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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Controlling Drug Absorption, Release, and Erosion of Photopatterned Protein Engineered Hydrogels

A protein-engineered triblock copolymer hydrogel composed of two self-assembling domains (SADs) has been fabricated by a photoactivatable diazirine group followed by ultraviolet (UV)-mediated crosslinking. The photocrosslinkable protein polymer CEC-D has been patterned into various features including different micrometer-scale stripes by using lithographic techniques. The patterned hydrogels are important for encapsulation of small molecules where a photopatterned fraction of 50% is optimal for maximum absorption. Stripe-patterned CEC-D 100–100 exhibits slightly lower swelling ratios, an 8.9 times lower erosion profile, and a 2.6-fold higher drug release compared to the unpatterned hydrogel control, CEC-D0. Our studies demonstrate the potential of photocrosslinkable protein polymer hydrogels to be used as scaffolds for therapeutic delivery of small molecules. Furthermore, through photolithographic techniques on the protein hydrogel, a variety of functionalities can be achieved by patterning different features enabling the mimicry of biological systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Chitosan as a Canvas for Studies of Macromolecular Controls on CaCO 3 Biological Crystallization

A mechanistic understanding of how macromolecules, typically as an organic matrix, nucleate and grow crystals to produce functional biomineral structures remains elusive. Advances in structural biology indicate that polysaccharides (e.g., chitin) and negatively charged proteoglycans (due to carboxyl, sulfate, and phosphate groups) are ubiquitous in biocrystallization settings and play greater roles than currently recognized. This review highlights studies of CaCO 3 crystallization onto chitinous materials and demonstrates that a broader understanding of macromolecular controls on mineralization has not emerged. With recent advances in biopolymer chemistry, it is now possible to prepare chitosan-based hydrogels with tailored functional group compositions. By deploying these characterized compounds in hypothesis-based studies of nucleation rate, quantitative relationships between energy barrier to crystallization, macromolecule composition, and solvent structuring can be determined. Finally, this foundational knowledge will help researchers understand composition-structure-function controls on mineralization in living systems and tune the designs of new materials for advanced applications.

15 GEOTHERMAL ENERGY↗
DOE OSTI2020

First-Principles Modeling of Sodium Ion and Water Intercalation into Titanium Disulfide Interlayers for Water Desalination

Recent experiments revealed the possibility of using titanium disulfide (TiS 2 ) as the cathode material in capacitive deionization (CDI) devices for water desalination. Although it performed stably up to 70 cycles with a salt removal capacity of 14 mg/g (corresponding to a sodium ion removal capacity of 35.8 mg/g) at high molar concentration (600 mM NaCl), the maximum capacity of TiS 2 as a CDI electrode was much lower (~70 mAh/g) than as a supercapacitor (239 mAh/g). Understanding why the ion capacities of these two configurations of the same material differ will entail elucidating detailed charge/discharge mechanisms at the atomic scale. Here, we present density functional theory simulations of sodium intercalation into TiS 2 interlayers in order to gain such understanding. We systematically investigated TiS 2 stacking patterns and ion intercalation sites, energetics of the intercalated compounds, and phase transformation during sodium intercalation. The calculated structural evolution and capacitance–voltage curve agree quite well with previous measurements. We conclude that the different maximum capacities of TiS 2 measured in aqueous and dry environments originate from weaker interlayer interactions with respect to shear strain after ~33% intercalation of Na + –H 2 O pairs, which is detrimental to the mechanical stability of TiS 2 . In conclusion, this study sheds light on the underlying mechanisms of ion intercalation into layered materials and contributes to understanding requirements for future design and optimization of CDI electrode materials for water desalination.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Polymorphism and Optoelectronic Properties in Crystalline Supramolecular Polymers

