during the synthesis of Pd particles, (ii) organic additives are then adsorbed on
the Pd cluster surface, and finally (iii) carbon atoms on the particle surface, which
are formed from the catalytic dissociation of the additives, diffuse in the Pd metal
lattice.
Similar studies in an organic solvent yielded almost the same product [66].
Nanostructured particles of amorphous carbon-activated palladium metallic clusters have been prepared (in situ) at room temperature by ultrasound irradiation
of an organometallic precursor, tris-m-[dibenzylideneacetone]dipalladium [(jaCHb
CHaCOaCHbCHaj) 3 Pd 2 ] in mesitylene. Characterization studies show that the
product powder consists of nanosize particles, agglomerated in clusters of approximately 800 A ˚ . Each particle is found to have a metallic core, covered by a carbonic
shell that plays an important role in the stability of the nanoparticles. The catalytic
activity in a Heck reaction, in the absence of phosphine ligands, has been demonstrated.
Gedanken and his group were searching to replace the Ni(CO) 4 , which was the
source for the preparation of nickel, and is known to be a hazardous material. They
found [67] a new precursor for the sonochemical preparation of amorphous nickel,
Ni(cyclooctadiene) 2 , which yielded relatively large (200 nm) amorphous nanoparticles composed of nickel and carbon atoms. Small nickel particles were dispersed
all over the particle. When these particles were heated slightly above their crystallization temperature, much smaller particles (5 nm) of encapsulated crystalline
nickel in amorphous carbon were obtained. The XPS spectrum reveals that the
crystallization process is also accompanied by the reduction of the surface Ni
þ2
ions by the amorphous carbon atoms. The DSC measurements substantiate this
assumption.
Walter and coworkers [68] intercalated small Pt nanoparticles into graphite using
a sonochemical process. H 2 PtCl 6 was intercalated into natural graphite by applying
ultrasound to a mixture of graphite, H 2 PtCl 6 , CCl 4 , and SOCl 2 for 3 days. X-ray
diffraction data showed that the host lattice was partly intercalated by H 2 PtCl 6 . A
mixture consisting of a third and fourth stage together with unreacted graphite was
observed. The intercalation compound was suspended in acetone with hydrogen
flowing through while the sonication took place for 2 days. Transmission electron microphotographs showed highly dispersed nanoparticles in a narrow size
range inside the carbon lattice. X-ray photoelectron spectroscopy gave evidence that
these particles are platinum metal (Pt(0)). Particle thickness estimated by X-ray
diffraction indicated an average particle thickness of two layers. Selected-area electron diffraction microphotographs showed a pattern that could be hexagonally indexed. A (2 Â alpha (graphite)) superstructure was observed for those quasi-twodimensional aggregates formed by self-organization. This indicates a templating
effect due to the carbon lattice.
Iijima and his group used ultrasound radiation to react carbon nanotubes [69].
They sonicated single-wall carbon nanotubes (SWNTs) in a monochlorobenzene
(MCB) solution of poly(methyl methacrylate) (PMMA) and were able to react
SWNTs with MCB or PMMA chemically. After the SWNTs reacted with these organic materials, they turned into ragged SWNTs (r-SWNTs) with many defects in
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
128
the Pd cluster surface, and finally (iii) carbon atoms on the particle surface, which
are formed from the catalytic dissociation of the additives, diffuse in the Pd metal
lattice.
Similar studies in an organic solvent yielded almost the same product [66].
Nanostructured particles of amorphous carbon-activated palladium metallic clusters have been prepared (in situ) at room temperature by ultrasound irradiation
of an organometallic precursor, tris-m-[dibenzylideneacetone]dipalladium [(jaCHb
CHaCOaCHbCHaj) 3 Pd 2 ] in mesitylene. Characterization studies show that the
product powder consists of nanosize particles, agglomerated in clusters of approximately 800 A ˚ . Each particle is found to have a metallic core, covered by a carbonic
shell that plays an important role in the stability of the nanoparticles. The catalytic
activity in a Heck reaction, in the absence of phosphine ligands, has been demonstrated.
Gedanken and his group were searching to replace the Ni(CO) 4 , which was the
source for the preparation of nickel, and is known to be a hazardous material. They
found [67] a new precursor for the sonochemical preparation of amorphous nickel,
Ni(cyclooctadiene) 2 , which yielded relatively large (200 nm) amorphous nanoparticles composed of nickel and carbon atoms. Small nickel particles were dispersed
all over the particle. When these particles were heated slightly above their crystallization temperature, much smaller particles (5 nm) of encapsulated crystalline
nickel in amorphous carbon were obtained. The XPS spectrum reveals that the
crystallization process is also accompanied by the reduction of the surface Ni
þ2
ions by the amorphous carbon atoms. The DSC measurements substantiate this
assumption.
Walter and coworkers [68] intercalated small Pt nanoparticles into graphite using
a sonochemical process. H 2 PtCl 6 was intercalated into natural graphite by applying
ultrasound to a mixture of graphite, H 2 PtCl 6 , CCl 4 , and SOCl 2 for 3 days. X-ray
diffraction data showed that the host lattice was partly intercalated by H 2 PtCl 6 . A
mixture consisting of a third and fourth stage together with unreacted graphite was
observed. The intercalation compound was suspended in acetone with hydrogen
flowing through while the sonication took place for 2 days. Transmission electron microphotographs showed highly dispersed nanoparticles in a narrow size
range inside the carbon lattice. X-ray photoelectron spectroscopy gave evidence that
these particles are platinum metal (Pt(0)). Particle thickness estimated by X-ray
diffraction indicated an average particle thickness of two layers. Selected-area electron diffraction microphotographs showed a pattern that could be hexagonally indexed. A (2 Â alpha (graphite)) superstructure was observed for those quasi-twodimensional aggregates formed by self-organization. This indicates a templating
effect due to the carbon lattice.
Iijima and his group used ultrasound radiation to react carbon nanotubes [69].
They sonicated single-wall carbon nanotubes (SWNTs) in a monochlorobenzene
(MCB) solution of poly(methyl methacrylate) (PMMA) and were able to react
SWNTs with MCB or PMMA chemically. After the SWNTs reacted with these organic materials, they turned into ragged SWNTs (r-SWNTs) with many defects in
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
128