2O3 Composites Research Articles

Thermophysical properties and oxygen transport in (Thx,Pu1-x)O2.

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Thx,Pu1−x)O2 (0 ≤ x ≤ 1) between 300–3500 K. In particular, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Thx,Pu1−x)O2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and the increase in oxygen diffusivity. The increase in oxygen diffusivity for (Thx,Pu1−x)O2 is explained in terms of lower oxygen defect formation enthalpies for (Thx,Pu1−x)O2 than PuO2 and ThO2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.

A facile one-pot cation-anion double hydrolysis approach to the synthesis of supported MgO/γ-Al2O3 with enhanced adsorption performance towards CO2

A series of supported MgO/γ-Al2O3 composites (denoted as Mg/Al-x) with enhanced adsorption performance towards CO2 were successfully synthesized via a facile one-pot cation-anion double hydrolysis approach. Their phase structures, morphologies, textural properties and basic properties were comparatively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption, in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) and CO2 temperature programmed desorption (CO2-TPD). Three kinds of carbonates including bicarbonate, bidentate and monodentate carbonate are formed during the adsorption process, indicating a synergistic adsorption mechanism for CO2. For the dynamic CO2 adsorption without water vapor, the adsorption capacity decreases in the order of Mg/Al-0.2>Mg/Al-0.3>Mg/Al-0.1>Mg/Al-0, which coincides with the trend of the amount of basic sites; especially, Mg/Al-0.2 with the Mg/Al molar ratio of 0.2 shows a stable adsorption capacity of 1.60mmol/g without loss after 11 cycles at 60°C. Furthermore, water vapor shows a positive effect on their adsorption, and Mg/Al-0.2 reaches an adsorption capacity of 2.10mmol/g for the simulated flue gas with 10vol% water vapor at 60°C. Its relatively high adsorption capacity, excellent cyclic adsorption/desorption stability and facile preparation process make it an attractive candidate for CO2 capture with flue gas conditions.

Solid solution Li2MoO4 – Li2WO4 crystal growth and characterization

Solid solution Li2Mo1−XWXO4 crystals were grown from two different melts (X=0.85 and 0.95) by Czochralski technique. The crystals were colorless and transparent within 300–1100nm wavelength range. They had dimensions of 25mm diameter and 100mm length. The crystal grown from the X=0.85 melt had an inhomogeneous composition which varied from 0.65 to 0.88. The crystal grown from the X=0.95 melt had a uniform distribution of X, corresponding to the average Li2Mo0.08W0.92O4 composition. Both crystals belong to a phenacite-type structure and they were characterized by X-ray diffraction, Raman and IR-spectroscopy.

An examination of active sites on Au-Ag bimetallic catalysts based on CO oxidation over Au/Ag2O and a comparison to Ag-contaminated Au powder

There are two theories regarding the origin of the remarkable synergistic effect observed in Au-Ag bimetallic catalysts when applied to various oxidative reactions. One is based on the importance of the contact interfaces between AgOx regions and the surface of the bulk Au as active working sites, while the other holds that charge transfer from Ag to Au in a surface Au-Ag alloy causes the catalytic activity. One key point in examining these theories and determining the origin of the synergy involves determining whether or not Ag exists as an oxide or as a metallic alloy on the Au surface. To confirm that enhanced activity results from contact between Ag2O and Au nanoparticles (NPs), a comparative study of catalytic CO oxidation over Au/Ag2O and Ag2O was performed in the present work, using a closed recirculation reaction system. A reaction mixture consisting of a stoichiometric composition of CO and O2 (CO/O2 = 2/1) was supplied to both catalysts and the resulting pressure decrease rates were tracked, from which the amounts of gas consumed as well as the quantity of CO2 produced were determined. The steady state reactions of both Au/Ag2O and Ag2O did not lead to any meaningful difference in the rate of pressure decrease during the oxidation. The pressure decrease over both catalysts was attributed to the reduction of surface lattice O on Ag2O by CO. The results obtained for Au/Ag2O are in good agreement with previous data resulting from the use of Ag-contaminated Au powder (Ag/Au-b) having an oxidized surfaces. This finding suggests that the perimeters between AgOx zones and the bulk Au surface may not function as active sites during CO oxidation. A review of previous results obtained with Ag/Au-b specimens having so-called steady state surfaces indicates that AgOx species in such materials are reduced to the 0 state to form a Ag-Au alloy that provides the active sites.

