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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A Comparative Techno-Economic Analysis of Sustainable Methanol Synthesis Pathways from Biomass and CO2

The call to reduce global CO2 emissions is at the forefront of research and development in the transportation and petrochemical industries. A potential solution which intersects both sectors is the adoption and commercialization of more sustainable technologies for methanol production. Currently, methanol is gaining popularity as a possible fuel additive, and as a polymer precursor via established methanol-to-olefins routes which are increasing in capacity and utilization, putting methanol in the spotlight and global methanol production on the rise. At the same time, experimental and computational studies have surged, illuminating a wide array of novel process designs to introduce sustainable methanol into the market. However, with numerous competing pathways identified across a variety of fossil and non-fossil feedstocks, there is a need to harmonize the analyses of these pathways using a consistent techno-economic approach and compare them to current commercial pathways to better understand the benefits or limitations inherent to each technology. In this work we conduct a consistent comparative analysis of three sustainable methanol synthesis pathways versus a commercial baseline, with biomass, CO2, and natural gas as the carbon sources. The three sustainable pathways of interest are biomass gasification to syngas with subsequent catalytic conversion of syngas to methanol, indirect conversion of CO2 to syngas via electrolysis with subsequent catalytic conversion of syngas to methanol, and direct conversion of CO2 to methanol via electrolysis. To elucidate the challenges and opportunities in the path to commercialization of each sustainable pathway, we investigate five key process metrics: production cost, carbon efficiency, carbon intensity, energy efficiency, and technology readiness level (TRL).

biomass↗
DOE OSTI2023

Position-specific carbon isotopes of Murchison amino acids elucidate extraterrestrial abiotic organic synthesis networks

The Murchison meteorite is a well-studied carbonaceous chondrite with relatively high concentrations of amino acids thought to be endogenous to the meteorite, in part because they are characterized by carbon isotope (δ 13 C) values higher than those typical of terrestrial amino acids. Past studies have proposed that extraterrestrial amino acids in the Murchison meteorite could have formed by Strecker synthesis (for α-amino acids), Michael addition (for β-amino acids), or reductive amination, but a lack of constraints have prevented confident discrimination among these possibilities, or assignment of specific formation pathways to each of several specific amino acids. Position-specific carbon isotope analysis differentiates amongst these mechanisms by relating molecular sites to isotopically distinct carbon sources and by constraining isotope effects associated with elementary chemical reactions. Prior measurements of the position-specific carbon isotopic composition of α-alanine from the Murchison CM chondrite demonstrated that alanine’s high δ 13 C VPDB value is attributable to the amine carbon (δ 13 C VPDB = +142 ± 20‰), consistent with Strecker synthesis drawing on 13 C-rich carbonyl groups in precursors (Chimiak et al., 2021). Here, we measured the δ 13 C composition of fragment ions generated by electron impact ionization of derivatized α-alanine, β-alanine, and aspartic acid from Murchison via gas chromatography-Fourier transform mass spectrometry. α-Alanine’s amine carbon yielded δ 13 C VPDB = +109 ± 21‰, which is consistent with the previously measured value and with formation from 13 C-rich precursors. β-Alanine’s amine carbon presents a lower δ 13 C VPDB = +33 ± 24‰, which supports formation from 13 C-rich precursors but potentially via a Michael addition mechanism rather than Strecker synthesis. Aspartic acid’s amine carbon has δ 13 C VPDB = -14 ± 5‰, suggesting synthesis from precursors distinct from those that generated the alanine isomers. Further, these measurements indicate that Murchison amino acids are a mixture of compounds made from different synthesis mechanisms, though some subsets likely drew on the same substrates; this conclusion highlights the complexity of extraterrestrial organic synthesis networks and the potential of emerging methods of isotope ratio analysis to elucidate the details of those networks.

