under argon, instantaneously oxidized to PdO [132]. The particles obtained were
stable and have a narrow size distribution with an average diameter of 10 nm. PdO
nanoparticles were reduced to Pd nanoparticles in an autoclave by treatment with
50 bar hydrogen at 140
C. The catalytic behavior of the Pd nanoparticles thus obtained is unusual in comparison with conventional Pd catalysts.
Two reports have been published on the sonochemical preparation of nanosized ceria, CeO 2 [133, 134]. Zhu and coworkers [133] synthesized nanocrystalline
ceria (CeO 2 ) particles via sonochemical and microwave assisted heating routes
from aqueous solutions containing (NH4) 2 Ce(NO3) 6 , hexamethylenetetramine and
poly (ethylene glycol) (PEG M w ¼ 19,000). Analysis of the results showed that the
products had a uniform shape, narrow size distribution, and displayed conspicuous quantum size effects.
In the second synthesis, cerium oxide (CeO 2 ) nanoparticles were prepared sonochemically by using cerium nitrate and azodicarbonamide as starting materials,
and ethylenediamine or tetraalkylammonium hydroxide as additives [134]. The
additives have a strong effect on the particle size and particle size distribution.
CeO 2 nanoparticles with small particle size and narrow particle size distribution
are obtained by the addition of additives; while highly agglomerated CeO 2 nanoparticles are obtained in the absence of additives. Monodispersed CeO 2 nanoparticles with a mean particle size of ca. 3.3 nm are obtained when tetramethylammonium hydroxide (TMAOH) is used as the additive and the molar ratio of
cerium nitrate/azodicarbonamine/TMAOH is 1/1/1. Blue shifts of the absorption
peak and the absorption edges of the products are observed in the UV–Vis absorption spectra as a result of the quantum size effect.
A composite material made of zinc oxide and polyvinyl alcohol was prepared by
a sonochemical method [135]. Annealing of the composite under air removed
the polymer, leaving porous spheres of ZnO. This change was accompanied by a
change in the surface area from 2 to 34 m
2 g
À1 . The porous ZnO particles were
used as the electrode material for dye-sensitized solar cells (DSSCs). They were
tested by forming a film of the doped porous ZnO on a conductive glass support.
The performance of the solar cell is reported.
A very unusual and previously unknown oxide of copper, the paramelaconite,
Cu 4 O 3 , was synthesized sonochemically in a polyaniline matrix [136]. An aqueous
solution of copper (II) acetate and aniline (1:10 molar ratio) is irradiated by ultrasound to produce nanophased Cu 4 O 3 embedded in a polyaniline matrix. The asprepared Cu 4 O 3 –polyaniline is characterized by X-ray diffraction (XRD), and other
methods. The mechanism for the fabrication of Cu 4 O 3 –polyaniline is proposed
and discussed. This method is general and works also for the production of nanocrystalline Fe 3 O 4 and Cu 2 O embedded in polyaniline. This technique is also an
easy route for the production of other metal oxides embedded in polyaniline.
Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO) 6 in diphenylmethane (DPhM) in the presence of an Ar (80%) and O 2 (20%) gaseous mixture at 90
C [137]. Heating this
amorphous powder at 550
C under Ar yields snowflake-like dendritic particles
consisting of a mixture of monoclinic and orthorhombic WO 2 crystals. Annealing
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
146
stable and have a narrow size distribution with an average diameter of 10 nm. PdO
nanoparticles were reduced to Pd nanoparticles in an autoclave by treatment with
50 bar hydrogen at 140
C. The catalytic behavior of the Pd nanoparticles thus obtained is unusual in comparison with conventional Pd catalysts.
Two reports have been published on the sonochemical preparation of nanosized ceria, CeO 2 [133, 134]. Zhu and coworkers [133] synthesized nanocrystalline
ceria (CeO 2 ) particles via sonochemical and microwave assisted heating routes
from aqueous solutions containing (NH4) 2 Ce(NO3) 6 , hexamethylenetetramine and
poly (ethylene glycol) (PEG M w ¼ 19,000). Analysis of the results showed that the
products had a uniform shape, narrow size distribution, and displayed conspicuous quantum size effects.
In the second synthesis, cerium oxide (CeO 2 ) nanoparticles were prepared sonochemically by using cerium nitrate and azodicarbonamide as starting materials,
and ethylenediamine or tetraalkylammonium hydroxide as additives [134]. The
additives have a strong effect on the particle size and particle size distribution.
CeO 2 nanoparticles with small particle size and narrow particle size distribution
are obtained by the addition of additives; while highly agglomerated CeO 2 nanoparticles are obtained in the absence of additives. Monodispersed CeO 2 nanoparticles with a mean particle size of ca. 3.3 nm are obtained when tetramethylammonium hydroxide (TMAOH) is used as the additive and the molar ratio of
cerium nitrate/azodicarbonamine/TMAOH is 1/1/1. Blue shifts of the absorption
peak and the absorption edges of the products are observed in the UV–Vis absorption spectra as a result of the quantum size effect.
A composite material made of zinc oxide and polyvinyl alcohol was prepared by
a sonochemical method [135]. Annealing of the composite under air removed
the polymer, leaving porous spheres of ZnO. This change was accompanied by a
change in the surface area from 2 to 34 m
2 g
À1 . The porous ZnO particles were
used as the electrode material for dye-sensitized solar cells (DSSCs). They were
tested by forming a film of the doped porous ZnO on a conductive glass support.
The performance of the solar cell is reported.
A very unusual and previously unknown oxide of copper, the paramelaconite,
Cu 4 O 3 , was synthesized sonochemically in a polyaniline matrix [136]. An aqueous
solution of copper (II) acetate and aniline (1:10 molar ratio) is irradiated by ultrasound to produce nanophased Cu 4 O 3 embedded in a polyaniline matrix. The asprepared Cu 4 O 3 –polyaniline is characterized by X-ray diffraction (XRD), and other
methods. The mechanism for the fabrication of Cu 4 O 3 –polyaniline is proposed
and discussed. This method is general and works also for the production of nanocrystalline Fe 3 O 4 and Cu 2 O embedded in polyaniline. This technique is also an
easy route for the production of other metal oxides embedded in polyaniline.
Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO) 6 in diphenylmethane (DPhM) in the presence of an Ar (80%) and O 2 (20%) gaseous mixture at 90
C [137]. Heating this
amorphous powder at 550
C under Ar yields snowflake-like dendritic particles
consisting of a mixture of monoclinic and orthorhombic WO 2 crystals. Annealing
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
146