The enhanced high cut-off voltage electrochemical performances of LiNi0.5Co0.2Mn0.3O2 by the CeO2 modification

The CeO2 nano-particles dispersed on the surface of commercial LiNi0.5Co0.2Mn0.3O2, have been prepared by a co-precipitation method, in which ammonium carbonate or ammonium oxalate is served as a precipitant to generate the different precursor of CeO2, respectively. CeO2-modified LiNi0.5Co0.2Mn0.3O2 composites with ammonium oxalate as the precipitant exhibit the best electrochemical properties with a reversible lithium storage capacity of 157.7mAhg−1 with a retention of 86.36% at 25°C at the current density 1C after 100 cycles under high cut-off voltage 4.6V. At higher temperature 55°C, its discharge capacity changes from 198.2mAhg−1 to 136.6mAhg−1 after 100 cycles, with a retention of 68.29%. Besides, it also displays an excellent rate performance with a capacity of 114.0mAhg−1 at 5C in the 100th cycle. All enhanced performances could be due to the dispersion of CeO2 on the surface of commercial LiNi0.5Co0.2Mn0.3O2 and the synergistic effects between the CeO2 and LiNi0.5Co0.2Mn0.3O2, which leads to the enhanced structural stability and electric conductivity.

Carbon Dots/NiCo2 O4 Nanocomposites with Various Morphologies for High Performance Supercapacitors.

A series of carbon dots/NiCo2 O4 composites with various morphologies are prepared and tested for supercapacitors. These samples have good electrical conductivities and efficient ions transport paths, so they exhibit high specific capacitances, superior rate performances, and high cycling stabilities. The optimal composite for hybrid supercapacitor exhibits a high energy density up to 62.0 Wh kg-1 .

Improved specific loss power on cancer cells by hyperthermia and MRI contrast of hydrophilic Fex Co1-x Fe2 O4 nanoensembles.

Ferrite-based ferri/superparamagnetic nanoparticles can be rapidly heated by an external alternating magnetic field (AMF) to induce tissue necrosis of the adjacent microenvironment, but in addition provide magnetic resonance imaging (MRI) contrast utilizing enhanced water relaxivity. Here we characterized nanoensembles of Fe-Co mixed spinel ferrites (i.e. Fex Co1-x Fe2 O4 , where x ranges from 0.2 to 0.8) synthesized by chemical co-precipitation. With nanoensembles of increasing Co content the saturation magnetization improved, while lattice parameter remained relatively constant. MRI water (transverse) relaxivity at 11.7 T was also boosted with increasing Co content. Efficiency of AMF-induced heating was quite comparable for the nanoensembles with either chitosan or polyethylene glycol (PEG) coating except for PEG-coated Fe0.2 Co0.8 Fe2 O4 , which was twice as less efficient as others. While toxicity of the nanoensembles with either coating examined on 9L tumor cell cultures showed no significant differences, upon AMF exposure (i.e. heat-induced necrosis) Fex Co1-x Fe2 O4 composition with different values of x showed quite dramatic effects on cell death of tumor cells with both coatings. This study lays the ground work for further characterization of other mixed spinel ferrites, and in addition we expect that chitosan and PEG coated Fex Co1-x Fe2 O4 of all the compositions will have good potential for preclinical applications in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Highly Dispersed Polyoxometalate‐Doped Porous Co3O4 Water Oxidation Photocatalysts Derived from POM@MOF Crystalline Materials

Rational design of earth-abundant photocatalysts is an important issue for solar energy conversion and storage. Polyoxometalate (POM)@Co3 O4 composites doped with highly dispersive molecular metal-oxo clusters, synthesized by loading a single Keggin-type POM cluster into each confined space of a metal-organic framework (MOF), exhibit significantly improved photocatalytic activity in water oxidation compared to the pure MOF-derived nanostructure. The systematic synthesis of these composite nanocrystals allows the conditions to be tuned, and their respective water oxidation catalytic performance can be efficiently adjusted by varying the thermal treatment temperature and the feeding amount of the POM. This work not only provides a modular and tunable synthetic strategy for preparing molecular cluster@TM oxide (TM=transition metal) nanostructures, but also showcases a universal strategy that is applicable to design and construct multifunctional nanoporous metal oxide composite materials.

