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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Green Synthesis of Silver Nanoparticle Capped with Allium cepa and Their Catalytic Reduction of Textile Dyes: An Ecofriendly Approach

Today, environment pollution control is a matter of concern, everybody is willing to make a product that should be ecofriendly. Nowadays, water resources are full of untreated waste materials, discharge of hazardous and toxic dyes coming from textile and other chemical industries. These environmental hazards are difficult to remove by commercial water treatment plans, thus we need something that would present an efficient means for removal of these hazards. In this research paper, we have synthesize silver nanoparticle in a green way by using aqueous extract of Allium cepa (onion), and further these silver nanoparticle were tested for the catalytic degradation of various dyes by UV/Visible spectroscopy and silver nanoparticle showed reduction in dyes intensity after a particular period of incubation time. SEM and TEM, Particle size and Zeta potential analysis was done to analyze the surface morphology, particle size range and stability of the silver nanoparticle. Greenly synthesized silver nanoparticle was found to be spherical in shape, having particle size value ranged from 50 to 100 nm with a zeta potential value of −29 mV. An EDX spectroscopy method was used to confirm the presence of silver nanoparticle in the synthesized material. An X-ray crystallography was done to ensure the crystallinity of the silver nanoparticle. Further an ATR-FTIR was performed to confirm the capping of the silver nanoparticle with the phenolic group of the onion. All these study emphasized that silver nanoparticle capped with onion (AgNPs@Ac) is the excellent catalyst for the reduction of hazardous and toxic dyes as well as they serve best purpose of the eco-friendly approach.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Thermo-Oxidative Aging of LDPE/Stearoyl Chloride-Grafted Cellulose Nanocrystals Blown Films

The effect of the incorporation of pristine and stearoyl chloride grafted CNCs on the chemical, mechanical, thermal and microstructural properties, during the thermo-oxidative aging, of LDPE blown films at 60 °C was studied. The success of the pristine CNCs grafting was assessed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Thermal-gravimetric analysis (TGA), Atomic Force Spectroscopy (AFM) and contact angle measurements. The results show that chemical modification decreases both, the CNCs thermal stability and the polar component of surface energy, i.e. increases the nanocrystals hydrophobicity. Also, it was found that neither CNCs crystalline structure nor its dimensions changed with grafting. The changes on the blown film properties during thermo-oxidative aging were monitored using FT-IR, DSC, DRX and tensile testing. It was found that the CNCs catalyzed the production of carboxylic acids as a final degradation by-product, whereas the CNC-g-C{sub 18} inhibits its formation, i.e. in presence of CNCs grafted with stearoyl chloride the catalytic effect attributed to the pristine CNCs was partially inhibited. The DSC, DRX and tensile testing results show the microstructural arrangements due to the annealing and the chains oxidation predominated during the first 30 days of aging and then chain scissions prevail. These findings suggest an analogous reduction in molecular weight at the end thermo-oxidative aging. In addition, the presence of a high concentration of carboxylic acid and the drop in molecular weight after LDPE aging will facilitate the biodegradation of these oxo-degradable films.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fabrication, Analysis of Microstructure and Oxidation Resistance of Cemented C/C Composites by Laser

Cylindrical carbon–carbon composites have been cemented using a CO{sub 2} laser actuated by a raster scanning mirror system in a four-step sequence. Complete and homogenous surface cementation as well as thermal stability of the composites was sought after and achieved. The line of heat created from the laser beam impinged parallel to the axis of the pre-coated cylinder, while suspended from one end and slowly rotated. Four slurry compositions, all containing chloride salts from refractory elements, some combined with silicon, were pre-deposited by air spraying it over each specimen and then laser treated sequentially. Confined heat sublimed the chlorine ions resulting in silicide compounds that reacted with the carbon substrate to form a bonding layer. Microstructure characterization was performed using scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction, immediately after the cementation was consolidated and after heat treated under argon. Preliminary oxidation weight loss tests were performed up to 1423 K under argon and air, revealing a 9.8 and 30.6% weight reduction, respectively, after 9 h of exposure. Cemented specimens were then coated with a glass overcoat layer that allowed them to perform moderately better against oxidation achieving up to a 28% weight loss after 20 h at 1273 K in air.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Electropulsing on Surface Mechanical Behavior and Microstructural Evolution of Inconel 718 during Ultrasonic Surface Rolling Process

