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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Singlet fission efficiency in tetracene-based organic solar cells

Singlet exciton fission splits one singlet exciton into two triplet excitons. Using a joint analysis of photocurrent and fluorescence modulation under a magnetic field, we determine that the triplet yield within optimized tetracene organic photovoltaic devices is 153% ± 5% for a tetracene film thickness of 20 nm. The corresponding internal quantum efficiency is 127% ± 18%. These results are used to prove the effectiveness of a simplified triplet yield measurement that relies only on the magnetic field modulation of fluorescence. Despite its relatively slow rate of singlet fission, the measured triplet yields confirm that tetracene is presently the best candidate for use with silicon solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Adding to the Arsenal of Zirconium‐Based Metal–Organic Frameworks: the Topology as a Platform for Solvent‐Assisted Metal Incorporation

Gaining control over the assembly of mesoporous Zr‐based metal–organic frameworks (MOFs) with modifiable metal nodes remains a challenge. The the topology is intriguing, particularly if considering postsynthetic modification, as it presents large sodalite‐like cages surrounded by 12 interconnected 1D channels that allow for efficient diffusion of guest molecules throughout the structure. Herein, we demonstrate the first Zr MOF with the topology, NU‐1200, which was synthesized by controlling the geometry of the organic building unit. In addition, by using NU‐1200 as a platform, we perform solvent‐assisted metal incorporation to form single‐site metalated nodes, a process that is characterized by single‐crystal X‐ray diffraction.

Liu, Tian‐Fu↗
DOE OSTI2018

Xenon Gas Separation and Storage using Metal-Organic Frameworks

The global demand for Xe, a noble gas with applications in electronics, lighting, and the medical industry, is expected to rise significantly over the coming decades. However, the low abundance of Xe in the earth’s atmosphere and the costly cryogenic distillation process that is used to obtain Xe commercially via air separation have limited the scale of applications of Xe. A physisorption-based separation using porous materials may be a viable and cost-effective alternative to cryogenic distillation. In particular, metal-organic frameworks (MOFs) have shown promise as highly Xe-selective, porous solids. In this review, we detail the recent advances of MOFs as adsorbents for noble gas adsorption/separation and the role of computer simulation in finding optimal materials for Xe adsorption.

MOFs, Xenon, Krypton↗
DOE OSTI2014

Water Adsorption in Porous Metal-Organic Frameworks and Related Materials

Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal organic frameworks (MOFs). Among the MOFs are 10 zirconium(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), -802, -805, -806, -808, -812, and -841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr6O4(OH)(4)(-CO2)(n) secondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temperature. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermolecular interaction between adsorbed water molecules within the pores.

Furukawa, H↗
DOE OSTI2014

Integrated optical and electrical modeling of plasmon-enhanced thin film photovoltaics: A case-study on organic devices

The nanoscale light control for absorption enhancement of organic photovoltaic (OPV) devices inevitably produces strongly non-uniform optical fields. These non-uniformities due to the localized optical modes are a primary route toward absorption enhancement in OPV devices. Therefore, a rigorous modeling tool taking into account the spatial distribution of optical field and carrier generation is necessary. Presented here is a comprehensive numerical model to describe the coupled optical and electrical behavior of plasmon-enhanced polymer:fullerene bulk heterojunction (BHJ) solar cells. In this model, a position-dependent electron-hole pair generation rate that could become highly non-uniform due to photonic nanostructures is directly calculated from the optical simulations. By considering the absorption and plasmonic properties of nanophotonic gratings included in two different popular device architectures, and applying the Poisson, current continuity, and drift/diffusion equations, the model predicts quantum efficiency, short-circuit current density, and desired carrier mobility ratios for bulk heterojunction devices incorporating nanostructures for light management. In particular, the model predicts a significant degradation of device performance when the carrier species with lower mobility are generated far from the collecting electrode. Consequently, an inverted device architecture is preferred for materials with low hole mobility. This is especially true for devices that include plasmonic nanostructures. Additionally, due to the incorporation of a plasmonic nanostructure, we use simulations to theoretically predict absorption band broadening of a BHJ into energies below the band gap, resulting in a 4.8% increase in generated photocurrent.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Increasing the Stability of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a new category of advanced porous materials undergoing study by many researchers for their vast variety of both novel structures and potentially useful properties arising from them. Their high porosities, tunable structures, and convenient process of introducing both customizable functional groups and unsaturated metal centers have afforded excellent gas sorption and separation ability, catalytic activity, luminescent properties, and more. However, the robustness and reactivity of a given framework are largely dependent on its metal-ligand interactions, where the metal-containing clusters are often vulnerable to ligand substitution by water or other nucleophiles, meaning that the frameworks may collapse upon exposure even to moist air. Other frameworks may collapse upon thermal or vacuum treatment or simply over time. This instability limits the practical uses of many MOFs. In order to further enhance the stability of the framework, many different approaches, such as the utilization of high-valence metal ions or nitrogen-donor ligands, were recently investigated. This review details the efforts of both our research group and others to synthesize MOFs possessing drastically increased chemical and thermal stability, in addition to exemplary performance for catalysis, gas sorption, and separation.