Supramolecular polymers can emulate some of the physical properties of covalent polymers but offer new opportunities given the possibility of designing monomers that will form highly ordered assemblies with defined shapes. Internally ordered supramolecular polymers formed through nucleation–elongation self-assembly are well-known but highly crystalline examples which exhibit important properties such as light harvesting, charge transport, and ferroelectricity are not common. We report here on a detailed study of supramolecular polymers formed in water by carboxylated naphtho-p-quinodimethane amphiphiles. We found that supramolecular polymerization of these amphiphiles in aqueous media yields crystalline assemblies with morphologies that included ribbons, helically rolled ribbons, and twisted filaments. This polymorphism was found to be controlled exclusively by repulsive electrostatic interactions controlled by the degree of protonation of the carboxylic head groups which also dictates the nature of supramolecular packing. Substoichiometric amounts of base lead to highly crystalline ribbons due to a decreased surface charge density and less electrostatic repulsion. Increasing deprotonation results in helically rolled ribbons with a different polymorph crystal lattice, whereas excessive deprotonation leads to twisted filaments with maximum surface charge density. Ribbons, helical rolled ribbons, and twisted filaments revealed an increasing red shift in their visible absorption maxima. These crystalline assemblies could be potential candidates for solar energy materials and photocatalytic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tunable Atomic Layer Deposition into Ultra-High-Aspect-Ratio (>60000:1) Aerogel Monoliths Enabled by Transport Modeling

Atomic layer deposition (ALD) modification of ultra-high-aspect-ratio structures (>10,000:1) is a powerful platform with applications in catalysis, filtration, and energy conversion. However, the deposition of conformal and tunable ALD coatings at these aspect ratios remains challenging, resulting in empirical tradeoffs between precursor utilization and reaction time. Here, we demonstrate tunable control of the ALD infiltration depth into an aerogel monolith (AM) and develop a reaction-diffusion model to accurately describe the coating process. Specifically, we investigate the ALD exposure time and precursor dose needed to conformally coat a silica AM with pore sizes of ~20 nm, a monolith thickness of ~2.5 mm, and aspect ratios exceeding 60,000:1. We demonstrate complete infiltration into the AM, which is quantified by elemental mapping. A reaction-diffusion model is developed, which accounts for multiple doses and precursor depletion in the ALD chamber during an exposure step. The experimentally validated model enables the prediction and tuning of infiltration depth into a tortuous, high-aspect-ratio structure such as an AM, allowing for the synthesis of rationally designed material architectures. Additionally, the model allows for co-optimization of the total deposition time and percentage of unreacted precursor, which are important for the manufacturability and sustainability of ALD processing. Lastly, we demonstrate that ultra-thin ALD Al 2 O 3 coatings can be used to stabilize silica AMs against structural degradation under high-temperature annealing conditions (700-800 °C), by limiting changes in surface area and monolith volume. As a result, this improved high-temperature stability has implications for numerous aerogel applications, including catalysis and thermal insulation.

14 SOLAR ENERGY↗
DOE OSTI2021

Phase-Controllable Synthesis of Ultrathin Molybdenum Nitride Crystals Via Atomic Substitution of MoS 2

MXenes are emerging members in the two-dimensional (2D) material family and are highlighted by their high electrical conductivity. Among different MXenes, molybdenum-based MXenes, especially molybdenum nitrides (MoN x ), are rarely accessible through the common synthetic approach of selective etching due to the absence of stable MAX phase precursors. In this work, we apply the atomic substitution approach to synthesize two phases of ultrathin nonlayered molybdenum nitrides (i.e., Mo 5 N 6 and δ-MoN) from 1.6 to 42.9 nm thickness by converting layered MoS 2 under different temperatures. The morphology and 2D nature of MoS 2 are well remained in both phases. These newly created 2D materials are further characterized using Raman spectroscopy, high-resolution transmission electron microscopy, and electrical measurements, suggesting that both phases are highly crystalline and highly conductive down to the thickness of a few nanometers. Moreover, Ohmic contacts are formed between the ultrathin nitrides and Cr/Au electrodes, suggesting the great potential of the obtained nitrides for nanoelectronic device applications. The stability test shows that the Ohmic contact is well maintained after 4 weeks under ambient conditions with a slight degradation in conductivity. Furthermore, this study extends the 2D family by providing highly conductive members, offering desired building blocks for solid-state nanoelectronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li $1–3x$ Fe $x$ Cl for Fe 3+ ). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. Importantly, this behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Orientational Order in Spin-Cast Lead-Iodide Perovskite Nanocrystal Solids

