systems known as CO 2 Binding Organic Liquids (CO 2 BOLs) are being developed in our group to advance this technology to commercialization. Herein, we present a logical design approach based on fundamental concepts of organic chemistry and computer simulations aimed at lowering solvent viscosity. Conceptually, viscosity reduction would be achieved by systemmatic methods such as introduction of steric hindrance on the anion to minimize the intermolecular cation-anion interactions, fine tuning the electronics, hydrogen bonding orientation and strength, and charge solvation. Conventional standard trial-and-error approaches while effective, are time consuming and economically expensive. Herein, we rethink the metrics and design principles of low-viscosity CO 2 capture solvents using a combined synthesis and computational modeling approach. We critically study the impacts of modyfying factors such as as orientation of hydrogen bonding, introduction of higher degrees of freedom and cation or anion charge solvation and assess if or how each factor impacts viscosity of CO 2 BOL CO 2 capture solvents. Ultimately, we found that hydrogen bond orientation and strength is predominantly influencing the viscosity in CO 2 BOL solvents. With this knowledge, a new 1-MEIPADM-2-BOL CO 2 BOL variant was synthesized and tested, resulting in a solvent that is approximately 60% less viscous at 25 mol% CO 2 loading with respect to our base compound 1-IPADM-2-BOL. The insights gained from the current study redefines the fundamental concepts and understanding of what influences viscosity in concentrated organic CO 2 capture solvents.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Divergent C–H Amidations and Imidations by Tuning Electrochemical Reaction Potentials

Electrochemical C–H functionalizations are attractive transformations, as they are capable of avoiding the use of transition metals, pre-oxidized precursors, or suprastoichiometric amounts of terminal oxidants. Herein an electrochemically tunable method was developed that enabled the divergent formation of cyclic amines or imines by applying different reaction potentials. Detailed cyclic voltammetry analyses, coupled with chronopotentiometry experiments, were carried out to provide insight into the mechanism, while atom economy was assessed through a paired electrolysis. Finally, selective C–H amidations and imidations were achieved to afford five- to seven-membered sulfonamide motifs that could be employed for late-stage modifications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

High-Performance CO 2 Capture from Air by Harnessing the Power of CaO- and Superbase-Ionic-Liquid-Engineered Sorbents

Direct air capture (DAC) of CO 2 by solid porous materials represents an attractive “negative emission” technology. However, state-of-the-art sorbents based on supported amines still suffer from unsolved high energy consumption and stability issues. For this work, taking clues from the CO 2 interaction with superbase-derived ionic liquids (SILs), high-performance and tunable sorbents in DAC of CO 2 was developed by harnessing the power of CaO- and SIL-engineered sorbents. Deploying mesoporous silica as the substrate, a thin CaO layer was first introduced to consume the surface-OH groups, and then active sites with different basicities (e. g., triazolate and imidazolate) were introduced as a uniformly distributed thin layer. The as-obtained sorbents displayed high CO 2 uptake capacity via volumetric (at 0.4 mbar) and breakthrough test (400 ppm CO 2 source), rapid interaction kinetics, facile CO 2 releasing, and stable sorption/desorption cycles. Operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) analysis under simulated air atmosphere and solid-state NMR under 13 CO 2 atmosphere demonstrated the critical roles of the SIL species in low-concentration CO 2 capture. The fundamental insights obtained in this work provide guidance on the development of high-performance sorbents in DAC of CO 2 by leveraging the combined advantages of porous solid scaffolds and the unique features of CO 2 -philic ionic liquids.

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

Evaluation of Aliphatic Alcohols for CO 2 Capture Using the Characteristic Carbonate Frequency

Control over CO 2 capture and utilization are important scientific and technological challenges. Although a variety of amine absorbents are used for capture, releasing the captured CO 2 is often difficult and limits their recyclability. Therefore, it is crucial to control the strength of the CO 2 bond with the absorbent. Furthermore, it is desirable to use a method that can conveniently report the strength of this bond. This motivates exploring adducts of CO 2 with alcohols in the presence of a base, using vibrational spectroscopy to report on the bond strength. Although reactions of alcohols with CO 2 to form alkyl carbonates are known, a systematic study of these adducts has not been conducted. Here we show formation of alkyl carbonates by a series of alcohols spanning the pK a range 9.5 to 16.8. We show experimental and computational results for the frequency of the characteristic asymmetric stretch of the carbonate and demonstrate that it correlates inversely with the pK a of the alcohol. Based on computations of the bond lengths and previous work, we propose that this frequency also correlates inversely with the adduct strength. As a result, this work extends the scope of CO 2 capture reagents and inspires further research in tuning alcohols as reversible absorbents.