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

Enterococcus faecalis immunoregulates osteoclastogenesis of macrophages

Highlights: • An in vitro infection model of osteoclast precursors by E. faecalis was established. • E. faecalis infection upregulated the inflammatory response of osteoclast precursors. • E. faecalis infection attenuated RANKL-induced osteoclastogenesis of RAW264.7 cells. Persistent apical periodontitis (PAP) is characterized by refractory inflammation and progressive bone destruction. Enterococcus faecalis infection is considered an important etiological factor for the development of PAP, although the exact mechanisms remain unknown. This study aimed at investigating the role of E. faecalis in cell proliferation, inflammatory reactions and osteoclast differentiation of macrophages using an in vitro infection model of osteoclast precursor RAW264.7 cells. A cell viability assay of cultured RAW264.7 cells exposed to live E. faecalis at a multiplicity of infection of 100 for 2 h, indicated that the infection exhibited no cytotoxic effect. Transmission electron microscopy images revealed no apoptotic changes but a rise of metabolic activity and phagocytic features in the infected RAW264.7 cells. Confocal laser scanning microscopic and flow cytometric analysis indicated that the phagocytosis of RAW264.7 cells was activated by E. faecalis infection. Furthermore, quantitative real-time PCR assays demonstrated that the expression of inflammatory cytokines was remarkably elevated in infected RAW264.7 cells. Differentiation of infected RAW264.7 cells into osteoclasts was remarkably attenuated, and expression of osteoclast marker genes as well as fusogenic genes significantly dropped. In summary, E. faecalis appears to attenuate osteoclastic differentiation of RAW264.7 precursor cells, rather stimulates them to function as macrophages.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Integration of proteomics and metabolomics into the Design, Build, Test, Learn cycle to improve 3-hydroxypropionic acid production in Aspergillus pseudoterreus

Biological engineering of microorganisms to produce value-added chemicals is a promising route to sustainable manufacturing. However, overproduction of metabolic intermediates at high titer, rate, and yield from inexpensive substrates is challenging in non-model systems where limited information is available regarding metabolic flux and its control in production conditions. Integrated multi-omic analyses of engineered strains offers an in-depth look at metabolites and proteins directly involved in growth and production of target and non-target bioproducts. Here we applied multi-omic analyses to overproduction of the polymer precursor 3-hydroxypropionic acid (3HP) in the filamentous fungus Aspergillus pseudoterreus. A synthetic pathway consisting of aspartate decarboxylase, beta-alanine pyruvate transaminase, and 3HP dehydrogenase was designed and built for A. pseudoterreus. Strains with single- and multi-copy integration events were isolated and multi-omics analysis consisting of intracellular and extracellular metabolomics and targeted and global proteomics was used to interrogate the strains in shake-flask and bioreactor conditions. Production of a variety of co-products (organic acids and glycerol) and oxidative degradation of 3HP were identified as metabolic pathways competing with 3HP production. Intracellular accumulation of nitrogen as 2,4-diaminobutanoate was identified as an off-target nitrogen sink that may also limit flux through the engineered 3HP pathway. Elimination of the high-expression oxidative 3HP degradation pathway by deletion of a putative malonate semialdehyde dehydrogenase improved the yield of 3HP by 3.4× after 10 days in shake-flask culture. This is the first report of 3HP production in a filamentous fungus amenable to industrial scale biomanufacturing of organic acids at high titer and low pH.

