Metal nanoparticles, sonochemical synthesis

Although various techniques have been reported, sonochemical reduction technique for the synthesis of metal nanoparticles in an aqueous solution are reviewed in this chapter. 

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. 

By using other templates, the size of metal nanoparticles can be also controlled. Chen et al. reported the sonochemical reduction of Au(III), Ag(I) and Pd(II) and synthesis of Au, Ag and Pd nanoparticles loaded within mesoporous silica [48,49]. Zhu et al. also reported the sonochemical reduction of Mn04 to Mn02 and synthesis of Mn02 nanoparticles inside the pore channels of ordered mesoporous cabon [50]. Taking into account these reports, the rigid pore of inorganic materials can be used as a template for the size controlled metal nanoparticle synthesis even in the presence of ultrasound. 

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. 

Metal nanoparticles can be prepared in a myriad of ways, e.g., by pulse radiolysis [110], vapor synthesis techniques [111], thermal decomposition of organometallic compounds [112], sonochemical techniques [113,114], electrochemical reduction [115,116], and various chemical reduction techniques. Some of the most frequently used reducing agents include alcohols [117,118], citrate [119,120], H2 [121], borohydrides [122], and, more recently, superhydride [123]. The chosen experimental conditions determine the size, size distribution, shape, and stability of the particles. Because naked metal particles tend to aggregate readily in solution, stabilizing the nanoparticles is the key factor for a successful synthesis. Sometimes the solvent can act as a stabilizer, but usually polymers and surfac-... 

Such a reaction of Fe(CO)5 (at 293-363 K, PVP) without ultrasonic radiation proceeds very slowly and only after few days there, a material is formed with very low Fe content (2%, the isolated particles 2-5 nm in size). It is of interest that the sonochemical decomposition of Fe(CO)5 does not proceed in the presence of PVP if THF is used as the solvent, but the reaction is very effective when anisole is used as the solvent and PFO is used as the polymer matrix [93]. A black product formed contains up to 10% (in mass) of the spheric particles of nonoxidized Fe (mainly y-Fe, with little content of a-Fe) with 1-12 nm in size (the mean diameter is 3nm, as shown in Figure 3.7). It is likely that the big particles present the flocks of little ones ( 2-2.5nm). The sonochemical synthesis allows us to produce the functionalized amorphous nanoparticles of ferric oxide with 5-16 nm in diameter [94]. The ultrasonic irradiation in the PFO presence allows us to also produce the stabilized nanoparticles of copper, gold, and so on. In the literature the findings are not about the bimetallic particle formation in the ultrasonic fields by carbonyl metal reduction in the polymer matrices presence (as, for example, in the case of the carbon-supported Pt-Ru from PtRu5C(CO)i6 reduced clusters [95]). 

JJi. Park, M. Atobe, and T. Fuchigami, Sonochemical synthesis of conducting polymer-metal nanoparticles nanocomposite, Electrochim. Acta, 51, 849-854 (2005). 

K. Okitsu, Sonochemical synthesis of metal nanoparticles, in Theoretical and Experimental Sonochemistry Involving Inorganic Systems, ed. by Pankaj, M. Ashokkumar, pp. 131-150... 

In addition to making metal nanoparticles such as Fe [26], Co [27], Pd [28] and Ni [29], the method was also applied for synthesising carbon nanotubes and luminescent silica nanoparticles [30]. Authors have speculated that black carbon polymer could be produced under the extreme heat generated within the cavitation bubble by the decomposition of organic compounds followed by fast annealing process by the turbulent flow and shockwaves generated on bubble collapse. Sonochemical synthesis of nanostructured M0S2 was achieved by the ultrasonic irradiation of... 

Various groups have employed a range of sonochemical approaches to s mthesize metal sulfate nanoparticles in aqueous solution. Wang et al. [194] have reported the sonochemical synthesis of CdS nanoparticles by irradiation of a mixture of cadmium chloride, sodium thiosulfate, and 2-propanol. Dhas et al. [191] have reported the surface synthesis of CdS nanoparticles on silica microspheres by using cadmium sulfate and thiourea as precursors. The mechanism of the sonochemical growth of metal particles consists of several steps. For example, ZnO/CdS core/shell-type composite particles are formed by four steps [195] ... 

Okitsu et al. [55], carried out the sonochemical synthesis of crystalline nanoparticles of Au, Ag, Pd, and Pt stabilized with polyethylene glycol monostearate (MS-PEG), sodium dodecyl sulfate (SDS, NaCl2H2sS04), and polyvinylpyrrolidone (Okitsu 1996a, b) [233, 234]. The metal particles were produced from 5 run order and are stable for months. 

Abstract This chapter discusses the effect of ultrasound propagation in water and aqueous solutions, in the atmosphere of inert and reactive gases. Sonochemical studies of aqueous solutions of divalent and trivalent metal ions and their salts have been reviewed and the precipitation behaviour of hydroxides of metal ions has been discussed. Synthesis of nanoparticles of many metals using ultrasound and in aqueous solutions has also been discussed briefly. Besides, the nephelometric and conductometric studies of sonicated solutions of these metal ions have been reported. 

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