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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Solvent-Engineering Method to Deposit Compact Bismuth-Based Thin Films: Mechanism and Application to Photovoltaics

Bismuth-based materials have been studied as alternatives to lead-based perovskite materials for photovoltaic applications. However, poor film quality has limited device performance. Here, we developed a solvent-engineering method and show that it is applicable to several bismuth-based compounds. Through this method, we obtained compact films of methylammonium bismuth iodide (MBI), cesium bismuth iodide (CBI), and formamidinium bismuth iodide (FBI). On the basis of film growth theory and experimental analyses, we propose a possible mechanism of film formation. Additionally, we demonstrate that the resultant compact MBI film is more suitable to fabricate efficient and stable photovoltaic devices compared to baseline MBI films with pinholes. We further employed a new hole-transporting material to reduce the valence-band offset with the MBI. The best-performing photovoltaic device exhibits an open-circuit voltage of 0.85 V, fill factor of 73%, and a power conversion efficiency of 0.71%, the highest reported values for MBI-based photovoltaic devices.

14 SOLAR ENERGY↗
DOE OSTI2018

Impact of Size Dispersity, Ligand Coverage, and Ligand Length on the Structure of PbS Nanocrystal Superlattices

Understanding self-assembly is a critical step toward controlling structure at the nanometer length scale. Furthermore, small changes in nanoscale morphology can have large impacts on the performance of nanomaterial devices. In this work, we experimentally explore how the physical properties of lead sulfide (PbS) nanocrystals, such as the surface ligands and core size dispersity, affect the ability of these nanocrystals to self-assemble. Here, we quantified the self-assembly quality by monitoring grain size and the percentage of nanocrystals with coherent alignment of their atomic planes. We found that the ensemble size dispersity plays a large role in superlattice formation and that even small improvements in size distribution led to shorter neighbor-to-neighbor distances in superlattices (more efficient packing), larger grain sizes, and increased nanocrystal alignment. Additionally, the ligand coverage on nanocrystal surfaces had a significant influence on the self-assembly, and excess precipitation steps were highly detrimental to the formation of ordered solids. We show that surface ligand length is a more flexible parameter and that high-quality superlattices can still be achieved with compact surface ligands, so long as the nanocrystal size dispersity and ligand coverage are sufficient. Lastly, we investigated several different colloidal solvents, finding toluene to provide the best ordering, and show that nanocrystal self-assembly is largely unhindered by nanocrystal age. Overall, these results guide our understanding of the underlying factors influencing nanocrystal self-assembly and provide strategies for forming well-engineered superlattices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Formation Mechanisms and Defect Engineering of Imine-Based Porous Organic Cages

The syntheses of porous organic cages (POCs) represent an important synthetic puzzle in dynamic covalent chemistry based self-sorting. Improved understanding of the formation mechanisms of POCs can lead to control and rational design of cages with desired functionality. Herein, we explore the formation mechanisms of imine-based POCs using time-resolved electrospray mass spectrometry, and electronic structure calculations at the density functional theory and correlated molecular orbital theory levels. We find that the synthesis of the [4+6] cycloimine cage CC3-R and the [2+3] cycloimine cage CC-pentane both proceed through similar intermediates via a series of consecutive reactions. The proposed reaction mechanisms are supported by electronic structure calculations. Based on our observations from both experiments and calculations, we propose a comprehensive method for designing and predicting new POC species. In addition, the observation of stable incomplete cages during CC3-R synthesis inspired us to design intentionally defective cages. These “missing-linker” type molecular defects are installed into CC3-R via non-solvent induced crystallization. The defective CC3-R materials are found to have enhanced CO2 interaction and improved CO 2 uptake capacity due to the additional functional groups present within the CC3 crystals.

