Search

Cobalt nanoparticles (CoNPs) exhibit quite unique magnetic, catalytic, and optical properties. In this work, imidazolium-based ionic liquids (ILs) are successfully used to elaborate magnetically responsive suspensions of quite monodisperse CoNPs with diameters below 5 nm. The as-synthesized CoNPs adopt the noncompact and metastable structure of ϵ-Co that progressively evolves at room temperature toward the stable hexagonal close-packed allotrope of Co. Accordingly, magnetization curves are consistent with zero-valent Co. As expected in this size range, the CoNPs are superparamagnetic at room temperature. Their blocking temperature is found to depend on the size of the IL cation. The CoNPs produced in an IL with a large cation exhibit a very high anisotropy, attributed to an enhanced dipolar coupling of the NPs, even though a larger interparticle distance is observed in this IL. Finally, the presence of surface hydrides on the CoNPs is assessed and paves the way toward the synthesis for Co-based bimetallic NPs. [ABSTRACT FROM AUTHOR]

The choice of suitable organometallic precursors, [Re2(C3H5)4] and [Ru(Me-Allyl)2COD] or [Ru(COD)(COT)], allows us to synthesize polyvinylpyrrolidone (PVP) stabilized bimetallic RuRe nanoparticles of ca. 1.3 nm with narrow size dispersity, displaying the hcp crystal structure and to control their chemical order: an alloy or Re rich surface. The structural features of these NPs were determined using complementary characterization techniques (TEM, HRTEM, STEM-HAADF, EDX, WAXS, FT-IR, MAS-NMR and ICP). In particular, surface state investigation based on CO adsorption and oxidation reactions provided useful information of the chemical order in these nanoparticles. The RuRe NPs were obtained as stable colloidal solutions or powders. Surface reactivity studies demonstrated that the alloy type RuRe/PVP NPs show better resistance to oxidation than the ones displaying a Re enriched surface and are more active towards CO dissociation than monometallic Re/PVP NPs as a result of the synergic effect between Ru and Re. Interestingly, the dissociation of CO was not observed with RuRe/PVP NPs displaying a Re enriched surface. Besides the synthetic aspect, this work highlights the crucial influence of the chemical order resulting from the choice of the metal sources in the control of the reactivity of ultra-small metal nanoparticles. [ABSTRACT FROM AUTHOR]

Enhancement 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. [ABSTRACT FROM AUTHOR]