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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Pore Structures in Detritusphere of Soils Under Switchgrass and Restored Prairie Vegetation Community

Root detritusphere, that is, the soil in the vicinity of decomposing root residues, plays an important role in soil microbial activity and C sequestration. Pore structure (size distributions and connectivity of soil pores) in the detritusphere serves as a major driver for these processes and, in turn, is influenced by the physical characteristics of both soil and roots. This study compared pore structure characteristics in the root detritusphere of soils of contrasting texture and mineralogy subjected to > 6 years of contrasting vegetation: monoculture switchgrass and polyculture prairie systems. Soil samples were collected from five experimental sites in the US Midwest representing three soil types. Soil texture and mineralogy were measured using a hydrometer and x-ray powder diffraction, respectively. The intact cores were scanned with x-ray computed micro-tomography to identify visible soil pores, biopores, and particulate organic matter (POM). We specifically focused on pore structure within the detritusphere around the POM of root origin. Results showed that the detritusphere of coarser textured soils, characterized by high sand and quartz contents, had lower porosity in the vicinity of POM compared with finer textured soils. POM vicinities in finer textured soils had high proportions of large (> 300 μm diameter) pores, and their pores were better connected than in the coarser soils. Lower porosity in the outer (> 1 mm) parts of the detritusphere of switchgrass than of prairie suggested soil compaction by roots, with the effect especially pronounced in the coarser soils. Here, the results demonstrated that soil texture and mineralogy played a major, while vegetation played a more modest, role in defining the pore structure in the root detritusphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO) 3

Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η 4 -2,3-dimethylbutadiene ruthenium tricarbonyl (Ru(DMBD)(CO) 3 ), a zero-valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. Here, we study the growth mechanism of this precursor by in situ quartz-crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO) 3 produces high-quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical CVD processes, with a strong dependence on both temperature and reaction timescale. The non-self-limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, we suggest that the findings can be generalized to the broader class of zero-oxidation state carbonyl-based precursors used in thermal ALD, with insight into the design of effective saturation studies.

chemical vapor deposition↗
DOE OSTI2023

Influence of contrasting redox conditions on iron (oxyhydr)oxide transformation and associated phosphate sorption

Iron (oxyhydr)oxides strongly adsorb phosphate and limit its bioavailability, but interactions between phosphate and various Fe (oxyhydr)oxides are poorly constrained in natural systems. An in-situ incubation experiment was conducted to explore Fe (oxyhydr)oxide transformation and effects on phosphate sorption in soils with contrasting saturation and redox conditions. Synthetic Fe (oxyhydr)oxides (ferrihydrite, goethite and hematite) were coated onto quartz sand and either pre-sorbed with phosphate or left phosphate-free. The oxide-coated sands were mixed with natural organic matter, enclosed in mesh bags, and buried in and around a vernal pond for up to 12 weeks. Redox conditions were stable and oxic in the upland soils surrounding the vernal pond but largely shifted from Fe reducing to Fe oxidizing in the lowland soils within the vernal pond as it dried during the summer. Iron (oxyhydr)oxides lost more Fe (- 41% ± 10%) and P (- 43 ± 11%) when incubated in the redox-dynamic lowlands compared to the uplands (- 18% ± 5% Fe and - 24 ± 8% P). Averaged across both uplands and lowlands, Fe losses from crystalline goethite and hematite (- 38% ± 6%) were unexpectedly higher than losses from short range ordered ferrihydrite (- 12% ± 10%). We attribute losses of Fe and associated P from goethite and hematite to colloid detachment and dispersion but losses from ferrihydrite to reductive dissolution. Iron losses were partially offset by retention of solubilized Fe as organic-bound Fe(III). Iron (oxyhydr)oxides that persisted during the incubation retained or even gained P, indicating low amounts of phosphate sorption from solution. In conclusion, these results demonstrate that hydrologic variability and Fe (oxyhydr)oxide mineralogy impact Fe mobilization pathways that may regulate phosphate bioavailability.

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

Establishing a Design Strategy for Corrosion Resistant Structural Materials in Molten Salt Technologies

To address the gap in material design strategies for structural components in molten salt-powered technologies, the current work aimed to identify key parameters governing corrosion induced degradation of materials during exposures in molten halide salts. The applicability of the data on dissolution rates of pure metals (e.g., Cr) in a given molten salt to enable predictions of corrosion behavior of multicomponent binary and ternary Fe-based model and Ni-based commercial alloys isothermally exposed in the purified KCl-MgCl 2 in quartz capsules at 700 and 800°C was evaluated. The influence of alloy chemistry on initial dissolution rates and the consequent impact on the time-dependent corrosion induced microstructural evolution in the alloy subsurface was predicted with a coupled thermodynamic-kinetic model. Finally, the model was well able to predict the Cr depletion in all investigated alloys demonstrating the ability of the proposed approach to enable a unique design strategy for structural materials in molten salts.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Colloidal metal transport in soils developing on historic coal mine spoil