Pomraning, Kyle R.↗
DOE OSTI2021

Quantifying the propagation of parametric uncertainty on flux balance analysis

Flux balance analysis (FBA) and associated techniques operating on stoichiometric genome-scale metabolic models play a central role in quantifying metabolic flows and constraining feasible phenotypes. At the heart of these methods lie two important assumptions: (i) the biomass precursors and energy requirements neither change in response to growth conditions nor environmental/genetic perturbations, and (ii) metabolite production and consumption rates are equal at all times (i.e., steady-state). Despite the stringency of these two assumptions, FBA has been shown to be surprisingly robust at predicting cellular phenotypes. In this paper, we formally assess the impact of these two assumptions on FBA results by quantifying how uncertainty in biomass reaction coefficients, and departures from steady-state due to temporal fluctuations could propagate to FBA results. In the first case, conditional sampling of parameter space is required to re-weigh the biomass reaction so as the molecular weight remains equal to 1 g mmol –1 , and in the second case, metabolite (and elemental) pool conservation must be imposed under temporally varying conditions. Results confirm the importance of enforcing the aforementioned constraints and explain the robustness of FBA biomass yield predictions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Combined Rotating Disk Slurry Electrodeposition–Spontaneous Galvanic Displacement for Pt-M (M = Co, Ni, and Cu) Catalyst Synthesis for the Oxygen Reduction Reaction in Alkaline Media

Here, platinum-modified first-row transition-metal catalyst (M = Ni, Co, and Cu) nanoparticles on a carbon black Vulcan XC-72R (CBV) support were synthesized using rotating disk slurry electrodeposition (RoDSE) followed by spontaneous galvanic displacement (SGD) reactions. These RoDSE–SGD catalysts were evaluated for the oxygen reduction reaction (ORR) in 0.1 M KOH using rotating disk electrode techniques. The Ni and Co RoDSEs were done by using an electrochemical applied potential of -0.75 V versus the RHE and for Cu, -0.80 V versus the RHE using a CBV slurry solution containing 0.1 M KClO 4 . These metal nanoparticles on CBV (M/CBV) catalysts were modified with a Pt precursor via a spontaneous galvanic displacement (SGD) reaction, producing a Pt-M/CBV material to catalyze the ORR in an alkaline medium. High-resolution scanning transmission electron microscopy (HR-STEM) analysis indicates that the PtM/CBV samples include M clusters and Pt single atoms. The ORR characterization measurements were done under a controlled temperature (25.0 °C) and with a mass loading of 100 μg/cm 2 on a glassy carbon (GC) rotating disk electrode at 1600 rpm. The PtCo/CBV showed the highest ORR mass activity of 0.741 A/mgPt at 0.90 V versus the reversible hydrogen electrode (RHE) compared with commercial Pt/CBV. The M/CBV RoDSE catalysts were also tested for the oxygen evolution reaction (OER), and Ni/CBV provided the lowest overpotential of 450 mV at 10 mA/cm 2 disk in 0.1 M KOH.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

The photocatalytic investigation of methylene blue dye with Cr doped zinc oxide nanoparticles

The present work reports eco-friendly and cost effective sol-gel technique for synthesis of Chromium doped ZnO nanoparticles at room temperature. In this process Zinc nitrate, Chromium nitrate were used as precursor. Structural as well as optical properties of Cr induced ZnO samples were analysed by X-ray diffraction technique (XRD), SEM, PL and UV-Visible spectroscopy (UV-Vis) respectively. XRD analysis shows that the samples have hexagonal (wurtzite) structure with no additional peak which suggests that Cr ions fit into the regular Zn sites of ZnO crystal structure. By using Scherrer’s formula for pure and Cr doped ZnO samples the average grain size was found to be 32 nm. Further band gap of pure and doped ZnO samples have been calculated by using UV-Vis spectra. The photo-catalytic degradation of methyl blue dye under UV irradiation was examined for synthesized samples. The results show that the concentration plays an important role in photo-catalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Comparison of the Physicochemical and Electrochemical Properties of Vanadium Oxide-Based Nanomaterials Prepared by Cryochemical Synthesis and Supercritical Drying Technique

