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At least 361 records · Page 20

Hydrothermal synthesis of nanosize phases based on non-ferrous and noble metals

Research is devoted to reactions of binary complexes containing noble (platinum, palladium) and non-ferrous (cobalt, chrome) metals. Reactions proceed under hydrothermal conditions by the autoclave technique. Initials complexes and products of autoclave thermolysis were characterized by the FT-IR spectroscopy, the transmission electron microscopy (TEM) and the energy-dispersive X-ray spectroscopy (EDX). Comparative catalytic experiments in the test reaction were conducted. The obtained results can form the basis of new methods of nanosize multicomponent phases synthesis under hydrothermal conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

New route of phase transition for enhanced TCO property of ZnO: A first-principles study

The ZnO is one of the best transparent conducting oxide (TCO) materials for optoelectronic properties. Primarilly three phases of ZnO namely wurtzite, rocksalt and zincblend along with other prominent phases under different pressure and with different phase transformation routes are reported. The route of phase transformation may differ and depends on the external parameters such as pressure. The conventional route for the phase transformation of wurtzite (B4) phase into CsCl type (B2) phase via rocksalt phase (B1) is estimated at the relatively high pressure value of the 256 GPa. In present paper, we propose a new route of transformation of B4 to B2 phase of ZnO via β-BeO type phase at relatively low pressure value of 43 GPa. In present study, the phase transformation analysis and the electronic structure analysis for different phases are carried out by using density functional theory (DFT). It is also observed that B2 phase have high dispersive nature of bottom of conduction band and consequently high mobility of charge carriers. It indicates the possibility of B2 phase may have better TCO properties among other phases of ZnO.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Hydrothermal synthesis of highly crystalline RuS{sub 2} nanoparticles as cathodic catalysts in the methanol fuel cell and hydrochloric acid electrolysis

Highlights: • Highly crystalline RuS{sub 2} nanoparticles have been first synthesized by a “one-step” hydrothermal method. • The product presents a pure cubic phase of stoichiometric ratio RuS{sub 2} with average particle size of 14.8 nm. • RuS{sub 2} nanoparticles were used as cathodic catalysts in methanol fuel cell and hydrochloric acid electrolysis. • The catalyst outperforms commercial Pt/C in methanol tolerance and stability towards Cl{sup −}. - Abstract: Highly crystalline ruthenium sulfide (RuS{sub 2}) nanoparticles have been first synthesized by a “one-step” hydrothermal method at 400 °C, using ruthenium chloride and thiourea as reactants. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy/energy disperse spectroscopy (SEM/EDS), thermo gravimetric-differential thermal analyze (TG-DTA), transmission electron microscopy equipped with selected area electron diffraction (TEM/SAED). Fourier transform infrared spectra (IR), and X-ray photoelectron spectroscopy (XPS). XRD result illustrates that the highly crystalline product presents a pure cubic phase of stoichiometric ratio RuS{sub 2} and the average particle size is 14.8 nm. SEM and TEM images display the products have irregular shape of 6–25 nm. XPS analyst indicates that the sulfur exists in the form of S{sub 2}{sup 2−}. Cyclic voltammetry (CV), rotating disk electrode (RDE), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements are conducted to evaluate the electrocatalytic activity and stability of the highly crystalline RuS{sub 2} nanoparticles in oxygen reduction reaction (ORR) for methanol fuel cell and hydrochloric acid electrolysis. The results illustrate that RuS{sub 2} is active towards oxygen reduction reaction. Although the activity of RuS{sub 2} is lower than that of Pt/C, the RuS{sub 2} catalyst outperforms commercial Pt/C in methanol tolerance and stability towards Cl{sup −}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Influence of compositional variation on electrical properties of PANI/SnO{sub 2} nanocomposites

Conducting polyaniline/tin oxide (PANI/SnO{sub 2}) nanocomposites have been successfully synthesized by in-situ polymerization technique. The PANI/SnO{sub 2} nanocomposites of different compositions were prepared by varying weight percentage of SnO{sub 2} nanoparticles such as 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% into the fixed amount of the aniline monomer. The prepared powder samples were characterized by X-ray diffractometer (XRD), Fourier Transform Infrared spectroscopy (FT-IR) and Scanning electron microscope (SEM). The intensity of diffraction peaks for PANI/SnO{sub 2} composites is increases with increasing SnO{sub 2} wt%. SEM observation showed that the prepared SnO{sub 2} nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer nanocomposite material. AC electrical conductivity and dielectric properties were studied in the frequency range of 1 KHz -1 MHz. At higher frequencies, the composites exhibit almost zero dielectric loss and maximum value of AC electrical conductivity (σ{sub ac}) of 0.21 S/m is found for a concentration of 30 wt% of SnO{sub 2} in polyaniline.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques

In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

43 PARTICLE ACCELERATORS↗

Secondary galactic electrons.