In the current study, the surface mechanical behavior and microstructural evolution of Inconel 718 superalloy processed by the ultrasonic surface rolling process (USRP) and electropulsing-assisted ultrasonic surface rolling process (EP-USRP) were carefully analyzed. The experimental results suggested that after EP-USRP with a frequency of 400 Hz, significant enhancements in Vickers microhardness and nanoindentation hardness were achieved compared to those of USRP specimens, with increases of 13.6 and 9.9%, respectively. Moreover, the machined surface quality, wear resistance, and thermal stability were also improved after EP-USRP (400 Hz). These enhancements in mechanical behavior are closely related to the microstructural evolution induced by electropulsing. Under the coupling of thermal and athermal effects of high-energy electropulsing, the deformation limit of USRP is surpassed and a new balance is achieved between the electropulsing softening effect and the ultrasonic rolling hardening effect. Therefore, further grain refinement, improved plastic deformation ability in the strengthened layer, and the interaction effect between nano-sized precipitates and grain boundaries are probably the main reasons for these results.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unseeded, spontaneous nucleation of spherulitic magnesium calcite

Most of the sedimentary carbonates deposited in the marine environments are composed of calcium carbonate minerals with varying amounts of incorporated Mg 2+ . However, understanding how interactions of impurities with carbonate and their incorporation affect sediments behavior remains a challenge. Here, a new insight is obtained by monitoring solution composition, morphology, and electrokinetic potential of carbonate particles formed in a spontaneous unseeded batch precipitation experiment using electrochemical and scanning electron microscopy methods. The solid composition and growth rate are extracted from changes in the bulk composition and fitted to chemical affinity rate law, revealing that the precipitation pathway consists of second-order dissolution and first-order precipitation. The molecular dynamics simulations show that the lattice strain induced by randomly substituting Ca 2+ by Mg 2+ stabilizes spherical nanoparticles and reduces their surface area and volume. Combining kinetics and thermodynamics insight, we conclude that variation in the carbonate bulk and interfacial energies, along with the solution supersaturation, lead to the dissolution-precipitation transformation pathway from Mg-rich to Mg-poor carbonate phase that preserves spherulitic morphology. Furthermore, our findings are relevant for long-standing questions of how impurities influence diagenesis of carbonate sediments and spherulitic carbonate particles' origin.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Lithium splashing from flowing liquid lithium limiter and its effect on high confinement plasma performance in EAST tokamak

To study the potential applications of liquid lithium (Li) as plasma facing material, the third generation of flowing liquid Li (FLiLi) limiter has been designed and successfully tested in EAST tokamak H-mode discharges in the 2018 run campaign. Here, the stability of liquid Li on FLiLi surface, and Li splashing and its effect on the plasma performance are investigated in detail. Li splashing was observed in L-mode and H-mode discharges due to Rayleigh-Taylor (R-T) instability, resulting from electromagnetic forces J → x B → . Li splashing in low-parameter plasma decreased both core and edge electron temperatures, resulting in the degradation of plasma energy confinement and even H-L back transition, however, it almost did not influence plasma confinement performance in high-parameter plasma. These findings indicate that high-parameter plasma has higher tolerance to Li impurities than low-parameter plasma. By contrast, tungsten splashing from the melted layer on the upper divertor was also induced by the R-T instability but generally resulted in plasma disruption, which suggests lower tolerance to tungsten impurities in EAST tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Radio-echo sounding of Crary Ice Rise reveals abundant marine ice in former ice shelf rifts and basal crevasses

Crary Ice Rise formed after the Ross Ice Shelf re-grounded ~1 kyr BP. We present new ice-penetrating radar data from two systems operating at center frequencies of 7 and 750 MHz that confirm the ice rise is composed of a former ice shelf buried by subsequent accumulation. Stacks of englacial diffraction hyperbolas are present almost everywhere across the central ice rise and extend up to ~350 m above the bed. In many cases, bed reflections beneath the diffraction hyperbolas are obscured for distances up to 1 km. Waveform modeling indicates that the diffraction hyperbolas are likely caused by marine ice deposits in former basal crevasses and rifts. The in-filling of rifts and basal crevasses may have strengthened the connection between the ice rise and the surrounding ice shelf, which could have influenced local and regional ice dynamics. Three internal reflection horizons mark the upper limit of disturbed ice and diffraction hyperbolas in different sections of the ice rise, indicating at least three stages of flow stabilization across the ice rise. A surface lineation visible in MODIS imagery corresponds spatially to deepening and strong deformation of these layers, consistent with the characteristics of former grounding lines observed elsewhere in Antarctica.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

