Au/Ag alloys

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

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

Au-Cu and Au-Ag alloys Isomer shift and electrical resistivity as function of alloy composition and, in CU3AU, of pressure model to describe 5 in terms of average atomic volume, of short-range parameter and alloy composition average charge density on Au... 

Au-Cu and Au-Ag alloys Correlation of isomer shift with Au 5d population... 

Papavassiliou GC (1976) Surface plasmons in small Au-Ag alloy particles. J Phys F Met Phys 6 L103-L105... 

Figure 5 shows two typical core-shell structures (a) contains a metal core and a dye doped silica shell [30, 32, 33, 78-85] and (b) has a dye doped silica core and a metal shell [31, 34]. There is a spacer between the core and the shell to maintain the distance between the fluorophores and the metal to avoid fluorescence quenching [30, 32, 33, 78-80, 83]. Usually, the spacer is a silica layer in this type of nanostructures. Various Ag and Au nanomaterials in different shapes have been used for fluorescence enhancement. Occasionally, Pt and Au-Ag alloys are selected as the metal. A few fluorophores have been studied in these two core-shell structures including Cy3 [30], cascade yellow [78], carboxyfluorescein [78], Ru(bpy)32+ [31, 34], R6G [34], fluorescein isothiocyanate [79], Rhodamine 800 [32, 33], Alexa Fluor 647 [32], NIR 797 [82], dansylamide [84], oxazin 725 [85], and Eu3+ complexes [33, 83]. 

Dissolution of gold and silver from Au/Ag alloys in aerated cyanide solutions has been investigated using rotating disc electrodes [551]. Dissolution was partially controlled by transport of either oxygen or cyanide. Kinetics of anodic dissolution of gold in cyanide solutions containing different metal ions has been extensively... 

Sun et al. [382] have studied the dissolution behavior of gold and silver from Au—Ag alloys in aerated cyanide solutions using rotating disc electrodes. 

Fig. 5.8 Examples of oxidative water treatment technologies used in industry, research and development [adapted from FIGAWA (1997), and supplemented by novel methods]. The numbers 1 to 9 refer to the generalized reaction sequences presented in Figure 5-9. a) Oxidation at elevated temperatures between 220°C < T <300°C or supercritical water oxidation at AT >374°C, Ap >221 bar (221000 kPa) (cf Chapter 1) b) oxidation in the presence of bimetallics Fe°/Ni° or Zn°/Ni° (Cheng and Wu, 2001) or heterogeneous oxidation in supercritical water catalyzed by metals Me = Cu, Ag, Au/Ag-alloy c) Fenton reaction at pH <5 d) photo-assisted Fenton reaction, irradiation in the UV-B/VIS range e) the mixture of oxidants O3/H2O2 is called PEROXONE f) ozonation using solid-bed catalysts with conditioned activated carbon (AC) g) vacuum-UV photolysis of water.

Fusarium semitectum (fungus) Au and Au-Ag alloy Extracellular Sawle et al. (2008)... 

There has been considerable success in employing silver nanocubes as sacrificial templates for gold deposition. Coating silver nanocubes with a layer of gold yields hollow, porous, Au/Ag alloy nanoboxes [76,81,133,134]. Additionally, it has proven possible to control the size of the pores. A typical example is shown in Figure 11.57 below [134]. 

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]. 

Table 9.2 compares the selectivity over all studied catalysts. The ethylene oxide selectivity of either the Ag/y-AhOa or Au-Ag/y-AhOa catalysts drastically decreased with increasing reaction temperature. This is because the total oxidation of ethylene is favorable at high temperatures. The addition of an appropriate amount (<0.63 wt.%) of Au to the 13.2 wt.% Ag catalyst (which exists in separate Au particles on Ag particles) was found to promote the ethylene epoxidation reaction by weakening the Ag-O bond in the reaction temperature range of 493-528 K [18,19]. When the Au loading was higher than 0.63 wt.%, the activity of the ethylene epoxidation decreased because of the formation of an Au-Ag alloy which resulted in a decrease in the adsorption capacity of molecular oxygen [18]. 

In this formula, Xg and Xg refer to the respective atom fractions of the tth component at the surface and in the bulk, and a is the surface area occupied by the atoms. From this equation it can be seen that the component with the lowest surface tension will accumulate at the surface. Calculations of the segregation of silver to the surface of a Au-Ag alloy after those of William and Nason " are shown in Figure 9... 

Let us show a few examples of how Eq. 3.55 predicts surface segregation. For Au-Ag alloys, the quantity 12 is constant and negative (exothermic heat of mixing) to within 17% throughout the entire composition range [24], which is about as close... 

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... 

Au—Ag alloys Oppenheim and coworkers monitored corrosion of Ag—Au (111) surfaces in 0.1 M HCIO4 by EC-STM with monolayer depth resolution. By choosing low-Ag content alloys with compositions well below the parting limit, the preferential dissolution of Ag was confined to the first few atomic layers. Under these... 

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. 

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