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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Vapor Phase Infiltration of Titanium Oxide into P3HT to Create Organic–Inorganic Hybrid Photocatalysts

Herein, we report for the first time the use of vapor phase infiltration (VPI) to infuse conducting polymers with inorganic metal oxide clusters that together form a photocatalytic material. While vapor infiltration has previously been used to electrically dope conjugated polymers, this is the first time, to our knowledge, that the resultant hybrid material has been demonstrated to have photocatalytic properties. The system studied is poly(3-hexylthiophene-2,5-diyl) (P3HT) vapor infiltrated with TiCl 4 and H 2 O to create P3HT-TiO x organic–inorganic hybrid photocatalytic materials. X-ray photoelectron spectroscopy analysis shows that P3HT-TiO x VPI films consist of a partially oxidized P3HT matrix, and the infiltrated titanium inorganic is in a 4+ oxidation state with mostly oxide coordination. Upon visible light illumination, these P3HT-TiO x hybrids degrade methylene blue dye molecules. The P3HT-TiO x hybrids are 4.6× more photocatalytically active than either the P3HT or TiO 2 individually or when sequentially deposited (e.g., P3HT on TiO 2 ). On a per surface area basis, these hybrid photocatalysts are comparable or better than other best in class polymer semiconductor photocatalysts. VPI of TiCl 4 + H 2 O into P3HT makes a unique hybrid structure and idealized photocatalyst architecture by creating nanoscale TiO x clusters concentrated toward the surface achieving extremely high catalytic rates. The mechanism for this enhanced photocatalytic rate is understood using photoluminescence spectroscopy, which shows significant quenching of excitons in P3HT-TiO x as compared to neat P3HT, indicating that P3HT acts as a photosensitizer for the TiO x catalyst sites in the hybrid material. This work introduces a new approach to designing and synthesizing organic–inorganic hybrid photocatalytic materials, with expansive opportunities for further exploration and optimization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

The Combined Detection of Morphological and Molecular Biomarkers: Implications for Astrobiology

Experience gathered by previous researchers during their hunt for evidence of early Earth life has shown the complexity in interpreting observations of possible microfossils and to establish the evidence to be positive. Similarly, the stillsimmering controversy on the nature of the nano-structures in Martian meteorite ALH84001 described by McKay et al. (1996) emphasizes the difficulties of conclusively identifying those structures as (a) fossilized bacterial cells and (b) establish their indigeneity. A better understanding of biological signatures in rocks is needed in order to identify traces of microbial life, which include morphological, mineralogical and chemical traces. It is thus considered crucial to tackle the problems emerging in the search for evidence of early life on Earth and in exopaleontological research with a multidisciplinary approach. With this is mind we applied surface sensitive Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) to a previously described 25 m.y. old fossil bacterial biofilm. This technique allows in situ analysis with high mass resolution as well as molecular imaging of micron sized structures. As no extraction or derivatisation of the sample is required for ToF-SIMS analysis, electron microscopical investigation of the same samples subsequent to analysis is possible, thus allowing the combination of molecular and morphological biomarkers. The analysed fossil bacterial biofilms were associated with macrofossils from volcanoclastic lacustrine sediments from the Upper Oligocene Enspel formation (Germany). Preliminary scanning electron microscopy (SEM) studies have shown that a fossil structure interpreted as a coprolite purely consisted of fossilized bacterial biofilm. For ToF-SIMS investigation small particles were taken from the fossil biofilm and mounted onto Au-coated In-foil and analysed in a Phi Evans T-2000 TRIFT system. The ToF-SIMS analysed samples were Au/Pd-sputter coated and imaged using a Philips XL40 Field Emission Gun SEM (FEG-SEM). ToF-SIMS analysis of the organic rich fossil biofilm (TOC 29%) in the 0-100 Dalton (Da) range showed significant amounts of inorganic species, confirming the results obtained previously by EDX analysis, clearly showing the bacterial fossils to be mineralised. ToF-SIMS furthermore revealed the presence of a variety of low- and high-mass organic molecules and fragments thereof. These include peaks indicative of alkenes and alkanes, aromatic organic species and the polycyclic aromatic hydrocarbon naphthalene. More tentatively, peaks indicative of alkyl pyrroles and pyridyl-CH2 were identified. Other peaks of interest include peaks indicative of C(n)H(2n)O2 and C(n)H(2n-2)O2, which according to their general formula would suggest the presence of both saturated and unsaturated fatty acids although further in situ derivatisation experiments and GC-MS (Gas Chromatography MS) need to be applied to verify this beyond doubt. Furthermore, peaks at m/z 370, 384, 398, 412, 426, 440, 454 and 468 were identified, which indicate the potential presence of bacterial hopanes, a class of biomarkers indicative of bacteria. The main diagnostic peak for this group of chemicals is the fragment at m/z 191.18. Our studies conducted on purified hopane standards have shown that in the high-mass resolution mode differentiation of this diagnostic hopane peak and polyethylene at m/z 191.05 is possible. However, the spectra discussed here were collected in the lower resolution mapping mode, therefore this differentiation was not possible. The centroids of the possible hopane peaks obtained on the fossil biofilms are well within the range associated with bacterial hopanes. There is a strong possibility therefore that hopanoids may be associated with the fossil bacterial cells. Due to the non-destructive nature of ToF-SIMS, analysed samples can be studied using SEM, thus allowing the combination of morphological and molecular biomarkers. Subsequent SEM analysis of the ToF-SIMS analysed samples confirmed that the analysed material purely consists of fossil bacterial cells. This is thus the first successful effort to demonstrate the combination of spectral and morphological biomarkers. The advantages of highly sensitive non-destructive in situ analysis techniques for biomarker detection are invaluable, particularly with respect to envisaged Mars sample return missions, as it may allow us to identify remains and traces of former microbial life in both ancient terrestrial and extraterrestrial materials. This technique may prove particularly useful in the quest for extraterrestrial life with respect to precious extraterrestrial materials, as minute quantities are sufficient to conduct analysis.