Alcohols↗
DOE OSTI2025

Electrocatalytic CN Coupling: Advances in Urea Synthesis and Opportunities for Alternative Products

Urea is an essential fertilizer produced through the industrial synthesis of ammonia (NH 3 ) via the Haber–Bosch process, which contributes ≈1.2% of global annual CO 2 emissions. Electrocatalytic urea synthesis under ambient conditions via CN coupling from CO 2 and nitrogen species such as nitrate (NO 3 − ), nitrite (NO 2 − ), nitric oxide (NO), and nitrogen gas (N 2 ) has gained interest as a more sustainable route. However, challenges remain due to the unclear reaction pathways for urea formation, competing reactions, and the complexity of the resulting product matrix. This review highlights recent advances in catalyst design, urea quantification, and intermediate identification in the CN coupling reaction for electrocatalytic urea synthesis. Furthermore, this review explores future prospects for industrial CN coupling, considering potential nitrogen and carbon sources and examining alternative CN coupling products, such as amides and amines.

Chemistry↗
DOE OSTI2025

Closed‐Loop Recyclable Vitrimer Plastics from PET Waste: A Design for Circularity

Plastics are essential to modern society, but their low recycling rates and inefficient end-of-life management pose a significant environmental challenge. Herein, the efficient strategy for upcycling postconsumer poly(ethylene terephthalate) (PET) waste into robust, closed-loop recyclable vitrimer plastics and composites is presented to address this issue. The catalyst-free aminolysis utilizes readily available amines to deconstruct diverse PET wastes into macromonomers, which are upcycled into vitrimers, exhibiting superior mechanical properties and exceeding the ultimate tensile stress and Young's Modulus of virgin PET by 80% and 150% respectively. These vitrimers exhibit excellent healability, shape memory, thermal reprocessability, and closed-loop chemical recyclability, enabling quantitative macromonomer recovery even from mixed plastic waste streams and glass/carbon fiber reinforced vitrimer (G/CFRV) composites. Furthermore, the vitrimer resin yields robust GFRV and CFRV composites with tensile strengths exceeding those of traditional epoxy composites by 100% and 80%, respectively, while maintaining complete chemical recyclability of both constituent materials. A preliminary technoeconomic analysis confirms the costeffectiveness and competitiveness of the facile PET deconstruction approach, which is potentially adaptable to other condensation polymers. Further, this study presents a facile approach to upcycling plastic waste into circular plastics and composites, offering a sustainable solution to global plastic waste management and fostering a circular economy.

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

Multielectron Redox Chemistry of Transition Metal Complexes Supported by a Non-Innocent N 3 P 2 Ligand: Synthesis, Characterization, and Catalytic Properties

A new redox-active, diarylamido-based ligand (L N3P2 ) capable of κ 5 -N,N,N,P,P chelation has been used to prepare a series of complexes with the general formula [M II (L N3P2 )]X, where M = Fe (1; X = OTf), Co (2; X = ClO 4 ), or Ni (3; X = ClO 4 ). The diarylamido core of monoanionic L N3P2 is derived from bis(2-amino-4-methylphenyl)amine, which undergoes condensation with two equivalents of 2-(diphenylphosphanyl)benzaldehyde to provide chelating arms with both arylphosphine and imine donors. X-ray structural, magnetic, and spectroscopic studies indicate that the N 3 P 2 coordination environment generally promotes low-spin configurations. Three quasi-reversible redox couples between +1.0 and –1.5 V (vs. Fc + /Fc) were observed in voltammetric studies of each complex, corresponding to M II /M III oxidation, L N3P2 -based oxidation, and MII/MI reduction (in order of highest to lowest potential). Spectroscopic and computational analyses of 3 ox – generated via chemical one-electron oxidation of 3 – revealed that a stable diarylaminyl radical (L N3P2· ) is formed upon oxidation. The ability of the Co II complex (2) to function as an electrocatalyst for H 2 generation was evaluated in the presence of weak acids. Moderate activity was observed using 4-tert-butylphenol as the proton source at potentials below –2.0 V. The insights gained here will assist in the future design of pentadentate mixed N/P-based chelates for catalytic processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis, Characterization, and HER Activity of Pendant Diamine Derivatives of NiATSM