Vanadium oxide-based nanomaterials have been prepared by cryochemical synthesis (CCS) and supercritical drying (SCD) in n-hexane and acetone. We have performed the first comparative analysis which demonstrates differences in the physicochemical and electrochemical properties of the products, related to the key features of the effect of the CCS and SCD approaches. The nanomaterials prepared from the same precursor using CCS and SCD (in acetone and n-hexane) have been shown to differ in phase composition and morphology. The oxidizing annealing of the resultant aerogels and cryogel at 500°C in air leads to the formation of only one phase: α-V{sub 2}O{sub 5}. In all cases except the aerogel prepared using SCD in n-hexane, the crystalline α-V{sub 2}O{sub 5} has a higher discharge capacity in comparison with the unannealed aerogels and cryogel. The highest discharge capacity among the annealed aerogels is offered by the sample prepared using SCD in acetone (255 mAh/g), and the highest discharge capacity among the unannealed materials is offered by the sample prepared using SCD in n-hexane (280 mAh/g). The samples range in energy density from 110 to 640 Wh/kg. The highest energy density is also offered by the aerogel prepared using SCD in n-hexane.

36 MATERIALS SCIENCE↗
DOE OSTI2015

GISAXS study of Au-coated light-induced polymer gratings

Surface Relief Gratings (SRGs) are inscribed in the Au-coated azobenzene containing photosensitive polymer films on a glass substrate. The structures consist of micrometer-period sinusoidal patterns of sub-micron amplitudes, formed by photo-isomerization and molecular reorientation processes in the polymer film during exposure to the light interference pattern that drove the formation of a SRG; the precursor is a stack sequence of Au, polymer, and glass. The SRG structures were exposed in GISAXS geometry to high-intensity X-ray radiation from a liquid Ga source (0.134 nm). Scattered photons were registered by a 2D detector, and their intensity distribution enabled us to characterize the structures. Analysis of the 2D patterns yielded information about the pitch of the gratings as well as the thickness of the films forming the gratings. The GISAXS experiments were carried out at the Research Center Juelich.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Design, Synthesis, and Characterization of Polymer Precursors to Li x PON and Li x SiPON Glasses: Materials That Enable All-Solid-State Batteries (ASBs)

LiPON-like glasses that form lithium dendrite impenetrable interfaces between lithium battery components are enabling materials that may replace liquid electrolytes permitting production of all-solid-state batteries (ASBs). Unfortunately, to date, such materials are introduced only via gas-phase deposition. Furthermore, we demonstrate the design and synthesis of easily scaled, lowtemperature, low-cost, solution-processable inorganic polymers containing LiPON/LiSiPON elements. OPCl 3 and hexachlorophosphazene [Cl 2 P=N] 3 provide starting points for elaboration using MNH 2 (M = Li/Na) or (Me 3 Si)NH followed by reaction with controlled amounts of LiNH 2 to produce oligomers/polymers with molecular weights (MWs) ≈1–2 kDa characterized by multinuclear NMR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and matrix-assisted laser desorption/ ionization (MALDI)-time-of-flight (ToF) offering stabilities to 150–200 °C and ceramic yields (800 °C) of 50–60%. 7 Li NMR suggests that precursor-bound Li + dissociates easily, beneficial for electrochemical applications. XPS shows higher N/P ratios (1–3) than via gas-phase methods (<1) correlating N/P ratios, 7 Li shifts, and Li + conductivities. Li 2 SiPHN offers the highest ambient conductivity of 3 × 10 –1 mS cm –1 at 400 °C/2 h/N 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Bioalcohol production from acidogenic products via a two-step process: A case study of butyric acid to butanol

This article presents the full study (lab-scale experimental study and large-scale techno-economic analysis) results of a two-step catalytic process for the conversion of organic waste–derived butyric acid to butanol. Butanol from biomass resources like organic waste promise to become an attractive and sustainable fuel and industrial precursor due to an increase in greenhouse gas content in the atmosphere. Therefore, research in this field is important for energy applications and reduction in greenhouse gas emissions. In this regard, a two-step process was applied in this study to produce butanol from butyric acid that can potentially be derived from organic waste. The two-step process consists of the (1) esterification of butyric acid to methyl butyrate and (2) hydrogenolysis of this methyl butyrate to butanol. The first reaction, esterification of butyric acid, was optimized using carbon-based catalysts. The production of butanol from methyl butyrate via hydrogenolysis was investigated using bimetallic Pt–Co catalysts. The hydrogenolysis of methyl butyrate on these catalysts under optimal conditions of 250 °C, 5 MPa H 2 , and a feed/catalyst weight ratio of 11.2 led to 54.1% selectivity toward 1-butanol. Based on the experimental results, an integrated process simulation model was developed to determine the economic potential of the two-step production of butanol from butyric acid. Using this model, the techno-economic feasibility of the two-step process was analyzed. Here, the minimum selling price (MSP) of 1-butanol produced from butyric acid using this process was US dollars 3.388 per gallon of gasoline equivalent (GGE). This MSP is in the range of recent biofuel market prices of US dollars 2.03/GGE to US dollars 3.83/GGE.

