ticles by a microwave high-pressure procedure with alcohol as the reducing agent.
The color of colloidal Au nanoparticles is blue–violet. The maximum absorption
spectrum of colloidal Au is at 580 nm, and the resonance scattering peak is at
580 nm. Using this method, the colloidal Au solution was very stable and the
preparation is described as simple and quick.
Poly(vinylpyrrolidone) (PVP) is a polymer capable of complexing and stabilizing
Ag and Au nanoparticles formed through the reduction of Ag
þ or AuCl
À 4 ions
with N,N-dimethylformamide [168]. The reduction is efficiently performed both at
reflux and under microwave irradiation, but each of these methods leads to different nanoparticle morphology and colloid stability. The use of microwave irradiation
provides an extra degree of control of the reduction process. The use of PVP with
different polymer chain lengths leads to particles with similar sizes, though with a
different degree of stability. The colloids are also stable in ethanol for months, but
only marginally stable in water. Alloys were also prepared by MWH thermal treatment of (h-C 2 H 4 )(Cl)Pt(m-Cl) 2 Ru(Cl)(h
3 :h
3 -2,7-dimethyloctadienediyl)/Vulcan carbon composites under appropriate oxidizing and reducing conditions. Using microwave dielectric loss heating affords PtRu/Vulcan carbon nanocomposites [169].
This composite consisted of PtRu alloy nanoparticles highly dispersed on a powdered carbon support. Two such nanocomposites containing 16 or 50 wt% total
metal and alloy nanoclusters of 3.4 or 5.4 nm average diameter are formed within
only 100 or 300 s of total microwave heating.
The polyol reaction was developed by Fivet’s group. It was the most popular
method for the fabrication of metallic nanoparticles using MWH. In the 1980s,
Fievet et al. [170] used ethylene glycol as a solvent and reducing agent for the
preparation of submicrometer particles of the transition metals. The mechanism
of this reaction is still only poorly understood. It is, however, known that the reduction is based on the decomposition of the ethylene glycol and its conversion to
diacetyl. Recently, Tarascon and co-workers [171] demonstrated that in these reactions the temperature is a dominant factor in affecting the reactivity. It is worth
mentioning that the preparation of nanophased chalcogenides was also based on
the polyol reaction [3].
The noble metals were the favorite metals for demonstrating the usefulness of
the microwave operation in conducting the polyol reaction. Among the noble
metals platinum was synthesized most frequently. Polymer-stabilized platinum
colloids with nearly uniform spherical shape were prepared by Yu and coworkers
by microwave dielectric heating [172]. The average diameters of the as-prepared
platinum colloids were 2–4 nm with a narrow size distribution in regard to the
preparation conditions.
The same group, using the polyol method, have prepared uniform and stable
polymer-stabilized colloidal clusters of Pt, Ir, Rh, Pd, Au and Ru by microwave
irradiation with a modified domestic microwave oven [173]. The as-synthesized
colloidal clusters have small average diameters and narrow size distribution. The
microwave method is characterized by rapid and homogeneous heating compared
with conventional heating methods, although its thermal effects are similar to
those of other heating methods.
Finally, using the polyol reaction and the same reactants as in [172] in a third
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
156
The color of colloidal Au nanoparticles is blue–violet. The maximum absorption
spectrum of colloidal Au is at 580 nm, and the resonance scattering peak is at
580 nm. Using this method, the colloidal Au solution was very stable and the
preparation is described as simple and quick.
Poly(vinylpyrrolidone) (PVP) is a polymer capable of complexing and stabilizing
Ag and Au nanoparticles formed through the reduction of Ag
þ or AuCl
À 4 ions
with N,N-dimethylformamide [168]. The reduction is efficiently performed both at
reflux and under microwave irradiation, but each of these methods leads to different nanoparticle morphology and colloid stability. The use of microwave irradiation
provides an extra degree of control of the reduction process. The use of PVP with
different polymer chain lengths leads to particles with similar sizes, though with a
different degree of stability. The colloids are also stable in ethanol for months, but
only marginally stable in water. Alloys were also prepared by MWH thermal treatment of (h-C 2 H 4 )(Cl)Pt(m-Cl) 2 Ru(Cl)(h
3 :h
3 -2,7-dimethyloctadienediyl)/Vulcan carbon composites under appropriate oxidizing and reducing conditions. Using microwave dielectric loss heating affords PtRu/Vulcan carbon nanocomposites [169].
This composite consisted of PtRu alloy nanoparticles highly dispersed on a powdered carbon support. Two such nanocomposites containing 16 or 50 wt% total
metal and alloy nanoclusters of 3.4 or 5.4 nm average diameter are formed within
only 100 or 300 s of total microwave heating.
The polyol reaction was developed by Fivet’s group. It was the most popular
method for the fabrication of metallic nanoparticles using MWH. In the 1980s,
Fievet et al. [170] used ethylene glycol as a solvent and reducing agent for the
preparation of submicrometer particles of the transition metals. The mechanism
of this reaction is still only poorly understood. It is, however, known that the reduction is based on the decomposition of the ethylene glycol and its conversion to
diacetyl. Recently, Tarascon and co-workers [171] demonstrated that in these reactions the temperature is a dominant factor in affecting the reactivity. It is worth
mentioning that the preparation of nanophased chalcogenides was also based on
the polyol reaction [3].
The noble metals were the favorite metals for demonstrating the usefulness of
the microwave operation in conducting the polyol reaction. Among the noble
metals platinum was synthesized most frequently. Polymer-stabilized platinum
colloids with nearly uniform spherical shape were prepared by Yu and coworkers
by microwave dielectric heating [172]. The average diameters of the as-prepared
platinum colloids were 2–4 nm with a narrow size distribution in regard to the
preparation conditions.
The same group, using the polyol method, have prepared uniform and stable
polymer-stabilized colloidal clusters of Pt, Ir, Rh, Pd, Au and Ru by microwave
irradiation with a modified domestic microwave oven [173]. The as-synthesized
colloidal clusters have small average diameters and narrow size distribution. The
microwave method is characterized by rapid and homogeneous heating compared
with conventional heating methods, although its thermal effects are similar to
those of other heating methods.
Finally, using the polyol reaction and the same reactants as in [172] in a third
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
156