Bosch, Mathieu↗
DOE OSTI2014

High Methane Storage Capacity in Aluminum Metal-Organic Frameworks

The use of porous materials to store natural gas in vehicles requires large amounts of methane per unit of volume. Here we report the synthesis, crystal structure and methane adsorption properties of two new aluminum metal–organic frameworks, MOF-519 and MOF-520. Both materials exhibit permanent porosity and high methane volumetric storage capacity: MOF-519 has a volumetric capacity of 200 and 279 cm 3 cm –3 at 298 K and 35 and 80 bar, respectively, and MOF-520 has a volumetric capacity of 162 and 231 cm 3 cm –3 under the same conditions. Furthermore, MOF-519 exhibits an exceptional working capacity, being able to deliver a large amount of methane at pressures between 5 and 35 bar, 151 cm 3 cm –3 , and between 5 and 80 bar, 230 cm 3 cm –3 .

Gándara, Felipe↗
DOE OSTI2016

Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm

ABSTRACT Although it is becoming clear that many microbial primary producers can also play a role as organic consumers, we know very little about the metabolic regulation of photoautotroph organic matter consumption. Cyanobacteria in phototrophic biofilms can reuse extracellular organic carbon, but the metabolic drivers of extracellular processes are surprisingly complex. We investigated the metabolic foundations of organic matter reuse by comparing exoproteome composition and incorporation of 13 C-labeled and 15 N-labeled cyanobacterial extracellular organic matter (EOM) in a unicyanobacterial biofilm incubated using different light regimes. In the light and the dark, cyanobacterial direct organic C assimilation accounted for 32% and 43%, respectively, of all organic C assimilation in the community. Under photosynthesis conditions, we measured increased excretion of extracellular polymeric substances (EPS) and proteins involved in micronutrient transport, suggesting that requirements for micronutrients may drive EOM assimilation during daylight hours. This interpretation was supported by photosynthesis inhibition experiments, in which cyanobacteria incorporated N-rich EOM-derived material. In contrast, under dark, C-starved conditions, cyanobacteria incorporated C-rich EOM-derived organic matter, decreased excretion of EPS, and showed an increased abundance of degradative exoproteins, demonstrating the use of the extracellular domain for C storage. Sequence-structure modeling of one of these exoproteins predicted a specific hydrolytic activity that was subsequently detected, confirming increased EOM degradation in the dark. Associated heterotrophic bacteria increased in abundance and upregulated transport proteins under dark relative to light conditions. Taken together, our results indicate that biofilm cyanobacteria are successful competitors for organic C and N and that cyanobacterial nutrient and energy requirements control the use of EOM. IMPORTANCE Cyanobacteria are globally distributed primary producers, and the fate of their fixed C influences microbial biogeochemical cycling. This fate is complicated by cyanobacterial degradation and assimilation of organic matter, but because cyanobacteria are assumed to be poor competitors for organic matter consumption, regulation of this process is not well tested. In mats and biofilms, this is especially relevant because cyanobacteria produce an extensive organic extracellular matrix, providing the community with a rich source of nutrients. Light is a well-known regulator of cyanobacterial metabolism, so we characterized the effects of light availability on the incorporation of organic matter. Using stable isotope tracing at the single-cell level, we quantified photoautotroph assimilation under different metabolic conditions and integrated the results with proteomics to elucidate metabolic status. We found that cyanobacteria effectively compete for organic matter in the light and the dark and that nutrient requirements and community interactions contribute to cycling of extracellular organic matter.