Enhanced dielectric properties in Nb-doped BT-BMT ceramics

The dielectric properties of lead-free solid solution, 0.5BaTiO3–0.5Bi(Mg1/2+x/6Ti(1−x)/2Nbx/3)O3 (x=0.01–0.25), synthesized via a conventional solid state route were investigated. The thermal stability range of relative permittivity remarkably increased with an increase in x from 0.01 to 0.25. 0.5BaTiO3–0.5Bi(Mg1/2+x/6Ti(1−x)/2Nbx/3)O3 (x=0.20) composition showed high temperature stable relative permittivity (1100), revealing a change of less than ±15% across 55–500°C and loss tangent (≤0.025) over the temperature range 102–425°C. In comparison with other known materials for high temperature applications, the excellent temperature stability and high electrical resistivity of the x=0.2 composition suggested that this material can be a promising base material for fabrication of high temperature ceramic capacitors.

Temperature Evolution of Physical Properties of BaTi0.9(Nb0.5Yb0.5)0.1O3 Lead-Free Ceramic

BaTi0.9(Nb0.5Yb0.5)0.1O3 lead-free ceramic was prepared by a solid-state reaction method. The structure of BaTi0.9(Nb0.5Yb0.5)0.1O3 has been characterized by means of x-ray diffraction, showing the coexistence of cubic (31.1%) and tetragonal (68.9%) phases at room temperature. Dielectric spectroscopy shows that BaTi0.9(Nb0.5Yb0.5)0.1O3 composition sintered at 1380°C exhibits a relaxor behavior with a weak diffuse phase transition obeying a Lorentz-type quadratic relationship. The ferroelectric–paraelectric phase transition TC decreased from 420 K for BaTiO3 to 284 K for BaTi0.9(Nb0.5Yb0.5)0.1O3. The dielectric loss of this ceramic was <0.09 over a wide temperature range (<400 K). The temperature behavior of the main piezoelectric parameters, such as the piezoelectric coefficient d31 and the electromechanical coupling factor kp, was investigated. d31 sets a maximum about 32.5 pC/N at temperature of 220 K. Nevertheless, kp undergoes more or less important changes between 120 K and 200 K. Over 200 K, kp degrades very rapidly due to the depoling effect deduced from the hysterisis measurements. Dielectric and structural properties of BaTi0.9(Nb0.5Yb0.5)0.1O3 were confirmed by Raman spectroscopy.

Carbon dioxide reforming of methane over mesoporous nickel aluminate/γ-alumina composites

A series of xNiAl2O4/γ-Al2O3 composites with various Ni contents have been prepared via one-step partial hydrolysis of metal nitrate salts in the absence of surfactants and used for carbon dioxide reforming of methane. The characterization results demonstrated that the NiAl2O4/γ-Al2O3 materials possessed mesoporous structures of uniform pore sizes; and the Ni2+ ions were completely reacted with alumina to NiAl2O4 spinel in the matrices using N2 sorption, XRD, TEM, and XPS. The NiAl2O4/γ-Al2O3 materials exhibited excellent catalytic properties and superior long-term stability for carbon dioxide reforming of methane. The effects of Ni content on the intrinsic activities and the amounts of coke disposition of the xNiAl2O4/γ-Al2O3 catalysts were discussed in detail for the carbon dioxide reforming of methane. The results revealed that the Ni particle sizes did not affect the intrinsic activity of metallic Ni, but smaller Ni particles could reduce the rate of coke deposition.

Enhanced electromagnetic properties and microwave attenuation of BiFeO3-BaFe7(MnTi)2.5O19 driven by multi-relaxation and strong ferromagnetic resonance

We report the original observation of the electromagnetic properties and microwave attenuation performances of BiFeO3-BaFe7(MnTi)2.5O19 composites in X-band. It is found that the permittivity of BiFeO3-BaFe7(MnTi)2.5O19 shows dielectric multi-relaxation behavior, which plays an important role in maintaining the high dielectric loss. Meanwhile, BiFeO3-BaFe7(MnTi)2.5O19 exhibits increased magnetic loss due to strong ferromagnetic resonance. For all BiFeO3-BaFe7(MnTi)2.5O19 composites, the minimum reflection loss surpasses −20dB. Especially, the minimum reflection loss of the composites with volume ratio of 2:1 and 3:1 reaches −50dB, which is almost 3 times of that of BiFeO3. The enhanced microwave attenuation is attributed to the improved electromagnetic properties and electromagnetic matching. This work opens up a promising feasible route to development of microwave attenuation materials in imaging, healthcare, information safety and military fields.

