Temperature effect on the synthesis of Au-Pt bimetallic nanoparticles

Pt-Au bimetallic nanoparticles have been synthesized by the polyol method and stabilized with poly(vinylpyrrolidone) (PVP), modifying the temperature of synthesis. Interesting structure changes were observed in the nanoparticles as the temperature was varied. At lower temperatures no bimetallic nanoparticles were detected, but as the temperature increased bimetallic nanoparticles started to appear, commonly obtaining core-shell nanoparticles, always covered by the polymer. This originates the modification of the optical response of the system in the UV-visible region. An absorption peak centered at 520 nm at low temperatures was observed (100-110 degrees C); at higher temperatures (130-170 degrees C) there were non detectable absorption peaks, and finally at the two highest temperatures (180-190 degrees C) the reappearance of an absorption feature centered at 510 nm was noticed. These UV-visible results indirectly imply the composition of the surface of the particle. The structure of the particles has been determined using transmission electron microscopy and high-angle annular dark field (HAADF), the latter being a powerful technique to determine the structural composition of the particles and allowing a direct correlation of the optical response with their structural composition. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were also performed on the samples and their results support the idea of a Pt(core)-Au(shell) structure with the elements segregated from each other. The combination of these experimental techniques with calculated UV-vis absorption spectra allowed, in a reliable way, the elucidation of the nanoparticles structure and elemental distribution.     

Au-Pt bimetallic nanoparticles formation via viologen-mediated reduction on polymeric nanospheres

Poly(vinylbenzyl chloride) nanospheres prepared via emulsion polymerization were surface functionalized with viologen moieties. Several methods were investigated to achieve the desired high surface concentration of viologen moieties with minimal aggregation of the nanospheres. The viologen-functionalized nanospheres were used for photoinduced reduction of gold ions and platinum ions, either individually, simultaneously or sequentially, to result in the formation of well-distributed Au-Pt nanoparticles of a few nanometers on the surface of the nanospheres. UV-visible absorption spectroscopy and XPS analyses of these bimetallic nanoparticles were carried out. The reaction time and the sequence of the reduction process play an important role in determining the composition of the bimetallic nanoparticles. High-resolution transmission electron microscopy analysis reveals the highly crystalline nature of the bimetallic nanoparticles.     

Sonochemically prepared platinum-ruthenium bimetallic nanoparticles

Colloidal bimetallic nanoparticles of Pt-Ru have been synthesized by sonochemical reduction of Pt(II) and Ru(III) in aqueous solutions. Transmission electron microscope (TEM) images indicate that sequential reduction of the Pt(II) followed by the Ru(III) produces particles with a core shell (Pt@Ru) morphology. In the presence of sodium dodecyl sulfate, SDS, as a stabilizer, the particles have diameters between 5 and 10 nm. When polyvinyl-2-pyrrolidone, PVP, is used as the stabilizer, the rate of reduction is much faster, giving ultrasmall bimetallic particles of approximately 5 nm diameter.     

Formation of bimetallic Au-Pd and Au-Pt nanoparticles under hydrothermal conditions and microwave irradiation

The reduction of chlorocomplexes of gold(III) from muriatic solutions by nanocrystal powders of palladium and platinum at 110 and 130 °C under hydrothermal conditions and the action of microwave irradiation has been investigated. The structure and composition of the solid phase have been characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical methods. Bimetallic particles with a core-shell structure have been revealed. The obtained particles are established to have a core of the metal reductant covered with a substitutional solid (Au, Pd) solution in case of palladium, and isolated by a gold layer in the case of platinum. The main reason for such a difference is the ratio between the rates of aggregation and reduction. It has been shown by the example of the Au-Pd system that the use of microwave irradiation allows us not only to accelerate the synthesis of particles but also to obtain more homogeneous materials in comparison with conventional heating.     

Pt nanoparticles decorated with a discrete number of DNA molecules for programmable assembly of Au-Pt bimetallic superstructures

Discrete DNA decorations of Pt nanoparticles (PtNPs) are realized for the first time, which provide a valence control over the quasi-molecular self-assembly of Au-Pt bimetallic heteronanostructures with DNA as the guide.     