09 BIOMASS FUELS↗
DOE OSTI2019

Organic-Mineral Interfacial Chemistry Drives Heterogeneous Nucleation of Sr-Rich (Bax, Sr1-x)SO4 from Undersaturated Solution

Sr-bearing marine barite [(Bax, Sr1-x)SO4] cycling has been widely used to reconstruct geochemical evolutions of paleoenvironments. However, an understanding of barite precipitation in the ocean, which is globally undersaturated with respect to barite, is missing. Moreover, the reason for the occurrence of higher Sr content in marine barites than expected for classical crystal growth processes remains unknown. Field data analyses suggested that organic molecules may regulate the formation and composition of marine barites; however, the specific organic–mineral interactions are unclear. Using in situ grazing incidence small-angle X-ray scattering (GISAXS), size and total volume evolutions of barite precipitates on organic films were characterized. The results show that barite forms on organic films from undersaturated solutions. Moreover, from a single supersaturated solution with respect to barite, Sr-rich barite nanoparticles formed on organics, while micrometer-size Sr-poor barites formed in bulk solutions. Ion adsorption experiments showed that organic films can enrich cation concentrations in the adjacent solution, thus increasing the local supersaturation and promoting barite nucleation on organic films, even when the bulk solution was undersaturated. The Sr enrichment in barites formed on organic films was found to be controlled by solid-solution nucleation rates; instead, the Sr-poor barite formation in bulk solution was found to be controlled by solid-solution growth rates. This study provides a mechanistic explanation for Sr-rich marine barite formation and offers insights for understanding and controlling the compositions of solid solutions by separately tuning their nucleation and growth rates via the unique chemistry of solution–organic interfaces.

Deng, Ning↗
DOE OSTI2017

Hydrogenation of organic matter as a terminal electron sink sustains high CO 2 :CH 4 production ratios during anaerobic decomposition

Once inorganic electron acceptors are depleted, organic matter in anoxic environments decomposes by hydrolysis, fermentation, and methanogenesis, requiring syntrophic interactions between microorganisms to achieve energetic favorability. In this classic anaerobic food chain, methanogenesis represents the terminal electron accepting (TEA) process, ultimately producing equimolar CO2 and CH4 for each molecule of organic matter degraded. However, CO2:CH4 production in Sphagnum-derived, mineral-poor, cellulosic peat often substantially exceeds this 1:1 ratio, even in the absence of measureable inorganic TEAs. Since the oxidation state of C in both cellulose-derived organic matter and acetate is 0, and CO2 has an oxidation state of +4, if CH4 (oxidation state -4) is not produced in equal ratio, then some other compound(s) must balance CO2 production by receiving 4 electrons. Here we present evidence for ubiquitous hydrogenation of diverse unsaturated compounds that appear to serve as organic TEAs in peat, thereby providing the necessary electron balance to sustain CO2:CH4 >1. While organic electron acceptors have previously been proposed to drive microbial respiration of organic matter through the reversible reduction of quinone moieties, the hydrogenation mechanism that we propose, by contrast, reduces C-C double bonds in organic matter thereby serving as 1) a terminal electron sink, 2) a mechanism for degrading complex unsaturated organic molecules, 3) a potential mechanism to regenerate electron-accepting quinones, and, in some cases, 4) a means to alleviate the toxicity of unsaturated aromatic acids. This mechanism for CO2 generation without concomitant CH4 production has the potential to regulate the global warming potential of peatlands by elevating CO2:CH4 production ratios.

