shape, with a diameter of approximately 50 nm. A comparison of the XRD pattern
with that obtained for the copper nanoparticles prepared without using a surfactant revealed an elongation taking place along the [111] and [200] planes of the
copper nanocrystals.
A comprehensive study on the sonochemical synthesis of colloidal solutions of
noble metals was conducted by Grieser and coworkers [32–34]. The 515 kHz
ultrasound-initiated reduction of AuCl 4
À1 to Au (0) was examined as a function of
the concentration of various surface-active solutes [32]. The amount of AuCl 4
À1
reduced in the presence of ethanol, 1-propanol, and 1-butanol was found to be dependent on the surface excess of the alcohol at the gas/solution interface, i.e., the
relative concentration of the alcohol at the gas/solution interface compared to the
bulk solution concentration. The efficiency of reduction of AuCl 4
À1 in the presence of
the surfactants sodium dodecyl sulfate or octaethylene glycol monodecyl ether was
found to be related to the monomer concentration of the surfactant in solution.
The ultrasound irradiation of aqueous solutions of PtCl 6
À2 was found to produce
colloidal platinum of about 3 nm in diameter [33]. The presence of aliphatic alcohols significantly enhanced the reduction process. It is shown that the extent of
reduction of PtCl 6
À2 in the presence of alcohol is directly related to the Gibbs surface excess of the alcohol at the air–water interface. The significance of this is discussed in relation to ultrasound-induced cavitation in solution. In a recent report
Caruso et al. [34] reduced AuCl 4
À1 to colloidal gold in the presence of aliphatic alcohols and sodium dodecyl sulfate in aqueous solutions using 20 kHz ultrasound.
The extent of reduction of AuCl 4
À1 was found to be directly dependent on the gas–
solution interfacial activity of the solutes used. The diameters of the gold colloids
produced were in the size range 9–25 nm. The particle size was dependent on the
alcohol concentration in solution and on the hydrophobicity of the alcohol. For a
particular alcohol concentration, the greater the hydrophobicity of the alcohol the
smaller were the particles obtained. The authors present a detailed mechanism
describing the overall sonochemically initiated reduction of AuCl 4
À1 leading to the
formation of colloidal gold. Finally, Grieser has also published an early review on
sonochemistry in colloidal systems [35].
6.1.1.3 Sonochemical Synthesis of Metallic Alloys
Nanophased amorphous Fe/Co was obtained by sonicating a mixture of Fe(CO) 5
and Co(CO) 3 NO in decalin [36]. The Fe/Co, nanostructured alloys are formed and
are non-crystalline by X-ray, neutron, and e-beam diffraction. In a further work, a
Fe/Ni alloy was similarly obtained [37]. Remarkably, a 1:1 molar solution of Fe:Ni
led to a Fe 20 Ni 80 solid composition, which can be attributed to the ratio of the
vapor pressure of the two carbonyls in the gas phase of the collapsing bubble.
Magnetic susceptibilities of Fe 40 Ni 60 and Fe 60 Ni 40 indicated blocking temperatures
of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe 20 Ni 80 gave Curie temperatures of 322
C for amorphous and 550
C
for crystallized forms. Differential scanning calorimetry exhibited an endothermic
transition at 335
C from a combination of the magnetic phase transition and alloy
crystallization. The r Mo ¨ssbauer spectrum of crystallized Fe 20 Ni 80 shows a sextet
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
120
with that obtained for the copper nanoparticles prepared without using a surfactant revealed an elongation taking place along the [111] and [200] planes of the
copper nanocrystals.
A comprehensive study on the sonochemical synthesis of colloidal solutions of
noble metals was conducted by Grieser and coworkers [32–34]. The 515 kHz
ultrasound-initiated reduction of AuCl 4
À1 to Au (0) was examined as a function of
the concentration of various surface-active solutes [32]. The amount of AuCl 4
À1
reduced in the presence of ethanol, 1-propanol, and 1-butanol was found to be dependent on the surface excess of the alcohol at the gas/solution interface, i.e., the
relative concentration of the alcohol at the gas/solution interface compared to the
bulk solution concentration. The efficiency of reduction of AuCl 4
À1 in the presence of
the surfactants sodium dodecyl sulfate or octaethylene glycol monodecyl ether was
found to be related to the monomer concentration of the surfactant in solution.
The ultrasound irradiation of aqueous solutions of PtCl 6
À2 was found to produce
colloidal platinum of about 3 nm in diameter [33]. The presence of aliphatic alcohols significantly enhanced the reduction process. It is shown that the extent of
reduction of PtCl 6
À2 in the presence of alcohol is directly related to the Gibbs surface excess of the alcohol at the air–water interface. The significance of this is discussed in relation to ultrasound-induced cavitation in solution. In a recent report
Caruso et al. [34] reduced AuCl 4
À1 to colloidal gold in the presence of aliphatic alcohols and sodium dodecyl sulfate in aqueous solutions using 20 kHz ultrasound.
The extent of reduction of AuCl 4
À1 was found to be directly dependent on the gas–
solution interfacial activity of the solutes used. The diameters of the gold colloids
produced were in the size range 9–25 nm. The particle size was dependent on the
alcohol concentration in solution and on the hydrophobicity of the alcohol. For a
particular alcohol concentration, the greater the hydrophobicity of the alcohol the
smaller were the particles obtained. The authors present a detailed mechanism
describing the overall sonochemically initiated reduction of AuCl 4
À1 leading to the
formation of colloidal gold. Finally, Grieser has also published an early review on
sonochemistry in colloidal systems [35].
6.1.1.3 Sonochemical Synthesis of Metallic Alloys
Nanophased amorphous Fe/Co was obtained by sonicating a mixture of Fe(CO) 5
and Co(CO) 3 NO in decalin [36]. The Fe/Co, nanostructured alloys are formed and
are non-crystalline by X-ray, neutron, and e-beam diffraction. In a further work, a
Fe/Ni alloy was similarly obtained [37]. Remarkably, a 1:1 molar solution of Fe:Ni
led to a Fe 20 Ni 80 solid composition, which can be attributed to the ratio of the
vapor pressure of the two carbonyls in the gas phase of the collapsing bubble.
Magnetic susceptibilities of Fe 40 Ni 60 and Fe 60 Ni 40 indicated blocking temperatures
of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe 20 Ni 80 gave Curie temperatures of 322
C for amorphous and 550
C
for crystallized forms. Differential scanning calorimetry exhibited an endothermic
transition at 335
C from a combination of the magnetic phase transition and alloy
crystallization. The r Mo ¨ssbauer spectrum of crystallized Fe 20 Ni 80 shows a sextet
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
120