Search NASA⌕ Search

SEARCH · Search NASA

Results for “synthesis (scalable processing)”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Exploring the Acid Gas Sorption Properties of Oxidatively Degraded Supported Amine Sorbents

Amine-supported mesoporous oxide materials have proven to be effective acid gas sorbents. While the primary application of these supported amine species has been CO 2 capture, they have also shown to be proficient at adsorbing other damaging flue gas impurities such as SO x and NO x . The precise nature of the amine (primary, secondary, or tertiary) is known to dictate the gas–amine interactions, with tertiary amines of particular interest due to their inability to adsorb dry CO 2 , favoring SO x and NO x species. The different amine sites also provoke differences in oxidative stability, when exposed to temperatures similar to those used for thermal desorption procedures. Herein we focus on the structural and chemical changes that occur in a range of class 1 (amine-impregnated) and class 2 (amine-grafted) sorbents upon oxidation and correlate these with their variation in acid gas (CO 2 , NO 2 , and SO 2 ) uptakes, as a function of the oxidation temperature. These studies suggest that oxidatively degraded or “spent” supported amine materials may have possible uses as NO x or SO x sorbents. Specifically, despite oxidative degradation these aminopolymer species maintain a reasonable level of NO 2 uptake, despite losing the ability to capture SO 2 or CO 2 , offering unique possibilities in selective NO 2 capture.

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

Efficient U(VI) Reduction and Sequestration by Ti 2 CT x MXene

Although reduction of highly mobile U(VI) to less soluble U(IV) has been long considered an effective approach to in situ environmental remediation of uranium, candidate reducing agents are largely limited to Fe-based materials and microbials. The importance of titanium-containing compounds in natural uranium ore deposits suggests a role for titanium in uranium migration. In this report, for the first time, a two-dimensional transition metal carbide, Ti 2 CT x , is shown to efficiently remove uranium via a sorption-reduction strategy. Batch experiments demonstrate that Ti 2 CT x exhibits excellent U(VI) removal over a wide pH range, with an uptake capacity of 470 mg g –1 at pH 3.0. The mechanism for U(VI) to U(IV) reduction by Ti 2 CT x was deciphered by X-ray absorption spectroscopy and diffraction and photoelectron spectroscopy. The reduced U(IV) species at low pH is identified as mononuclear with bidendate binding to the MXene substrate. At near-neutral pH, nanoparticles of the UO 2+x phase adsorb to the substrate with some Ti 2 CT x transformed to amorphous TiO 2 . A subsequent in-depth study suggests Ti 2 CT x materials may be potential candidates for permeable reactive barriers in the treatment of wastewaters from uranium mining. Finally, this work highlights reduction-induced immobilization of U(VI) by Ti 2 CT x MXene including a pH-dependent reduction mechanism that might promote applications of titanium-based materials in the elimination of other oxidized contaminants.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Kinetic Studies of Acid Hydrolysis of Food Waste-Derived Saccharides

Starch saccharified glucose from food waste can be an important precursor for renewable chemicals and fuels. Despite numerous studies on hydrolysis of biomass, detailed kinetic studies and associated models of hydrolysis are lacking. We investigated the kinetics of glycosidic bond scission of malto-oligosaccharides in lithium bromide acidified molten salt hydrate (AMSH) medium and estimated rate parameters from experimental data. Our data support the hypothesis that the terminal, nonreducing bonds hydrolyze faster than the interior and terminal-reducing C–O bonds. Next, we extended the model to simulate the hydrolysis of linear and cyclic saccharides of varying degree of polymerization and of potato starch. We characterize starch using X-ray diffraction (XRD) and light scattering methods. The model is in excellent agreement with the experimentally determined concentrations of glucose and other oligosaccharides. Finally, the chain length of saccharides is found to be directly related to their hydrolysis rate constant, but inversely proportional to the glucose formation rate constant

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Properties of Cerium Hydroxides from Matrix Infrared Spectra and Electronic Structure Calculations

Reactions of laser ablated cerium atoms with hydrogen peroxide or hydrogen and oxygen mixtures diluted in argon and condensed at 4 K produced the Ce(OH) 3 and Ce(OH) 2 molecules and Ce(OH) 2 + cation as major products. Additional minor products were identified as the Ce(OH) 4 , HCeO, and OCeOH molecules. These new species were identified from their matrix infrared spectra with D 2 O 2 , D 2 , and 18 O 2 isotopic substitution and correlating observed frequencies with values calculated by density functional theory. We find that the amounts of Ce(OH) 3 and of the Ce(OH) 2 + cation increase on UV ($λ$ > 220 nm) photolysis, while Ce(OH) 2 , Ce(OH) 4 , and HCeO are photosensitive. The observed major species for Ce are in the +III or +II oxidation state, and the minor product, Ce(OH) 4 , is in the +IV oxidation state. The calculations for the vibrational frequencies with the B3LYP functional agree well with the experiment. The NBO analysis shows significant backbonding to the metal 4f and 5d orbitals for the closed shell species. Most open shell species have the excess spin in the 4f with paired spin in the 5d due to backbonding. The heats of formation of the observed species were derived from the available data from experiment and the calculated reaction energies. The major products in this study are different from similar reactions for Th where the tetrahydroxide was the major species.