Energy spectrum of secondary galactic electrons obtained by kinematic transformation based on model of high energy collisions

HIGH ENERGY ELECTRON↗

Characterisation of strain-induced precipitation behaviour in microalloyed steels during thermomechanical controlled processing

The temperature at which thermomechanical controlled processing is undertaken strongly influences strain-induced precipitation (SIP) in microalloyed steels. In this study, the recrystallisation-precipitation-time-temperature curve was simulated to determine the full recrystallisation temperature, recrystallisation-stop temperature and the temperature where precipitation would occur at the shortest time. The calculated temperatures were verified by experimental testing for rolling between 1100 °C and 850 °C. On the basis of this a finishing deformation of 850 °C was chosen in order to maximise the precipitate number density formed in a fully unrecrystallised austenite. The orientation relationship between the SIP in austenite, and subsequent transformation to ferrite was identified by calculation from the coordinate transformation matrix, and by electron diffraction in the transmission electron microscope. The NbC formed as coherent/semi-coherent precipitates in the austenite, and remained coherent/semi-coherent in the ferrite, indicating a Kurdjumov-Sachs orientation relationship between the austenite and ferrite on transformation. - Highlights: •The austenite deformation temperature will influence strain-induced precipitation. •Precipitates are NbC, exhibiting an NaCl structure and lattice parameter 0.447 nm. •Fine NbC (< 10 nm) formed in austenite as coherent or semi-coherent precipitates. •Confirmed cube-on-cube orientation relationship between the NbC, the austenite and the ferrite.

36 MATERIALS SCIENCE↗

Bio-cellulose Production by Beijerinckia fluminensis WAUPM53 and Gluconacetobacter xylinus 0416 in Sago By-product Medium

Bio-cellulose is the microbial extracellular cellulose that is produced by growing several microorganisms on agriculture by-products, and it is used in several food applications. This study aims to utilize sago by-product, coconut water, and the standard medium Hestrin-Schramm as the carbon sources in the culture medium for bio-cellulose production. The bacteria Beijerinkia fluminensis WAUPM53 and Gluconacetobacter xylinus 0416 were selected based on their bio-cellulose production activity. The structure was determined by Fourier transform infrared spectroscopy and scanning electron microscopy, while the toxicity safety was evaluated by brine shrimp lethality test. The results of Fourier transform infrared spectroscopy showed that the bio-cellulose produced by B. fluminensis cultivated in sago by-products was of high quality. The bio-cellulose production by B. fluminensis in the sago by-product medium was slightly higher than that in the coconut water medium and was comparable with the production in the Hestrin-Schramm medium. Brine shrimp lethality test confirmed that the bio-cellulose produced by B. fluminensis in the sago by-product medium has no toxicity, which is safe for applications in the food industry. This is the first study to determine the high potential of sago by-product to be used as a new carbon source for the bio-cellulose production.

60 APPLIED LIFE SCIENCES↗

Photoluminescent and Thermoluminescent Studies of Dy{sup 3+} and Eu{sup 3+} Doped Y{sub 2}O{sub 3} Phosphors

Eu{sup 3+} doped and Dy{sup 3+} codoped yttrium oxide (Y{sub 2}O{sub 3}) phosphors have been prepared using solid-state reaction technique (SSR). The prepared phosphors were characterized by X-ray diffractometer (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR) techniques. Photoluminescence (PL) and Thermoluminescence (TL) properties were studied in detail. PL emission spectra were recorded for prepared phosphors under excitation wavelength 254 nm, which show a high intense peak at 613 nm for Y{sub 2}O{sub 3}:Dy{sup 3+}, Eu{sup 3+} (1:1.5 mol %) phosphor. The correlated color temperature (CCT) and CIE analysis have been performed for the synthesized phosphors. TL glow curves were recorded for Eu{sup 3+}doped and Dy{sup 3+}codoped phosphors to study the heating rate effect and dose response. The kinetic parameters were calculated using peak shape method for UV and γ exposures through computerized glow curve deconvolution (CGCD) technique. The phosphors show second order kinetics and activation energies varying from 5.823 × 10{sup − 1} to 18.608 × 10{sup − 1} eV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Solvothermal synthesis of V{sub 4}O{sub 9} flake-like morphology and its photocatalytic application in the degradation of methylene blue

