Structure and Spatial Distribution of Ge Nanocrystals Subjected to Fast Neutron Irradiation

The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of GeNC samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 800 0 C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of Ge-NC changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface regio

Studies of the Electrochemical Behavior of LiNi0.80Co0.15Al0.05O2 Electrodes Coated with LiAlO2

In this paper, we studied the influence of LiAlO2 coatings of 0.5, 1 and 2 nm thickness prepared by Atomic Layer Deposition onto LiNi0.8Co0.15Al0.05O2 electrodes, on their electrochemical behavior at 30 and 60 degrees C. It was demonstrated that upon cycling, 2 nm LiAlO2 coated electrodes displayed similar to 3 times lower capacity fading and lower voltage hysteresis comparing to bare electrodes. We established a correlation among the thickness of the LiAlO2 coating and parameters of the self-discharge processes at 30 and 60 degrees C. Significant results on the elevated temperature cycling and aging of bare and LiAlO2 coated electrodes at 4.3 V were obtained and analyzed for the first time. By analyzing of X-ray diffraction patterns of bare and 2 nm coated LiNi0.8Co0.15Al0.05O2 electrodes after cycling, we concluded that cycled materials preserved their original structure described by R-3m space group and no additional phases were detected. (c) The Author(s) 2017. Published by ECS. All rights reserved.Peer reviewe

Preparation of “Cauliflower-Like” ZnO Micron-Sized Particles

Porous polydivinyl benzene (PDVB) microspheres of narrow size distribution were formed by a single-step swelling process of template uniform polystyrene microspheres with divinyl benzene (DVB), followed by polymerization of the DVB within the swollen template microspheres. The PDVB porous particles were then formed by dissolution of the template polystyrene polymer. Unique “cauliflower-like” ZnO microparticles were prepared by the entrapping of the ZnO precursor ZnCl2 in the PDVB porous microspheres under vacuum, followed by calcination of the obtained ZnCl2-PDVB microspheres in an air atmosphere. The morphology, crystallinity and fluorescence properties of those ZnO microparticles were characterized. This “cauliflower-like” shape ZnO particles is in contrast to a previous study demonstrated the preparation of spherical shaped porous ZnO and C-ZnO microparticles by a similar method, using zinc acetate (ZnAc) as a precursor. Two diverted synthesis mechanisms for those two different ZnO microparticles structures are proposed, based on studies of the distribution of each of the ZnO precursors within the PDVB microspheres

Engineering Of Air-Stable Fe/C/Pd Composite Nanoparticles For Environmental Remediation Applications

International audienc

Engineering of Iron-Based Magnetic Activated Carbon Fabrics for Environmental Remediation

International audienceMagnetic Fe3O4, Fe and Fe/Pd nanoparticles embedded within the pores of activated carbon fabrics (ACF) were prepared by impregnation of the ACF in iron acetylacetanoate (Fe(acac)3) ethanol solution, followed by thermal decomposition of the embedded iron precursor at 200, 400 and 600 °C in an inert atmosphere. The effect of the annealing temperature on the chemical composition, shape, crystallinity, surface area, pore volume, and magnetic properties of the various functionalized ACF was elucidated. The Fe nanoparticles within the ACF were also doped with tinier Pd nanoparticles, by impregnation of the Fe/ACF in palladium acetate ethanol solution. The potential use of the functionalized ACF for removal of a model azo-dye, orange II, was demonstrated. This study illustrated the enhanced removal of the dye from an aqueous solution according to the following order: Fe/Pd/ACF > Fe/ACF > ACF. In addition, the enhanced activity of Fe3O4/ACF in the presence of increasing concentrations of H2O2 (Fenton catalysts) was also illustrated

Synthesis and characterization of iron, iron oxide and iron carbide nanostructures

International audienceMagnetic iron oxide (Fe3O4 and γ-Fe2O3) and iron carbide (Fe3C) nanoparticles of different geometrical shapes: cubes, spheres, rods and plates, have been prepared by thermal decomposition of a mixture containing the metal precursor Fe(CO)5 and the stabilizer polyvinylpyrrolidone (PVP) at 300 1C in a sealed cell under inert atmosphere. The thermal decomposition process was performed for 4 or 24 h at ([PVP]/[Fe(CO)5]) (w/v) ratio of 1:1 or 1:5. Elemental iron nanospheres embedded within a mixture of amorphous and graphitic carbon coating were obtained by hydrogen reduction of the prepared iron oxide and iron carbide nanoparticles at 450 1C. The formation of the graphitic carbon phase at such a low temperature is unique and probably obtained by catalysis of the elemental iron nanoparticles. Changing the annealing time period and the ([PVP]/[Fe(CO)5]) ratio allowed control of the composition, size, size distribution, crystallinity, geometrical shape and magnetic properties of the different magnetic nanoparticles

