Figure 20. X-ray diffraction patterns of the as-prepared ZnSe after sonication of (a) 1, (b) 2, and (c) 3 h. Reprinted with permission from [86], J. Zhu et al., Chem. Mater. 12, 73 (2000). © 2000, American Chemical Society.

Li et al. [88] recently prepared nanophase lead chalco-genides, via the sonochemical route, using Pb(CH3COO)2. 3H2O and the corresponding elemental chalcogens were used as the reactants, while ethylenediamine (en) was used as the solvent. Ultrasonic irradiation was found to have two main effects: (1) it favored the dissolution of chalcogens (E) and the formation of E2-, and thus accelerated the reaction; (2) it prevented the aggregation of the resulting nanoparticles [89].

The sonochemical preparation of mercury(II) selenide nanoparticles based on the reaction between mercury acetate and sodium selenosulfate in an aqueous system was reported by Wang et al. The products obtained are well dispersed, and the nanoparticles are of small sizes [90].

4.6. Nanometal Carbides and Nitrides and Phosphides

The sonochemical synthesis of nanophase molybdenum carbide from the ultrasonic irradiation of molybdenum hex-acarbonyl has been prepared by heating the product at 450 ° C under a helium gas flow. Since the synthesis of Mo2C is particularly prone to substantial oxygen contamination [91], the sonicated product is subjected to heating in a flow of (1:1) CH4/H2 mixture at 300 ° C for 1 h, then at 400 ° C for 1 h, and finally at 500 ° C for 48 h. The flow rate of the CH4/H2 mixture was 27.5 cm3 (STP)/min. After this carburization, excess carbon, hydrogen, and oxygen had been largely removed [92]. Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(lV) ^-diketonates Th(HFAA)4 and Th(DBM)4, where HFAA and DBM are hexafluoroacety-lacetone and dibenzoylmethane, respectively, causes them to decompose in hexadecane solutions, forming solid thorium compounds. The rate of the sonochemical reaction increased with the rising ^-diketonate volatility, and decreased with the rising hydrocarbon solvent vapor pressure. Solid soni-cation products consisted of a mixture of thorium carbide ThC2 and Th(IV) ^-diketonate partial degradation products. The average ThC2 particle size was estimated to be about 2 nm. ThC2 formation was attributed to the high-temperature reaction occurring within the cavitating bubble. The thorium ^-diketonate partial degradation products formed in the liquid reaction zones surrounding the cavitat-ing bubbles [93]. This is the first study of the "direct" effect of power ultrasound on 5f -transition elements using volatile Th(IV) ^-diketonate precursors.

Li et al. [94] prepared InP nanocrystals with a diameter of nm under high-intensity ultrasonic irradiation for 4 h from the reaction of InCl3 • 4H2O, yellow phosphorus, and KBH4 in the mixed solvents of ethanol and benzene. The sonochemical reaction of Fe(CO)5 and triethylphosphine has been found to produce a solid amorphous iron phosphide of composition FeP. This reaction provides the first use of ultrasound to sonochemically synthesize amorphous phosphide semiconductor materials from organometallic precursors [95]. Unlike the sonication on W(CO)6 and triphenyl phos-phine, where the monosubstituted product W(CO)5(PPh3) was principally formed [96], sonication of the volatile species Fe(CO)5 and P(CH2CH3)2 produced a complete loss of the ligand sets to produce FeP as the principal product. The difference in reactivity is most probably due to the difference c

0 0

Post a comment