In this study, we report a rapid sonochemical synthesis of monodisperse nonaggregated Fe(3)O(4)@SiO(2) magnetic nanoparticles (NPs). We found that coprecipitation of Fe(II) and Fe(III) in aqueous solutions under the effect of power ultrasound yields smaller Fe(3)O(4) NPs with a narrow size distribution (4-8 nm) compared to the silent reaction. Moreover, the coating of Fe(3)O(4) NPs with silica using an alkaline hydrolysis of tetraethyl orthosilicate in ethanol-water mixture is accelerated many-fold in the presence of a 20 kHz ultrasonic field. The thickness of the silica shell can be easily controlled in the range of several nanometers during sonication. Mossbauer spectra revealed that nonsuperparamagnetic behavior of obtained core-shell NPs is mostly related to the dipole-dipole interactions of magnetic cores and not to the particle size effect. Core-shell Fe(3)O(4)@SiO(2) NPs prepared with sonochemistry exhibit a higher magnetization value than that for NPs obtained under silent conditions owing to better control of the deposited silica quantities as well as to the high speed of sonochemical coating, which prevents the magnetite from oxidizing.

Systematic Mn 2p XPS and Mn K-edge XAS analyses together with the electrochemical measurement have been carried out for the spinel LiMn 2 O 4 prepared at various sintering temperatures in order to elucidate an origin of the dependence of electrochemical properties on synthetic conditions. From the comparative experiments, it becomes clear that a lowering of synthetic temperature gives rise to an increase of structural disorder and of the average oxidation state of manganese, which is more prominent on the surface than in the bulk. Such results suggest that the modification of surface property induced by a decrease of particle size is closely related to the electrochemical performance. The nanocrystalline LiMn 2 O 4 prepared at 250 °C shows excellent cyclability at the 3 V region compared to that of microcrystalline LiMn 2 O 4 prepared at 700 °C. For the purpose of examining the evolution of the chemical bonding nature of inserted lithium, 7 Li MAS NMR studies have been performed for both the spinel compounds before and after Li + intercalation. While the intercalation of 0.2 mol Li + does not induce any remarkable spectral change for the microcrystalline LiMn 2 O 4 , it leads to a dramatic suppression of the NMR signal for the nanocrystalline LiMn 2 O 4 , indicating that the process of grafting Li into the latter phase results in significant modifications of the chemical environment of lithium. On the basis of present experimental findings, it can be concluded that the lowering of synthetic temperature modifies the surface properties, which facilitates the grafting process of Li + ion and, thereby, enhances the electrochemical properties for the 3 V region corresponding to the Li insertion.

No abstract

Ceramics possess osteoconductive properties but exhibit no intrinsic osteoinductive capacity. Consequently, they are unable to induce new bone formation in extra osseous sites. In order to develop bone substitutes with osteogenic properties, one promising approach consists of creating hybrid materials by associating in vitro biomaterials with osteoprogenitor cells. With this aim, we have developed a novel strategy of biomimetic modification to enhance osseointegration of hydroxyapatite (HA) implants. RGD-containing peptides displaying different conformations (linear GRGDSPC and cyclo-DfKRG) were grafted onto HA surface by means of a three-step reaction procedure: silanisation with APTES, cross-linking with N-succinimidyl-3-maleimidopropionate and finally immobilisation of peptides thanks to thiol bonding. Whole process was performed in anhydrous conditions to ensure the reproducibility of the chemical functionalisation. The three-step reaction procedure was characterised by high resolution X-ray photoelectron spectroscopy. Efficiency of this biomimetic modification was finally demonstrated by measuring the adhesion of osteoprogenitor cells isolated from HBMSC onto HA surface.

