Sonochemical techniques

In this review, the potential uses of sonochemistry for the preparation of monometallic and bimetallic metal nanoparticles and metal-loaded semiconductor nanoparticles have been highlighted. While specific examples available in the literature were discussed, the sonochemical technique seems to offer a platform technique that could be used for synthesizing a variety of functional materials. Most of the studies to date deal with laboratory scale exploration , it would be ideal if the concepts are tested under large scale experimental conditions involving specific applications. The authors sincerely hope that the information provided in this review would prompt such experimental investigation in a new dimension. 

Srivastava DN, Perkas N, Seisen Bueva GA, Koltypin Y, Kessler VP, Gedanken A (2003) Preparation of porous cobalt and nickel oxides from corresponding alkoxides using a sonochemical technique and its application as a catalyst in the oxidation of hydrocarbons. Ultrason Sonochem 10(1) 1-9... 

A review on using sonochemistry for the fabrication of nano-materials has been published by Gedanken (2004). It has been remarked that, in almost all the sono-chemical reactions leading to inorganic products, nano-materials were obtained and it was observed that, in the field of materials science, among the methods developed to prepare nano-particles, the sonochemical techniques are superior to the other methods in the following aspects ... 

A very reactive form of a finely divided metal is a so-called Rieke powder [79]. These materials are produced as fine powders by chemical precipitation during the reduction of various metal halides ivith potassium metal in refluxing tetrahydrofuran. Obviously this is a potentially hazardous laboratory procedure and ultrasound has provided an alternative method of preparation of these extremely valuable reagents [80]. The sonochemical technique involves the reduction of metal halides with lithium in TH F at room temperature in a cleaning bath and gives rise to metal powders that have reactivities comparable to those of Rieke powders. Thus powders of Zn, Mg, Cr, Cu, Ni, Pd, Co and Pb were obtained in less than 40 min by this ultrasonic method compared with reaction times of 8 h using the experimentally more difScult Rieke method (Tab. 3.1). 

Considerable acceleration of cycloadditions involving electron-rich 1-aza-1,3-butadienes by ultrasound irradiation has been observed recently [252,253]. Thus, the application of sonochemical techniques might emerge as helpful tool for Diels-Alder reactions of 1-aza-l, 3-butadienes. 

Sonochemical techniques have been used predominantely in the lithium Barbier reaction [142-145]. 

Soluble triarylbismuth oxides, (AraBiO) , which oxidize activated alcohols and triphenylphosphine (in 60% yields) are formed efficiently by a sonochemical technique. 

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-... 

If the reaction occurs in the boundary region, the nanoparticles acquire a form of nanotubes, nanorods and alike [249]. For instance, sonochemical synthesis of the vanadium oxide nanorods by treating bulk V2O5 with high intensity sonochemical technique has been described in [252]. 

This preparation of LDA is a typical example of the use of sonochemical techniques in synthetic chemistry. It is accomplished in a short time... 

Srivastava DN, Pol VG, Palchik O et al (2005) Preparation of stable porous nickel and cobalt oxides using simple inorganic precursor, instead of aUcoxides, by a sonochemical technique. Ultrason Sonochem 12 205-212... 

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