Bimetallic nanoparticle synthesis

Chandler BD, Gilbertson JD (2006) Dendrimer-Encapsulated Bimetallic Nanoparticles Synthesis, Characterization, and Applications to Homogeneous and Heterogeneous Catalysis. 20 97-120... 

Bimetallic Nanoparticles Synthesis and Dose Rate Effect... 

Ag Au bimetallic nanoparticle synthesis is easily done on a resin surface and in the absence of resin support this process becomes thermodynamically impossible and leads to Au Ag bimetallic particles. Another unique feature of resin support has recently been discovered, where it offers a great stability to the synthesized metal and metal oxide nanoparticles when Ni and Fc304 are considered. 

PAMAM dendrimers can also be used as templating agents and nanoparticle stabilizers for the synthesis of bimetallic particles. The unique ability of dendrimers to host various metal precursors enables the simultaneous complexation of multiple metallic species at its various internal functional groups. The three primary methods of bimetallic nanoparticle synthesis through dendrimer stabilization are partial displacement, co-complexation, and sequential complexation. 

Bimetallic nanoparticle synthesis via partial displacement is a natural extension of the intradendrimer redox displacement described earlier for the case of silver... 

The synthesis of bimetallic nanoparticles is mainly divided into two methods, i.e., chemical and physical method, or bottom-up and top-down method. The chemical method involves (1) simultaneous or co-reduction, (2) successive or two-stepped reduction of two kinds of metal ions, and (3) self-organization of bimetallic nanoparticle by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after-treatments. Bimetallic nanoparticle alloys are prepared usually by the simultaneous reduction while bimetallic nanoparticles with core/shell structures are prepared usually by the successive reduction. In the preparation of bimetallic nanoparticles, one of the most interesting aspects is a core/shell structure. The surface element plays an important role in the functions of metal nanoparticles like catal5dic and optical properties, but these properties can be tuned by addition of the second element which may be located on the surface or in the center of the particles adjacent to the surface element. So, we would like to use following marks to inscribe the bimetallic nanoparticles composed of metal 1, Mi and metal 2, M2. 

We have extended the seed-mediated technique for the synthesis of bimetallic nanoparticles, having core-shell type structure appending photoreduction of metal ions. It has been proved that the deposition of a less noble metal (M) as shell on a preformed nobler nanoparticle core (M ) seems to be very effective by UV activation. Using this seed-mediated method we were able to synthesize Aucore Agsheii particles. First for the preparation of gold seeds (S), TX-lOO (10 M) and HAuC (5.0 x 10 %) were taken in a quartz cuvette so that the final concentration of Au(III) ion remained 5.0 x 10 M. Then the... 

Anandan et al. [37] reported the sonochemical synthesis of gold-silver bimetallic nanoparticles with core-shell geometry by the sonochemical co-reduction of Au and... 

Anandan S, Ashokkumar M, Grieser F (2008) Sonochemical synthesis of Au-Ag core-shell bimetallic nanoparticles. J Phys Chem C 112 15102-15105... 

Sathish Kumar P, Manivel A, Anandan S, Zhou M, Grieser F, Ashokkumar M (2010) Sonochemical synthesis and characterization of gold-ruthenium bimetallic nanoparticles. Colloids Surf A 356 140-144... 

Kan C, Cai W, Li C, Zhang L, Hofmeister H (2003) Ultrasonic synthesis and optical properties of Au/Pd bimetallic nanoparticles in ethylene glycol. J Phys D Appl Phys 36 1609-1614... 

The team of Crooks is involved in the synthesis and the use of dendrimers and, more particularly, poly(amidoamine) dendrimers (PAMAM), for the preparation of dendrimer-encapsulated mono- or bimetallic nanoparticles of various metals (Pt, Pd, Cu, Au, Ag, Ni, etc.) [55, 56]. The dendrimers were used as nanocatalysts for the hydrogenation of allyl alcohol and N-isopropylacrylamide or other alkenes under different reaction conditions (water, organic solvents, biphasic fluorous/or-ganic solvents or supercritical COz). The hydrogenation reaction rate is dependent on dendrimer generation, as higher-generation dendrimers are more sterically... 