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

Synthesis and Crystal Structure of the Layered Lanthanide Oxychlorides Ba 3 Ln 2 O 5 Cl 2

Single crystals of a new family of layered lanthanide oxychlorides, Ba 3 Ln 2 O 5 Cl 2 (Ln = Gd–Lu), have been synthesized from a molten barium flux. This family crystallizes in the space group I4/ mmm (No. 139; Z = 2) with lattice parameters a = 4.3384(1)–4.4541(1) Å and c = 24.5108(7)–24.8448(9) Å. Ba 3 Ln 2 O 5 Cl 2 phases are built up of two different blocks: a perovskite double layer of stoichiometry Ba 2 Ln 2 O 5 formed by corner-connected LnO 5 tetragonal bipyramids and a puckered rock-salt-like interlayer of composition BaCl 2 . A complete structural study along with bond-valence-sum calculations shows that, for lanthanides larger than gadolinium, the structure becomes unstable. Density functional theory calculations show that the valence-band edge is dominated by oxygen orbitals, whereas the conduction band forms from Ba 5d orbitals. Finally, the synthesis of this family suggests a route to other potential multianion phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental and Theoretical Comparison of Transition-Metal and Actinide Tetravalent Schiff Base Coordination Complexes

A series of homoleptic tetravalent transition-metal and actinide Schiff-base coordination complexes, ML 2 {M = Zr, Hf, Th, U; L = N,N'-bis[(4,4'-diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized that feature a rigid phenyl backbone. These complexes create the opportunity for comparing a series of complexes containing metal cations in the formal IV+ oxidation state by structural, spectroscopic, and theoretical analysis that also incorporate the previously reported Ce(IV) and Pu(IV) analogues. X-ray crystallographic analysis reveals that all complexes are isomorphous and feature a co-facial ligand geometry. TD-DFT and other quantum mechanical methods were used to explore bonding differences across between the complexes, and resulting calculated absorbance spectra for ML 2 are in good agreement with the experimental data. The computational results also suggest that U(IV) and Pu(IV) analogs have more covalent character in their bonding than found with the other metal cations reported here.

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

Electronic, Magnetic, and Theoretical Characterization of (NH 4 ) 4 UF 8 , a Simple Molecular Uranium(IV) Fluoride

The simple system of tetraammonium octafluorouranate is employed to derive a fundamental understanding of the uranium–fluorine interaction. The structure is composed of isolated molecules, enabling a detailed examination of the U 4+ (ƒ 2 ) ion. Characterization of single-crystals by X-ray diffraction, absorption spectroscopy, and magnetic analysis up to 45 T is combined with extensive theoretical treatment by CASSCF. The influence of different active spaces and representations of the structure is examined in the context of the experimental evidence. The Interacting Quantum Atoms method (IQA) is used to examine the nature of the U–F bond, concluding that there is a non-negligible degree of covalent character (9% of the total bond energy) in [UF8] 4- . For the structural and theoretical reasons discussed herein, it is proposed that the structure of (NH 4 ) 4 UF 8 may be appropriately employed as a benchmark compound for future theoretical characterization of U(IV).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Tailored Perovskite Waste Forms for Plutonium Trapping

Perovskite ceramics have been extensively studied as host matrixes for radionuclide entrapment for nuclear waste disposal. As an expansion of these investigations, cerium, neodymium, and plutonium were incorporated into a perovskite phase, ACu 3 FeTi 3 O 12 (A = Nd, Ce, Pu), using sol–gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce 3+ and Nd 3+ on the A site, yielding potential compositions of Nd 1–x Ce x Cu 3 FeTi 3 O 12 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce 3+ loading is achieved near x ≈ 0.2. A single composition with plutonium was targeted, Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , in order to properly model more realistic loading levels for a repository-destined material. These compounds were characterized using powder X-ray diffraction with Rietveld refinements of the structures and by a variety of spectroscopic techniques. Finally, the data suggest that, in order to achieve Pu 3+ substitution onto the A sites in the Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , a reducing atmosphere must be employed. Otherwise, the redox activity of plutonium results in substitution onto multiple sites in the material as well as the formation of secondary phases such as TiO 2 .

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2015

An Adsorption Study of CH 4 on ZSM-5, MOR, and ZSM-12 Zeolites

CH 4 adsorption was studied experimentally and theoretically on ZSM-5, MOR, and ZSM-12 zeolites using calorimetric measurements at 195 K and plane wave DFT calculations. Differential heats measured on four different H-ZSM-5 samples were determined to be 22.5 ± 1 kJ/mol, independent of Brønsted site density or defect concentration. However, DFT calculations performed using various functionals and on the most stable Brønsted site indicated that CH4 should bind to this site by an additional 1–7 kJ/mol, a discrepancy that is due to the inability of standard DFT methods to capture hydrogen-bonding effects accurately with CH 4 . Differential heats for CH 4 in MOR were 30±1 kJ/mol at low coverages, falling to 25 kJ/mol for coverages above one molecule per 8-membered-ring side pocket, while differential heats on ZSM-12 were initially 22.5 kJ/mol, decreasing to 21 kJ/mol with coverage. DFT calculations on the siliceous form of the zeolites were able to predict these values within 5 kJ/mol in most cases. The results indicate that CH 4 is an excellent probe molecule for characterizing the pore structure of zeolites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