A pair of bis-thiosemicarbazonato-Ni(II) complexes with pendant polyamines, (N,N'-(dimethylethylenediaminothiosemi-carbazonato)-4-(methylthiosemi-carbazonato)butane-2,3-diimine)-nickel(II) (1) and (N,N'-bis(dimethylethyl-enediaminothiosemi-carbazonato)butane-2,3-diimine)-nickel(II) (3), have been synthesized. Methylation at the terminal amines yields the cationic derivatives 2 and 4. All complexes are fully characterized by spectroscopic, electrochemical, and single-crystal X-ray diffraction methods. Single crystal X-ray diffraction studies on all four Ni(II) complexes confirm a square planar Ni(II) framework with no significant changes in the coordination environment as a function of the pendant groups. Spectroscopic studies are consistent with a similar electronic structure in all complexes. However, electrochemical investigations reveal significant cathodic shifts in the Ni(II)L/Ni(II)L ·– and Ni(II)L ·– /Ni(I)L ·2– reduction potentials of the methylated vs. non-methylated species. The HER activity of all four nickel complexes were evaluated in acetonitrile with glacial acetic acid. The 3 complex was shown to have the highest activity with a TOF of 6.3 × 10 3 s -1 , an overpotential of 0.56 V, and faradaic efficiency of 100%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Construction of the Bioconjugate Py‐Macrodipa‐PSMA and Its In Vivo Investigations with Large 132/135 La 3+ and Small 47 Sc 3+ Radiometal Ions

To harness radiometals in clinical settings, a chelator forming a stable complex with the metal of interest and targets the desired pathological site is needed. Toward this goal, we previously reported a unique set of chelators that can stably bind to both large and small metal ions, via a conformational switch. Within this chelator class, py-macrodipa is particularly promising based on its ability to stably bind several medicinally valuable radiometals including large 132/135 La 3+ , 213 Bi 3+ , and small 44 Sc 3+ . Here, in this study, we report a 10-step organic synthesis of its bifunctional analogue py-macrodipa-NCS, which contains an amine-reactive −NCS group that is amenable for bioconjugation reactions to targeting vectors. The hydrolytic stability of py-macordipa-NCS was assessed, revealing a half-life of 6.0 d in pH 9.0 aqueous buffer. This bifunctional chelator was then conjugated to a prostate-specific membrane antigen (PSMA)-binding moiety, yielding the bioconjugate py-macrodipa-PSMA, which was subsequently radiolabeled with large 132/135 La 3+ and small 47 Sc 3+ , revealing efficient and quantitative complex formation. The resulting radiocomplexes were injected into mice bearing both PSMA-expressing and PSMA-non-expressing tumor xenografts to determine their biodistribution patterns, revealing delivery of both 132/135 La 3+ and 47 Sc 3+ to PSMA+ tumor sites. However, partial radiometal dissociation was observed, suggesting that py-macrodipa-PSMA needs further structural optimization.

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

Elucidating the Structure of the Eu‐EDTA Complex in Solution at Various Protonation States

Abstract Ethylenediaminetetraacetic acid (EDTA), which has two amine and four carboxylate protonation sites, forms stable complexes with lanthanide ions. This work analyzes the coordination structure, in atomic resolution, of the Eu 3+ ion complexed with EDTA in all its protonation states in aqueous solution. Eu‐EDTA complexes were modeled using classical molecular dynamics (MD) simulations using force field parameters optimized with ab initio molecular dynamics (AIMD) simulations. Structures from the MD simulations were used to predict extended X‐ray absorption fine structure (EXAFS) spectra and compared with EXAFS measurements of the Eu 3+ aqua ion and Eu‐EDTA complexes at pH 3 and 11. This work details how Eu‐EDTA complex coordination structures change with increasing protonation of the EDTA ligand in the complex, from the tightly bound unprotonated complex to the unbinding of the fully protonated EDTA ligand from the Eu 3+ ion as both become solvated by water. Agreement between predicted and measured EXAFS spectra supports the findings from simulation.

Chemistry↗