G. Cheng and T. Guo, Surface segregation in Ni/Co bimetallic nanoparticles produced in single-walled carbon nanotube synthesis, J. Phys. Chem. B 106, 5833-5839 (2002). 

An alcohol reduction method has been applied to the synthesis of polymer-stabilized bimetallic nanoparticles. They have been prepared by simultaneous reduction of the two corresponding metal ions with refluxing alcohol. For example, colloidal dispersions of Pd/Pt bimetallic nanoparticles can be prepared by refluxing the alcohol-water (1 1 v/v) mixed solution of palladium(II) chloride and hexachloro-platinic(IV) acid in the presence of poly(/V-vinyl-2-pyrrolidone) (PVP) at about 90-95°C for 1 h (Scheme 9.1.5) (25). The resulting brownish colloidal dispersions are stable and neither precipitate nor flocculate over a period of several years. Pd/ Pt bimetallic nanoparticles thus obtained have a so-called core/shell structure, which is proved by an EXAFS technique (described in Section 9.1.3.3). 

Just as DENs particle sizes have some distribution (albeit relatively narrow), there is surely some distribution in particle compositions for bimetallic DENs. This is a fundamentally important aspect of DENs, particularly with regard to their catalytic properties however, there are presently no reliable characterization methods for evaluating particle composition distributions. One method that has been applied to PdAu [21] and PtPd [19] DENs, as well as dendrimer-templated PtAu [24] is to collect single particle EDS spectra from several (15-20) nanoparticles. These experiments indicate that individual particle composition distributions may vary widely, but the difficulty in obtaining data from the smallest particles may skew the results somewhat. EDS spectra collected over large areas, which sample tens or hundreds of particles, generally agree well with the bulk composition measurements [24] and with stoichiometries set in nanoparticle synthesis [19,21,24]. 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

In summary, in this Section we have described how electronic and geometric effects may contribute to facilitate the ORR reaction on a bimetallic alloy. The next question is, what elements are on the surface of a bimetallic alloy, and even more complex, what is on the surface of a nanoalloy Obviously this question is closely dependent on the nanoparticle synthesis, but it also relates to the thermodynamic and kinetic conditions that make an alloy particle of a given size and shape to be stable or to adopt other configurations such as core-shell stractures, which is the topic of the next Section. 

Synthesis of alloyed silver-palladium bimetallic nanoparticles was achieved by /-irradiation of aqueous solutions containing a mixture of Ag and Pd metal ions using different Ag/Pd ratios. The synthesis of alloys implies the simultaneous radio-induced reduction of silver and palladium ions. The nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The Ag-Pd nanoparticles display a face-centered cubic (fee) crystalline structure. The lattice parameter was measured for several Ag/Pd ratios and was found to closely follow Vegard s law, which indicates the formation of homogeneous alloys. In order to avoid the simultaneous reduction of silver and palladium ions which leads to alloyed bimetallic nanoparticles. 

While 7-radiolysis at relatively low dose rates enabled the synthesis of a few alloyed clusters such as Ag-Pd nanoparticles (also chemically synthesized), radiolysis at very high dose rates (by electron beams) led to the synthesis, at room temperature, of a lot of new alloys such as Au-Pd bimetallic nanoparticles/ Like in the case of Ag-Au system, at low dose rate (7-irradiation), bilayered Au -Pd.i,ii nanoparticles were obtained. However, at high dose rates (electron beams), the reduction is faster than the possible inter-metal electron transfer, then alloyed clusters were prepared. Moreover, since the radio-induced reduction of metal ions is faster at high dose rates, the synthesized particles are, in these conditions, always smaller with a narrow distribution in size. 

Anisotropic bimetallic nanoparticles can also be synthesized by radiolysis. Indeed, /-irradiation of an aqueous solution containing silver and platinum metal ions and a polymer (PVA), at dose rates lower than 0.5 kGy.h , led to the synthesis of wire-like Ag-Pt structures with lengths up to 3.5 pm and diameters between 3 and 20 nm.ii7... 

Part III presents the state of the art of the synthesis of nanoparticle catalysts and electrocatalysts, including bimetallic nanoparticles. Particular emphasis is given to carbon-supported nanoparticles due to their technological signihcance in the fabrication of electrodes for PEM fuel cells. 

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