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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Volatile organic compound sensing based on coral rock-like ZnO

Highlights: • A coral rock-like ZnO with porous structure was successfully synthesized. • Coral rock-like ZnO realized the large gas response towards VOCs. • The porous structure may play an essential role in the surface sensing reaction. - Abstract: This work presented highly sensitive coral rock-like ZnO to investigate the sensing performances for volatile organic compounds (VOCs), including formaldehyde, methylbenzene, methanol and acetone. The coral rock-like ZnO with porous structure was synthesized using a solvothermal process and subsequent calcination. The gas response of the sensor based on the coral rock-like ZnO was reported for the four types of VOC vapors at different operating temperatures and gas concentrations. It was found that the fabricated sensor was sensitive to the four gases, revealing large gas response as well as fast response and recovery speed, which was ascribed to its distinctive porous nanostructure, resulting in adequate surface sensing reaction and effective gas diffusion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Grain boundary scavenging through reactive sintering of strontium and iron in samarium doped ceria electrolyte for ITSOFC applications

Highlights: • Addition of iron and strontium to Samarium doped ceria by combustion method and sintered at 1000 °C, 1200 °C, 1300 °C. • Viscous phase sintering of iron at 1200 °C modified to reactive sintering of iron and strontium at 1300 °C. • Grain boundary activation energy lowered without compensating the grain activation energy. • The highest scavenging factor of 10.52 with the lowest activation energy of 1.02eV was achieved. - Abstract: Lowering the operational temperature of ceria based electrolytes is important for commercialization of solid oxide fuel cells. Here, we report the effect of iron, strontium and iron/strontium co-addition in samarium (20 mol %) doped ceria (SDC) with respect to sintering, microstructural modifications and ionic conductivity. The nanoparticle synthesized through glycine-nitrate combustion method was sintered at 1000, 1200 and 1300 °C. An increase in density was observed in iron doped SDC due to viscous flow sintering while co-addition of strontium and iron lead to the reactive sintering at 1300 °C by forming a eutectic liquid phase which resulted in the density of 99%. The presence of iron and strontium generated a compensatory tensile strain in the lattice and an enhancement in oxygen vacancy concentration which resulted in higher ionic conductivity. Co-addition of strontium and iron in SDC, not only increases the density but also reduces the activation energy for grain boundary conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Significant enhancement in structural, dielectric, piezoelectric and ferromagnetic properties of Ba0.9Sr0.1Zr0.1Ti0.9O3-CoFe2O4 multiferroic composites

Highlights: • (1-x)Ba{sub 0.9}Sr{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3}-(x)CoFe{sub 2}O{sub 4} multiferroic composite has been synthesized using mechano-chemical activation technique. • An improvement in dielectric, ferroelectric and piezoelectric properties over the pristine BSZT sample has been observed. • The composite samples also show a substantial enhancement in ferromagnetic characteristics compare to bare BSZT sample. - Abstract: Multiferroic composites (1 − x)Ba{sub 0.9}Sr{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3}-(x)CoFe{sub 2}O{sub 4} (x = 0.0, 0.05, 0.10, 0.20 & 0.30) were prepared using mechanochemical activation method. Rietveld refined XRD patterns confirm the diphasic nature of composite samples. All of the diffraction peaks of (1 − x)BSZT-(x)CFO can be identified for the separate perovskite (BSZT) and inverse spinal (CFO) phases and no other impurity phase were observed for the composites. (1 − x)BSZT-(x)CFO sample with x = 0.05 have shown significant improvement in microstructural, dielectric, ferroelectric and piezoelectric properties over the pristine BSZT sample. Such an improvement in electrical properties can be attributed to larger grain size, improved density and easier ferroelectric domain wall motion inside the grain. Dielectric breakdown strength of the composites also shows a similar trend and is observed to be maximum for the sample with x = 0.05 CFO concentration. The composite samples also show a substantial enhancement in ferromagnetic characteristics and increases progressively with increase in ferrite (CFO) content.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In-situ fabrication of 3D flower-like NH4NiPO4 on Ni foam without nickel salts added for high sensitive nonenzymatic glucose detection