No abstract

The outstanding characteristics of fluorine gas, e.g., extreme reactivity and oxidizing power, and the utmost electronegativity of F À ion, lead to very strong bonds between fluorine and most of the other elements of the periodical table. Treatments involving F 2 , fluorinated gases and rf plasmaenhanced fluorination (PEF) constitute exceptional tools for modifying the surface properties of materials. Many advantages of these techniques can be indeed outlined, when compared to more conventional methods: low-temperature reactions (even at room temperature), chemical modifications limited to surface only without changing the bulk properties, possible non-equilibrium reactions. Depending on the type of starting materials and employed techniques, the improved properties may concern wettability, adhesion, chemical stability, barrier properties, biocompatibility, grafting, mechanical behavior. Several examples of surface fluorination will be given on various types of carbon-based materials, elastomers and polymers. #

A chemically modified cellulose filter paper with ethylenediaminetetraacetic acid (EDTA) is described as a device for metal remediation. This new material was prepared by esterification of the paper with EDTA dianhydride. The high hydrophilicity of cellulose paper associated with the strong chelating properties of the EDTA moieties for metals allow the treatment of water samples containing various metal cations, including Ag(I), Pb(II), Cd(II), Ni(II), Zn(II), Sn(II), and Cu(II), with 90− 95% removal efficiency. The mechanism of adsorption was deeply studied with the support of kinetic experiments and adsorption isotherms. As a practical feature, one can note that the cellulose−EDTA material works at a wide range of pH values and can be used either as a solid adsorbent or a membrane for continuous wastewater treatment.

Layered Li 1+x (Ni 0.425 Mn 0.425 Co 0.15 ) 1-x O 2 materials (0 x 0.12) were prepared at 1000°C for 12 h in air by a coprecipitation method. As x increased in Li 1+x (Ni 0.425 Mn 0.425 Co 0.15 ) 1-x O 2 , the substitution of x Li + ions for x transition metal ions induced for charge compensation an increase in the average transition metal oxidation state. X-ray photoelectron spectroscopy analyses showed that cobalt and manganese were present in these materials in the trivalent and tetravalent states, respectively, and that increasing overlithiation led to the oxidation of Ni 2+ ions into Ni 3+ ions. The refinement of the crystal structure of these materials in the R m space group and magnetic measurements showed a decrease in the Ni occupancy in the Li layers with increasing overlithiation. From an electrochemical point of view, the reversible capacity in the 2-4.3 V range decreased with overlithiation Keywords :Although LiCoO 2 is suitable for the lithium-ion battery application, its high cost and toxicity prevent its use in low-price or large devices. Positive electrodes with LiNiO 2 revealed an attractive reversible capacity 1 but suffered from a quite poor capacity retention 2 and also from a low thermal stability of their deintercalated phases. 3,4,5,6 Partial substitution for nickel allowed an optimization of these properties for compositions such as LiNi (1-x-y) Co x Al y O 2 . 7,8,9 Nevertheless, there is still a need for cheaper and safer positive electrode materials with higher electrochemical performances. Recently lithium-rich manganese-based materials such as Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 and Li[Co x Li (1/3x/3) Mn (2/3-2x/3) ]O 2 were extensively studied by various research groups. 10,11,12,13 Interesting results were obtained, for instance for the Li[Ni 1/3 Li 1/9 Mn 5/9 ]O 2 phase with a capacity of 230 mAh/g between 2.0 and 4.6 V at 55°C. 14 In all these materials, the manganese ions are in the tetravalent state in the pristine material 15 so that they are electrochemically inactive. Because there are no Mn 3+ ions, no structural evolution to the spinel structure is expected to occur upon cycling, on the contrary to what was observed for the layered LiMnO 2 . 16,17,18,19 Furthermore, the presence of a large amount of manganese ions at the stable tetravalent oxidation state is thought to be responsible for a higher thermal stability. Differential scanning calorimetry experiments (DSC) on charged electrodes of Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 for x=5/12 indicate that this material should be thermally safer than LiCoO 2 . 10 The DSC profiles of the fully oxidized Li x [Li 0.12 Ni z Mg 0.32-z Mn 0.56 ]O 2 (z=0.3) material also demonstrate much higher thermal stability than Li x CoO 2 . 20 Note also that most of these overlithiated materials exhibit an irreversible plateau at around 4.5 V/Li during the first charge. The origin of this plateau was attributed by Lu and Dahn to be due to an irreversible oxygen loss. 14