Dendrimer-templated Ag-Pd bimetallic nanoparticles

Ultrafine dendrimer-templated Ag-Pd bimetallic nanoparticles with various metal compositions have been prepared successfully using silver(I)-bis(oxalato)palladate(II) complex. The use of an oxalate complex, in which two metal ions exist in one complex, is found to be effective in preventing unfavorable silver halide formation and thus suitable for the formation of Ag-Pd bimetallic nanoparticles.     

Size and composition control of Pt-In nanoparticles prepared by seed-mediated growth using bimetallic seeds

A two-step method has been developed for precise size and composition control of bimetallic Pt-In nanoparticles. Very small (1.62 nm) PtIn seed nanoparticles with 1:1 metal ratio were prepared in the absence of capping agents followed by growth of Pt on their surface in the presence of oleyl amine as reducing and stabilizing agent. Nanoparticles with bulk compositions of Pt(4)In, Pt(3)In, and Pt(2)In could be synthesized with average diameter smaller than 3 nm. TEM, EDX, and XPS provided evidence for homogeneous growth without separate nucleation of pure platinum nanoparticles in the reaction solution. Pt(3)In nanoparticles were deposited onto SiO(2) surface by incipient wetness impregnation. Temperature-induced changes in the particle surface were monitored by in situ IR spectroscopy and CO adsorption. It was found that surface alloy composition of the particles could be tuned by using oxidizing or reducing atmospheres.     

Formation of Au-Pt bimetallic nanoparticles in a two-layer SiO2 films doped with Au and Pt, respectively, through interlayer diffusion

Bimetallic Au-Pt nanoparticles have been generated inside a relatively porous SiO2 film matrix by a two-layer (2L) coating methodology. Two overlapping coating layers were deposited on glass substrates from Au- and Pt-doped inorganic-organic hybrid silica sols and air dried at 60 degrees C. The 2L coating assembly was then UV- and followed by heat-treated at 450 and 550 degrees C in air. UV-treatment decomposes AuCl(4)(-) and PtCl(6)(2-) ions in the respective layers and the subsequent heat treatment in air influences the diffusion of Au and Pt nanometals to each other to form bimetallic Au-Pt nanoparticles inside the silica matrix. A UV-visible study showed damping of Au-plasmon after heat treatments. GIXRD and TEM analyses reveal the formation of a partial Au/Pt solid solution with a small fraction of Pt ( approximately 16%), while the major fraction of Pt remains fused with the Au(Pt) solid solution.     

Polyelectrolyte-templated synthesis of bimetallic nanoparticles

Bimetallic nanoparticles (NPs) are known to exhibit enhanced optical and catalytic properties that can be optimized by tailoring NP composition, size, and morphology. Galvanic deposition of a second metal onto a primary metal NP template is a versatile method for fabricating bimetallic NPs using a scalable, solution-based synthesis. We demonstrate that the galvanic displacement reaction pathway can be controlled through appropriate surface modification of the NP template. To synthesize bimetallic Au-Ag NPs, we used colloidal Ag NPs modified by layer-by-layer (LBL) assembled polyelectrolyte layers to template the reduction of HAuCl(4). NPs terminated with positively and negatively charged polyelectrolytes yield highly contrasting morphologies and Au surface concentrations. We propose that these charged surface layers control galvanic charge transfer by controlling nucleation and diffusion at the deposition front. This surface-directed synthetic strategy can be advantageously used to tailor both overall NP morphology and Au surface concentrations.     

Co-Pt and Fe-Pt bimetallic nanoparticles in a carbon matrix are prepared by a plasma arc process

Nanoparticle ensembles in Co-Pt and Fe-Pt systems embedded in a carbon matrix are prepared by a plasma-arc method. Two-phase samples based on disordered FCC solid solutions are prepared in both systems. In the Co-Pt system, the solid solujtions are mixed within one ensemble; in the Fe-Pt system, they are spatially separated. A magnetization hysteresis curve from Co-Pt nanoparticles (3–12 nm) fully coincides with a magnetization curve from a single-phase disordered solid solution Co_0.50Pt_0.50 (7–9 nm) prepared at 325°C by thermolysis of the precursor double complex salt (DCS). Metal ratios, solid solution structures, and particle sizes being the same, the magnetic response is dictated exclusively by the amount of a magnetic phase of mixed and interacting particles and is independent of the distribution of the magnetic phase over the solid solution phases.     