Combined synthetic control over size and composition renders colloidal lead-halide perovskite nanocrystals a tunable platform for high-efficiency optoelectronic applications. However, the properties and operational stability of devices based on nanocrystal solids are often dictated by the method of the evaporation-induced assembly. Ubiquitous slow evaporation techniques can produce highly ordered nanocrystal domains but limit the prospects for scalable fabrication of continuous device layers, calling for investigation of approaches to more rapidly form ordered perovskite nanocrystal solids. Here, we study orientationally ordered lead-iodide perovskite nanocrystal solids prepared by conventional spin coating with molecular additives (excess ligand) to enhance ordering within the arrays. In situ X-ray scattering measurements reveal that orientational ordering occurs rapidly upon solvent removal during spin coating and can be further enhanced by manipulating the spin speed. We vary the additive ligand length and explore trade-offs between ordering and layered perovskite impurity formation. Arrays treated with the intermediate-length octylamine ligand exhibit increased in-plane electronic conductivity, suggesting orientational ordering and internanocrystal electronic coupling can be enhanced by the treatment. In conclusion, these results highlight the prospects of establishing long-range order in lead-halide perovskite nanocrystal solids by using simple and fast coating methods.

14 SOLAR ENERGY↗
DOE OSTI2024

Generic Behavior of Ultrastability and Anisotropic Molecular Packing in Codeposited Organic Semiconductor Glass Mixtures

Vapor-deposited glass mixtures of organic semiconductors commonly serve as active layers in organic electronic devices, whose lifetime and performance are strongly influenced by the stability and structure of these mixed glasses. Here, we study the stability and anisotropic molecular packing of six co-deposited organic semiconductor glass mixtures with 50:50 weight ratio, by differential scanning calorimetry and spectroscopic ellipsometry. We also find that all six binary systems exhibit high kinetic stability and significantly reduced enthalpy relative to the corresponding liquid-cooled glassy mixtures (ultrastable behavior), even for systems where the glass transition temperatures of the components differ by more than 90 K. Furthermore, we demonstrate that the birefringence of a co-deposited glass mixture, a measure of its anisotropic packing, can be predicted from the birefringence of glasses of the two pure components. These results for stability and structure are expected to be applicable to other co-deposited organic semiconductor glass mixtures, so long as the two components mix well in the glass and individually can form ultrastable glasses. Therefore, our findings are significant for designing novel electronic devices with enhanced device lifetime and increased operational efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unraveling the Growth Mechanism of Strongly Confined CsPbBr 3 Perovskite Quantum Dots under Thermodynamic Equilibrium Control

Size-confined lead halide perovskite quantum dots (PQDs) are promising materials for optoelectronic devices. Large quantities of PQDs with high ensemble uniformity are often needed for device fabrication. The thermodynamic-equilibrium-controlled synthesis can produce PQDs with good size and shape uniformity. Unfortunately, scaling up this synthesis often produces unwanted perovskite nanoplatelets (NPLs). To date, the PQD and NPL growth mechanism under thermodynamic equilibrium control remains unexplored. We discovered that the growth of size-confined CsPbBr 3 PQDs is mediated by ultrasmall (~ 2.4 nm) metastable nanoclusters. These nanoclusters can eventually grow into PQDs when sufficient Cs-precursors are provided. Otherwise, the unreacted nanoclusters will self-assemble and fuse into NPLs during the synthesis and/or PQD purification. Furthermore, by controlling the homogeneous growth of nanoclusters, strongly confined (≤ 5 nm) PQDs with high size uniformity can be produced at the gram scale.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

(NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a Vacancy-Ordered Three-Dimensional Tin(II) Perovskite-Derived Semiconductor