Some lead-free ceramics of ferroelectric andphotoelectrochemical applications

The main ferroelectric materials are lead-based which cause serious environmental problem. Then, to develop environment friendly materials, lead-free ceramics derived from BaTiO3 were found to be interesting owing to their attractive ferroelectric performances. Moreover, the ferroelectric materials present interesting characteristics suitable for photoelectrochemical applications. In this perspective, ferroelectric and photoelectrochemical properties of Ba0.785Bi0.127Y0.017TiO3 (BBiYT), Ba0.975Eu0.017(Ti0.75Zr0.25)O3 (BETZ) and Ba(Ti0.96Mg0.013Nb0.026)O3 (BTMN) compositions are presented and discussed. The relative permittivity and losses are determined under dry helium as a function of both temperature(77-450 K) and frequency (102-2.105 Hz). BTMN compositions are characterized by a normal ferroelectric behaviour, while BBiYT and BETZ present relaxor ferroelectric properties. All these compounds present photoelectrochemical properties with different applications: eosin oxidation under solar light (BTMN), chromate reduction (BETZ) after 6 h of exposition to sunlight and H2 production upon visible light (BBiYT).

Enhanced piezoelectric properties and thermal stability in tetragonal-structured (Ba,Ca)( Zr,Ti)O3 piezoelectrics substituted with trace amount of Mn

Piezoelectric properties and thermal stability of tetragonal-structured (Ba0.838Ca0.162)(Ti0.908−xMnxZr0.092)O3 (0.46BZT–0.54BCTMn) compositions away from morphotropic phase boundary (MPB) were investigated. The results demonstrated that the addition of small amounts of Mn did not cause a remarkable change in crystal structure, but resulted in an evident evolution in piezoelectric properties and thermal stability. Mn could induce combinatory hard and soft piezoelectric characteristics due to aliovalent substitutions and improve thermal stability. The optimal electrical properties were obtained in the modified composition at x=0.006 with piezoelectric constant d33=410pC/N, planar electromechanical coupling factor kp=0.40, mechanical quality factor Qm=150, remnant polarization Pr=14.1μC/cm2, coercive field Ec=4.44kV/cm and a high Curie temperature Tc~99°C, respectively. It can be expected that the improved piezoelectric material can be a promising candidate for lead-free piezoelectric applications.

Setting a chronology for the basal ice at Dye-3 and GRIP: Implications for the long-term stability of the Greenland Ice Sheet

The long-term stability of the Greenland Ice Sheet (GIS) is an important issue in our understanding of the climate system. Limited data suggest that the northern and southern sections extend well back into the Pleistocene, but most age constraints do not definitively date the ice. Here, we re-examine the GRIP and Dye-3 ice cores to provide direct ice core observations as to whether the GIS survived previous interglacials known to be warmer (∼130 ka) or longer (∼430 ka) than the present interglacial. We present geochemical analyses of the basal ice from Dye-3 (1991–2035 m) and GRIP (3020–3026 m) that characterize and date the ice. We analyzed the elemental and isotopic composition of O2, N2, and Ar, of trapped air in these two cores to assess the origin of trapped gases in silty ice. Dating of the trapped air was then achieved by measuring the paleoatmospheric δ40Ar/38Ar and the 17O anomaly (Δ17) of O2. The resulting age is a lower limit because the trapped air may be contaminated with crustal radiogenic 40Ar. The oldest average age of replicates measured at various depths is 970±140 ka for the GRIP ice core and 400 ka±170 ka for Dye-3. Δ17 data from Dye-3 also argue strongly that basal ice in this core predates the Eemian. This confirms that the Greenland Ice Sheet did not completely melt at Southern Greenland during the last interglacial, nor did it completely melt at Summit Greenland during the unusually long interglacial ∼430 kyr before present.

Effects of nano-TiO2 -LDPE packaging on postharvest quality and antioxidant capacity of strawberry (Fragaria ananassa Duch.) stored at refrigeration temperature.

