Metal ions sonochemical reduction

To synthesize metal nanoparticles in an aqueous solution, the reduction reactions of the corresponding metal ions are generally performed. Gutierrez et al. [21] reported the reduction of A11CI4 and Ag+ ions in an aqueous solution by ultrasonic irradiation under H2-Ar mixed atmosphere. They found that the optimum condition of these reductions was under the 20 vol% H2 and 80 vol% Ar atmosphere. Following this study, many papers reported the sonochemical reduction of noble metal ions under pure Ar atmosphere to produce the corresponding metal nanoparticles [22-28],... 

It is also observed in Fig. 5.3 that Pd(II) ions are partly adsorbed on AI2O3 before ultrasonic irradiation the concentration of Pd(II) just before irradiation becomes ca. 0.8 mM, although 1 mM Pd(II) was added in the sample solution. From a preliminary adsorption experiment, the rate of Pd(II) adsorption on A1203 was found to be slow compared with those of Pd(II) reduction in the presence of alcohols. Therefore, it is suggested that the sonochemical reduction of Pd(II) in the presence of alcohols mainly proceeds in the bulk solution. The mechanism of the Pd/Al203 formation is also described in the section of sonochemical synthesis of supported metal nanoparticles. 

The effects of various parameters on the rates of sonochemical reduction of metal ions were described in the previous sections. From this section, the effects of such parameters on the properties of metal nanoparticles are described in relation to the rates of reduction. 

It has been reported that bimetallic nanoparticles with core/shell structure can be prepared by ultrasonic irradiation. Mizukoshi et al. reported the formation of bimetallic nanoparticles of Au core/Pd shell structure [42,43] from the sonochemical reduction of Au(III) and Pd(II), where the stepwise reduction of metal ions was observed to proceed during ultrasonic irradiation. That is, the reduction of Pd(II) started after the reduction of Au(III) finished. Vinodgopal et al. reported... 

Abstract A convenient method to synthesize metal nanoparticles with unique properties is highly desirable for many applications. The sonochemical reduction of metal ions has been found to be useful for synthesizing nanoparticles of desired size range. In addition, bimetallic alloys or particles with core-shell morphology can also be synthesized depending upon the experimental conditions used during the sonochemical preparation process. The photocatalytic efficiency of semiconductor particles can be improved by simultaneous reduction and loading of metal nanoparticles on the surface of semiconductor particles. The current review focuses on the recent developments in the sonochemical synthesis of monometallic and bimetallic metal nanoparticles and metal-loaded semiconductor nanoparticles. 

The objective of this chapter is to compile work related to the beginning of sonochemical research and its extension to the aqueous solutions of metal ions. Ultrasound propagation in aqueous salt solutions leads to the hydrolysis, reduction, complexation, decomplexation and crystallization. Such works from different laboratories, along with the effect of dissolved gases on the production of free radicals in water and aqueous solutions upon sonication has been reviewed in this chapter. The generation of turbidity, due to the formation of metal hydroxides and changes in the conductivity of these aqueous solutions, carried out in this laboratory, has also been reported, to give firsthand information of the ultrasound interaction of these solutions. 

Abstract The behaviour of many metal ions which are stable in more than one oxidation states in their aqueous solutions has been studied under sonochemical reaction conditions. Fe(II) is oxidized to Fe(III) and Fe(III) is reduced to Fe(II) with equal ease under sonochemical conditions. Besides, the oxidizing power of Cr2072 is found to be less than the MnO ions, therefore, in a system containing both species, Cr3+ is susceptible to oxidation to Cr61 and the MnO to reduction to Mn2+. 

The role of the surfactant was further studied in sonochemical reduction [20, 21] processes of Pt (IV) ions in water. It was investigated in the presence of various kinds of surfactants such as sodium dodecylsulfate (SDS) and sodium dodecyl-benzenesulfonate (DBS) as anionic surfactants, polyethylene glycol monostearate (PEG-MS) as non-ionic, and dodecyltrrmethylammonium chloride (DTAG) and bromide (DTAB) as cationic surfactants. An improved colorimetric determination reveals that Pt (IV) ion is reduced to zero-valent metal in two steps step (1) Pt (IV) ion to Pt (II) ion, and step (2) Pt (II) ion to Pt (0), and after the completion of step (1), step (2) sets in. 

There have been a number of synthetic protocols for the preparation of transition-metal nanoparticles, for example, vapor condensation, sonochemical reduction, chemical liquid deposition, reflux alcohol reduction, decomposition of organometallic precursors, hydrogen reduction, etc. Of these, the colloidal reduction route provides a powerful platform for the ready manipulation of particle structure and functionalization. One excellent example is the biphasic Brust method, in which nanoparticles are formed by chemical reduction of a metal salt precursor in the presence of stabilizing ligands. In a typical reaction, a calculated amount of a metal salt precursor is dissolved in water, and the metal ions are then transferred into the toluene phase by ion-pairing with a... 

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