Highlights: • The 3D-flowerlike NH{sub 4}NiPO{sub 4} grown directly on the Ni foam without nickel salts added. • The 3D-flowerlike NH{sub 4}NiPO{sub 4} assembled by sheet-like crystals (stacked by nanoflakes). • The NH{sub 4}NiPO{sub 4/}Ni foam exhibited a low detection limit of 0.015 μM. • The electrode showed high sensitivity (6135 and 2205 μA mM{sup −1} cm{sup -2}). - Abstract: The 3D flower-like NH{sub 4}NiPO{sub 4} was successfully fabricated on nickel foam via one-step hydrothermal route without nickel salts added. In our design, nickel ions were originated from the acid corrosion of nickel foam, which decreased the concentration of nickel ion in the solution and effectively control the environmental pollution. The 3D flowers-like NH{sub 4}NiPO{sub 4} was arranged on the Ni foam, and the 3D flower-like structures were assembled by sheet-like crystals with an average thickness of 380 nm. Furthermore, the sheet-like crystals are also stacked by many layers of nanoflakes. The 3D flower-like NH{sub 4}NiPO{sub 4} modified Ni foam can be used as a binder-free electrode for non-enzymatic glucose detection. And the electrode exhibits excellent electrochemical properties with high sensitivity (6135 μA mM{sup −1} Cm{sup -2} and 2205 μA mM{sup −1} Cm{sup −2}), wide linear range (covered from 0.001–1 mM and 2–5 mM) and a low detection limit of 0.015 (3S/N) at an applied bias of 0.5 V vs. Ag/AgCl.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Strong photoluminescence emission at low dopant amount in YAG:Ce and YAG:Eu phosphors

Highlights: • YAG:Ce and YAG:Eu materials were prepared by solid state reaction. • Pure YAG phase can be obtained at 1300 °C. • High density materials were synthesized at 1600 °C for 10 h. • The highest PL emission was observed for the YAG:Ce{sub 0.01} and YAG:Eu{sub 0.1} samples. - Abstract: YAG:Ce and YAG:Eu phosphors have been prepared by solid state reaction. The use of submicrometric powders allows preparing pellets with high density, enhancing the photoluminescence (PL) properties. Pellets were prepared by uniaxial pressing and the influence of the thermal treatment on the microstructural and optical properties were also studied. Pure YAG phase was obtained at 1400 °C during 1 h and high density pellets (97%) after sintering at 1600 °C for 10 h. The highest PL emission was achieved for the sintered YAG:Ce and YAG:Eu pellets doped with low dopant concentrations (0.01 mol% for Ce and 0.1 mol% for Eu). Finally, increasing the Ce and Eu concentration the PL intensity decreases and the dopants occupy different positions than the Y one in the YAG lattice.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Research of sensing characteristic and dynamic measurement of graphene oxides modified flexible arrayed RuO2 chlorine ion sensor

Highlights: • Sensitivity of the flexible arrayed RuO2/GO chlorine ion sensor was improved with optimal GO concentration, which could increase the reaction area between the chlorine ion and chlorine sensing membrane. • The electrochemical impedance spectroscopy (EIS) and atomic force microscope (AFM) were utilized to explain the relationships among the electron transfer resistance, GO modified amount and sensitivity. • The 30 μL/min flow rate of dynamic measurement for flexible arrayed RuO2/0.010 wt% GO chlorine ion sensor was obtained the best sensitivity and linearity 66.673 mV/pCl and 0.998, respectively. - Abstract: In this study, we used the graphene oxide (GO) solution, in which the concentration was from 0.005 wt% to 0.500 wt%, to modify the flexible arrayed ruthenium dioxide (RuO{sub 2}) chlorine ion sensor. It is found that the flexible arrayed RuO{sub 2}/0.010 wt% GO chlorine ion sensor had the best sensitivity (44.445 mV/pCl) and the linearity was 0.971. The electrochemical impedance spectroscopy (EIS) and atomic force microscope (AFM) were utilized to explain the relationships among the electron transfer resistance, GO modified amount and sensitivity. After that, we used the flexible arrayed RuO{sub 2}/0.010 wt% GO chlorine ion sensor and the microfluidic measurement system to investigate the dynamic sensing characteristics with different flow rates from 5 μL/min to 40 μL/min. According to the experimental results, the best sensitivity and linearity of flexible arrayed RuO{sub 2}/0.010 wt% GO chlorine ion sensor were 66.673 mV/pCl and 0.992 at 30 μL/min.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation on zinc substituted highly porous improved catalytic activity of NiFe2O4 nanocrystal by co-precipitation method

