Facile synthesis of near-monodisperse Ag@Ni core-shell nanoparticles and their application for catalytic generation of hydrogen.

Magnetically recyclable Ag-Ni core-shell nanoparticles have been fabricated via a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as a surfactant. As characterized by transmission electron microscopy (TEM), the as-synthesized Ag-Ni core-shell nanoparticles exhibit a very narrow size distribution with a typical size of 14.9 ± 1.2 nm and a tunable shell thickness. UV-vis absorption spectroscopy study shows that the formation of a Ni shell on Ag core can damp the surface plasmon resonance (SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magnetic measurement indicates that all the as-synthesized Ag-Ni core-shell nanoparticles are superparamagnetic at room temperature, and their blocking temperatures can be controlled by modulating the shell thickness. The as-synthesized Ag-Ni core-shell nanoparticles exhibit excellent catalytic properties for the generation of H(2) from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogen generation rate of Ag-Ni core-shell nanoparticles is found to be much higher than that of Ag and Ni nanoparticles of a similar size, and the calculated activation energy for hydrogen generation is lower than that of many bimetallic catalysts. The strategy employed here can also be extended to other noble-magnetic metal systems.

High frequency characteristics of Fe65Co35 alloy cluster-assembled films prepared by energetic cluster deposition.

Size-monodispersed Fe65Co35 alloy clusters whose average sizes ranged from 7 to 12 nm were produced by a plasma-gas-condensation (PGC)-type cluster deposition apparatus. Fe65Co35 alloy cluster-assembled films were further prepared at room temperature by energetic cluster deposition method. Positively charged clusters in a cluster beam were accelerated electrically and deposited onto a negatively biased substrate together with neutral clusters from the same cluster source, leading to the formation of a high-density Fe65Co35 alloy cluster-assembled films with good soft magnetic properties. High frequency magnetic characteristics of these films were studied at room temperature using a high-frequency permeameter (RMF-3000, Ryowa). The real part (micro') of permeability for the Fe65Co35 alloy cluster-assembled films prepared at bias voltage V(a) = -20 kV has a large value of micro' = 135 at f = 1.5 GHz, and imaginary part (micro") of permeability has a maximum (micro" approximately 190) at about 2.5 GHz.

Preparation of anisotropic transition metal phosphide nanocrystals: the case of nickel phosphide nanoplatelets, nanorods, and nanowires.

We have synthesized anisotropic nickel phosphide nanocrystals, including triangular/hexagonal nanoplatelets, nanorods and nanowires, via a solution-phase synthetic method that uses nickel(II) acetylacetonate as a metal precursor and trioctylphosphine as a phosphorus source. Nickel phosphide nanoplatelets have been prepared from a one-pot reaction, and their dimensions in the length mostly vary from 20 to 50 nm, while their thicknesses are in a narrow range of 7-9 nm. Nickel phosphide nanorods with a width of approximately 6 nm and a typical length of 25-32 nm can be synthesized from either the one-pot reaction or the multi-injection approach, although the latter can generate nanorods with a much higher uniformity. A continuous injection approach has been used to synthesize nanowires that have a typical width of approximately 6 nm and a length ranging from tens of nanometers up to several hundred nanometers. Major factors that influence the growth of nickel phosphide nanocrystals have been investigated, and a multi-surfactant system is found to be essential for the formation of anisotropic nanostructure. Magnetic studies have revealed paramagnetic characteristics for all the synthesized samples.

A nonaqueous approach to the preparation of iron phosphide nanowires.

Previous preparation of iron phosphide nanowires usually employed toxic and unstable iron carbonyl compounds as precursor. In this study, we demonstrate that iron phosphide nanowires can be synthesized via a facile nonaqueous chemical route that utilizes a commonly available iron precursor, iron (III) acetylacetonate. In the synthesis, trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) have been used as surfactants, and oleylamine has been used as solvent. The crystalline structure and morphology of the as-synthesized products were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The obtained iron phosphide nanowires have a typical width of ~16 nm and a length of several hundred nanometers. Structural and compositional characterization reveals a hexagonal Fe2P crystalline phase. The morphology of as-synthesized products is greatly influenced by the ratio of TOP/TOPO. The presence of TOPO has been found to be essential for the growth of high-quality iron phosphide nanowires. Magnetic measurements reveal ferromagnetic characteristics, and hysteresis behaviors below the blocking temperature have been observed.

Chemical synthesis of monodisperse Fe-Ni nanoparticles via a diffusion-based approach.

We report a chemical route for the preparation of monodisperse Fe-Ni nanoparticles with tunable compositions and sizes. Unlike commonly used synthetic approaches that involve the simultaneous reduction of metal precursors in the presence of reducing agents, the approach developed in this study utilizes pre-formed Ni nanoparticles to react with Fe(III) acetylacetonate in high boiling-point solvents, wherein newly-generated Fe atoms diffuse into Ni nanoparticles to form Fe-Ni nanoparticles. The analytic results of powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the as-synthesized Fe-Ni nanoparticles possess a face-centered cubic (fcc) crystalline structure and have a spherical or near-spherical morphology. X-ray photoelectron spectroscopy (XPS) study reveals metallic characteristics for the chemical state of Fe and Ni. The particle morphology and size distribution of the as-synthesized Fe-Ni nanoparticles are regulated by the pre-formed Ni nanoparticles, while the composition can be adjusted to some extent by the ratio of Fe precursor to Ni nanoparticles. Magnetic measurements reveal a superparamagnetic characteristic above the blocking temperature for the as-synthesized Fe-Ni nanoparticles. The synthetic approach may also be applied to other bimetallic nanoparticle systems.

Size- and structure-controlled synthesis and characterization of nickel nanoparticles.

Nearly monodisperse face-centered cubic (fcc) and hexagonal close-packed (hcp) nickel nanoparticles have been prepared via the thermal decomposition of nickel organometallic precursors in a reaction mixture containing alkylamine, and characterized by powder X-ray diffraction, transmission electron microscopy and magnetic measurement. The employed alkylamine can serve as both solvent and reducing agent. The as-synthesized nickel nanoparticles are air-stable, and their sizes can be readily tuned by the variation of surfactant concentration and reaction temperature. The crystalline phase control was achieved by adjusting alkylamine concentration, heating rate and reaction temperature. Magnetic measurements showed that hcp Ni nanoparticles have quite different magnetic properties compared to fcc Ni nanoparticles.