Toporski, J.↗
NASA NTRS2011

Mass Spectrometry on Future Mars Landers

Mass spectrometry investigations on the 2011 Mars Science Laboratory (MSL) and the 2018 ExoMars missions will address core science objectives related to the potential habitability of their landing site environments and more generally the near-surface organic inventory of Mars. The analysis of complex solid samples by mass spectrometry is a well-known approach that can provide a broad and sensitive survey of organic and inorganic compounds as well as supportive data for mineralogical analysis. The science value of such compositional information is maximized when one appreciates the particular opportunities and limitations of in situ analysis with resource-constrained instrumentation in the context of a complete science payload and applied to materials found in a particular environment. The Sample Analysis at Mars (SAM) investigation on MSL and the Mars Organic Molecule Analyzer (MOMA) investigation on ExoMars will thus benefit from and inform broad-based analog field site work linked to the Mars environments where such analysis will occur.

Brinckerhoff, W. B.↗
DOE OSTI2021

Probabilistic Deep Learning Approach to Automate the Interpretation of Multi-phase Diffraction Spectra

Autonomous synthesis and characterization of inorganic materials requires the automatic and accurate analysis of X-ray diffraction spectra. For this task, we designed a probabilistic deep learning algorithm to identify complex multi-phase mixtures. At the core of this algorithm lies an ensemble convolutional neural network trained on simulated diffraction spectra, which are systematically augmented with physics-informed perturbations to account for artifacts that can arise during experimental sample preparation and synthesis. In this work, larger perturbations associated with off-stoichiometry are also captured by supplementing the training set with hypothetical solid solutions. Spectra containing mixtures of materials are analyzed with a newly developed branching algorithm that utilizes the probabilistic nature of the neural network to explore suspected mixtures and identify the set of phases that maximize confidence in the prediction. Our model is benchmarked on simulated and experimentally measured diffraction spectra, showing exceptional performance with accuracies exceeding those given by previously reported methods based on profile matching and deep learning. We envision that the algorithm presented here may be integrated in experimental workflows to facilitate the high-throughput and autonomous discovery of inorganic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In situ reductive dissolution to remove Iodine-129 from aquifer sediments

