Jean-François Hochepied

Magnetic properties of mixed cobalt–zinc ferrite nanoparticles

Solid solutions of nonstoichiometric mixed cobalt–zinc ferrite nanoparticles Co0.73yZn0.73(1−y)Fe2.18□0.09O4, were prepared in order to study their magnetic properties as a function of cobalt content y. The saturation magnetization changes with increasing y due to the various occupancies of cations in tetrahedral and octahedral sites and/or to an increase in the disorder of the ferrimagnetic structure. The cobalt content and particle size effects on the coercive field were studied. The increase in the ratio between remanent and saturation magnetizations indicates that, with increasing y, a transition takes place from uniaxial to cubic anisotropy. Field cooled (FC) curves drastically change with the cobalt content. At zero cobalt, this curve is characterized by a well-defined peak that disappears progressively with increasing y. This is attributed to the particles themselves and neither to their interactions nor to experimental procedures. The fit of the zero FC (ZFC) curve indicates an unrealistically hig...

Influence of precipitation conditions (pH and temperature) on the morphology and porosity of boehmite particles

Syntheses of boehmite particles were performed by precipitation of aluminium nitrates with soda in conditions of controlled pH and temperature. If precipitation conditions lead first to an isolable amorphous hydroxide subsequently transformed into boehmite, then porous particles constituted by the agglomeration of boehmite nanocrystals are formed. In contrast, if conditions directly lead to a crystallized boehmite phase, polycrystalline nanofibers are obtained. These experiments show that anisotropic growth can be obtained by monitoring pH and temperature, without using any additives.

Effect of the mixing procedure on aluminium (oxide)-hydroxide obtained by precipitation of aluminium nitrate with soda

Abstract Three different mixing procedures of aluminium nitrate with soda were compared keeping identical aging conditions ( T =60 °C, pH=9, 120-min aging): injection of nitrate aluminium solution into soda, injection of soda into nitrate aluminium solution and double jet. Each procedure led to a specific compound: microporous boehmite, bayerite and fibrillar boehmite, respectively. For single jet procedures, reactions were therefore driven locally in the mixing zone where the most influent parameter was the nature of injected solution. This allows obtainment of bayerite or boehmite at unexpected pH.

Ferromagnetic resonance of nonstoichiometric zinc ferrite and cobalt-doped zinc ferrite nanoparticles

Ferromagnetic resonance spectra of zinc ferrite and cobalt doped zinc ferrite nanoparticles, measured at various temperatures, exhibit an invariant point at a given field. This makes it possible to determine the equation relating the resonance field shift to the peak-to-peak linewidth. When particles are frozen in a matrix in a magnetic field, the anisotropy constant of the material can be derived from the angular variation of the resonance field. This procedure is useful to determine the thermal dependence of the anisotropy constant, but is shown to require various freezing temperatures experiments to estimate the accuracy of the deduced anisotropy constant values. It is also shown that the angular dependence of the resonance field is similar for a uniaxial (zinc ferrite) and cubic (zinc ferrite containing 40% cobalt ions) anisotropy. This unexpected result is explained by the weakness of the texturation, leading to a distribution in easy axes directions.

Toxicity of boehmite nanoparticles: impact of the ultrafine fraction and of the agglomerates size on cytotoxicity and pro-inflammatory response

Abstract Boehmite (γ-AlOOH) nanoparticles (NPs) are used in a wide range of industrial applications. However, little is known about their potential toxicity. This study aimed at a better understanding of the relationship between the physico-chemical properties of these NPs and their in vitro biological activity. After an extensive physico-chemical characterization, the cytotoxicity, pro-inflammatory response and oxidative stress induced by a bulk industrial powder and its ultrafine fraction were assessed using RAW264.7 macrophages. Although the bulk powder did not trigger a significant biological activity, pro-inflammatory response was highly enhanced with the ultrafine fraction. This observation was confirmed with boehmite NPs synthesized at the laboratory scale, with well-defined and tightly controlled physico-chemical features: toxicity was increased when NPs were dispersed. In conclusion, the agglomerates size of boehmite NPs has a major impact on their toxicity, highlighting the need to study not only raw industrial powders containing NPs but also the ultrafine fractions representative of respirable particles.

Liposomes : support à la formation de capsules plus stables à base de polyéléctrolytes réticulés ou de silice☆

Resume L’utilisation d’enzyme en therapie ou en biodetection necessite de les isoler de leur environnement afin d’eviter leur degradation par des agents proteolytiques, par des variations de pH ou encore par effet de dilution, et d’eviter egalement le developpement de reaction immunitaire dans le cas d’injection. Cet isolement sous-entend de les encapsuler dans des conditions non denaturantes pour l’enzyme, dans une capsule suffisamment resistante et a l’echelle nanometrique pour diminuer la degradation par le systeme reticulo-endothelial. Les liposomes representent une methode de choix d’encapsulation de proteine dans des conditions non denaturantes mais ne sont pas suffisamment stables. En revanche, d’autres capsules offrent une tres bonne stabilite mais les conditions requises pour leur formation ne permettent pas de travailler en presence d’enzyme. Nos travaux utilisent les liposomes comme structure support a la formation de capsules plus stables a partir de deux types de materiaux. D’une part, nous avons forme en surface du liposome une capsule de polyelectrolytes qui est ensuite rigidifiee par pontage covalent entre les polyelectrolytes. D’autre part, nous avons utilise la silice afin de former une coque inorganique autour du liposome. Ces deux techniques ont permis d’obtenir une nanocapsule stable en presence de detergent et permettant de preserver de la degradation par des proteases de l’acetylcholinesterase, enzyme hautement sensible aux pesticides et utilisable pour le developpement de biodetecteurs.