Chemical weathering of pyrite via oxidative dissolution is well-known for generating Fe(III)-bearing colloids at acid mine drainage (AMD) sites; however, the potential for physical weathering of pyrite-bearing materials and subsequent release and transport of colloidal pyrite and associated trace metals has not been studied. Here, we monitored the colloidal metal transport in soil developing on abandoned coal mine spoil with a history of AMD generation to systematically study the contribution of colloids to base and trace metal transport and determine the elemental and mineralogical composition of colloids. Additionally, we collected soil pore water using lysimeters with a pore size of approximately 1.3 μm and centrifugation was used to separate the colloids from aqueous fractions. Metal concentrations of Na, Ca, Mg, K, Si, Al, Mn, Fe, Cu, and Zn were analyzed. Our results show only 14% of the total Al and Cu were present in colloidal fractions whereas 23%, 43%, and 54% of Fe, Mn, and Zn were transported in the colloidal phase, respectively. In contrast, all base metals were primarily present in the aqueous concentration with a small fraction (<10%) present in the colloidal phase. The colloidal fractions of the base metals were inferred to be associated with the concentration of clay colloids. The release of colloids exhibited possible sensitivity toward weather conditions such as alternating high temperatures and rainfall during summer (May–July) compared to fall (August–November). The morphology, elemental, and mineral composition of colloids were determined by a scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Colloids were dominated by phyllosilicates (biotite, muscovite, and kaolinite) with minor quartz and feldspars. Other minerals phases identified in colloidal fractions were hematite, goethite, arsenopyrite, and chalcopyrite. Colloids consisting of Fe, S, and O with structures resembling framboidal pyrite were identified, which is consistent with the non-silicates minerals identified by XRD. Our study suggests that the physical weathering of pyrite in the mine spoil can generate colloidal pyrite, which is mobilized and transported by soil pore water. Our results also indicate that these pyritic colloids are associated with toxic trace metals including Cu, Mn, and Zn. Colloid mobilization is also impacted by changes in temperature and precipitation, where clay mobilization afer rain events is favored. Further, sudden spikes in aqueous and/or colloidal concentrations may be the result of local heterogeneity within soils developing on mine spoil, indicating that further field-based work is necessary to better characterize pore-scale processes that control aqueous and colloid transport at similar sites to have a better understanding of potential contaminant transport from mine spoil systems.

58 GEOSCIENCES↗
DOE OSTI2023

Paragenetic controls on CO 2 -fluid-rock interaction and weakening in a macroporous-dominated sandstone

The injection and storage of anthropogenic CO 2 in the subsurface is being deployed as a climate change mitigation tool; however, diagenetic-paragenetic heterogeneity in sandstone reservoirs often contributes to interval specific chemomechanical changes that affect injection and can increase leakage risk.In this paper we address reservoir heterogeneities’ impact on chemomechanical changes in a macroporous-dominated lithofacies of Morrow B sandstone, a formation containing several diagenetically-distinct hydraulic facies while undergoing enhanced oil recovery (EOR) and carbon dioxide (CO 2 ) sequestration. We performed three flow-through experiments using a CO 2 -charged or uncharged formation water combined with four indirect tensile strength tests per post-test sample. We then used the microstructure and paragenetic sequence to understand chemomechanical weakening with key observations as follows: dissolution of carbonates and feldspars changed porosity; increased permeability led to reclassifying each sample in a different hydraulic flow unit; decreased ultrasonic velocity; and did not lead to a loss of tensile strength. Tensile strength maintenance occurred due to the low abundance and minor dissolution of siderite, the stability of quartz, and the relative position of diagenetic ankerite within feldspar. This macroporous-dominated lithofacies is the primary reservoir for the Morrow B Sandstone, and is analogous to other porous sandstone reservoirs. It represents an end-member of a chemomechanically low-risk siliceous CO 2 sequestration and CO 2 -EOR reservoir.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Using mid-infrared spectroscopy to estimate soil microbial properties at the continental scale

Understanding microbial community properties is critical to improving the predictions of biogeochemical processes for enhancing soil carbon sequestration. Here, in this observational study, mid-infrared (MIR) spectroscopy and partial least squares regression was used to predict soil microbial and chemical properties from diverse ecosystems across the continental USA. Random calibration and validation demonstrated the prediction potential for soil properties using MIR spectra, with the strongest predictions for microbial respiration, followed by microbial biomass carbon and nitrogen, ß-glucosidase activity, as well as soil chemical properties including organic carbon and total nitrogen. Microbial properties were mainly positively correlated to spectral regions associated with aliphatic C-H groups and C=O stretches of polysaccharides and negatively correlated to quartz and silicate-associated regions. We conclude that MIR spectroscopy can characterize soil microbial functions and be useful for the improvement of continental-scale soil carbon modeling and prediction programs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Vapor-phase grafting of a model aminosilane compound to Al 2 O 3 , ZnO, and TiO 2 surfaces prepared by atomic layer deposition

Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Here we use ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface organic modification. Vapor-phase (3-aminopropyl)triethoxysilane (APTES) surface silanization of ALD Al 2 O 3 , ZnO and TiO 2 surfaces were studied at 100 °C, 150 °C and 200 °C. In situ quartz crystal microbalance (QCM) and Fourier-transform infrared (FTIR) spectroscopy measurements, and ex situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements showed uniform monolayer silane formation through self-limiting APTES reaction. We observed a higher surface density of grafted APTES species following silanization at 100 °C compared to 200 °C, and we attribute this to the temperature-dependent reactivity of the surface hydroxyls and changes in the mode of APTES reaction. The FTIR and XPS measurements revealed that APTES reacts with Al 2 O 3 and ZnO exclusively through metal siloxy bond formation. However, APTES reacts with TiO 2 through both siloxy bond formation and ammonium salt formation via the amine group.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mixed Tin-Titanium Oxides by Atomic Layer Deposition on Planar Substrates: Physical and Electronic Structure

Ternary atomic layer deposition of Sn-doped TiO x (Sn:TiO x ) and Ti-doped SnO x (Ti:SnO x ) was performed using tetrakisdimethylamidotitanium (IV) and tin(IV) with water at 150 °C on (1 0 0) Si and quartz substrates. The physical structure of the films was investigated using scanning electron, atomic force, and Kelvin probe force microscopies as well as spectroscopic ellipsometry, Raman spectroscopy, and X-ray diffraction. All as-deposited films are amorphous and possessed flat and conformal topographies with low surface roughness (<1 nm). Annealed Sn:TiO x and Ti:SnO x crystallize into the tetragonal anatase TiO 2 and cassiterite SnO 2 structures, respectively, without large variations to the film topography. The chemical composition of the as-deposited and annealed films was investigated through X-ray photoelectron spectroscopy. While dopants are homogenously mixed, the ternary ALD to form Sn:TiO x and Ti:SnO x surprisingly does not follow the rule of mixtures, despite similarities in both the growth rates of binary SnO x and TiO x and the precursors used. This finding is also supported by spectroscopic ellipsometry. Here, we postulate the deviation from the rule of mixtures is due to non-ideal surface chemistry of the binary ALD of SnO x . The optical bandgap of all films was quantified by the Tauc analysis and the valence band position was investigated by valence band X-ray photoelectron spectroscopy. Intra-bandgap states above the valence band maximum were observed for as-deposited Ti:SnO x and Sn:TiO x and ascribed to 5 s states from Sn 2+ ions. The presence of these intra-bandgap states induces enhanced visible absorption and bathochromic shifts to the apparent bandgap for all as-deposited films. Annealing the films removes the intra-bandgap states and increases the optical bandgap. Simplified band diagrams created using the data available demonstrated that the conduction and valence band positions did not vary between the positions of pure TiO 2 or SnO 2 with monotonic increases to the dopant incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. Finally, this review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Graphene-polyelectrolyte multilayer membranes with tunable structure and internal charge

One great advantage of graphene-polyelectrolyte multilayer (GPM) membranes is their tunable structure and internal charge for improved separation performance. In this study, we synthesized GO-dominant GPM membrane with internal negatively-charged domains, polyethyleneimine (PEI)-dominant GPM membrane with internal positively-charged domains and charge-balanced dense/loose GPM membranes by simply adjusting the ionic strength and pH of the GO and PEI solutions used in layer-by-layer membrane synthesis. A combined system of quartz crystal microbalance with dissipation (QCM-D) and ellipsometry was used to analyze the mass deposition, film thickness, and layer density of the GPM membranes. The performance of the GPM membranes were compared in terms of both permeability and selectivity to determine the optimal membrane structure and synthesis strategy. One effective strategy to improve the GPM membrane permeability-selectivity tradeoff is to assemble charge-balanced dense membranes under weak electrostatic interactions. This balanced membrane exhibits the highest MgCl 2 selectivity (~86%). Another effective strategy for improved cation removal is to create PEI-dominant membranes that provide internal positively-charged barrier to enhance cation selectivity without sacrificing water permeability. Finally, these findings shine lights on the development of a systematic approach to push the boundary of permeability-selectivity tradeoff for GPM membranes.

