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A versatile synthesis for multifunctional magnetic nanoplatforms. – MAG@M

Submission summary

Expanding from single component nanoparticles, research in nanomaterials now focuses on multi-component NPs with discrete domains of different materials arranged in a controlled manner. This evolution is driven by the obvious advantages of multifunctionality, the possibility to create novel functions or to reach enhanced properties. However, reliable synthesis processes are still to be invented. This three years project aims at developing a novel synthesis pathway to afford multifunctional fully metallic core@shell nanoplatforms (2-10nm), the core and the shell being responsible for different properties. More specifically we have decided to focus on the synthesis of bimetallic systems with an iron core and shell of rhodium, gold or bismuth to have binary systems of different intermiscibility, thus testing the versatility of our process. Placing the 3d element in the core of the nanoparticles (NPs) is a real challenge whatever the shell metal but is mandatory to protect it from air oxidation, and to allow further surface functionalization by coordination of suitable ligands without altering the magnetic properties of this core. Due to the multifunctional character of the target materials, a large audience is foreseen and multiple application fields can be envisaged such as catalysis (Fe@Rh), biology (Fe@Au), physics (Fe@Bi and derivatives from this system namely Fe@Bi2O3), etc...The synthesis route is designed to respect the principle of economy of atoms and to use commercial or easily prepared reagents. This should ensure that the large scientific community working in the nanoscience area be able to use it. The key point of our strategy is the use of amine-borane complexes, seldom used reagents in the field of NPs synthesis, in combination with metal-organic and organometallic complexes of very different reactivities towards these amine-borane adducts. Indeed, such adducts react selectively with certain metal precursors (such as amido or amidinato complexes) in the presence of olefinic complexes leading to the formation of a core NP and a by-product (H2 or surface hydrides) able to reduce the olefinic complex into a metal shell. The dihydrogen produced in the first step (formation of the core of the nanoplatform) is thus recycled for the second step of the building of the multifunctional core@shell NPs (formation of the shell). This novel pathway is strongly based on the expertise of the consortium in the synthesis of metal-organic and organometallic complexes, on organometallic synthesis of monometallic and bimetallic NPs and on recent research efforts world-wild aiming at producing H2 from amine borane adducts. Preliminary, unpublished results show the relevance of this approach (Fe@Rh systems). The segregation between the two metals is achieved via a strong difference in reduction kinetics of the two metal precursors occurring even at low temperature, which means that the core@shell chemical distribution inside the NPs is kinetically trapped. This allows the formation of metastable systems, of completely new physical properties, which cannot be obtained by classical high temperature reduction routes. To reach this goal and demonstrate the effectiveness of the synthetic approach, four laboratories joined into a consortium will work together. The synthetic work will be carried out at the LCC (Toulouse) and the nanoplatforms' electronic, magnetic, and structural properties will be investigated by a combination of global and local probe techniques such as Mossbauer spectrometry, XPS, EELS, WAXS, EXAFS, EDX, HRTEM, EFTEM, etc' available at CEMES (Toulouse), LPEC (LeMans) and IPREM (Pau) or through already existing research programs. The project will deal first with the monometallic NPs, to get quantitative data on the kinetics of the reduction of the metal precursors and to have the mandatory reference samples to optimize the investigation conditions for the characterization of the bimetallic core@shell nanoplatforms. Then Fe@M (M=Rh, Au, Bi) and Au@Bi NPs will then be synthesized with the aim of producing NPs with different core sizes and/or shell thicknesses. At this stage careful electronic, magnetic and structural characterization will allow us to understand how the shell metal grows over the metal core. Finally, ligands will be coordinated at the surface of the bimetallic NPs to stabilize these potentially metastable systems and investigation of the segregation into core@shell chemical distribution will be carried out on selected samples. At the end of this project we should have fully characterized Fe@M (M=Rh, Au, Bi) and Au@Bi NPs, qualifying for applications in catalysis, biology and/or physics. These NPs will have enhanced magnetic properties as compared to existing oxide based systems while still being air stable. Collaborations have been initiated with partners outside this consortium for the development of these nanoplatforms.

Project coordination

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

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