Highlights: • A thriftily viable co-precipitation technique has been used to synthesize Zn substituted NiFe{sub 2}O{sub 4} nanoparticles. • An essential structural, optical and magnetic property has been investigated. • Augmentation of Photo-Fenton activity after increasing the zinc concentration has been observed and deliberated. • Strong dependence of photo-fenton activity and cumulative increase degradation efficiency. - Abstract: Connecting to various applications of nickel ferrite as a ceramic magnetic nanocomposite in diverse manufacturing and technical categories, it is essential to optimize its optical, magnetic and microstructural characteristics. Hence a facile route was developed to fabricate nickel zinc ferrite (Ni{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4}) nanocomposites by co-precipitation route. The enviable spinel phase was studied by X-ray diffractometer and the crystallite size was found to vary from 8 to 15 nm. By Transmission Electron Microscopy, the micro structural and speck distribution was found in the range of 5–12.5 nm. Surface characterization was done using the isothermal BET technique which presents a high surface area that is exhibited by synthesized nanoparticles. Using Kubelka-Munk plot, bandgap was found to be decreasing with the increase of Zn concentration.The synthesized Ni{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4} was studied for its application in photo-Fenton degradation of organic Methylene blue (MB) dye. The synthesized nanocatalyst can bereused further which makes itself a proficient candidate in industrial effluent degradation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Substitution defect enhancing thermoelectric properties in CuInTe2

Highlights: • Pure phase of Cu1-xAgxInTe2 solid solutions is synthesized successfully via solid state reaction. • Solid solution is an effective way to lower lattice thermal conductivity. • A zT larger than 1.0 is obtained in CuInTe2 based compounds. - Abstract: Solid solution is an effective way to optimize thermoelectric performance because of the enhanced phonon scattering from point defect. In this article we describe the synthesis and discuss thermoelectric properties of Cu{sub 1-x}Ag{sub x}InTe{sub 2} solid solutions (x = 0, 0.05, 0.15, 0.30, 0.50). The effect of the substitution of Ag for Cu site on the microstructure and thermoelectric performance in CuInTe{sub 2} is investigated. The enlarged Seebeck coefficient coupled with reduced electrical conductivity is observed due to the diminished carrier concentration upon Ag substitution. Meanwhile, the lattice thermal conductivity is significantly depressed in solid solutions due to the strong phonon scattering. As a result, a zT value of 1.07 is achieved at 823 K with x = 0.05, which is a 90% improvement as compared with that of the pristine CuInTe{sub 2}. These results demonstrate a valid approach to improve the thermoelectric properties of the compounds in the same family.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hierarchically MoS2 nanospheres assembled from nanosheets for superior CO gas-sensing properties

Highlights: • Preparation of 3D Hierarchical large surface area MoS{sub 2} nanospheres from nansheets. • The efficient enhanced gas-sensing response of 92.6 at 500 ppm for CO at 230 °C. • Higher selectivity towards CO than other gases at different temperature ranges. - Abstract: Hierarchical three dimensional MoS{sub 2}nanostructures composed of small sheet-like nanostructures are successfully prepared using a simple two-step hydrothermal process with sodium dodecyl sulfate (SDS), as a surface modifier. The as-preparedMoS{sub 2}nanospheres are characterized by XRD, BET, XPS, EDS, SEM and HRTEM. The gas–sensing properties of as–prepared MoS{sub 2}nanostructures are tested at 175–230 °C temperatures for 50–500 ppm concentration range, using an efficient ceramic-tube sensor system via an intelligent gas testing system. A high response and selectivity towards carbon monoxide than other gases is observed. Comparative studies of MoS{sub 2}nanostructures for different concentration of carbon monoxide gas and definite sensor-stability for different gases are studied, as well. The sensor fabrication and sensing mechanism is discussed as well.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Photoluminescence properties and efficient energy transfer of Ce3+/Eu2+ activated K2Ba7Si16O40 phosphors