High-Loading Intermetallic Pt 3 Co/C Core–Shell Nanoparticles as Enhanced Activity Electrocatalysts toward the Oxygen Reduction Reaction (ORR)

A facile, seed-mediated growth method and postannealing treatment have been employed to synthesize a single-phase 40% mass loading intermetallic Pt 3 Co/Vulcan electrocatalyst, enabling the electrocatalytic layer to be thinner and thus lowering the mass transport resistance for the ORR in proton exchange membrane fuel cells (PEMFCs). These 40% Pt 3 Co/C nanocatalysts exhibited superior kinetics toward the ORR, relative to a 20% Pt 3 Co/C catalyst, and only showed a slight degradation in the half-wave potential and electrochemical surface area after a 4000-cycle stability test. The high activity and stability are attributed to a stable intermetallic Pt3Co core with a Pt shell two to three atomic layers thick, as well as to its good dispersion on the support. This seed-mediated growth approach and postannealing treatment provide a new strategy to ensure single-phase formation and uniform particle size distribution for other high-mass-loading binary intermetallic/alloy electrocatalyst systems and can contribute to the practical commercialization of PEMFCs, especially in high-current-density applications, such as automotive

36 MATERIALS SCIENCE↗
DOE OSTI2019

Enhanced Formation of Solvent-Shared Ion Pairs in Aqueous Calcium Perchlorate Solution toward Saturated Concentration or Deep Supercooling Temperature and Its Effects on the Water Structure

As a candidate of Martian salts, calcium perchlorate [Ca(ClO 4 ) 2 ] has the potential to stabilize liquid water on the Martian surface because of its hygroscopicity and low freezing temperature when forming aqueous solution. These two properties of electrolytes in general have been suggested to result from the specific cation–anion–water interaction (ion pairing) that interrupts the structure of solvent water. To investigate how this concentration-dependent and temperature-dependent ion pairing process in aqueous Ca(ClO 4 ) 2 solution leads to its high hygroscopic property and the extreme low eutectic temperature, we have conducted two sets of experiments. First, the effects of concentration on aqueous calcium perchlorate from 3 to 7.86 m on ion pairing were investigated using Raman spectroscopy. Deconvolution of the Raman symmetric stretching band (ν 1 ) of ClO 4 – showed the enhanced formation of solvent-shared ion pairs upon increasing salt concentration at room temperature. We have confirmed that the low tendency of forming contact ion pairs in concentrated solution contributes to the high hygroscopicity of the salt. Second, the near eutectic samples were studied as a function of temperature by both combined differential scanning calorimetry–Raman spectroscopic experiments and in situ X-ray diffraction. The number of solvent-shared ion pairs was found to increase with decreasing temperature when cooled below the temperature of maximum density of the solution, driven by a change in water toward an ice-like structure in the supercooled regime. The massive presence of solvent-shared ion pairs in turn limits the development of the long-range order in the tetrahedral networks of water molecules, which is responsible for the extremely low eutectic point and deep supercooling effects observed in the Ca(ClO 4 ) 2 –H 2 O system.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Mechanistic Study of the Li–Air Battery with a Co 3 O 4 Cathode and Dimethyl Sulfoxide Electrolyte

The lithium–air battery, a powerful competitor to replace the traditional lithium-ion battery, has attracted increasing attention due to its extremely high theoretical energy density. However, its development is limited by the cathode and electrolyte properties, which should include high stability, conductivity, and electrocatalytic properties in oxygen-rich environments. Here, we employ a systematic first-principles study of Li–O 2 discharge and charge reactions on the Co 3 O 4 -based cathode with the assistance of dimethyl sulfoxide (DMSO) electrolyte. The structure, stability, and electronic properties of different surface reconstructions of the Co 3 O 4 (100) facet are investigated. In addition, the mechanisms and thermodynamic overpotentials of multi-step reactions between Li + /e – and O 2 are provided, where lithium suboxide products (Li 2 O 2 or Li 3 O 2 ) are formed on the different Co 3 O 4 (100) terminations. The solvation shell of Li + components in explicit DMSO solvent is investigated through ab initio molecular dynamics simulations. In general, we find that the Co 3 O 4 (100)-O (oxidized) surface is the most stable one under standard conditions, and the stable Li + solvation structure is found in a tetrahedral Li(DMSO) 4 + shell in the DMSO-based electrolyte. Moreover, in the system of the Co 3 O 4 (100)-O cathode and DMSO electrolyte, the solution model pathway is energetically favorable for the Li–O 2 discharge reaction. It provides a low constant overpotential of 0.17 V during a long-term discharging process, thus causing the final toroid Li 2 O 2 formation on the cathode. During the charging process, an overpotential of 0.36 V is required to rapidly decompose Li 2 O 2 .