Composition-controlled synthesis of bimetallic gold-silver nanoparticles

This paper reports findings of an investigation of the synthesis of monolayer-capped binary gold-silver (AuAg) bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The synthesis of alkanethiolate-capped AuAg nanoparticles was carried out using two related synthetic protocols using aqueous sodium borohydride as a reducing agent. One involves a two-phase reduction of AuCl(4)(-), which is dissolved in organic solution, and Ag(+), which is dissolved in aqueous solution. The other protocol involves a two-phase reduction of AuCl(4)(-) and AgBr(2)(-), both of which are dissolved in the same organic solution. AuAg nanoparticles of 2-3 nm core sizes with different compositions in the range of 0-100% Au have been synthesized. The two synthetic routes were compared in terms of bimetallic composition and size properties. Our new findings have allowed us to establish the correlation between synthetic feeding of metals and metal compositions in the bimetallic nanoparticles, which have important implications to the exploration of gold-based bimetallic nanoparticles for constructing sensing and catalytic nanomaterials.     

Temperature-dependent structuring of Au-Pt bimetallic nanoclusters on a thin film of Al2O3/NiAl(100)

Au-Pt bimetallic nanoclusters on a thin film of Al(2)O(3)/NiAl(100) undergo significant structural evolution on variation of the temperature. Au and Pt deposited sequentially from the vapor onto thin-film Al(2)O(3)/NiAl(100) at 300 K form preferentially bimetallic nanoclusters (diameter ≦ 6.0 nm and height ≦ 0.8 nm) with both Au and Pt coexisting at the cluster surface, despite the order of metal deposition. These bimetallic clusters are structurally ordered, have a fcc phase and grow with their facets either (111) or (001) parallel to the θ-Al(2)O(3)(100) surface. Upon annealing the clusters to 400-500 K, the Au atoms inside the clusters migrate toward the surface, resulting in formation of a structure with a Pt core and an Au shell. Annealing the sample to 500-650 K reorients the bimetallic clusters--all clusters have their (001) facets parallel to the oxide surface--and induces oxidation of Pt. Such annealed bimetallic clusters become encapsulated with the aluminium-oxide materials and a few Au remain on the surface.     

Electrooxidation of insulin at silicon carbide nanoparticles modified glassy carbon electrode

For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and electrocatalytic oxidation of insulin. In comparison to bare glassy carbon (GC) electrode, the oxidation of insulin at GC electrode modified with SiC nanoparticles occurred at reduced overpotentials. The modified electrode was applied for insulin detection using cyclic voltammetry, differential pulse voltammetry (DPV) and flow injection analysis (FIA). Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range up to 600 pM, sensitivity of 710 pA pM^?1 cm^?2 and detection limit of 3.3 pM. In addition interference effect of the electroactive existing species (uric acid, glucose, lactic acid, l-cysteine and cholesterol) was diminished and for ascorbic acid eliminated by covering the surface of modified electrode with nafion film. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long term stability and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit and antifouling properties of this insulin sensor are better than all of the reports in the literature for insulin detection at physiological pH solutions.     

Titania-supported PdAu bimetallic catalysts prepared from dendrimer-encapsulated nanoparticle precursors

We report the synthesis, characterization, and catalytic activity of titania-supported bimetallic PdAu particles prepared using dendrimer-encapsulated nanoparticle (DEN) precursors. Single-particle energy-dispersive spectroscopy indicates a homogeneous distribution of bimetallic nanoparticles having compositions closely related to the metal-ion ratios used to prepare the DEN precursors. The catalytic activity of the supported PdAu catalysts was compared to that of supported Pd-only and Au-only catalysts; the enhanced CO oxidation activity of the PdAu catalysts is indicative of a synergetic bimetallic interaction.     

