We present an eco-friendly synthesis of magnetic nanocomposites which may be used in water-treatment. They are composed of iron oxide nanoparticles encapsulated in a silica matrix. In addition to the benefits of their low environmental impact, the synthetic methods described here have led to particles structured on several scales. Two types of synthesis have been studied. Perfectly monodisperse millimetric beads were obtained by a sol-gel method using a non-toxic and biodegradable biopolymer as structuring agent. Microspheres or magnetic nanospheres were prepared using sol-gel reactions in emulsions of vegetable oil. We tested these solids as magnetic adsorbents for water-treatment processes with magnetic separation. Here we show the first results on the application of these materials as adsorbents for dyes and heavy metals after a possible chemical modification of their surface.

Nous présentons la synthèse par chimie verte de nanocomposites magnétiques qui pourraient être utilisés dans le traitement de l’eau. Ils sont constitués par une matrice de silice encapsulant des nanoparticules d’oxyde de fer. Outre les avantages liés à leur faible impact sur l’environnement, les méthodes de synthèse décrites ici ont conduit à des particules structurées sur plusieurs échelles de taille. Deux types de synthèse ont été étudiés. Des billes millimétriques parfaitement monodisperses ont été obtenues par voie sol-gel en utilisant comme agent structurant des biopolymères non-toxiques et biodégradables. Des microsphères ou des nanosphères magnétiques ont été préparées à l’aide de réactions sol-gel dans des émulsions à base d’huile végétale. Nous avons testé ces solides comme adsorbants magnétiques dans des procédés de dépollution des eaux utilisant la séparation magnétique. Nous montrons ici les premiers résultats quant à l’application de ces matériaux comme adsorbants de colorants et de métaux lourds après une éventuelle modification chimique de leur surface.

A series of LiNi1/3Mn1/3Co1/3O2 samples with α-NaFeO2 structure were synthesized using tartaric acid as a chelating agent by wet chemical method. Different acid to metal-ion ratios R have been used to investigate the effect of this parameter on the physical and electrochemical properties. The cationic mixing (Ni on the 3a Li sites) have been evaluated by Rietveld refinement and magnetic measurements We determined that the LiNi1/3Mn1/3Co1/3O2 sintered at 900 {degree sign}C for 15 h with an acid to metal ion ratio R=2 was the optimum condition for this synthesis. For this optimized sample, only 1.26% of nickel-ions occupied the 3a Wyckoff site of the lithium-ion sublattice. This material delivered an initial discharge capacity of 172 mAh/g and displayed Coulomb efficiency of 94%.

Co–Sn alloys were prepared by an electrochemical route in molten LiCl–KCl between 400 and 550°C. The Sn(IV)/Sn(II), Sn(II)/Sn(0) and Co(II)/Co(0) redox couples were studied by cyclic voltammetry and/or chronopotentiometry over the temperature range. The diffusion coefficient values of Co(II) ions were measured. For example, it was found that the DCo(II) values deduced from chronopotentiometry range from DCo(II)=1.65×10−5cm2s−1 at 400°C to 4.95×10−5cm2s−1 at 550°C. The standard potential of the Co(II)/Co(0) redox couple in molten LiCl–KCl was measured at 400°C: ECo(II)/Co(0)0=−1.35V vs Cl2/Cl−. Finally, Co–Sn alloys were prepared in potentiostatic mode. The influence of the temperature of molten LiCl–KCl, the applied potential and the deposition time on the morphology and the composition of the Co–Sn alloys were also investigated. For T>450°C, the following tendency has been observed: the more negative the potential, the higher the Sn content in the deposited alloy. Thus, depending on the operating conditions, pure CoSn or CoSn2 can be prepared.

When treated at high temperatures, petroleum coke materials exhibit structures which are formed of graphitized closed tips. The external surface of these materials is mostly formed of hemispherical tips similar to those found in carbon nanotubes. By low- temperature fluorination using CF4 radio- frequency plasmas, an opening mechanism of the closed tips occurs, thus allowing a drastic increase of possible intercalation into the structure. The interest for Li+ storage in Li- ion batteries has been demonstrated by capacity measurements which show an enhancement of the Li+ capacity retention into the host materials. (c) 2007 The Electrochemical Society.