09 BIOMASS FUELS↗
NASA NTRS2019

Evolution and Impact of Saturn V on Space Launch System from a Guidance, Navigation, and Mission Analysis Perspective

The Saturn V launch vehicle represented a jump in capability for heavy lift launch vehicles, enabling the Lunar Orbit Rendezvous approach to planetary exploration employed by the Apollo program 50 years ago. Following Apollo, and the development of the Space Transportation System, the NASA space exploration program shifted focus from lunar exploration to long-term, sustained, re-usable access to Low Earth Orbit. With the recent focus of NASA on the Artemis program and continued exploration of cislunar space as a precursor to Martian exploration, the shift has swung back to heavy lift capability. To meet this need, NASA has developed the Space Launch System. While the vehicle is a new design, it is heavily influenced by the engineering solutions and approach used on the Saturn V while taking advantage of the state of the art of launch vehicle design. The approach to abort, for example, shares many familiarities with the triggers and concept of operations used on Saturn V. Analysis approaches to dispersed trajectory performance are also very similar, but advances in computing technology have enabled a much more expanded set of inputs that can be modelled and assessed in a rapid manner. Additionally, guided flight algorithms share similar first principles but have expanded to include day of launch wind information. Trajectory optimization has also advanced significantly due to the availability of computing resources, but similar maneuvers and profiles are flown across both vehicles. Also, while the approach of onboard inertial navigation has been maintained between the two programs, the shift from platform to strapdown systems enables reduced complexity in the system design while maintaining required performance. As described, the Space Launch System is the evolution of NASA launch vehicle designs, owing a large heritage to the Saturn vehicle program and incorporating advances in propulsion systems, avionics, computing, and sensor technology over the past 50 years.

Ahmad, Naeem↗
DOE OSTI2022

Interlayer spacing in pillared and grafted MCM-22 type silicas: density functional theory analysis versus experiment

Pillaring of synthetic layered crystalline silicates and aluminosilicates provides a strategy to enhance their adsorption and separation performance, and can facilitate the understanding of such behavior in more complex natural clays. In this study, we perform the first-principles density functional theory calculations for the pillaring of the pure silica polymorph of an MCM-22 type molecular sieve. Starting with a precursor material MCM-22P with fully hydroxylated layers, a pillaring agent, (EtO) 3 SiR, can react with hydroxyl groups (–OH) on adjacent internal surfaces, 2(–OH) + (EtO) 3 SiR + H 2 O → (–O) 2 SiOHR + 3EtOH, to form a pillar bridging these surfaces, or with a single hydroxyl, –OH + (EtO) 3 SiR + 2H 2 O → (–O)Si(OH) 2 R + 3EtOH, grafting to one surface. For computational efficiency, we replace the experimental organic ligand, R, by a methyl group. We find that the interlayer spacing in MCM-22 is reduced by 2.66 Å relative to weakly bound layers in the precursor MCM-22P. Including (–O) 2 SiR bridges for 50% (100%) of the hydroxyl sites in MCM-22P increases the interlayer spacing relative to MCM-22 by 2.52 Å (2.46 Å). For comparison, we also analyze the system where all –OH groups in MCM-22P are replaced by non-bridging grafted (–O)Si(OH) 2 R which results in a smaller interlayer spacing expansion of 2.17 Å relative to MCM-22. Our results for the interlayer spacing in the pillared materials are compatible with experimental observations for a similar MCM-22 type material with low Al content (Si : Al = 51 : 1) of an expansion relative to MCM-22 of roughly 2.8 Å and 2.5 Å from our x-ray diffraction and scanning transmission electron microscopy analyses, respectively. The latter analysis reveals significant variation in individual layer spacings.