Ni–Cu bimetallic colloids prepared in nonaqueous solvents

Colloidal dispersions in nonaqueous media were obtained by simultaneous evaporation of Ni and Cu. The metals were cocondensed at 77 K in an organic matrix of 2-methoxyethanol, 2-propanol or acetone. The metallic dispersions were characterized by transmission electron microscopy, electron diffraction and UV–vis spectroscopy. The stability at room temperature was also measured. The stability of the Ni–Cu bimetallic dispersions is less than that of the Ni and Cu dispersions alone. The presence of more than one phase was observed. It is interesting to note that Ni/Cu ratio does not change the stability of the bimetallic dispersions dramatically. The polarity of the solvent should play a very important role in stabilizing the metal particles by solvatation effects. Transmission electron microscopy studies show the size control effect of Cu with small colloidal size in the bimetal. The electron diffraction studies reveal the presence of amorphous bimetallic particles and particles with crystallinity show typical particles formed for more than one phase (NiO, CuO, Cu, Ni and Cu–Ni). Cu and Ni, for example, are amorphous and crystalline particles, respectively. Differential scanning calorimetry and X-ray spectroscopy characterized the bimetallic solids of Ni–Cu/2-methoxyethanol obtained by evaporation of solvent. The differential scanning calorimetry studies of the solids show transition characteristics of crystalline growth; no glass transitions were observed. The X-ray diffractograms show that the crystallites are too small (less than 100 Å), giving rise to low intensity and wide peaks.     

Microwave synthesis of core-shell gold/palladium bimetallic nanoparticles

The microwave-assisted polyol reduction method was applied to the synthesis of core-shell gold/palladium bimetallic nanoparticles by the simultaneous reduction of the AuIII and PdII ions. The thickness of the palladium shell was calculated to be approximately 3 nm, and the gold core diameter is 9 nm. The structure and composition of the bimetallic particles were characterized by high-resolution transmission electron microscopy equipped with a nanoarea energy-dispersive X-ray spectroscopy attachment, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy.     

Local structural characterization of Au/Pt bimetallic nanoparticles

In this study, we examined the amount-dependent change in morphology for a series of Au/Pt bimetallic nanoparticles synthesized using chemical reduction. The Au/Pt molar ratio was varied from 1/1 to 1/4 to synthesize Pt shell layers with different thicknesses. We have obtained that these bimetallic nanoparticles can form flower-like nanoparticles. Moreover, an extended X-ray absorption fine structure (EXAFS) analysis was used to demonstrate the structure of Au/Pt bimetallic nanoparticles. The EXAFS results confirmed the formation of a core–shell structure and inter-diffusion between Au and Pt atoms. The composition of the shell layer was found to be Pt-enriched Au/Pt alloy.     

Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles

We theoretically study the spectrum of radial vibrational modes in composite metal nanostructures such as bimetallic core-shell particles and metal nanoshells with dielectric core in an environment. We calculate frequencies and damping rates of fundamental (breathing) modes for these nanostructures along with those of two higher-order modes. For metal nanoshells, we find that the breathing mode frequency is always lower than the one for solid particles of the same size, while the damping is higher and increases with a reduction in the shell thickness. We identify two regimes that can be characterized as weakly damped and overdamped vibrations in the presence of external medium. For bimetallic particles, we find periodic dependence of frequency and damping rate on the shell thickness with period being determined by the mode number. For both types of nanostructures, the frequency of higher modes is nearly independent of the environment, while the damping rate shows a strong sensitivity to the outside medium.     

New high-selectivity hydrogenation catalysts prepared from bimetallic acetate complexes

The catalytic properties of new Pd-Zn/Al₂O₃ catalysts in selective acetylene hydrogenation in an acetylene-ethylene mixture at 30–120°C and atmospheric pressure are reported. The catalysts prepared from the bimetallic complex Pd-Zn(OOCMe)₄(OH₂) are much more selective than the catalysts prepared by simultaneously supporting the homonuclear complexes Pd₃(OOCMe)₆ and Zn(OOCMe)₂ · 2H₂O. It is demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO that the heat treatment of the supported bimetallic complex at 250°C in flowing H₂ yields a Pd-Zn alloy on the surface. It is this alloy that ensures the high selectivity of the Pd-Zn/Al₂O₃ catalysts.