Controlled precipitation of zinc oxide particles

The scope of this work consisted of precipitating directly zinc oxide particles from zinc nitrate and zinc sulphate solutions using sodium hydroxide at pH 10,5, 2 h and 25 or 60 °C. For the zinc nitrate system, the effect of additives at 25 °C, such as sodium sulphate and sodium dodecyl sulphate, was also investigated. Precipitated powders were characterized in terms of their crystalline structure (X-ray diffraction), morphology and size (scanning electron microscopy, transmission electron microscopy). Precipitation in distilled water with zinc nitrate produced homogeneous star-type particles (1 μm) composed of assembled 30-nm crystallites at 25 °C and ellipsoidal and spherical particles (100 nm to 1 μm) at 60 °C. On the other hand, for the zinc sulphate system at 25 °C, several different morphologies were obtained as ellipsoids (250 × 800 nm), half ellipsoids (250 × 350 nm), fibres (40 × 700 nm) and unshaped particles (700 nm), whilst half ellipsoids (100 nm) were precipitated as well as smaller particles (25–60 nm) at 60 °C. The investigation of the additive effect showed that precipitation from zinc nitrate solution in the presence of sodium sulphate led to half ellipsoids with a size range from 100 to 300 nm. In contrast, the addition of sodium dodecyl sulphate resulted in a mixture of morphologies that included half ellipsoids (150–200 nm), asymmetrical and symmetrical ellipsoids, as well as small particles of 30 nm. This study evidenced the effect of additives on morphology and size control of submicrometric particles constituted of assembled nanocrystallites.

Room-Temperature Precipitation of Zinc Oxide Particles: Building Submicronic Particles with Nanocrystals

The scope of this work was to investigate the precipitation of zi nc oxide particles from zinc nitrate and soda. All experiments were performed at regulat d pH (10.5 or 9.5) and temperature (25°C or 60°C). At room temperature, 1 μm particles made up of self-assembled 30nm nanocrystals were obtained with pH-dependent morphology: star-like (pH=10.5) or ellips oidal (pH=9.5). Additives were used to block particle self-assembly without changin g nanocrystal size, whereas a temperature increase disrupts totally self-assembly, leading to ill-sha ped particles. Introduction Among the ceramic materials, zinc oxide (ZnO) plays an importa nt role due to its diversified applications in catalysis, electronic devices, luminescent devices, pigments and components for the pharmaceutical and cosmetic industries. In the literature, severa l synthesis techniques are available for the production of zinc oxide particles, including sol-gel [1] or mic ellar systems [2] to limit particle size to a few nanometers, or more classical precipit ation techniques for submicronic particles [3-5]. A very simple system (precipitation with soda) focusing on conditions leading to remarkable particle shapes was employed, and additives were us d to block particle growth in order to reveal self-assembly mechanisms. Experimental Zinc nitrate Zn(NO3)2.6 H2O, sodium hydroxide NaOH (flakes), sodium sulfate Na 2SO4.10 H2O and sodium dodecylsulfate (SDS) CH 3(CH2)11OSO3Na were purchased from Prolabo with 99%, 97%, 99% and 98% purities, respectively. Two solutions were prepared: solution A 0.1 mol Zn(NO3)2 dissolved in 200mL distilled water , and solution B 0.2 mol NaOH in 200mL distilled water. Solutions A and B were injected at a rate of 28mL/min in a double-ja cketed thermostically controlled vessel at 25°C with hemispherical base, equipped with teflon ba ffles, containing 600 mL of distilled water or 600 mL of solutions containing 0.1 mol Na 2SO4 or 0.1 mol SDS, stirred mechanically at 500 rpm with a T4/45 propeller. The pH of the reaction system was adjusted by using a 0.1M NaOH solution. A pH stat PHM290 from Radiometer Analytical was employed for pH control. After addition of the reagents, the mixture was stirred for 2h at controlled pH and temperature. The pr ecipitate was washed with distilled water and vacuum dried. The diffractograms of the dried powders were recorded on a Bruker D8 diffractometer in θ−θ configuration, with cobalt Kα radiation ( λ=1,789 Å) and equipped with a position-sensitive detector. Scanning electron microscopy was performed with a Zeiss Leo 982 model and transmission electron microscopy with a Philips EM430 model, operating t 300 kV. Nitrogen gas adsorption /desorption isotherms were measured at 77K using a ASAP 2010 model from Micromeritics. Solid State Phenomena Online: 2003-06-20 ISSN: 1662-9779, Vol. 94, pp 171-176 doi:10.4028/www.scientific.net/SSP.94.171

Precipitation of Nickel Hydroxides from Nickel Dodecylsulphate

Classical precipitation techniques applied to a nickel di-dodecylsulphate Ni(DS)2 precursor were developed. In the range of concentrations studied this precursor forms direct micelles in water. In pH-controlled double jet precipitation with soda at 60°C, the pure a, poorly crystallised bbc and well crystallised b phases are successively obtained by pH shifts from 8 to 11, whereas the platelet morphology remains similar. In the same conditions, classical salts never lead to a phase and the particle size and morphology is pH dependent. Hydroxide precipitation by ammonia decomplexation, via heating at 60°C, Ni(DS)2 leads to well-calibrated stacks of b- Ni(OH)2 nanopancakes (300 nm in diameter and 200 nm stacking length) whereas classical salts lead to micrometric particles characterised by thin interconnected walls.