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

Mineralogical, nanostructural, and Ca isotopic evidence for non-classical calcium phosphate mineralization at circum-neutral pH

Growth pathways of calcium (Ca) phosphate minerals are still under debate, but non-classical growth pathways, which encompass any mode of growth involving attachment of primary particles instead of monomer ions, are currently thought to dominate over classical mechanisms under a wide range of growth conditions. Cation desolvation during ion-by-ion growth is associated with the preferential uptake of isotopically light Ca in Ca-bearing phases, so the Ca isotope composition of Ca-bearing minerals can help to elucidate the dominant growth mechanism. Here, we combine stable Ca isotope analysis with mineralogical characterization and nanoscale imaging of growth features to determine for the first time the rate-dependent Ca isotope fractionation during seeded growth of hydroxyapatite (HAP) involving an octacalcium phosphate (OCP) precursor. Our data reveal that growth rates are strongly attenuated by pH, and that Ca isotope fractionation between the solid and growth solution is independent of growth rate between 1.9 × 10 -9 and 2.8 × 10 -8 mol Ca m -2 s -1 . Moreover, nanoscale images of surface topography reveal direct deposition of primary particles on the HAP seed surface following sustained growth, providing visual evidence of a non-classical growth pathway. Together, these findings support the hypothesis that hydroxyapatite growth is dominantly non-classical. The process of cluster nucleation from the bulk solution and attachment of these clusters to the seeded HAP apparently does not involve a significant kinetic isotope effect, which implies that abiogenically formed Ca-phosphates likely preserve the Ca isotope composition of the fluid from which the crystals originated.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A cobalamin-dependent pathway of choline demethylation from the human gut acetogen Eubacterium limosum

Elevated serum levels of trimethylamine N-oxide (TMAO) are reported to promote the development of atherosclerosis. TMAO is produced by hepatic oxidation of trimethylamine (TMA) produced by the gut microbiome from dietary quaternary amines such as choline. Net TMA production in the gut depends on microbial enzymes that either produce or consume TMA and its precursors. Here we report the elucidation of a novel microbial pathway consuming choline without TMA production. The human gut acetogen Eubacterium limosum grows by demethylating choline to N-N-dimethylaminoethanol. Quantitative mass spectral analysis of the proteome revealed a multi-protein choline to tetrahydrofolate (THF) methyltransferase system present only in choline-grown cells. The components are encoded in a gene cluster on the genome and include MthB, an MttB superfamily member; MthC, homologous to methylotrophic cobalamin-binding proteins; MthA, homologous to cobalamin:THF methyltransferases; and MthK, a protein related to serine kinases. Together, MthB, MthC, and MthA methylate THF with phosphocholine, but not choline or other quaternary amines. MthB specifically methylates Co(I)-MthC with phosphocholine. MthK acts as a bifunctional choline kinase which can utilize ATP or the MthB demethylation product, N,N-dimethylaminoethanol phosphate, to phosphorylate choline. Together, MthK, MthB, MthC, and MthA are proposed to carry out the methylation of THF with choline. These results outline a THF methylation pathway in which choline is first activated with ATP to phosphocholine prior to demethylation to form N,N-dimethylaminoethanol phosphate. Furthermore, the latter can be recycled by MthK to form more phosphocholine without expending additional ATP, thus minimizing energy utilization during choline-dependent acetogenesis.