42 ENGINEERING↗
DOE OSTI2020

Optimization of fluorescence and surface adsorption of citric acid/ethanolamine carbon nanoparticles for subsurface tracers

The tunable fluorescence and biocompatibility of fluorescent carbon nanoparticles (FCNs) makes them appealing tracers in geothermal, environmental, and clinical applications. Here, we address FCNs synthesized from reaction and pyrolysis of citric acid and ethanolamine. We examine the fluorescence and the adsorption of these FCNs as critical parameters that influence their use in applications. FCN fluorescence was observed to develop during pyrolysis and measured at pyrolysis temperatures ranging from 190 to 250 °C. Transmission electron microscopy shows that the FCN average diameter of approximately 13 nm is unaffected by pyrolysis temperature. However, pyrolysis temperature strongly affects fluorescence, which peaks at 210 °C. Here, the surface hydrophobicity of the FCNs increases with pyrolysis temperature as measured by retention on reverse phase chromatography. Together, these results suggest that particle surface functionalities provide both fluorescence and hydrophilicity, and that these surface functionalities are destroyed with excessive pyrolysis. To examine their surface adsorption, quartz crystal microbalance measurements demonstrate that pyrolysis temperature increases FCN adsorption on mineral surfaces. Surfaces with greater hydrophobicity show greater FCN adsorption. Adsorption is unaffected by the presence of mono- or divalent ions in solution. This suggests adsorption by hydrophobic interaction for the Fe 2 O 3 , SiO 2 , and AlSiO surfaces studied.

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

Growth of carbon nanotube forests on flexible metal substrates: Advances, challenges, and applications

Owing to their remarkable properties and ordered architecture, vertically aligned CNT forests (VACNT) hold promises for countless applications ranging from energy storage to multifunctional fiber production. Over the last three decades, studies of carbon nanotube (CNT) growth have provided invaluable insight into the CNT nucleation and growth mechanism and enabled critical advancements in nanotechnology. Nevertheless, the ability to fully harness the exceptional VACNT properties in commercial devices is bottlenecked by compatibility of current CNT synthesis processes with large-scale manufacturing. Metal foil substrates present an economic alternative to traditional insulating substrates, like silicon or quartz, and are compatible with both roll-to-roll and automated, large-scale, batch processes. Compared to CNT growth on Si substrates, metal foils present additional challenges, such as increased roughness and reactivity at high temperatures. Nonetheless, many successful VACNT growths on conducting metal foils have been reported, which demonstrate the feasibility of metal substrate use for large-volume production of high-quality CNTs. Here, in this review, we discuss advancements in the field of VACNT growth on metal foil and specifically examine different choices for metal substrates, barrier and catalyst layers, deposition and growth methods, resulting CNT characteristics, and highlight a number of applications that benefit from CNT growth on metal substrates and transition to large-scale manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Direct non-oxidative methane coupling on vitreous silica supported iron catalysts

Direct non-oxidative methane coupling (NMC) is one of the promising pathways for methane upgrading into value-added olefin and aromatic hydrocarbons. The silica-supported iron (i.e., Fe/SiO 2 ) catalyst has been reported effective for NMC, but the effects of silica support on the catalyst property and NMC performance have rarely been explored. Here, in this work, we prepared a vitreous silica-supported iron (Fe/SiO 2 -V) catalyst by flame fusion of a mixture of quartz silica and fayalite. The physicochemical properties and NMC performance of the as-prepared catalysts were measured. Compared to crystalline cristobalite support in Fe/SiO 2 catalyst that has been studied previously, vitreous silica support has disordered Si-O bonds and structural defects, enabling better iron dispersion and more vital metal-support interaction. The as-prepared Fe/SiO 2 -V catalyst had a shorter induction period in methane activation and lower coke yield in NMC. The increase in iron concentration in Fe/SiO 2 -V catalysts elongated the catalyst induction period and promoted aromatics and coke formation. The coke type of the spent Fe/SiO 2 -V catalyst is more uniform than the cristobalite-supported iron catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Comprehensive parametric study of CO 2 sequestration in deep saline aquifers

Carbon dioxide injection in deep saline aquifers is a key method for permanently sequestering anthropogenic CO 2 . Here this study employs a reactive transport model to explore mineral precipitation/dissolution and its impact on reservoir properties in deep saline aquifers. We also assess capillary pressure and relative permeability hysteresis on various CO 2 trapping mechanisms. Results from this study reveal the significant influence of initial brine composition on mineral precipitation/dissolution. The dissolution and precipitation of minerals have different effects around the wellbores compared to the overall reservoir. Additionally, salt concentration (Ca ++ and Mg ++ ) and quartz surface area affect CO 2 mineralization, while Na + impacts halite precipitation, altering flow properties. The effect of capillary pressure is significant, as including the capillary pressure in the simulation case resulted in significantly improved CO 2 trapping, achieving almost total dissolution of the injected CO 2 in around 300 years. This study offers novel insights into the interactions of reservoir minerals, brine properties, and the injected CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