Ag-Au alloy nanoparticles

Scheme 3. Reaction mechanism of Au-Ag alloy nanoparticle formation.

Table 3 shows properties of Au-Ag alloy nanoparticles obtained by this preparative procedure. 

Highly dispersed gold with particle sizes of 2-5 nm seem to be an absolute requirement for this low-temperature activity [6,7,9,18,38,41,53,74,77,110, 159,202]. Nprskov and co-workers [317] have suggested that the main effect of decreasing the gold particle size is to increase the concentration of low-coordinated An atoms. However, the Au-Ag alloy nanoparticles supported on mesoporous aluminosilicate, referred above, inspite of the large particle size (of about 20-30 nm) were surprisingly very active at room temperature [123]. 

Gold I Silver Alloy Formation A simple and usually not quite justified approach to predicting the position of the SPR maximum of an (Au/Ag)-alloy nanoparticle would be to calculate a linear combination of the dielectric functions of gold and silver nanoparticles [g(a) = (1 )sau + Unfortunately, this approach... 

Mondal, S., Roy, N., Laskar, R.A., Sk, I., Basu, S., Mandal, D., et al., 2011. Biogenic synthesis of Ag, Au and bimetallic Au/Ag alloy nanoparticles using aqueous extract of mahogany Swietenia mahogany JACQ.) leaves. Colloids Surf. B Biointerfaces 82 (2), 497-504. 

A continuous tuning of the positions of the plasmon absorption peak by alloy formation has been demonstrated. The dependence of the absorption spectra of Au—Ag alloy nanoparticles on the composition is reproduced in Fig. 5.3-16 [3.74]. 

Fig. 5.3-16 Effect of formation of a gold-silver alloy on the surface plasmon absorption measured UV-VIS absorption spectra of spherical Au—Ag alloy nanoparticles of various compositions. The gold mole fraction xau varies between 1 and 0.27. The plasmon absorption maximum is blueshifted with decreasing Xau- (After [3.74])...

Extracellular biosynthesis of bimetallic Au-Ag alloy nanoparticles. Small, 1(5),... 

Interestingly, this technique also enables to produce alloy nanoparticles by placing different elements as a target. Figure 6 shows the first attempt to prepare Au-Ag alloy nanoparticles... 

The synthesized Au-Ag alloys were fully characterized before and after acetylation. It was demonstrated that both Au atom/Ag atom/dendrimer molar ratio and the acetylation modification influence the size of binary nanoparticles. With constant total metal atom/dendrimer molar ratio, the size of alloy nanoparticles decreases with gold composition. For particles with similar metal composition, the size of the particles becomes slightly larger after acetylation [47]. 

Evaluation of colloidal stability of synthesized binary nanoparticles at different pH and temperature conditions indicated their stability at different pH (pH = 5-8) and temperature (4-50°C) conditions. To assess the potential application of Au-Ag alloy as CT imaging agents, their X-ray attenuation characteristics were also studied. It was demonstrated that the attenuation of the binary nanoparticles is dependent on both gold content and the particle surface characteristics [47]. 

EDX-STEM line scanning across the nanoparticles was carried out to analyze the distribution of the chemical composition. For example in the Au core systems, especially the samples with high Ag/Au ratio, the maximum of the Au signal is in the center of nanoparticles, supporting the formation of Au-core Ag-shell nanostructures (Fig. 2b). On Ae contrary, samples with low amount of Ag exhibit a typical Au-Ag alloy behavior. 

Ag-core/Au-shell bimetallic nanoparticles were prepared by NaBH4 reduction method [124]. UV-Vis spectra were recorded and compared with various ratios of AuAg alloy nanoparticles. The UV-Vis spectra of bimetallic nanoparticles suggested the formation of core/shell structure. Furthermore, the high-resolution transmission electron microscopy (HRTEM) image of the nanoparticles confirmed the core/shell type configuration directly. 

Chen et al. [123] examined the amount-dependent change in morphology for a series 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 AuPt alloy. They also characterized bimetallic Ag-core/Au-shell nanoparticles by the EXAFS [124]. 

The solvent-free controlled thermolysis of metal complexes in the absence or presence of amines is the simple one-pot synthesis of the metal nanoparticles such as gold, silver, platinum, and palladium nanoparticles and Au-Ag, Au-Pt, and Ag-Pd alloy nanoparticles. In spite of no use of solvent, stabilizer, and reducing agent, the nanoparticles produced by this method can be well size regulated. The controlled thermolysis in the presence of amines achieved to produce narrow size dispersed small metal nanoparticles under milder condition. This synthetic method may be highly promising as a facile new route to prepare size-regulated metal nanoparticles. Finally, solvent-free controlled thermolysis is widely applicable to other metal nanoparticles such as copper and nickel... 

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