Ordering vacancies in hybrid Sn(II) halide semiconductors provides a strategy for preventing uncontrolled oxidation and formation of mobile holes. In this study, we report the structure and optical and electronic properties of (NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a vacancy-ordered perovskite derivative with three-dimensional inorganic connectivity. The crystal structure resembles that of a Dion–Jacobson layered perovskite derivative, but with [SnI 5 ] square pyramids bridging the layers. UV–vis diffuse reflectance spectroscopy reveals a sharp onset of light absorption at 1.86(1) eV with the photoluminescence emission maximum at 1.90(1) eV. However, the maximum excitation occurs from 3.42 to 3.81 eV (325 to 370 nm), revealing a significant Stokes shift of 1.3 eV. The electronic properties determined from dark and time-resolved microwave conductivity measurements reveal a minimum carrier mobility of 4.3 × 10 –2 cm 2 V –1 s –1 and a maximum carrier density of 5.96 × 10 16 cm –3 , a uniquely low value for a hybrid Sn(II) halide semiconductor. The transport behavior in combination with first-principles calculations of the electronic band structure and dielectric permittivity suggest polaron-mediated electronic transport, yet the photogenerated carriers have a fast and fluence-dependent nonradiative recombination rate, suggestive of localized “defect-like” states at the band edge. The observed photoluminescence is most consistent with single-ion-like behavior of an asymmetric Sn(II) environment. Together, these results suggest that defect ordering presents a strategy for the reduction of mobile charge carriers at equilibrium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Supramolecular Assembly of Multielement Ribbon-like Structures Derived from Halide Perovskites

Halide perovskites are crucial materials with broad applications owing to their exceptional optoelectronic properties. Vacancy-ordered double perovskites, featuring highly tunable transition metal sites, enable controllable optoelectronic properties through multielement compositional design. Here, in this study, we introduced 18-crown-6 into the vacancy-ordered double perovskites system and developed two-dimensional ribbon-like single crystals (18C6@K) 2 {PtSnTeIrRe} 1 Cl 6 via an antisolvent supramolecular assembly method, demonstrating morphology modulation through multielement composition design. The crystals crystallize in the centrosymmetric space group $P\bar{1}$. The dumbbell-shaped structural units (crown ether@A)2MX6 pack along a and b axes to form a 2-dimensional (2D) monolayer, and these monolayers further stack along the c axis to generate the ribbon-like single crystals. Energy-dispersive X-ray spectroscopy (EDX) qualitatively confirmed the uniform distribution of the five transition metals throughout the crystal, while inductively coupled plasma atomic emission spectroscopy (ICP–AES) quantitatively verified their atomic ratios. We further investigated the origin of the morphology, distinct from the previously reported cube-like single crystals with the $R\bar{3}$ space group. When acetonitrile was used as the solvent, three-dimensional crystals with $R\bar{3}$ symmetry were obtained, whereas dimethylformamide (DMF) was essential for forming two-dimensional ribbon-like single crystals. The essential role of DMF could be ascribed to its capability to maintain a higher concentration of the building blocks. Moreover, Ir 4+ and Pt 4+ cations also played critical roles in inducing the two-dimensional ribbon-like morphology. The three-element (18C6@K) 2 {PtSnTe}1Cl 6 single crystals exhibited bright yellow emission under 375 nm laser excitation, demonstrating the tunability of optoelectronic properties of this class of material.

Zhu, Heqing [University of California, Berkeley, C↗
DOE OSTI2026

Site-Selective Doping and Oxidation State Control of Copper in Gold Nanorods

We report the synthesis of plasmonic gold–copper nanostructures with tunable copper spatial distribution and oxidation state. Au–Cu alloy shells were deposited in aqueous solution onto colloidal gold nanorods that functioned as seeds, and the resulting shell morphology was found to depend strongly on the nanorod aspect ratio. For relatively fat gold nanorods (16 x 31 nm), Au–Cu growth was preferentially localized near the rod midsections, forming belt-like structures, whereas for skinnier nanorods (9 x 32 nm), Au–Cu growth produced patchy surface coverage around the entire rod. The shell thickness was tuned from 1 to 4 nm; upon air exposure, thicker shells exhibited a higher Cu(I) fraction compared to the initial shell. Incorporation of the Au–Cu shell led to pronounced shifts in the plasmonic features of the gold nanorods. These tunable plasmonic Au–Cu nanorods provide a materials basis for Cu-based plasmonic materials in the context of electrochemical CO₂ reduction.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Dithionite Inhibits Iron(III) (Hydr)oxide Formation during Olivine Dissolution Advancing Simultaneous CO 2 Mineralization and Nickel Recovery