Highlights: ► Flake-like nanocrystalline V{sub 4}O{sub 9} was synthesized by a solvothermal route. ► Photocatalytic activity has been evaluated by the degradation of methylene blue under visible light irradiation. ► V{sub 4}O{sub 9} nanoflakes exhibited much higher photocatalytic activity two times higher than the bulk V{sub 2}O{sub 5}. -- Abstract: Flake-like nanocrystalline V{sub 4}O{sub 9} has been successfully synthesized by solvothermal process using V{sub 2}O{sub 5} as vanadium source and phenolphthalein as a reducing agent and a structure-directing template. Techniques X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and ultraviolet–visible (UV–vis) spectroscopy have been used to characterize the structure, the morphology and the composition of the material. The photocatalytic activity of the material has been evaluated by the degradation of methylene blue under visible light irradiation. As a result, after the lapse of 150 min, around 93.54% bleaching was observed, with V{sub 4}O{sub 9} nanoflakes yielding more photodegradation compared to that of bulk V{sub 2}O{sub 5}. This presents a degradation percentage of about 44.67%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Improvements in electrical and dielectric properties of substituted multiferroic LaMnO{sub 3} based nanostructures synthesized by co-precipitation method

Graphical abstract: Display Omitted Highlights: ► Simultaneous double ion substitutions philosophy is introduced in LaMnO{sub 3}. ► La{sub 1−x}Gd{sub x}Mn{sub 1−y}Cr{sub y}O{sub 3} nanoparticles are not reported previously. ► La{sub 1−x}Gd{sub x}Mn{sub 1−y}Cr{sub y}O{sub 3} nanoparticles are synthesized by co-precipitation method. ► The 12 fold increase in resistivity of LaMnO{sub 3} nanostructures is observed. -- Abstract: A series of La{sub 1−x}Gd{sub x}Mn{sub 1−y}Cr{sub y}O{sub 3} nanoparticles (where x, y = 0, 0.25, 0.50, 0.75 and 1.0) has been synthesized by the chemical co-precipitation method, involving double ion substitution philosophy. The nanoparticles were characterized by thermo gravimetric analysis (TGA), X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometer (VSM), DC electrical resistivity and dielectric measurements. The XRD and FTIR analysis confirmed the single orthorhombic phase and the crystallite size were found in the range of 16–34 nm. DC resistivity exhibited very interesting behavior which increased from 1.41 × 10{sup 8} to 16.35 ± 0.2 × 10{sup 8} Ω cm upon complete double ions replacement of La and Mn with Gd and Cr, respectively. This very high resistivity variation upon substitution definitely would open new avenues for applications of these materials in microwave devices and other related areas. The dielectric properties of these nanoparticles were also studied at room temperature in the range of 6 kHz to 5 MHz and the maximum dielectric behavior (ε′ = 2.86 × 10{sup 3}, tan δ = 5.41, ε″ = 15.5 × 10{sup 3}) was exhibited by La{sub 0.75}Gd{sub 0.25}Mn{sub 0.75}Cr{sub 0.25}O{sub 3} at 6 kHz. Hysteresis loops measurements showed that the synthesized nanomaterials are paramagnetic in nature at room temperature.

36 MATERIALS SCIENCE↗

Rod-like nanocrystalline B-VO{sub 2}: Hydrothermal synthesis, characterization and electrochemical properties

Graphical abstract: - Highlights: • Rod-like nanocrystalline VO{sub 2}(B) was prepared by hydrothermal process. • Reaction time on the morphology has been investigated. • CV has revealed reversible redox behavior with charge–discharge cycling. • Average coulombic efficiency is upper 98%. • Energy-related applications such as cathodes in lithium batteries. - Abstract: Rod-like nanocrystalline VO{sub 2}(B) has been successfully synthesized via a simple hydrothermal process by using V{sub 2}O{sub 5} as vanadium source and 4-butylaniline H{sub 3}C–(CH{sub 2}){sub 3}–(C{sub 6}H{sub 4})–HH{sub 2} as reducing and structure directing agent. The compounds were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV–visible spectroscopy. The VO{sub 2}(B) nanorods are up to several micrometers in length and about 80 nm in thickness with a large optical band gap of ∼2.709 eV. Thin films of VO{sub 2}(B) nanorods deposited on ITO substrates were electrochemically characterized by cyclic voltammetry. The voltammograms show reversible redox behavior with charge–discharge cycling process corresponding to the reversible lithium intercalation/deintercalation into the crystal lattice. The average coulombic efficiency to this redox processes is upper 98% during the electrochemistry measurements.

