Reduction of Silver and Palladium Ion

Naturally, the chemical form that the cation will have in solution, in the interlayer, and on the outer surfaces of montmorillonite, is governed by thermodynamics. As seen in Section 2.10.2 iron(III) ions can be hydrolyzed in the water of the interlayer even if the hydrolysis is avoided through the application of an organic solvent. Similarly, manganese(II) ions are oxidized in the interlayer space 

Besides oxidation, reduction processes can also take place spontaneously or by chemical treatments when the redox potential of the sorbed cation makes it possible. As an example, the spontaneous reduction of silver ions in silver-mont-morillonite is shown here (Konya et al. 2005). 

FIGURE 2.23 Scanning electron microscopic (SEM) picture of silver-montmorillonite. Left side morphology of the sample made by backscattered electrons. Right side silver map made by characteristic x-ray photons. Silver concentration is proportional to the density of the light spots. The arrows show spots with 100% silver concentration. (Reprinted from Konya et al. 2005, with permission from Springer.) 

FIGURE 2.24 Thermoanalytical curves of silver-montmorillonite. (Reprinted from Konya et al. 2005, with permission from Springer.) 

The thermal analytical curves of silver-montmorillonite in the figure show the usual reactions of monovalent montmorillonites (Section 2.1.2). An additional exothermal reaction appears at 361°C. It corresponds to the oxidation of metallic silver, and this correspondence is further confirmed by the change of the color of silver-montmorillonite, which is originally dark gray and becomes light after heat treatment. 

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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. 

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