25 ENERGY STORAGE↗
DOE OSTI2023

Electroluminescence and Plasmon-Assisted Directional Photoluminescence from 2D HgTe Nanoplatelets

In the visible range, 2D nanoplatelets (NPLs) have brought significant benefits compared to their 0D counterpart with an inherently anisotropic emission, a narrower photoluminescence (PL) signal, and new degrees of freedom to design heterostructures. Compared to the properties of cadmium chalcogenide NPLs in the visible, similar research is still mostly lacking in the infrared, in spite of existing synthetic paths to obtain narrow band gap semiconductors in 2D colloidal form. Here, in this paper, we focus on 2D HgTe NPLs and show how their PL can be stabilized through the proper choice of surface chemistry. We then demonstrate two important steps toward bright infrared light emitting diodes (LEDs) which are (i) the coupling to a plasmonic grating to control the magnitude and spatial direction of the PL signal and (ii) the observation of electroluminescence at 1300 nm, which is near telecom wavelength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Silicon Photoelectrode Thermodynamics and Hydrogen Evolution Kinetics Measured by Intensity-Modulated High-Frequency Resistivity Impedance Spectroscopy

Here, we present an impedance technique based on light intensity-modulated high-frequency resistivity (IMHFR) that provides a new way to elucidate both the thermodynamics and kinetics in complex semiconductor photoelectrodes. We apply IMHFR to probe electrode interfacial energetics on oxide-modified semiconductor surfaces frequently used to improve the stability and efficiency of photoelectrochemical water splitting systems. Combined with current density-voltage measurements, the technique quantifies the overpotential for proton reduction relative to its thermodynamic potential in Si photocathodes coated with three oxides (SiO x , TiO 2 , and Al 2 O 3 ) and a Pt catalyst. In pH 7 electrolyte, the flatband potentials of TiO 2 - and Al 2 O 3 -coated Si electrodes are negative relative to samples with native SiO x , indicating that SiO x is a better protective layer against oxidative electrochemical corrosion than ALD-deposited crystalline TiO 2 or Al 2 O 3 . Adding a Pt catalyst to SiO x /Si minimizes proton reduction overpotential losses but at the expense of a reduction in available energy characterized by a more negative flatband potential relative to catalyst-free SiO x /Si.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Antifouling Properties of a Self-Assembling Glutamic Acid-Lysine Zwitterionic Polymer Surface Coating

There is a necessity for the development of antifouling materials to resist adsorption of biomacromolecules. Here we describe the preparation of a novel zwitterionic block copolymer with the potential to prevent or delay the formation of microbial biofilms. The block copolymer comprised a zwitterionic (hydrophilic) section of alternating glutamic acid (negatively charged) and lysine (positively charged) units and a hydrophobic polystyrene section. Cryo-TEM and dynamic light-scattering (DLS) results showed that, on average, the block copolymer self-assembled into 7-nm-diameter micelles in aqueous solutions (0 to 100 mM NaCl, pH 6). Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and contact angle measurements demonstrated that the block copolymer self-assembled into a brush-like monolayer on polystyrene surfaces. The brush-like monolayer produced from a 100 mg/L block copolymer solution exhibited an average distance, d, of approximately 4-8 nm between each block copolymer molecule (center to center). Once the brush-like monolayer self-assembled, it reduced EPS adsorption onto the polystyrene surface by similar to 70% (mass), reduced the rate of bacterial attachment by >80%, and inhibited the development of thick biofilms. QCM-D results revealed that the EPS molecules penetrate between the chains of the brush and adsorb onto the polystyrene surface. Additionally, AFM analyses showed that the brush-like monolayer prevents the adhesion of large (>d) hydrophilic colloids onto the surface via hydration repulsion; yet, molecules or colloids small enough to fit between the brush polymers (<d) were able to be adsorbed onto the surface via van der Waals interactions. Overall, we found that the penetration of extracellular organelles, as well as biopolymers through the brush, is essential for the failure of the antifouling coating, and likely could be prevented through tuning of the brush density. Stability and biofilm development testing on multiple surfaces (polypropylene, glass, and stainless steel) support practical applications of this novel block copolymer.