Highlights: • K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}:Ce{sup 3+}/Eu{sup 2+} phosphors have been synthesized by a high temperature solid-state method with CO atmosphere. • The resonance-type energy transfer by dipole-dipole interaction from Ce{sup 3+} to Eu{sup 2+} in K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is demonstrated. • The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å. • The thermal activation energy of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is calculated to be 0.26 eV. - Abstract: Ce{sup 3+}/Eu{sup 2+} activated K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} phosphors have been synthesized via a high-temperature solid-state method with CO atmosphere. Under ultraviolet (UV) light pump, the photoluminescence (PL) spectra of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+} is composed of a broadband from 300 nm to 500 nm ascribed to the spin-allowed 5d–4f transition of Ce{sup 3+} ions. The optimal concentration is 8% for Ce{sup 3+} single doped K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} due to the ernergy dispersion between Ce{sup 3+} ions and the critical distance between Ce{sup 3+} ions is 15.05 Å. K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Eu{sup 2+} emits a broad green emission peaking at 498 nm. The spectral overlap between the emission of Ce{sup 3+} and the excitation of Eu{sup 2+} suggests the resonance-type energy transfer from Ce{sup 3+} to Eu{sup 2+}, which is further demonstrated by the decay curves of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: 8 mol% Ce{sup 3+}, m Eu{sup 2+}. The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å by Dexter’s theory. Furthermore, the energy transfer mechanism is dipole-dipole interaction. In addition, the thermal activation energy is calculated to be 0.26 eV. The CIE coordinates can be tuned from blue to green by increasing Eu{sup 2+} ions. All results suggest that K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+}, Eu{sup 2+} is potentially useful for near-UV pumped white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Photoluminescent properties and Judd–Ofelt analysis of novel Na0.5Sr0.25NbO3: Eu3+ red phosphor with high quantum efficiency

Highlights: • The Na{sub 0.5}Sr{sub 0.25}NbO{sub 3}: Eu{sup 3+} phosphor with high quantum efficiency has been successfully synthesized by using a molten salt synthesis method. • The effect of the crystal field surrounding the Eu{sup 3+} ions on the luminescent performance was analyzed by the Judd–Ofelt theory. • Photoluminescent properties of Na{sub 0.5}Sr{sub 0.25}NbO{sub 3}: Eu{sup 3+} phosphor were investigated for the first time. - Abstract: We report on a novel Na{sub 0.5}Sr{sub 0.25}NbO{sub 3}: Eu{sup 3+} phosphor fabricated by a molten salt synthesis method with the potential application in white light-emitting diodes (WLEDs) as a red phosphor. The crystal structure, morphology, emission/excitation spectra, as well as decay curves were characterized with X-ray diffraction, Scanning Electron Microscope and photoluminescence spectrometer, respectively. Concentration quenching occurred when the concentration of Eu{sup 3+} was beyond 5 mol% due to the dipole-dipole interaction by nonradiative energy transfer. Besides, the effect of the crystal field surrounding the Eu{sup 3+} ions on the luminescent performance under 396 nm and 466 nm excitions has been investigated by the Judd–Ofelt theory. The result indicated that the quantum efficiency of the phosphor was 62.65% excited by 466 nm, which was superior to 41.43% excited by 396 nm. The optimal sample’s CIE coordinates were (0.6471, 0.3504) with the color purity of 97%, showing a potential application in (WLEDs) illumination field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Near-infrared and blue cooperative Yb3+ luminescence in Lu3Sc2Ga3O12 nano-garnets

Highlights: • Lu{sub 3}Sc{sub 2}Ga{sub 3}O{sub 12} nano-garnets doped with Yb{sup 3+} ions were synthesized by sol-gel method. • Concentration dependent structural and luminescence properties were investigated. • Variation of blue cooperative luminescence as a function of laser pump power has been studied. • Mechanism of blue cooperative luminescence of Yb{sup 3+} ions in these nano-garnets has been described. - Abstract: Nanocrystalline Lu{sub 3}Sc{sub 2}Ga{sub 3}O{sub 12} garnet powders doped with different concentrations of trivalent ytterbium (Yb{sup 3+}) ions have been prepared by sol-gel method. These garnet nano-powders have been characterized for their structural and luminescence properties using X-ray diffraction, diffuse reflectance and luminescence spectra. Near-infrared and blue cooperative upconversion luminescence spectra and decay curves of Yb{sup 3+} ions in these nano-garnets have been measured as a function of the optically active ion concentration. Quenching of near-infrared and cooperative luminescence intensity beyond 5.0 mol% of Yb{sup 3+} ion concentration have been observed. Variation of blue cooperative luminescence intensity with pump power has also been discussed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Bio-template assisted solvothermal synthesis of broom-like BaTiO3: Nd3+ hierarchical architectures for display and forensic applications

