η-Carbides (Co, Mo, or W) Nanoparticles from Octacyanometalates Precursors-Based Network.

This paper describes a simple, two-steps chemical pathway to obtain bimetallic carbide nanoparticles (NPs) of general formula MxM″yC, also called η-carbides. This process allows for a control of the chemical composition of metals present in the carbides (M = Co and M″ = Mo or W). The first step involves the synthesis of a precursor consisting of a network of octacyanometalates. The second step consists in a thermal degradation of the previously obtained octacyanometalates networks under neutral atmosphere (Ar or N2 ). It is shown that this process results in the formation of carbide NPs with diameter of ≈ 5nm, and the stoichiometries Co3 M'3 C, Co6 M'6 C, Co2 M'4 C for the CsCoM' systems.

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.

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.