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

Deep Eutectic Solvent Assisted Facile Synthesis of Lignin-Based Cryogel

In this study, we reported a method to prepare a lignin based cryogel by cross-linking deep eutectic solvent (DES) extracted lignin and formaldehyde as an alternative to replace resorcinol-formaldehyde (RF) based aerogel. The resulting lignin-formaldehyde cryogel has a highly porous structure (172.8 m2/g surface area) with a high dimension stability. We found that the hydroxyl group and carbonyl group of DES lignin provide reactive sites to cross-link with formaldehyde through electrophilic addition and aldol condensation reaction. We also found that using choline chloridelactic acid (ChCl-Lac) DES as a solvent during the lignin-formaldehyde cryogel formation is critical to prevent the shrinkage of the final cyrogel. The ensuing lignin-formaldehyde cryogel has promising properties such as high thermostability, low thermal conductivity, and good fire retardancy.

Lin, Kuan-Ting↗
DOE OSTI2019

Understanding the Origin of the Ultrahigh Rate Performance of a SiO 2 -Modified LiNi 0.5 Mn 1.5 O 4 Cathode for Lithium-Ion Batteries

LiNi 0.5 Mn 1.5 O 4 (LNMO) is one of the most promising cathode materials for next-generation lithium-ion batteries for rapid charging-discharge applications. The surfaces of LNMO samples are coated with different amounts (0.5-2.0 wt. %) of silica (SiO 2 ) using a cost-effective and scalable ball milling process, and the surface-modified samples showing excellent electrochemical stability with conventional liquid electrolyte. The advantage of this coating is clearly demonstrated by the improved electrochemical performance at ambient and elevated temperatures (25 °C and 55 °C) using half- and full-cell configurations. The solid electrolyte interface (SEI) and coating properties have been highlighted by Ex situ TEM analysis, which indicates the close attachment and good wetting of the SiO 2 layer with the LNMO active particles. Importantly, the 1 wt. % SiO 2 -coated material cycled at 10 C, 40 C and 80 C rates for 400 cycles and excellent cycling stability with capacity retentions of 96.7, 87.9 and 82.4 %, respectively. The 1 wt. % SiO 2 -coated material also shows excellent cycling stability when charged at 6C (10 min.) and discharged at C /3 for 500 cycles. Here, the interfacial resistances of the SiO 2 -coated LiNi 0.5 Mn 1.5 O 4 is found to be much lower compared to bare material and does not considerably increase with the amount of coating. Overall, the scalable and cost-effective strategy of SiO 2 coating applied to LiNi 0.5 Mn 1.5 O 4 lowers the interfacial charge transfer resistance and enables the materials to be suitable for extremely fast-charging electric vehicle battery applications.

25 ENERGY STORAGE↗
DOE OSTI2021

Exploiting the Liquid Phase to Enhance the Cross-Coupling of Alcohols over Nanoporous Gold Catalysts

Controlling selectivity in the cross-coupling of two similar compounds is a classic challenge in heterogeneous catalysis. Here it is shown that the phase in which the catalysis is performed has a dramatic impact on the selectivity of the oxidative coupling of alcohols to esters over unsupported nanoporous gold catalysts, affording nearly optimal cross-coupling to a single ester at equimolar concentrations in the liquid. Operation in the liquid vs the gas phase affects 1) the relative C-H activation rates of methoxy and 1-propoxy, 2) the fraction of C-H activation which leads to esters vs aldehydes, and 3) the fraction of esters which result from cross-coupling vs self-coupling. While activation of the critical adsorbed reactive alkoxy intermediate is faster for 1-propoxy than methoxy in both phases, the liquid phase is more effective in coupling the resulting aldehyde with adsorbed methoxy or 1-propoxy to yield an ester. Additionally, operation in the liquid phase promotes cross-coupling to methyl propionate, whereas in the gas-phase self-coupling of 1-propanol to propyl propionate is favored. The promotion of self-coupling in the gas phase results from the stabilization of larger alkoxides on the surface by Au-alkyl van der Waals forces. However, such forces do not appear dominant in the liquid phase, as evidenced by similar cross-coupling selectivities of methanol with ethanol, 1-propanol, and 1-butanol. Introducing steric hindrance into the higher alcohol (i.e., 2-methyl-1-propanol) further promotes cross-coupling. Here, this promotion is attributed to a kinetic preference for an aldehyde to couple with less-hindered alkoxides. Altogether, these findings demonstrate that alcohol cross-coupling selectivities are strongly impacted by the phase in which the catalysis is conducted, thus altering the phase provides opportunities for selective and efficient chemical syntheses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