Nanopartides bimetallic

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

Fig. 8. Digital photograph of starch capped metallic and bimetallic nanopartides in aqueous medium. A Cu B-D Cu-Ag E Ag.

Fig. 1.6 Summary of representative morphologies of bimetallic nanopartides (Reprinted with permission from ref 16a, Kunitake and Toshima groups,/ Am. Chem. Soc. 2003, 725, 11034).

The same team has also described the selective hydrogenation of cis-2-pentenenitrile with surfactant-stabiUzed ammonium perfluorotetradecanoate bimetallic Pd-Ru nanopartides prepared via in situ reduction of their simple salts in reverse micelles in SCCO2 [22]. The optimized ratio Pd Ru nanopartide (1 1) shows the highest activity for the hydrogenation of functionalised alkene under mild conditions. No hydrogenation of the terminal nitrile of the molecule in amine was observed and, finally, this fluorinated micelle-hosted bimetallic catalyst gives relevant activity and selectivity in the supercritical fluid without deactivation for at least three catalytic cycles. 

With these considerations in mind, synthetic chemists have begun to address the needs of metal particle research by developing the synthetic chemistry of nanosized metals, with a view to using the strategies of molecular chemistry to prepare well-defined metal nanopartides. The goal may be stated as ... the search for synthetic methods for metal nanopartides of narrow size distribution and, if possible, with shape-control. Furthermore, bimetallic spedes will be considered, either with core-shell architecture or in alloyed form. 

The AuPt nanopartides thus prepared are fully alloyed with uniform bimetallic distribution in the nanopartides. As shown by the HRTEM images for Au22Pt78/C samples (Figure 11.1), the observation of the indicated lattice fringes of 0.235 nm indicates that the carbon-supported nanopartides are highly crystalline with a subtle difference in inter atomic... 

The catalytic modification of the bimetallic composition is in fact further reflected by the remarkable difference of the voltammetric characteristic observed in the reverse scan, especially in the alkaline electrolyte. For Pt/C and PtRu/C, the reverse wave for alkaline electrolyte occurs at a potential less positive than the forward wave by 2(X)mV. In contrast, the reverse wave for Aug2Pti8/C occurs at a potential which differs from the potential for the wave in the forward sweep by only 20mV. The relative peak current of the reverse/forward wave is also found to be dependent on Au% in the bimetallic nanopartide. The oxides formed on the catalyst surface at the potential beyond the anodic peak potential in the positive sweep are reduced in the reverse sweep [171]. Poisonous CO spedes formed on Pt surface can also be removed in the reverse sweep. The observation of the more positive potential for the reverse wave likely reflects the bimetallic effect on the re-activation of the catalyst surface after the anodic sweep, a scenario that is under further investigation using FTIR spectroscopic techniques. The re-activation of the surface catalytic sites after the anodic sweep is likely modified by the presence of Au in the catalyst, which leads to the shift of the peak potential of the reverse wave to a more positive potential (by 200mV) for Aug2Pti8/C than for Pt/C. 

This finding, together with the XRD data for the nanocrystal core properties [58], demonstrated that both the core and the surface of the bimetallic nanopartides exhibit bimetallic alloy properties. The detection of both Au-atop and Pt-atop CO bands on the surface of the alloy nanoparticles of a wide range of bimetallic composition can be correlated with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals. There exists a stronger electron donation to the CO band by a Pt-atop site surrounded by Au atoms in the bimetallic alloy surface than that from the monometallic Pt surface as a consequence of the upshift in d-band center of Pt atoms surrounded by Au atoms, which explains the preference of Pt-atop CO over the Au-atop CO adsorption. The observed decrease of the Pt-atop CO band frequency with increasing Au concentration is in agreement with the d-band theory for the bimetallic system [172]. 

Additives can be used to further stabilize nanopartides in imidazolium based ionic liquids. Stabilization with polyvinylpyrrolidone (PVP) is necessary to obtain stable mono- and bimetallic Pt/Au nanopartides immobilized in [C4MIm ][PF6 ].1971 Also, ionic liquid-like copolymers can be used to stabilize Rhi ] and Pt 199] nanopartides, where [C4MIm+][BF4-] itself can not stabilize the platinum nanopartides sufficiently. 199]... 

In an electrochemical way of making metal nanopartides, a solution of stabilizer e.g., tetraalkylammonium bromide in THF) is electrolyzed using an anode made of the metal of interest and an inert cathode.l Under the conditions of the electrolysis, dissolution of the anode material takes place via oxidation. The metal cations transfer to the cathode, where reduction, nucleation and finally stabilization occur. The size of thus-prepared nanopartides can be easily controlled by the current density. The method is applicable to many transition metals. Moreover, systems with two anodes of different metals result in the formation of bimetallic nanopartides. When oxidation of the anode metal is difficult, the metal of interest can be introduced as inorganic salt.h67] pd nanopartides, e.g., prepared via this method were found to be catalyticaUy active in the Heck reaction and the... 

Ag-Au bimetallic nanopartide f Thermo-responsive nonlinear PEG-based hydrogel — Hyaluronic acid... 

Shankar, S.S., Rai, A., Ahmad, A. and Sastry, M. (2004) Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanopartides using neem (Azadirachta indica) leaf broth. Journal of Colloid and Interface Science, 275, 496-502. 

Use of bimetallic catalysts such as Pt-Ru has been commonly accepted in order to improve catalytic efSdency and protect Pt from CO poisoning. Homogeneously dispersed catalyst nanopartides with a size range from 60 to 80 nm were prepared by potentiostatic methods in 0.5 M H2SO4 aqueous solutions of ruthenium chloride and chloroplatinic acid at a potential of -0.25V. ° The Pt-Ru particles were found to exhibit higher catalytic activity and stability compared to pure Pt nanopartides. Consequently, it is reasonable to enhance the catalytic artivity by incorporating bimetallic nanopartides into CNTs. ... 

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