Sonochemical Synthesis of Other Nanomaterials

Metals, metal oxides, and chalcogenides constitute the main body of the sonochemical research. Only very few other groups of materials have been prepared by using power ultrasound. There may be two reasons for this first, the difficulty in preparing these materials and, secondly, lack of interest. However, we believe that the first reason can explain why an important material such as GaN, for example, has not been prepared sonochemically. 

More publications were found related to carbides. First, Suslick s early report [64] that certain carbonyls sonicated in a decalin solvent under argon. For Fe and Co, nanostructured metals are formed for Mo and W, metal carbides (e.g., M02C) are produced. Molybdenum carbide was used later as a catalyst. The selectivity and catalytic activity of the Mo and W carbides was examined in the dehydrogenation of alkanes [140]. Another carbide that has already been mentioned is that of Pd [65], which was prepared by Maeda s group. Iron carbide was a byproduct that served as protective layer in Nikitenko s work on air-stable iron nanoparticles [70]. 

Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) yS-diketonates Th(HFAA)4 and Th(DBM)4, where HFAA and DBM are hexafluoroacetylacetone and dibenzoylmethane respectively, causes them to decompose in hexadecane 

It is more difficult to prepare III-V semiconductors than the II-VI. Two sonochemical investigations reported on the preparation of these materials. The first paper details a safe method for the preparation of transition metal arsenides, FeAs, NiAs, and CoAs [142]. At room temperature, well-crystallized and monodispersed arsenide particles were successfully obtained under high-intensity ultrasonic irradiation for 4 h from the reaction of transition metal chlorides (FeCla, NiCl2, and C0CI2), arsenic (which is the least toxic arsenic feedstock) and zinc in ethanol. Different characterization techniques show that the product powders consist of nanosize particles. The ultrasonic irradiation and the solvent are both important in the formation of the product. 

Another III-V semiconductor was prepared by Li and coworkers [143]. A room temperature sonochemical method for the preparation of GaSb nanoparticles using less hazardous Ga and antimony chloride (SbClj) as the precursors has been described. TEM and SAED results show that the as-prepared solid consists of nanosized GaSb crystals with sizes in the 20-30 run range. The photoacoustic spectrum result reveals that the GaSb nanopartides have a direct band gap of about 1.21 eV. On the basis of the control experiments and the extreme conditions produced by ultrasound, an ultrasound-assisted in situ reduction/combination mechanism has been proposed to explain the reaction. 

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