acetogenesis↗
DOE OSTI2019

Mechanistic Insight into Photocatalytic Pathways of MIL-100(Fe)/TiO 2 Composites

The integration of metal organic frameworks (MOFs) with semiconductors has attracted mounting attention for photocatalytic applications. However, more efforts are needed to unravel the interface structure in MOF/semiconductor composites and its role in charge transfer. In this paper, a MIL-100(Fe)/TiO 2 composite was synthesized as a prototypical photocatalyst and studied systematically to explore the interface structure and unravel the charge transfer pathways during the photocatalytic processes. The composite was fabricated by growing MIL-100(Fe) crystals on TiO 2 using surface-coated FeOOH as the precursor. The as-prepared MIL-100(Fe)/TiO 2 exhibited significantly improved photocatalytic performance over pristine TiO 2 , which was mainly because of the enhanced charge separation as confirmed by transient absorption spectroscopy analysis. This enhancement partially arose from the special chemical structure at the interface, where the Fe-O-Ti bond was formed. As verified by the density functional theory calculation, this distinct structure would create defect energy levels adjacent to the valence band maximum of TiO 2 . During the photocatalytic processes, the defect energy levels serve as sinks to capture excited charge carriers and retard the recombination, which subsequently leads to the increased charge density and promoted photocatalytic efficiency. Meanwhile, the intimate interactions between MIL-100(Fe) and TiO 2 would also help to improve the charge separation by transferring photo-induced holes through the ligands to Fe-O clusters. Lastly, these findings would advance the fundamental understanding of the interface structure and the charge transfer pathways in MOF/semiconductor composite photocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Origin and effect of film sub-stoichiometry on ultraviolet, ns-laser damage resistance of hafnia single layers

Understanding the origin of laser damage-prone precursors in high index materials such as hafnia holds the key to the development of laser damage-resistant multilayer dielectric coated optics for high power and energy laser systems. In this study, we investigate the source of sub-stoichiometry, a potent laser damage precursor, in hafnia films produced by an ion beam sputtering (IBS) deposition method and the effect of such defects on the film performance upon ns ultraviolet (UV) laser (8 ns, 355 nm) exposure. Chemical analysis of data obtained via Rutherford backscattering spectroscopy (RBS) suggests that hafnia films deposited at two different planetary locations from the same deposition run exhibit anisotropic and location-dependent stoichiometries. While the oxygen-to-hafnium ratio is at the stoichiometric value of 2 for the hafnia film at the edge location, the ratio is significantly deviated and is 1.7 for that deposited at the planetary center. The sub-stoichiometric hafnia films display a much lower 1-on-1 damage onset at 1.6 ± 0.2 J/cm 2 compared to 2.3 ± 0.2 J/cm 2 in a stoichiometric film. The low damage performance films also have an over three times higher damage density at fluences above initiation. Coupled with Monte Carlo simulations, we reveal that sub-stoichiometry is primarily attributed to preferential removal of oxygen during film deposition by the bombardment of energetic reflected argon neutrals. The resulting oxygen deficiencies create the sub-bandgap states which facilitate the strong laser energy coupling and reduce the resistance to laser-induced damage in the hafnia single layer films.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Annealing of aromatic polyimide precursors

A study has been made of the thermal behavior of polyimide precursors: an isomeric pair of crystals of the complex formed by p-phenylenediamine with the separated isomers of the di-isopropyl ester of pyromellitic acid. Specimens of this material were isothermally annealed in the temperature range 120 C to 170 C for periods of time up to 1 week. Although this temperature range is well below that customarily used for imidizations, the working hypothesis was that it would be more likely that a polymer embodying at least part of the precursor structure could be formed if the molecular motion was minimized to that actually required for the formation of the imide linkage. The progress of the annealing was followed by: infrared spectroscopy, differential thermal analysis, powder X-ray diffraction, and thermal gravimetric analysis. Single crystal X-ray analysis of the meta monomer yields a structure of chains of alternating acid and base and suggests that this monomer is amenable to polymerization with a minimum of geometrical disruption.

Wakelyn, N. T.↗