Nano-TiO2 -low-density polyethylene (NTLDPE) packaging was prepared, and the effects of NTLDPE packaging on quality and antioxidant capacity of strawberry fruits were investigated. With increased barrier properties, NTLDPE packaging quickly formed a relative lower O2 and higher CO2 air composition in comparison with LDPE. It was also more efficient in maintaining the overall quality of strawberry fruit, as reflected by lower decay rate and weight loss, as well as retarding the decrease in firmness and titratable acid. Meanwhile, reactive oxygen species (ROS) including superoxide anion and hydrogen peroxide in NTLDPE-packed fruits were 10.8% and 21.9% lower, respectively. Furthermore, the activities of antioxidant enzymes involved in ROS scavenging in NTLDPE-packed fruits were significantly higher at the later period of storage time. Anthocyanin accumulation was inhibited, whereas ascorbic acid and total phenolics contents were better retained and 1-diphenyl-2-picrylhydrazyl radical scavenging activity was 13.2% higher in NTLDPE-packed fruit by the end of storage. These data indicate that the beneficial effects of NTLDPE packaging on postharvest quality and antioxidant capacity of strawberry are probably associated with the promotion of ROS scavenging and related antioxidant enzyme activities, and NTLDPE packaging together with refrigeration storage is a promising method for strawberry fruit preservation. © 2016 Society of Chemical Industry.

A systematic study of cobalt doped In2O3 nanoparticles and their applications

An assortment of various properties of Cobalt (Co)-doped In2O3 nanoparticles has been presented. Nanoparticles in the range 15–25 nm have been prepared by a solution combustion method. Thermal analysis (TG–DSC) and infrared spectroscopy (IR) has been employed to study the precursors. Phase identification of the calcined samples has been done by X-ray diffraction (XRD). Nanometric particle size and porous nature has been observed in microscopic analysis. X-ray photoelectron spectroscopy (XPS) validates the presence of high-spin divalent Co2+ in the doped samples. Two probe DC electrical resistivity measurements show increase in resistivity values on Co doping. Magnetic measurements carried out on vibrating sample magnetometer (VSM) reveal weak ferromagnetism at 300 K, whereas paramagnetic/antiferromagnetic ordering is found to be more favourable at lower temperature. The potential of nanoparticles as a catalyst for CO oxidation has been evaluated, complete CO conversion is obtained at 130 °C for In1.88Co0.12O3 composition.

Uniaxial extrusion as an enhancement method of piezoelectric properties of ceramic micro fibers

Currently, the (Pb0.97La0.03)(Zr0.52Ti0.48)O3 composition has one of the largest photoelectric conversion efficiency, while microfibers have the highest surface to volume ratio promising high performance. In the present work chemical, physical and structural behavior of melt extruded PLZT fibers are investigated to be able effectively convert light into electrical energy. In spite of deficiencies revealed by XPS analysis, the fabricated by uniaxial extrusion micro fibers showed significant texture resulting in remanent polarization as high as 45.4 μC/cm2, which is 10% higher than ever reported in literature for not textured PZT type ceramics. Similarly a high electrical field induced strain of 0.63% is achieved at 3 kV/mm, which is even comparable to single crystal PMN-24%PT value level of 0.75%.

On the origin of pronounced O3 gradients in the thunderstorm outflow region during DC3

AbstractUnique in situ measurements of CO, O3, SO2, CH4, NO, NOx, NOy, VOC, CN, and rBC were carried out with the German Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)‐Falcon aircraft in the central U.S. thunderstorms during the Deep Convective Clouds and Chemistry experiment in summer 2012. Fresh and aged anvil outflow (9–12 km) from supercells, mesoscale convective systems, mesoscale convective complexes, and squall lines were probed over Oklahoma, Texas, Colorado, and Kansas. For three case studies (30 May and 8 and 12 June) a combination of trace species, radar, lightning, and satellite information, as well as model results, were used to analyze and design schematics of major trace gas transport pathways within and in the vicinity of the probed thunderstorms. The impact of thunderstorms on the O3 composition in the upper troposphere/lower stratosphere (LS) region was analyzed. Overshooting cloud tops injected high amounts of biomass burning and lightning‐produced NOx emissions into the LS, in addition to low O3 mixing ratios from the lower troposphere. As a dynamical response, O3‐rich air from the LS was transported downward into the anvil and also surrounded the outflow. The ΔO3/ΔCO ratio was determined in the anvil outflow region. A pronounced in‐mixing of O3‐rich stratospheric air masses was observed in the outflow indicated by highly positive or even negative ΔO3/ΔCO ratios (+1.4 down to −3.9). Photochemical O3 production (ΔO3/ΔCO = +0.1) was found to be minor in the recently lofted pollution plumes. O3 mixing ratios within the aged anvil outflow were mainly enhanced due to dynamical processes.

Preparation of LiNi0.5Mn1.5O4 cathode materials by electrospinning

LiNi0.5Mn1.5O4 cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi0.5Mn1.5O4 composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg−1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.