First synthesis by liquid-liquid phase transfer of magnetic CoxPt100-x nanoalloys

Chemical Evolution of Pt-Zn Nanoalloys Dressed in Oleylamine

We report on the shape, composition (from Pt₉₅Zn₅ to Pt₇₇Zn₂₃), and surface chemistry of Pt-Zn nanoparticles obtained by reduction of precursors M²⁺(acac)₂^- (M²⁺: Pt²⁺ and Zn²⁺) in oleylamine, which serves as both solvent and ligand. We show first that the addition of phenyl ether or benzyl ether determines the composition and shape of the nanoparticles, which point to an adsorbate-controlled synthesis. The organic (ligand)/inorganic (nanoparticles) interface is characterized on the structural and chemical level. We observe that the particles, after washing with ethanol, are coated with oleylamine and the oxidation products of the latter, namely, an aldimine and a nitrile. After exposure to air, the particles oxidize, covering themselves with a few monolayer thick ZnO film, which is certainly discontinuous when the particles are low in zinc. Pt-Zn particles are unstable and prone to losing Zn. We have strong indications that the driving force is the preferential oxidation of the less noble metal. Finally, we show that adsorption of CO on the surface of nanoparticles modifies the oxidation state of amine ligands and attribute it to the displacement of hydrogen adsorbed on Pt. All the structural and chemical information provided by the combination of electron microscopy and X-ray photoelectron spectroscopy allows us to give a fairly accurate picture of the surface of nanoparticles and to better understand why Pt-Zn alloys are efficient in certain electrocatalytic reactions such as the oxidation of methanol.

Directed Organization of Platinum Nanocrystals through Organic Supramolecular Nanoporous Templates

We propose a novel approach to trap 2 nm Pt nanocrystals using nanoporous two-dimensional supramolecular networks for cavity-confined host-guest recognition process. This will be achieved by taking advantage of two features of supramolecular self-assembly at surfaces: First, its capability to allow the formation of complex 2D architectures, more particularly, nanoporous networks, through noncovalent interactions between organic molecular building-blocks; second, the ability of the nanopores to selectively host and immobilize a large variety of guest species. In this paper, for the first time, we will use isotropic honeycomb networks and anisotropic linear porous supramolecular networks to host 2 nm Pt nanocrystals.

Role of the nanocrystallinity on the chemical ordering of Co(x)Pt(100-x) nanocrystals synthesized by wet chemistry

Co(x)Pt(100-x) nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in situ annealing of the different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 °C. This in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase.

Platinum and platinum based nanoalloys synthesized by wet chemistry

Platinum nanocrystals and their derivatives with palladium and cobalt are of fundamental interest due to their wide field of application in chemistry and physics. Their properties are strongly dependent on their shape and composition. However the chemical route is far from allowing control of both shape and composition. In this paper, we show both experimentally and theoretically the important role of the interaction of small adsorbed molecules on the shape but also on the composition. This has been studied by comparing the case of pure palladium and platinum nanocrystals and the case of PtPd and PtCo nanoalloys synthesized by the liquid–liquid phase transfer method.

A solventless mix–bake–wash approach to the facile controlled synthesis of core–shell and alloy Ag–Cu bimetallic nanoparticles

A solventless mix–bake–wash method using salt powder was developed to fabricate uniform Ag–Cu core–shell and alloy bimetallic nanoparticles.

Revealing chemical ordering in Pt–Co nanoparticles using electronic structure calculations and X-ray photoelectron spectroscopy

Pt_YCo_1−Y-core@Co-rich-subsurface@Pt-shell structure is identified in several nm large Pt–Co particles using X-ray photoelectron spectroscopy and an optimization method based on density-functional calculations.

Transmetallation as an effective strategy for the preparation of bimetallic CoPd and CuPd nanoparticles

The preparation of palladium alloy nanoparticles is of great interest for many applications, especially in catalysis. Starting from presynthesized nanoparticles of a less noble metal, a transmetallation reaction involving a redox process at the nanoparticle surface can be exploited to modify the nanoparticle composition and crystalline phase. As an example, monodispersed ε-cobalt and face-centered cubic copper nanoparticles were synthesized in organic solvents at high temperature and the as-formed nanoparticles were reacted with palladium(ii) hexafluoroacetylacetonate resulting in the formation of alloyed nanoparticles whose composition closely follows the reactant ratio. The oxidative state of the nanoparticle surface greatly affects the success of the transmetallation reaction and a reduction treatment was necessary to achieve the desired final product. Electron microscopy and X-ray diffraction showed that for cobalt a limiting palladium content for the ε-phase alloy is found, above which an fcc alloy nucleates, while for copper the fcc crystalline phase is preserved throughout the whole composition range.

Colloidal nanocube supercrystals stabilized by multipolar Coulombic coupling

We explore microscopic principles governing the self-assembly of colloidal octylamine-coated platinum nanocubes solvated in toluene. Our experiments show that regular nanocubes with an edge length of l(RC) = 5.5 nm form supercrystals with simple cubic packing, while slightly truncated nanocubes with an edge length of l(TC) = 4.7 nm tend to arrange in fcc packing. We model by averaged force fields and atomistic molecular dynamics simulations the coupling forces between these nanocrystals. Our detailed analysis shows that the fcc packing, which for cubes has a lower density than simple cubic packing, is favored by the truncated nanocubes due to their Coulombic coupling by multipolar electrostatic fields, formed during charge transfer between the octylamine ligands and the Pt cores.

Size-dependent properties of magnetic iron oxide nanocrystals

The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3-xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x=1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.

Defect-induced junctions between single- or double-wall carbon nanotubes and metal crystals

Interfaces between the ends of single- or double-wall carbon nanotubes and metal crystals (Fe, Co, Pd, and Pt) are established by electron irradiation with nanometre precision at metal-nanotube contact areas. Calculations of the bonding energies at the metal-nanotube interfaces confirm that the formation of these covalent junctions is energetically favourable in the presence of a certain concentration of structural defects in the nanotubes. The process may be endothermic or exothermic in comparison with the unconnected configuration, but in either case atomic defects in carbon nanotubes are a necessary condition for joining them with metals.