The use of an aqueous reductant (Na-dithionite) with pH buffer (K-carbonate, pH 12) was evaluated in this laboratory study as a potential remedial approach for removing Fe oxide associated iodine and enhancing pump-and-treat extraction from iodine-contaminated sediments in the unconfined aquifer in the 200 West Area of the Hanford site. X-ray fluorescence data of untreated sediment indicated that iodine was largely associated with Fe (i.e., incorporated into Fe oxides), however, XANES data was inconclusive as to valence state. During groundwater leaching, aqueous and adsorbed iodine was quickly released, then additional iodine was slowly released potentially from dissolution of one or more surface phases. The Na-dithionite treatment removed greater iodine mass (2.9x) at a faster rate (1 to 4 orders of magnitude) compared to leaching with groundwater alone. Iron extractions for untreated and treated sediments showed a decrease in Fe(III)-oxides, which likely released iodine to aqueous solution. Solid phase inorganic carbon and aqueous Ca and Mg analysis further confirmed that significant calcite dissolution did not occur in these experiments meaning these phases did not release significant iodine. Although it was expected that, after treatment, 127 I concentrations would eventually be lower than untreated sediments, leaching experiments showed continued, elevated iodine concentrations for treated samples over 750 hours. Stop flow events during 1-D column leaching suggested that some iodide precipitated within the first few pore volumes. In the survey of metals during leaching, some silver was detected which could have been solubilized by the elevated pH of initial Na-dithionite injection. Then, silver (or other metals) could have subsequently precipitated with iodide during the initial stop flow event forming a slowly dissolving source. Although significantly greater iodine is removed with treatment, the long-term leaching needs to be investigated further as it may limit dithionite treatment at the field scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Tuning Metal–Organic Framework (MOF) Topology by Regulating Ligand and Secondary Building Unit (SBU) Geometry: Structures Built on 8-Connected M 6 (M = Zr, Y) Clusters and a Flexible Tetracarboxylate for Propane-Selective Propane/Propylene Separation

Topology evolution originating from variations of linker and SBU (Secondary Building Unit) geometries could largely enrich the chemistry of metal–organic frameworks (MOFs). Here we report the synthesis and characterization of three MOF structures built on the same organic linker, N,N,N',N'-Tetrakis(4-carboxyphenyl)-1,4-phenylenediamine (tcppda) and similar 8-connected M 6 (M = Zr or Y) clusters. The three compounds, HIAM-402, HIAM-403, and HIAM-311, feature 4,8-connected sqc, scu, and flu topology, respectively. Detailed structural analysis revealed that different geometries of the inorganic M 6 SBUs as well as the organic linker have led to the formation of distinct MOF nets. In particular, HIAM-402 features exceptional framework stability and high porosity and acts as a propane-selective adsorbent for the discrimination of propane and propylene. Its balanced adsorption selectivity (S propane/propylene = 1.43) and capacity (Q propane = 133.3 cm 3 /g, 298 K and 1 bar) endow it with the capability of separating propane and propylene mixtures and one-step production of highly pure propylene (purity >99.9%), as validated by column breakthrough measurements, with the presence of moisture or propyne. As a result, ab initio calculations further confirm that the propane-selective behavior of HIAM-402 is a result of its higher binding energy toward propane compared to that of propylene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Rhizosphere and detritusphere habitats modulate expression of soil N-cycling genes during plant development

Interactions between plant roots and rhizosphere bacteria modulate nitrogen (N)-cycling processes and create habitats rich in low molecular weight compounds (exudates) and complex organic molecules (decaying root litter) compared to those of bulk soil. Microbial N-cycling is regulated by edaphic conditions and genes from many interconnected metabolic pathways, but most studies of soil N-cycling gene expression have focused on single pathways. Currently, we lack a comprehensive understanding of the interplay between soil N-cycling gene regulation, spatial habitat, and time. We present results from a replicated time series of soil metatranscriptomes; we followed gene expression of multiple N transformations in four soil habitats (rhizosphere, detritusphere, rhizo-detritusphere, and bulk soil) during active root growth for the annual grass, Avena fatua. The presence of root litter and living roots significantly altered the trajectories of N-cycling gene expression. Upregulation of assimilatory nitrate reduction in the rhizosphere suggests that rhizosphere bacteria were actively competing with roots for nitrate. Simultaneously, ammonium assimilatory pathways were upregulated in both rhizosphere and detritusphere soil, which could have limited N availability to plants. The detritusphere supported dissimilatory processes DNRA and denitrification. Expression of nitrification genes was dominated by three phylotypes of Thaumarch aeota and was upregulated in bulk soil. Unidirectional ammonium assimilation and its regulatory genes (GS/GOGAT) were upregulated near relatively young roots and highly decayed root litter, suggesting N may have been limiting in these habitats (GS/GOGAT is typically activated under N limitation). In conclusion, our comprehensive analysis indicates that differences in carbon and inorganic N availability control contemporaneous transcription of N-cycling pathways in soil habitats.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1989

