Synthèse et étude des propriétés de nanoparticules magnétiques de type cœur-coquille.

The bimetallic magnetic nanoparticles (NPs) of core-shell type exhibit a huge potential of application due to the wide range of properties available for this type of objects. Each potential application requires particles of specific optimised properties which needs on the one hand, the development of synthesis methods and on the other, a thorough study of their properties. In this thesis we have developed methods allowing the direct synthesis of 3d/4d NPs (here Fe/Rh) of core-shell 3d@4d and 4d@3d type by reversing the kinetics of reduction of the 3d and 4d elements precursors. The Rh atoms production is faster under dihydrogène and those of Fe atoms in the presence of amine borane. For this system, which combines a magnetic metal (Fe) and a magnetic polarisable one (Rh) we were able to study the influence of the chemical order and of the structure (evidenced by WAXS , XANES and EXAFS) on the magnetic properties through measures SQUID, Mössbauer and XMCD. In the second part we have developed the synthesis of CoAl alloy and used the higher reactivity of aluminium towards the oxygen to cause the segregation of Co and the formation of alumina in order to obtain in fine systems of Co@Al2O3 type. This segregation was followed by magnetic measurements.Les nanoparticules (NPs) bimétalliques magnétiques de type cœur-coquille présentent un énorme potentiel d'application dû à l'éventail de propriétés envisageables pour ce type d'objets. Chaque application requiert des particules aux propriétés optimisées spécifiques ce qui nécessite d'une part le développement de méthodes de synthèse et d'autre part une étude approfondie de leurs propriétés. Au cours de cette thèse nous avons mis au point des méthodes de synthèse permettant l'obtention directe de NPs 3d/4d (ici Fe/Rh) de type cœur-coquille 3d@4d ou 4d@3d en renversant les cinétiques de réduction des précurseurs des éléments 3d ou 4d. Ainsi, sous dihydrogène, les atomes de rhodium sont engendrés plus rapidement que ceux de Fe (formation de NPs Rh@Fe) alors que le contraire est observé en présence de complexe amine-borane (d'où la formation de NPs Fe@Rh). Sur ce système qui combine un métal magnétique (Fe) et un métal magnifiquement polarisable (Rh) nous avons pu étudier l'influence de l'ordre chimique et de la structure (sondés par WAXS, EXAFS et XANES) sur les propriétés magnétiques des NPs par des mesures couplées SQUID, Mössbauer et XMCD. Nous avons dans un deuxième temps développé la synthèse de NPs d'alliage CoAl et utilisé la plus forte réactivité de l'aluminium vis-à-vis du dioxygène pour engendrer la ségrégation du Co et la formation d'alumine dans le but d'obtenir in fine de systèmes Co@Al2O3. Cette ségrégation a été suivie par des mesures d'aimantation au SQUID

Easy colorimetric detection of gadolinium ions based on gold nanoparticles: key role of phosphine-sulfonate ligands

International audienceThe possibility to easily and rapidly assess the presence of Gd 3+ ions in solution is of paramount importance in many domains like magnetic resonance imaging. In that context, the use of easy to implement colorimetric sensing probes based on gold nanoparticles (AuNPs) is of special interest. Herein, AuNPs functionalized with a commercial bis(p-sulfonatophenyl)phenyl phosphine ligand (BSPP) (AuNP@BSPP), bearing negatively charged sulfonate groups are used as a colorimetric sensing probe. The addition of Gd 3+ ions onto these NPs was studied through UV-visible absorbance measurements, Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and transmission electron microscopy and compared with citrate covered AuNPs. We evidenced interactions between the Gd 3+ ions and their water rich coordination sphere and sulfonate groups on the surface of AuNP@BSPP via electrostatic interactions and hydrogen bonding. These interactions induce the reversible aggregation of AuNP@BSPP in the presence of concentrations of Gd 3+ ions at a mM level. We took advantage of this phenomenon to develop a simple and fast bench colorimetric assay for the detection of free Gd 3+ ions, based on the determination of a flocculation parameter thanks to UV-visible measurements. Limits of detection and quantification were found equal to 0.74 mM and 4.76 mM of Gd 3+ ions, respectively, with a high sensitivity that competes with conventional methods used for lanthanide detection