58 GEOSCIENCES↗
DOE OSTI2014

Organ localization: Toward prospective patient-specific organ dosimetry in computed tomography

Purpose: With increased focus on radiation dose from medical imaging, prospective radiation dose estimates are becoming increasingly desired. Using available populations of adult and pediatric patient phantoms, radiation dose calculations can be catalogued and prospectively applied to individual patients that best match certain anatomical characteristics. In doing so, the knowledge of organ size and location is a required element. Here, the authors develop a predictive model of organ locations and volumes based on an analysis of adult and pediatric computed tomography (CT) data. Methods: Fifty eight adult and 69 pediatric CT datasets were segmented and utilized in the study. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width, midpoint, and volume of each organ were calculated. Linear correlations between these three organ parameters and patient age, BMI, weight, and height were determined. Results: No statistically significant correlations were found in adult patients between the axial width, midpoint, and volume of the organs versus the patient age or BMI. Slight, positive linear trends were found for organ midpoint versus patient weight (max r{sup 2} = 0.382, mean r{sup 2} = 0.236). Similar trends were found for organ midpoint versus height (max r{sup 2} = 0.439, mean r{sup 2} = 0.200) and for organ volume versus height (max r{sup 2} = 0.410, mean r{sup 2} = 0.153). Gaussian fits performed on probability density functions of the adult organs resulted in r{sup 2}-values ranging from 0.96 to 0.996. The pediatric patients showed much stronger correlations overall. Strong correlations were observed between organ axial midpoint versus age, height, and weight (max r{sup 2} = 0.842, mean r{sup 2} = 0.790; max r{sup 2} = 0.949, mean r{sup 2} = 0.894; and max r{sup 2} = 0.870, mean r{sup 2} = 0.847, respectively). Moderate linear correlations were also observed for organ axial width versus height (max r{sup 2} = 0.772, mean r{sup 2} = 0.562) and for organ volume versus height (max r{sup 2} = 0.781, mean r{sup 2} = 0.601). Conclusions: Adult patients exhibited small variations in organ volume and location with respect to height and weight, but no meaningful correlation existed between these parameters and age or BMI. Once adulthood is reached, organ morphology and positioning seem to remain static. However, clear trends are evident between pediatric organ locations versus age, height, and weight. Such information can be incorporated into a matching methodology that may provide the highest probability of representing the anatomy of a patient undergoing a clinical exam to prospectively estimate the radiation dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

The Ecosystem as Super-Organ/ism, Revisited: Scaling Hydraulics to Forests under Climate Change

Synopsis Classic debates in community ecology focused on the complexities of considering an ecosystem as a super-organ or organism. New consideration of such perspectives could clarify mechanisms underlying the dynamics of forest carbon dioxide (CO2) uptake and water vapor loss, important for predicting and managing the future of Earth’s ecosystems and climate system. Here, we provide a rubric for considering ecosystem traits as aggregated, systemic, or emergent, i.e., representing the ecosystem as an aggregate of its individuals or as a metaphorical or literal super-organ or organism. We review recent approaches to scaling-up plant water relations (hydraulics) concepts developed for organs and organisms to enable and interpret measurements at ecosystem-level. We focus on three community-scale versions of water relations traits that have potential to provide mechanistic insight into climate change responses of forest CO2 and H2O gas exchange and productivity: leaf water potential (Ψcanopy), pressure volume curves (eco-PV), and hydraulic conductance (Keco). These analyses can reveal additional ecosystem-scale parameters analogous to those typically quantified for leaves or plants (e.g., wilting point and hydraulic vulnerability) that may act as thresholds in forest responses to drought, including growth cessation, mortality, and flammability. We unite these concepts in a novel framework to predict Ψcanopy and its approaching of critical thresholds during drought, using measurements of Keco and eco-PV curves. We thus delineate how the extension of water relations concepts from organ- and organism-scales can reveal the hydraulic constraints on the interaction of vegetation and climate and provide new mechanistic understanding and prediction of forest water use and productivity.

Zoology↗
DOE OSTI2014

Photochromic Metal–Organic Frameworks: Reversible Control of Singlet Oxygen Generation

Abstract The controlled generation of singlet oxygen is of great interest owing to its potential applications including industrial wastewater treatment, photochemistry, and photodynamic therapy. Two photochromic metal–organic frameworks, PC‐PCN and SO‐PCN, have been developed. A photochromic reaction has been successfully realized in PC‐PCN while maintaining its single crystallinity. In particular, as a solid‐state material which inherently integrates the photochromic switch and photosensitizer, SO‐PCN has demonstrated reversible control of 1 O 2 generation. Additionally, SO‐PCN shows catalytic activity towards photooxidation of 1,5‐dihydroxynaphthalene.

Park, Jihye↗