Highlights: • Broom-like BaTiO{sub 3}:Nd{sup 3+} structures were prepared by solvothermal route using CTAB surfactant. • Morphologies were highly dependent on temperature, pH, surfactant concentration and time durations. • LFPs were visualized on various porous and non-porous surfaces. • Photometric studies were carried out for display applications. - Abstract: Broom-like hierarchical structures of BaTiO{sub 3}:Nd{sup 3+} (1–11 mol %) nanophosphors (NPs) were fabricated via CTAB assisted solvothermal route. Controlled experiments namely, reaction temperature, surfactant concentration, pH and time duration were performed and its influences on morphology of the product was investigated. These conditions may tune the simple structures to broom-like hierarchical structures. The energy band gap (E{sub g}) of the synthesized NPs were estimated to be ∼3.29–3.42 eV. Judd–Ofelt (J–O) intensity parameters were calculated by utilizing the photoluminescence emission spectra instead of normal absorption spectra. The CIE and CCT results indicates that the NPs exhibit intense blue light applicable for fabrication of cool LEDs. LFPs visualized by staining optimized NPs following powder dusting technique exhibits well defined level 1–3 ridge characteristics. Hence, it evidences versatility of the development techniques and NPs for visualization of LFPs with excellent sensitivity, selectivity, and without background hindrance. The obtained results evidence that the optimized NPs can be explored as a novel labeling marker for probing visualization of LFPs and solid state lightning.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Graphene-elastomer nanocomposites based flexible piezoresistive sensors for strain and pressure detection

Highlights: • Fabricating flexible piezoresistive sensors based on PDMS/GNPs nanocomposites. • Positive strain sensitive capacity occurs during increasing pressure-loading process but before the threshold of forces loading. • Tunable strain and pressure sensitivity are achieved by controlling GNPs incorporation, and improved to 140 and 260 at 5 wt% GNPs respectively. • Superior dynamic correspondence with applied pressure and relatively high repeatability. • Application of the GNPs/PDMS piezoresistive sensors as detecting the finger motions. - Abstract: Strain and pressure sensitive flexible piezoresistive sensors have been fabricated based on nanocomposites of graphene nanoplatelets (GNPs) and Polydimethylsiloxane (PDMS) elastomer. The strain detective sensors show positive piezoresistive characteristic under diverse levels of static strain up to 20% due to the flexibility and stretchability of PDMS elastomer. Tunable strain sensitivity of GNPs/PDMS piezoresistive sensors can be achieved by controlling GNPs incorporation into PDMS elastomer, which will be improved to 140 at 5 wt% GNPs concentration. In addition, pressure sensitive response, which exists when the pressure loading is less than threshold pressure, also can be observed in GNPs/PDMS piezoresistive sensors. The GNPs network-elastomer nanocomposite based pressure sensors show tunable piezoresistivity in the ranges of ∼260 under increasingly higher GNPs concentrations. During the cyclic pressure loading, the pressure sensitive behavior of GNPs/PDMS nanocomposites manifests a superior dynamic correspondence with applied pressure while the resistance response can retain at a relatively high level under multiple loading-unloading cycles. Since the GNPs/PDMS piezoresistive sensors can not only respond to subtle bending but also distinguish them accurately for detecting the finger motions, it will make the GNPs/PDMS nanocomposite a good candidate for artificial skin and wearable sensor applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Synthesis and thermoelectric properties of doubly substituted La0.95Sr0.05Co1-xCrxO3 (0 ≤ x ≤ 0.5)

Highlights: • Dense doubly substituted La{sub 0.95}Sr{sub 0.05}Co{sub 1-x}Cr{sub x}O{sub 3} (0 ≤ x ≤ 0.5) was synthesized. • High temperature (323 −1020 K) thermoelectric properties were studied. • A combination of two mechanisms explains its electrical conduction. • ZT (700 −1000 K) increases by adding Cr, reaching 0.04 at 1000 K for x = 0.5. - Abstract: Dense La{sub 0.95}Sr{sub 0.05}Co{sub 1-x}Cr{sub x}O{sub 3} (0 ≤ x ≤ 0.5) ceramics were synthesized by solid-state reaction and conventional sintering. Room-temperature crystal structure and microstructure were investigated and the thermoelectric properties were measured in the temperature range 323 K–1020 K. La{sub 0.95}Sr{sub 0.05}Co{sub 1-x}Cr{sub x}O{sub 3} is a p-type small polaron conductor. The charge carrier concentration is determined by both substitution of La{sup 3+} with Sr{sup 2+} and thermally-activated charge disproportionation of Co{sup 3+} and /or Cr{sup 3+}. The variation of electrical conductivity versus Cr content is ascribed to the trapping of p-type polarons at Cr sites. By substituting Co with Cr, the power factor below 800 K is reduced and that above 800 K is improved. The thermal conductivity is effectively reduced by doping Cr. Substitution of Co with Cr greatly enhances the high-temperature (700 K–1000 K) ZT values, reaching 0.04 at 1000 K for La{sub 0.95}Sr{sub 0.05}Co{sub 0.5}Cr{sub 0.5}O{sub 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The effect of Gd3+ ions on fabrication and luminescence properties of Nd3+-doped (Ca1-xGdx)F2+x transparent ceramics

