As-prepared Samples (as-prepared + sample)

Distribution by Scientific Domains

Selected Abstracts

Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid system

AICHE JOURNAL, Issue 7 2006
Izumi Taniguchi
Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Synthesis and Characterization of Single-Crystalline Lanthanum Fluoride with a Ring-Like Nanostructure

Yang Tian
Abstract LaF3 ring-like nanostructures with a diameter of less than 2 ,m have been fabricated by a facile, effective, and environmentally friendly molten salt synthesis route in which NaNO3 and KNO3 (2:1 molar ratio) act as reaction media and the rare-earth nitrate and NaF as precursor. X-ray diffraction, TEM, HR-TEM, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy are all used to characterize the as-prepared samples. Experiments peformed with different reaction times indicate that a central-etching of the plates from the inner part towards the edge during nanocrystal growth plays a key role in the formation of LaF3 nanorings since no other templates/surfactants are present in our system. Additionally, the luminescence properties of LaF3 nanorings doped with Eu3+ cation have been investigated andcompared with those of bulk materials and nanoparticles with a size of approximately 50 nm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Electrochemical Method for Synthesis of a ZnFe2O4/TiO2 Composite Nanotube Array Modified Electrode with Enhanced Photoelectrochemical Activity

Yang Hou
Abstract An electrode with intimate and well-aligned ZnFe2O4/TiO2 composite nanotube arrays is prepared via electrochemical anodization of pure titanium foil in fluorine-containing ethylene glycol, followed by a novel cathodic electrodeposition method. The deposition of ZnFe2O4 is promoted in the self-aligned, vertically oriented TiO2 nanotube arrays but minimized at the tube entrances. Thus, pore clogging is prevented. Environmental scanning electron microscopy, energy-dispersive X-ray spectra, high-resolution transmission electron microscopy, X-ray diffraction patterns, and X-ray photoelectron spectroscopy indicate that the as-prepared samples are highly ordered and vertically aligned TiO2 nanotube arrays with ZnFe2O4 nanoparticles loading. The TiO2 nanotubes are anatase with the preferential orientation of <101> plane. Enhanced absorption in both UV and visible light regions is observed for the composite nanotube arrays. The current,voltage curve of ZnFe2O4 -loaded TiO2 nanotube arrays reveals a rectifying behavior. The enhanced separation of photoinduced electrons and holes is demonstrated by surface photovoltage and photocurrent measurements. Meanwhile, the photoelectrochemical investigations verify that the ZnFe2O4/TiO2 composite nanotube array modified electrode has a more effective photoconversion capability than the aligned TiO2 nanotube arrays alone. In addition, the photoelectrocatalytic ability of the novel electrode is found enhanced in the degradation of 4-chlorophenol. [source]

Blue Luminescence of ZnO Nanoparticles Based on Non-Equilibrium Processes: Defect Origins and Emission Controls

Haibo Zeng
Abstract High concentrations of defects are introduced into nanoscale ZnO through non-equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420,nm (2.95,eV,<,Eg,=,3.26,eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488,nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial-zinc-related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as-prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co-emission of blue and green emissions and peak adjustment from blue to yellow. [source]

A Rapidly Responding Sensor for Methanol Based on Electrospun In2O3,SnO2 Nanofibers

Wei Zheng
In this paper, we presented a simple and effective electrospinning technique for the preparation of In2O3,SnO2 composite nanofibers. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that large quantities of In2O3,SnO2 composite nanofibers with diameters from 60 to 100 nm were obtained. The In2O3,SnO2 composite nanofibers exhibited excellent gas sensing properties to methanol, such as fast response/recovery properties, high sensitivity, and good selectivity. [source]

Effect of pH on the Carbonate Incorporation into the Hydroxyapatite Prepared by an Oxidative Decomposition of Calcium,EDTA Chelate