Water Transfer of Hydrophobic Nanoparticles: Principles and Methods

International audienceThis chapter gives an overview of the main methods available to transfer hydrophobic inorganic nanoparticles (metal, oxides, and semiconductors) into water such as place exchange of the capping agent, intercalation strategy with amphiphilic compounds or direct synthesis in the presence of those, and silica coating. The underlying principles are presented for each method, including respective advantages and drawbacks

Insights into the chemistry of bismuth nanoparticles

International audienceEnhancement of the thermoelectric properties of bismuth due to size reduction has prompted a large body of studies and recent interest in the nanochemistry of this material. The size control at the nanometer scale is complicated because of bismuth's low melting point and little known surface chemistry. We report herein an efficient synthetic method producing bismuth nanoparticles (Bi NPs) of sizes below 10 nm, and of rhombohedral structure based on transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) analysis. The nature and dynamics of the ligands at their surface have been investigated by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectroscopy. We demonstrate that alkynyl ligands, seldom used in nanochemistry, efficiently coordinate at the surface and afford stable Bi NPs that can be easily purified, leading to powders with high bismuth payload which can be redispersed into stable colloidal solutions

Effect of a side reaction involving structural changes of the surfactants on the shape control of cobalt nanoparticles

International audienceCobalt nanoparticles with different sizes and morphologies including spheres, rods, disks, and hexagonal prisms have been synthesized through the decomposition of the olefinic precursor [Co(η3-C8H13)(η4-C8H12)] under dihydrogen, in the presence of hexadecylamine and different rhodamine derivatives, or aromatic carboxylic acids. UV–vis spectroscopy, X-ray diffraction, low and high resolution transmission electron microscopy, and electron tomography have been used to characterize the nanomaterials. Especially, the Co nanodisks formed present characteristics that make them ideal nanocrystals for applications such as magnetic data storage. Focusing on their growth process, we have evidenced that a reaction between hexadecylamine and rhodamine B occurs during the formation of these Co nanodisks. This reaction limits the amount of free acid and amine, usually at the origin of the formation of single crystal Co rods and wires, in the growth medium of the nanocrystals. As a consequence, a growth mechanism based on the structure of the preformed seeds rather than oriented attachment or template assisted growth is postulated to explain the formation of the nanodisks

Stable single domain Co nanodisks: synthesis, structure and magnetism

International audienceColloidal synthesis of morphologically stable oxide-free cobalt nanodisks (diameter ≈ 21 nm, thickness ≈ 12 nm) has been achieved. The hcp c-axis is found to be perpendicular to the flat side of the disk which is explained by surface energy considerations. Magnetic measurements and comparisons with simulations show that the nanodisks are single magnetic domains with a magnetisation oriented perpendicular to the plane of the disks and reaching that of bulk cobalt, and high anisotropy field. These disks are thus potential candidates for magnetic data storage, magnetic sensor arrays, and cheap permanent magnets

Single-Crystalline Co Nanowires: Synthesis, Thermal Stability, and Carbon Coating

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Towards MRI T2 contrast agents of increased efficiency

Magnetic nanoparticles can be efficient contrast agents for T2 weighted magnetic resonance imaging (MRI) after tuning of some key parameters such as size, surface state, colloidal stability and magnetization, thus motivating the development of new synthetic pathways. In this paper we report the effects of surface coating on the efficiency of two different types of iron based nanoparticles (NPs) as MRI contrast agents. Starting from well-defined hydrophobic iron oxide nanospheres and iron nanocubes of 13 nm size, we have used three methods to increase their hydrophilicity and transfer them into water: surface ligand modification, ligand exchange or encapsulation. The NPs obtained have been characterized by dynamic light scattering and transmission electron microscopy, and the relaxivities of their stable colloidal solutions in water have been determined. Among all samples prepared, iron nanocubes coated by silica display the highest relaxivity (r2) value: 628 s-1 mM-1.This work was partially supported by the Spanish Ministry of Economy and Competitiveness (Project MAT2011-23641), the European Union (EU-FP7 MULTIFUN project, ref. 246479; Nanoalloy COST-STSM, MP0903 Action), and the Labex NEXT. The authors wish to thank Dr. Fernando Herranz from CNIC (Madrid, Spain) for relaxometry measurements