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

U 8 Al 19 Si 6 , A Uranium Aluminide Silicide with a Stuffed Supercell Grown from Aluminum Flux

In this work, U 8 Al 19 Si 6 is formed from the reaction of uranium oxide and silicon in aluminum flux. Growth of this material is dependent on the presence of surface hydroxyl groups on alumina in the crucible. The compound forms as large cuboid crystals with a complex new structure that is a cubic stuffed supercell of UAl 3 (AuCu 3 parent structure type). It features a 4-fold expansion of the unit cell axis and the addition of atoms on two extra positions resulting in Pm$\bar{3n}$ symmetry. The ordered distribution of aluminum and silicon was determined using single crystal neutron diffraction. The magnetic susceptibility shows temperature independent paramagnetic behavior, while heat capacity measurements are consistent with Fermi liquid characteristics at low temperatures where the Sommerfeld constant is enhanced in comparison to that of a conventional metal. Lastly, these bulk thermodynamic properties indicate that U 8 Al 19 Si 6 is an itinerant electron Pauli paramagnet with moderately enhanced mass charge carrier quasiparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Selective Transfer of Rotationally Commensurate MoS 2 from an Epitaxially Grown van der Waals Heterostructure

We report that large-scale synthesis of high-quality two-dimensional (2D) semiconductors is critical for their incorporation in emerging electronic and optoelectronic technologies. In particular, chemical vapor deposition (CVD) of transition-metal dichalcogenides (TMDs) via van der Waals epitaxy on epitaxial graphene (EG) leads to rotationally commensurate TMDs in contrast to randomly aligned TMDs grown on amorphous oxide substrates. However, the interlayer coupling between TMDs and EG hinders the investigation and utilization of the intrinsic electronic properties of the resulting TMDs, thus requiring their isolation from the EG growth substrate. To address this issue, we report here a technique for selectively transferring monolayer molybdenum disulfide (MoS 2 ) from CVD-grown MoS 2 -EG van der Waals heterojunctions using copper (Cu) adhesion layers. The choice of Cu as the adhesion layer is motivated by density functional theory calculations that predict the preferential binding of monolayer MoS 2 to Cu in contrast to graphene. Atomic force microscopy and optical spectroscopy confirm the large-scale transfer of rotationally commensurate MoS 2 onto SiO 2 /Si substrates without cracks, wrinkles, or residues. Furthermore, the transferred MoS 2 shows high performance in field-effect transistors with mobilities of up to 30 cm 2 /V s and on/off ratios of up to 10 6 at room temperature. Lastly, this transfer technique can likely be generalized to other TMDs and related 2D materials grown on EG, thus offering a broad range of benefits in nanoelectronic, optoelectronic, and photonic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tuning Anionic Chemistry To Improve Kinetics of Mg Intercalation

Rechargeable Mg batteries (RMBs) hold great promise for high energy density in consumer electronics because of the high theoretical volumetric capacity and dendrite-free stripping/plating of Mg. Their development, however, is severely limited by the sluggish diffusion of Mg 2+ in inorganic cathodes, mainly induced by strong interaction between Mg 2+ and host anions. In this paper, for the first time, we systematically investigate how anionic chemistry (O, S, and Se) affects Mg 2+ migration in layered MX 2 (M = Ti and V; X = O, S, and Se), by combining theoretical density functional theory (DFT) calculations with electrochemical characterizations. At room temperature, TiSe 2 and VSe 2 achieve much better electrochemical performance than TiS 2 and VS 2 , due to the faster migration of Mg 2+ in selenide than in sulfide and oxide, as demonstrated by electrochemical kinetic characterizations and DFT calculations. The improved kinetics of selenide can be attributed to three criteria: (i) larger diffusion channel, (ii) weaker interaction between Mg 2+ and anion lattice, and (iii) higher electronic conductivity. Finally, the three criteria might not only be applicable to layered materials but also be generalizable to materials with other structures, like Chevrel phase, spinel, olivine, etc., which paves the way for the future design and modification of intercalation materials for RMBs.

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

Role of Amine Structure on Hydrogen Sulfide Capture from Dilute Gas Streams Using Solid Adsorbents

The hydrogen sulfide composition in biogas ranges from 0 to 5% depending on the feed source to the biogas digester. To meet renewable natural gas specifications of 0–4 ppm of H 2 S content, technologies that remove H 2 S from raw biogas feeds are needed. This contribution assesses three adsorbents with similar textural and physical properties but with different amines grafted to the surface. Specifically, materials containing primary, secondary, and tertiary amines at the end of a propyl surface linker grafted on a silica support are explored. H 2 S adsorption isotherms and cyclic studies are presented for these materials, and it is shown that secondary amines have the best amine efficiency while tertiary amines are the most stable for H 2 S capture, of the materials studied. The results suggest the consideration of secondary and tertiary amines for the design of amine adsorbents suitable for H 2 S removal in dilute gas streams over multiple cycles.

09 BIOMASS FUELS↗
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 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↗