Highlights: • Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} transparent ceramics were fabricated by hot-pressing method. • Concentration effect of Gd{sup 3+} ion on the optical properties are discussed. • The emission properties have been greatly enhanced by codoping with Gd{sup 3+}ions. • The fluorescence parameters were compared to other Nd{sup 3+}-doped optical materials. - Abstract: Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} (x = 0.01–0.1) transparent ceramics were fabricated by hot-pressing the co-precipitated synthetic nanopowders in vacuum. The as-fabricated Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} transparent ceramics exhibit nearly pore-free and uniform microstructure, the in-line transmittance of all samples is beyond 86% at 1064 nm. The effect of Gd{sup 3+} ions on the transparency and grain size of Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} transparent ceramics has been demonstrated. The dependence of emission intensity and lifetime on Gd{sup 3+} concentration for Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} transparent ceramics is investigated and discussed. The introducing of Gd{sup 3+} is found to increase emission intensity and lifetime dramatically. The fitting results of fluorescence decay curves show the lifetime of 1 at.% Nd:(Ca{sub 0.9}Gd{sub 0.1})F{sub 2.1} transparent ceramic is to be 373.80 μs which is greatly larger than that of 1 at.% Nd:CaF{sub 2} transparent ceramic. The spectroscopic parameters of Nd:(Ca{sub 1-x}Gd{sub x})F{sub 2+x} transparent ceramics and other Nd{sup 3+}-doped optical materials have been compared and discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The band structure and photocatalytic mechanism of MoS2-modified C3N4 photocatalysts with improved visible photocatalytic activity

Highlights: • A series of MoS{sub 2}/g-C{sub 3}N{sub 4} photocatalyst were prepared by water exfoliation method. • The heterojunction enhanced the visible response and separated charge carriers. • The MoS{sub 2}/g-C{sub 3}N{sub 4} exhibits enhanced visible photocatalytic activity. - Abstract: A series of MoS{sub 2}/g-C{sub 3}N{sub 4} photocatalysts were prepared by modifying g-C{sub 3}N{sub 4} with different concentration of MoS{sub 2} via a water exfoliation method. The crystal structure, morphology, band structure of heterojunction, behaviors of charge carries and the redox ability were characterized by XRD, HR-TEM, absorption spectra, XPS, PL, cyclic voltammetry curves and transient photocurrent spectra. It is revealed that the introduction of MoS{sub 2} on the surface of g-C{sub 3}N{sub 4} nanosheets to form micro-heterojunction could enhance the visible response and separate photogenerated charge carriers effectively. Moreover, the ability of the photocatalyst for generating reactive oxygen species (ROS, such as O{sub 2}{sup −} and OH) was also investigated. Therefore, MoS{sub 2}/g-C{sub 3}N{sub 4} samples exhibit better photocatalytic performance for the photodegradation of HCHO than g-C{sub 3}N{sub 4} and MoS{sub 2} under visible irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Chitosan supported palladium nanoparticles: The novel catalysts for hydrogen generation from hydrolysis of ammonia borane

Highlights: • Chitosan is used to anchor the in-situ reduced ultrafine palladium nanoparticles. • The Pd NPs/CS catalysts display superior catalytic behavior for H{sub 2} generation from AB. • The reaction kinetics over the catalysts is also studied in details. - Abstract: Chitosan supported palladium nanoparticles (Pd NPs/CS) catalysts were facilely prepared via an in-situ reduction of PdCl{sub 2} method and characterized by various techniques. The results showed that the palladium particles were in the range of 4–8 nm and evenly dispersed on chitosan. Furthermore, the resulting Pd NPs/CS catalysts showed high catalytic activity for the hydrolytic dehydrogenation of ammonia borane (NH{sub 3}BH{sub 3}, AB) in aqueous solution. As for the catalytic reaction with an activation energy (E{sub a}) of 36.25 kJ mol{sup −1}, the orders of palladium and AB concentrations were 0.81 and 0.45, respectively. The maximum turnover frequency was as high as 24.76 mol{sub H{sub 2}}·mol{sub Pd}{sup -1}·min{sup -1} at 30 °C. In addition, the Pd NPs/CS catalysts still kept satisfied catalytic activity even after eleven runs.

08 HYDROGEN↗