36 MATERIALS SCIENCE↗

Blue–green afterglow of BaAl{sub 2}O{sub 4}:Dy{sup 3+} phosphors

Highlights: • Afterglow can be achieved when Eu{sup 2+} is absent in the DyAl{sub 2}O{sub 4}:Dy{sup 3+} phosphors. • The afterglow of DyAl{sub 2}O{sub 4}:Dy{sup 3+} phosphors is discernible to naked eyes for minutes. • Dy{sup 3+} introduced trap centers are believed to be responsible for the afterglow. - Abstract: Dy{sup 3+} doped barium aluminate (BaAl{sub 2}O{sub 4}:Dy{sup 3+}) phosphors were prepared via the sol–gel combustion route at the ignition temperature of 600 °C. The phosphors were characterized with X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Regardless of the absence of Eu{sup 2+} luminescent centers, broadband blue–green afterglow with its peak at about 490 nm was recorded in the BaAl{sub 2}O{sub 4}:Dy{sup 3+} phosphors. The decay profile of the blue–green afterglow can be best fitted into a two-component exponential function with the two lifetime decay constants to be 8.81 and 45.25 s, respectively. The observation of blue–green afterglow from BaAl{sub 2}O{sub 4}:Dy{sup 3+} in the absence of Eu{sup 2+} provides unique opportunity in unveiling the afterglow mechanisms of rare-earth doped alkaline-metal aluminates. Possible mechanisms on the blue–green afterglow in BaAl{sub 2}O{sub 4}:Dy{sup 3+} phosphors are discussed in terms of the Dy{sup 3+} ions introduced trap centers as well as luminescent centers in the crystal lattice.

36 MATERIALS SCIENCE↗

Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

We present measurements of photon absorption by free electrons as a solid is transformed to plasma. A femtosecond x-ray free-electron laser is used to heat a solid, which separates the electron and ion heating time scales. The changes in absorption are measured with an independent probe pulse created through high-order-harmonic generation. We find an increase in electron temperature to have a relatively small impact on absorption, contrary to several predictions, whereas ion heating increases absorption. Here, we compare the data to current theoretical and numerical approaches and find that a smoother electronic structure yields a better fit to the data, suggestive of a temperature-dependent electronic structure in warm dense matter.

36 MATERIALS SCIENCE↗

Starch-assisted synthesis and optical properties of ZnS nanoparticles

Highlights: • ZnS spherical nanostructure was prepared via starch-assisted method. • The crystalline lattice structure, morphologies, chemical and optical properties of ZnS nanoparticles. • The forming mechanism of ZnS nanoparticles. • ZnS spherical nano-structure can show blue emission at 460–500 nm. - Abstract: ZnS nanoparticles are fabricated via starch-assisted method. The effects of different starch amounts on structure and properties of samples are investigated, and the forming mechanism of ZnS nanoparticles is discussed. By X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectroscopy and fluorescence (FL) spectrometer, their phases, crystalline lattice structure, morphologies, chemical and optical properties are characterized. The results show that ZnS has polycrystalline spherical structure with the mean diameter of 130 nm. Sample without starch reveals irregular aggregates with particle size distribution of 0.5–2 μm. The band gap value of ZnS is 3.97 eV. The chemical interaction exists between starch molecules and ZnS nanoparticles by hydrogen bonds. The stronger FL emission peaks of ZnS synthesized with starch, indicate a larger content of sulfur vacancies or defects than ZnS synthesized without starch.