AlAl doping for mitigating the capacity fading and voltage decay of layered Li and Mn-rich cathodes for Li-ion batteries

Li and Mn-rich layered cathodes, despite their high specific capacity, suffer from capacity fading and discharge voltage decay upon cycling. Both specific capacity and discharge voltage of Li and Mn-rich cathodes are stabilized upon cycling by optimized Al doping. Doping Li and Mn-rich cathode materials Li1.2Ni0.16Mn0.56Co0.08O2 by Al on the account of manganese (as reflected by their stoichiometry) results in a decrease in their specific capacity but increases pronouncedly their stability upon cycling. Li1.2Ni0.16Mn0.51Al0.05Co0.08O2 exhibits 96% capacity retention as compared to 68% capacity retention for Li1.2Ni0.16Mn0.56Co0.08O2 after 100 cycles. This doping also reduces the decrease in the average discharge voltage upon cycling, which is the longstanding fatal drawback of these Li and Mn-rich cathode materials. The electrochemical impedance study indicates that doping by Al has a surface stabilization effect on these cathode materials. The structural analysis of cycled electrodes by Raman spectroscopy suggests that Al doping also has a bulk stabilizing effect on the layered LiMO2 phase resulting in the better electrochemical performance of Al doped cathode materials as compared to the undoped counterpart. Results from a prolonged systematic work on these cathode materials are presented and the best results that have ever been obtained are reported.

Changes to the Disordered Phase and Apatite Crystallite Morphology during Mineralization by an Acidic Mineral Binding Peptide from Osteonectin

Noncollagenous proteins regulate the formation of the mineral constituent in hard tissue. The mineral formed contains apatite crystals coated by a functional disordered calcium phosphate phase. Although the crystalline phase of bone mineral was extensively investigated, little is known about the disordered layer’s composition and structure, and less is known regarding the function of noncollagenous proteins in the context of this layer. In the current study, apatite was prepared with an acidic peptide (ON29) derived from the bone/dentin protein osteonectin. The mineral formed comprises needle-shaped hydroxyapatite crystals like in dentin and a stable disordered phase coating the apatitic crystals as shown using X-ray diffraction, transmission electron microscopy, and solid-state NMR techniques. The peptide, embedded between the mineral particles, reduces the overall phosphate content in the mineral formed as inferred from inductively coupled plasma and elemental analysis results. Magnetization transfers between disordered phase species and apatitic phase species are observed for the first time using 2D ¹H–³¹P heteronuclear correlation NMR measurements. The dynamics of phosphate magnetization transfers reveal that ON29 decreases significantly the amount of water molecules in the disordered phase and increases slightly their content at the ordered-disordered interface. The peptide decreases hydroxyl to disordered phosphate transfers within the surface layer but does not influence transfer within the bulk crystalline mineral. Overall, these results indicate that control of crystallite morphology and properties of the inorganic component in hard tissue by biomolecules is more involved than just direct interaction between protein functional groups and mineral crystal faces. Subtler mechanisms such as modulation of the disordered phase composition and structural changes at the ordered–disordered interface may be involved

Multiphase LiNi0.33Mn0.54Co0.13O2 Cathode Material with High Capacity Retention for Li-Ion Batteries

An integrated layered-spinel LiNi0.33Mn0.54Co0.13O2 material was synthesized through a self-combustion reaction (SCR), characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and Raman spectroscopy. It was studied as a cathode material for Li-ion batteries and its electrochemical performance was compared with that of the layered cathode material LiNi0.33Mn0.33Co0.33O2 when operated over a wide potential window. The Rietveld analysis of LiNi0.33Mn0.54Co0.13O2 indicated the presence of monoclinic Li[Li1/3Mn2/3]O-2 (31%) and rhombohedral (LiNixMnyCozO2) (62%) phases as the major components, and the spinel (LiNi0.5Mn1.5O4) (7%) as a minor component, which is supported by TEM and electron diffraction analyses. A discharge specific capacity of about 170mAhg(-1) is obtained in the potential range of 2.3-4.9V versus Li at low rate (C/10) with excellent capacity retention upon cycling. On the other hand, LiNi0.33Mn0.33Co0.33O2 (NMC111) synthesized through SCR exhibits an initial discharge capacity of about 208mAhg(-1) in the potential range of 2.3-4.9V, which decreases to a value of 130mAhg(-1) after only 50 cycles. In turn, the multiphase structure of LiNi0.33Mn0.54Co0.13O2 seems to stabilize the behavior of this cathode material, even when polarized to high potentials. LiNi0.33Mn0.54Co0.13O2 shows superior retention of the average discharge voltage upon cycling, as compared to that of LiNi0.33Mn0.33Co0.33O2 when cycled over a wide potential range. Overall, LiNi0.33Mn0.54Co0.13O2 can be considered as a promising low-cobalt-content cathode material for Li-ion batteries.