Yusuf Yusufoglu
In this study, the carbonate incorporation into the hydroxyapatite (HAp) lattice under various pH conditions was investigated. Crystalline-sodium and carbonate-containing calcium HAp (NaCO3HAp) powders were prepared using an oxidative decomposition of calcium,EDTA chelates in a sodium phosphate solution with hydrogen peroxide. The powders obtained were characterized by X-ray diffraction, infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and elemental analysis. Depending on pH, spherical particles approximately 3.5 ,m in diameter or hexagonal prismatic particles measuring 3,9 ,m in length were obtained. Various characterization techniques showed that the precipitates were a single-phase NaCO3HAp. The carbonate content and the lattice parameters of the HAp were a function of solution pH. Maximum carbonate incorporated into the HAp lattice was at pH=10, corresponding to lattice parameters of a=0.93880 nm and c=0.69070 nm. Furthermore, spectroscopic analyses indicate that the as-prepared samples are B-type carbonated HAp, in which carbonate ions occupy the phosphate sites. After heat treatment at 965°C, most of the carbonate is removed from the HAp lattice. [source]

Solid-Solution Formation in the Synthesis of Fe-Zircon

Enrique Carreto Cortés
To investigate solid-solution formation in the iron-doped silicate (zircon) system, different samples were prepared by the ceramic method with addition of LiF as a mineralizer. The results of X-ray powder diffraction (XRD), 57Fe Mössbauer, and UV,visible spectroscopy showed that in the as-prepared samples, only a small fraction of iron, i.e., about 2.5 mol%, is hosted in the zircon structure as paramagnetic Fe3+ species, while the remaining Fe3+ cations form magnetic ,-Fe2O3 particles that are trapped in the zircon matrix. [source]

Effect of water treatment on analyte and matrix ion yields in matrix-assisted time-of-flight secondary ion mass spectrometry: the case of insulin in and on hydroxycinnamic acid

Wilfried Szymczak
A systematic study was performed to identify the origin of surprisingly high analyte-to-matrix yield ratios recently observed in time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of oligo- and polypeptides mixed in matrices of ,-cyano-4-hydroxycinnamic acid (4HCCA). Several sets of samples of porcine insulin in 4HCCA (1:3100 molar) were prepared from liquid solutions by a nebuliser technique, with more than one order of magnitude variation in sprayed material (substrate silicon). Following different periods of storage in air and/or vacuum as well as exposure to high-purity water, TOF-SIMS analysis was performed under oblique impact of 22 keV SF5+. Treatment with water involved either deposition of a droplet covering the whole sample for times between 1 and 20,min or spraying with water in droplet equivalent quantities. The analyte and matrix molecules were detected as protonated molecules (insulin also in doubly protonated form). Even the as-prepared samples usually showed insulin-to-4HCCA yield ratios exceeding the molar ratio of the mixed material. Upon ageing in vacuum the matrix ion yields remained constant but the analyte yields decreased, partly due to break-up of intrachain disulfide bonds. Water treatment resulted in a pronounced decrease in the 4HCCA yield, typically by a factor of five, in parallel with an increase of the insulin yield, by up to a factor of four. Evidence is provided that these changes occur concurrently with a partial dissolution of 4HCCA at the sample surface. The enhanced insulin yield was not correlated with the Na+ yield. The typically 20-fold increase in the insulin-to-4HCCA yield ratio, generated by water exposure of the samples, provides the explanation for the high yield ratios observed previously with water-treated samples. Spraying with water or repeated exposure to water droplets caused a pronounced degradation of the insulin parent yields in combination with an increasing appearance of signals due to the B- and A-chains of insulin. To clarify the issue of surface segregation, a few samples were prepared by spraying acetone-diluted solutions of insulin on previously deposited layers of 4HCCA. Whereas the insulin yields from as-prepared samples were rather low, the yields observed after water treatment were comparable with those observed with samples of insulin in 4HCCA. The results suggest that a large amount of insulin is present at the surface of samples prepared from liquid mixtures of insulin in 4HCCA. With both methods of sample preparation, however, high secondary ion yields of insulin were only obtained after exposure of the samples to water. The chemical changes responsible for this beneficial effect still need to be identified. Copyright © 2002 John Wiley & Sons, Ltd. [source]