Increasing CO 2 concentration poses significant global challenges, impacting both environmental and human health. As we strive for a carbon-neutral energy technology transition, the demand for critical elements (e.g., nickel and cobalt) continues to increase, while high-grade ores are depleting. Combining CO 2 mineralization with the recovery of critical elements from low-grade ores offers an innovative solution. Olivine, a magnesium-rich ultramafic with trace amounts of critical elements, is a promising mineral; however, its impurities, such as iron (Fe(III)), hinder the dissolution of Ni and Mg from olivine, reducing its carbonation and critical element recovery. Here, to address this challenge, this study examined Ni dissolution from San Carlos olivine at high temperatures and high CO 2 pressure. We found that iron(III) (hydr)oxide layers impeded olivine dissolution; however, with sodium dithionite (Na 2 S 2 O 4 ), a reducing agent, olivine dissolution is significantly improved by preventing iron(III) (hydr)oxide formation. With Na 2 S 2 O 4 , within 24 h, Mg and Ni dissolution from olivine increased 2.85-fold and 2.66-fold, respectively, compared to samples without Na 2 S 2 O 4 . After seven cycles, with solutions replaced every 24 h, 98.9% of the total Mg and 84.6% of the total Ni were recovered. This approach enhances olivine’s CO 2 mineralization and improves the sustainability of critical element supply.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Lignin-Derived Magnetic Activated Carbons for Effective Methylene Blue Removal

Large-scale environmental remediation of polluted water requires an effective and recyclable adsorbent produced from an abundant, low-cost, and renewable feedstock via a simple processing procedure. In this work, we demonstrate that lignin-derived magnetic activated carbons (mACs) uniquely satisfy these five criteria for (i) high-performance adsorption, (ii) high regeneration efficiency, (iii) feedstock economic and environmental viability, (iv) single-step processing and (v) large-scale production. The mACs are synthesized via an efficient co-carbonization and activation with simultaneous impregnation of ferric sulfate. Here, the Langmuir model closely fits the adsorption of methylene blue (MB) by mACs within the temperature range of 298–323 K, where the adsorption capacity increases as temperature increases. This capacity increased from 55.0 mg g -1 to 220.2 mg g -1 with the presence of magnetic nanoparticles. In addition, the magnetite nanoparticles on the ACs surface significantly improve its recycling ability with the removal percentage above 95% after four cycles for 5:1 mAC.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Structural Features of Zirconium-Based Metal–Organic Frameworks Affecting Radiolytic Stability

Metal–organic frameworks (MOFs) NU-1000 and UiO-66 are herein exposed to two different gamma irradiation doses and dose rates and analyzed to determine the structural features that affect their stability in these environments. MOFs have shown promise for the capture and sensing of off-gases at civilian nuclear energy reprocessing sites, nuclear waste repositories, and nuclear accident locations. However, little is understood about the structural features of MOFs that contribute to their stability levels under the ionizing radiation conditions present at such sites. This study is the first of its kind to explore the structural features of MOFs that contribute to their radiolytic stability. Both NU-1000 and UiO-66 are MOFs that contain Zr metal-centers with the same metal absorption cross section. However, the two MOFs exhibit different linker connectivities, linker aromaticities, node densities, node connectivities, and interligand separations. In this study, NU-1000 and UiO-66 were exposed to high (423.3 Gy/min, 23 min, and 37 s) and low (0.78 Gy/min, 4320 min) dose rates of 60 Co gamma irradiation. NU-1000 displayed insignificant radiation damage under both dose rates due to its high linker connectivity, low node density, and low node connectivity. However, low radiation dose rates caused considerable damage to UiO-66, a framework with lower aromaticity and smaller interligand separation. Finally, results suggest that chronic, low-radiation environments are more detrimental to Zr MOF stability than acute, high-radiation conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