Vanadium oxide films were synthesised by chemical vapour deposition (CVD) from pure of triisopropoxyvanadium oxide (VO(OC3H7)3) and oxygen as precursors. The influence of the substrate on the crystallinity of the vanadium oxide films was studied before and after annealing at 500°C. On mica substrates, as-deposited film was composed of crystalline V2O5 as revealed by XRD. On Pt, Ti, stainless steel, glass and F-doped SnO2 substrates, an annealing procedure was required to get V2O5. SEM investigations have clearly evidence V2O5 plates but the kinetics growth seems to be strongly dependent on the nature of the substrate. The insertion/extraction of Li+ into the host structure was investigated in 1M LiClO4-PC with annealed V2O5 films deposited on Ti, Pt and stainless steel substrates. The best electrochemical performances were obtained in the potential range 3.8–2.8V versus Li/Li+ with V2O5 films deposited onto stainless steel substrate: the reversible capacity reaches after subsequent cycles was about 115mAhg−1 (rate C/23). In a wider potential range (between 3.8 and 2.2V versus Li/Li+), V2O5 deposited onto Ti substrate exhibited the higher electrochemical performances (220mAhg−1 for a rate of C/23).

This study addresses the lithium insertion performances of amorphous vanadium oxide films, synthesized by atomic layer chemical vapour deposition (ALCVD). AFM and SEM investigations showed that the as-deposited films are amorphous, compact and homogeneous. As revealed by XPS and Raman spectroscopy, the ALCVD oxide films after deposition are mainly composed of V2O5, with V4+ surface content (about 10%). The insertion of Li+ into the lattice was investigated in 1M LiClO4-PC. The results show that the electrochemical performances obtained with amorphous vanadium oxide films, with an optimal thickness of 200nm (455mAhg−1, i.e. composition of Li2.9V2O5), were superior to crystalline V2O5 films. The amorphous films exhibit higher capacity and better cycle ability even for deep lithium insertion ratio compared to crystalline V2O5 films. The chemical diffusion coefficients, deduced from numerical simulation of chronopotentiograms, were comprised between 3×10−12and 10−13cm2s−1 for a lithium insertion ratio comprised between 0 and 2.9. AFM and Raman spectroscopy performed before and after lithiation showed that neither the morphology nor the local order of the amorphous films were significantly affected by the insertion/extraction of lithium. Raman measurements also revealed that a very small amount of lithium are locally trapped in the oxide lattice.

Thin films of vanadium oxide were grown on vanadium metal surfaces W in air at ambient conditions, (ii) in 5 mm H2SO4 (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10(-5) mbar) at temperatures between 350 and 550 degrees C and (iv) at near-atmospheric oxygen pressure (750 mbar) at 500 degrees C. The oxide films were investigated by atomic force microscopy (AIM), X-ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed Of V2O3. In air and in aqueous solution at RT, the oxide films are ultra-thin and hydroxylated. At 500 degrees C, nearly atmospheric oxygen pressure is required to form crystalline V2O5 films. The oxide films grown at pO(2) = 750 mbar for 5 min are about 260-nm thick, and consist of a 115-nm outer layer of crystalline V2O5. The inner oxide is mainly composed Of VO2. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 degrees C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well-crystallized V2O5 film, formed by oxidation for 5 min at 500 degrees C and 750 mbar O-2, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright (C) 2005 John Wiley & Sons, Ltd.

Surface modification of graphite powder has been performed by chemical fluorination using elemental fluorine at 200 degrees C and 300 degrees C. This process leads to an increase of the BET surface area due to partial C-C bond breaking. Surface analyses performed by secondary ions mass spectrometry have shown that the H + 0 content at the surface of graphite is significantly decreased by this fluorination treatment. Fluorinated graphite powders have been tested as negative electrodes in Li-ion battery, chronopotentiometry measurements have shown that the fluorinated graphite exhibits better electrochemical performances than raw graphite powder notably due to an increase of the surface area which allows the storage of a higher amount of lithium into the host lattice. In addition, impedance measurements performed in a delithiated state have shown a significant decrease of the total cell resistance, i.e. a decrease of both the charge transfer resistance and the resistance related to the solid electrolyte interface (SEI) layer. (c) 2005 Elsevier B.V. All rights reserved.