In Situ Insights into the Nucleation and Growth Mechanisms of Gold Nanoparticles on Tobacco Mosaic Virus.

Biotemplated syntheses have emerged as an efficient strategy to control the assembly of metal nanoparticles (NPs) and generate promising plasmonic properties for sensing or biomedical applications. However, understanding the nucleation and growth mechanisms of metallic nanostructures on biotemplate is an essential prerequisite to developing well-controlled nanotechnologies. Here, we used liquid cell Transmission Electron Microscopy (TEM) to reveal how the formation kinetics of gold NPs affects their size and density on Tobacco Mosaic Virus (TMV). These in situ insights are used as a guideline to optimize bench-scale synthesis with the possibility to homogenize the coverage and tune the density of gold NPs on TMV. In line with in situ TEM observations, fluorescence spectroscopy confirms that the nucleation of NPs occurs on the virus capsid rather than in solution. The proximity of gold NPs on TMV allows shifting the plasmonic resonance of the assembly in the biological window.

Synthesis and structural properties of high-entropy nanoalloys made by physical and chemical routes.

The development of synthesis methods with enhanced control over the composition, size and atomic structure of High Entropy Nano-Alloys (HENA) could give rise to a new repertoire of nanomaterials with unprecedented functionalities, notably for mechanical, catalytic or hydrogen storage applications. Here, we have developed two original synthesis methods, one by a chemical route and the other by a physical one, to fabricate HENA with a size between 3 and 10 nm and a face centered cubic structure containing three (CoNiPt), four (CoNiPtCu and CoNiPtAu) or five (CoNiPtAuCu) metals close to the equiatomic composition. The key point in the proposed chemical synthesis method is to compensate the difference in reactivity of the different metal precursors by increasing the synthesis temperature using high boiling solvents. Physical syntheses were performed by pulsed laser ablation using a precise alternating deposition of the individual metals on a heated amorphous carbon substrate. Finally, we have exploited aberration-corrected transmission electron microscopy to explore the nanophase diagram of these nanostructures and reveal intrinsic thermodynamic properties of those complex nanosystems. In particular, we have shown (i) that the complete mixing of all elements can only occur close to the equiatomic composition and (ii) how the Ostwald ripening during HENA synthesis can induce size-dependent deviations from the equiatomic composition leading to the formation of large core-shell nanoparticles.

Structural Size Effect in Capped Metallic Nanoparticles.

The surfactant used during a colloidal synthesis is known to control the size and shape of metallic nanoparticles. However, its influence on the nanoparticle (NP) structure is still not well understood. In this study, we show that the surfactant can significantly modify the lattice parameter of a crystalline particle. First, our electron diffraction measurements reveals that NiPt nanoparticles around 4 nm in diameter covered by a mixture of oleylamine and oleic acid (50:50) display a lattice parameter expansion around 2% when compared to the same particles without surfactant. Using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX) techniques, we show that this expansion can not be explained by crystal defects, twinning, oxidation, or atoms insertion. Then, using covered NPs in the 4-22 nm size range, we show that the lattice parameter evolves linearly with the inverse of the NP size, as it is expected when a surface stress is present. Finally, the study is extended to pure nickel and pure platinum NPs, with different sizes, coated by different surfactants (oleylamine, trioctylphosphine, polyvinylpyrrolidone). The surfactants induce lattice parameter variations, whose magnitude could be related to the charge transfer between the surfactant and the particle surface.

A simple and efficient process for the synthesis of 2D carbon nitrides and related materials.

We describe here a new process for the synthesis of very high quality 2D Covalent Organic Frameworks (COFs), such a C2N and CN carbon nitrides. This process relies on the use of a metallic surface as both a reagent and a support for the coupling of small halogenated building blocks. The conditions of the assembly reaction are chosen so as to leave the inorganic salts by-products on the surface, to further confine the assembly reaction on the surface and increase the quality of the 2D layers. We found that under these conditions, the process directly returns few layers material. The structure/quality of these materials is demonstrated by extensive cross-characterizations at different scales, combining optical microscopy, Scanning Electron Microscopy (SEM)/Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS). The availability of such very large, high-quality layers of these materials opens interesting perspectives, for example in photochemistry and electronics (intrinsic transport properties, high gap substrate for graphene, etc...).

Colloidal synthesis of nanoparticles: from bimetallic to high entropy alloys.

At the nanoscale, the synthesis of a random alloy (i.e. without phase segregation, whatever the composition) by chemical synthesis remains a difficult task, even for simple binary type systems. In this context, a unique approach based on the colloidal route is proposed enabling the synthesis of face-centred cubic and monodisperse bimetallic, trimetallic, tetrametallic and pentametallic nanoparticles with diameters around 5 nm as solid solutions. The Fe-Co-Ni-Pt-Ru alloy (and its subsets) is considered a challenging task as each element has fairly different physico-chemical properties. Particles are prepared by temperature-assisted co-reduction of metal acetylacetonate precursors in the presence of surfactants. It is highlighted how the correlation between precursors' degradation temperatures and reduction potential values of the metal cations is the driving force to achieve a homogeneous distribution of all elements within the nanoparticles.

Nickel platinum (Ni x Pt1-x ) nanoalloy monodisperse particles without the core-shell structure by colloidal synthesis.

We report a new and versatile colloidal route towards the synthesis of nanoalloys with controlled size and chemical composition in the solid solution phase (without phase segregation such as core-shell structure or Janus structure) or chemical ordering. The principle of the procedure is based on the correlation between the oxidation-reduction potential of metal cations present in the precursors and the required synthesis temperature to nucleate particles without phase segregation. The procedure is demonstrated via the synthesis of Face Centered Cubic (FCC) Ni x Pt1-x nanoparticles, which was elaborated by the co-reduction of nickel(ii) acetylacetonate and platinum(ii) acetylacetonate with 1,2-hexadecanediol in benzyl ether, using oleylamine and oleic acid as surfactants. The chemical composition and solid solution FCC structure of the nanoalloy are demonstrated by crosslinking imaging and chemical analysis using transmission electron microscopy and X-ray diffraction techniques. Whatever the chemical composition inspected, a systematic expansion of the lattice parameters is measured in relation to the respective bulk counterpart.