36 MATERIALS SCIENCE↗

Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas

Understanding plasmon-mediated electron emission and energy transfer on the nanometer length scale is critical to controlling light–matter interactions at nanoscale dimensions. In a high-resolution lithographic material, electron emission and energy transfer lead to chemical transformations. Here, we employ such chemical transformations in two different high-resolution electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and hydrogen silsesquioxane (HSQ), to map local electron emission and energy transfer with nanometer resolution from plasmonic nanoantennas excited by femtosecond laser pulses. We observe exposure of the electron-beam resists (both PMMA and HSQ) in regions on the surface of nanoantennas where the local field is significantly enhanced. Exposure in these regions is consistent with previously reported optical-field-controlled electron emission from plasmonic hotspots as well as earlier work on low-electron-energy scanning probe lithography. For HSQ, in addition to exposure in hotspots, we observe resist exposure at the centers of rod-shaped nanoantennas in addition to exposure in plasmonic hotspots. Optical field enhancement is minimized at the center of nanorods suggesting that exposure in these regions involves a different mechanism to that in plasmonic hotspots. Our simulations suggest that exposure at the center of nanorods results from the emission of hot electrons produced via plasmon decay in the nanorods. Our results provide a means to map both optical-field-controlled electron emission and hot-electron transfer from nanoparticles via chemical transformations produced locally in lithographic materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Solvothermal synthesis of monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} microspheres and their application as microwave absorber

Graphical abstract: Monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} porous microspheres with shell structure were synthesized via a combined solvothermal method and calcination route. The radar-wave absorbability of the purple sample calcined at 900 Degree-Sign C was strongest at the frequency of about 8.5 GHz. Highlights: Black-Right-Pointing-Pointer In this study we synthesized monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} porous microspheres as microwave absorber. Black-Right-Pointing-Pointer The relationship between microstructures and the electromagnetic properties was indicated. Black-Right-Pointing-Pointer The radar-wave absorbability of the sample was included. -- Abstract: Monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} microspheres with a diameter of 40 {mu}m were achieved via a combining solvothermal and calcination route. The crystallinity of the calcined microspheres with shell structure was improved, while the monodisperse property and morphologies remained. The possible formation mechanism of the porous CoZr{sub 4}(PO{sub 4}){sub 6} microspheres with nanoshell was proposed. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) technologies, thermal analysis (TG and DSC), nitrogen adsorption-desorption isotherms and network analyzer. The sample calcined at 900 Degree-Sign C shows a strongest absorbability in the radar-wave absorbability test.

36 MATERIALS SCIENCE↗

Controllable synthesis and enhanced photocatalytic properties of Cu{sub 2}O/Cu{sub 31}S{sub 16} composites

Highlights: ► Facile sonochemical route. ► The content of Cu{sub 31}S{sub 16} in the Cu{sub 2}O/Cu{sub 31}S{sub 16} can be easily controlled. ► Structure and optical properties of Cu{sub 2}O/Cu{sub 31}S{sub 16} were discussed. ► Enhanced photocatalytic property of Cu{sub 2}O/Cu{sub 31}S{sub 16}. ► Cu{sub 2}O/Cu{sub 31}S{sub 16} core/shell structures were more stable than single Cu{sub 2}O particles. -- Abstract: The controlled synthesis of Cu{sub 2}O/Cu{sub 31}S{sub 16} microcomposites with hierarchical structures had been prepared via a convenient sonochemical route. Ultrasonic irradiation of a mixture of Cu{sub 2}O and (NH{sub 2}){sub 2}CS in an aqueous medium yielded Cu{sub 2}O/Cu{sub 31}S{sub 16} composites. The content of Cu{sub 31}S{sub 16} in the Cu{sub 2}O/Cu{sub 31}S{sub 16} can be easily controlled by adjusting the synthesis time. The Cu{sub 31}S{sub 16} layer not only protected and stabilized Cu{sub 2}O particles, but also prohibited the recombination of photogenerated electrons–holes pair between Cu{sub 31}S{sub 16} and Cu{sub 2}O. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) spectra, ultraviolet–visible (UV–Vis) spectroscopy and photoluminescence (PL) spectroscopy were used to characterize the products. Photocatalytic performance of the Cu{sub 2}O/Cu{sub 31}S{sub 16} hierarchical structures was evaluated by measuring the decomposition rate of methyl orange solution under natural light. To the best of our knowledge, this is the first report on the preparation and photocatalytic activity of Cu{sub 2}O/Cu{sub 31}S{sub 16} microcomposite. Additionally, the Cu{sub 2}O/Cu{sub 31}S{sub 16} core/shell structures were more stable than single Cu{sub 2}O particles during photocatalytic process since the photocatalytic activity of the second reused architecture sample was much higher than that of pure Cu{sub 2}O. The Cu{sub 2}O/Cu{sub 31}S{sub 16} microcomposites may be a good promising candidate for wastewater treatment.

36 MATERIALS SCIENCE↗