Analytical electron microscopy of biogenic and inorganic carbonates

In the terrestrial sedimentary environment, the mineralogically predominant carbonates are calcite-type minerals (rhombohedral carbonates) and aragonite-type minerals (orthorhombic carbonates). Most common minerals precipitating either inorganically or biogenically are high magnesium calcite and aragonite. High magnesium calcite (with magnesium carbonate substituting for more than 7 mole percent of the calcium carbonate) is stable only at temperatures greater than 700 C or thereabouts, and aragonite is stable only at pressures exceeding several kilobars of confining pressure. Therefore, these carbonates are expected to undergo chemical stabilization in the diagenetic environment to ultimately form stable calcite and dolomite. Because of the strong organic control of carbonate deposition in organisms during biomineralization, the microchemistry and microstructure of invertebrate skeletal material is much different than that present in inorganic carbonate cements. The style of preservation of microstructural features in skeletal material is therefore often quite distinctive when compared to that of inorganic carbonate even though wholesale recrystallization of the sediment has taken place. Microstructural and microchemical comparisons are made between high magnesium calcite echinoderm skeletal material and modern inorganic high magnesium calcite inorganic cements, using analytical electron microscopy and related techniques. Similar comparisons are made between analogous materials which have undergone stabilization in the diagenetic environment. Similar analysis schemes may prove useful in distinguishing between biogenic and inorganic carbonates in returned Martian carbonate samples.

Blake, David F.↗
NASA NTRS2010

ISS Expeditions 16 Thru 20: Chemical Analysis Results for Potable Water

This slide presentation reviews the results of the chemical analysis of the potable water supply from the International Space Station (ISS) expeditions 16 thru 20. Both Russian ground water and shuttle-transferred water are available for the use of the ISS crew's requirements. This is supplemented with condensate water and water form the Water Recovery System (WRS). An overview of the condensate H2O recovery system is given and the WRS is described and diagrammed. The water quality requirements, the handling, and analytical methods for the inorganic and organic tests are reviewed. The chemical analysis results for expeditions 16-20 archival water samples collected from the various water sources indicate that all of the ISS potable water supplies were acceptable for crew consumption.

Straub, John E., II↗
NASA NTRS1974

Fabrication and test of inorganic/organic separators

Completion of testing and failure analysis of MDC 40 Ahr silver zinc cells containing largely inorganic separators was accomplished. The results showed that the wet stand and cycle life objectives of the silver zinc cell development program were accomplished. Building, testing and failure analysis of two plate cells employing three optimum separators selected on the basis of extensive screening tests, was performed. The best separator material as a result of these tests was doped calcium zirconate.

Smatko, J. S.↗
NASA NTRS2016

Effect of the Presence of Chlorates and Perchlorates on the Pyrolysis of Organic Compounds: Implications for Measurements Done with the SAM Experiment Onboard the Curiosity Rover

The Mars Science Laboratory (MSL) Curiosity Rover carries a suite of instruments, one of which is the Sample Analysis at Mars (SAM) experiment. SAM is devoted to the in situ molecular analysis of gases evolving from solid samples collected by Curiosity on Mars surface/sub-surface. Among its three analytical devices, SAM has a gaschromatograph coupled to a quadrupole mass spectrometer (GC-QMS). The GC-QMS is devoted to the separation and identification of organic and inorganic material. Before proceeding to the GC-QMS analysis, the solid sample collected by Curiosity is subjected to a thermal treatment thanks to the pyrolysis oven to release the volatiles into the gas processing system. Depending on the sample, a derivatization method by wet chemistry: MTBSTFA of TMAH can also be applied to analyze the most refractory compounds. The GC is able to separate the organic molecules which are then detected and identified by the QMS (Figure 1). For the second time after the Viking landers in 1976, SAM detected chlorinated organic compounds with the pyrolysis GC-QMS experiment. The detection of perchlorates salts (ClO4-) in soil at the Phoenix Landing site suggests that the chlorohydrocarbons detected could come from the reaction of organics with oxychlorines. Indeed, laboratory pyrolysis experiments have demonstrated that oxychlorines decomposed into molecular oxygen and volatile chlorine (HCl and/or Cl2) when heated which then react with the organic matter in the solid samples by oxidation and/or chlorination processes.

Millan, M.↗