aid of sonication. Acetate anions are intercalated into the interlayer region of the
as-prepared a-cobalt hydroxide in the form of a free ion state. b-Cobalt hydroxide
has also been prepared and formed as crystallized thin hexagonal platelets with a
diameter of 100 nm. Pure cobalt oxyhydroxide with a particle size of 10–30 nm has
also been obtained.
6.1.2.9 Sonochemical Preparation of Nanosized Titania
Because of its many applications, a few attempts are known in which ultrasonic
waves have been applied for the synthesis of nanosized titania. Yu and coworkers
[126] discovered a novel method for preparing highly photoactive nano-sized TiO 2
photocatalysts with anatase and brookite phases. The method has been developed
by hydrolysis of titanium tetraisopropoxide in pure water or a 1:1 EtOH:H 2 O solution under ultrasonic irradiation; the photocatalytic activity of TiO 2 particles prepared by this method exceeded that of Degussa P25.
Huang, in a similar reaction [127], found a way to selectively prepare anatase
or rutile as well as their mixtures. This was achieved by using various precursors
and employing ultrasound irradiation. The products, the particle sizes of which are
nanometric (<9 nm), are dependent both upon the reaction temperature and the
precursor used; a substantial reduction in reaction time, as well as reaction temperature is observed, as compared to the corresponding hydrothermal processes.
A novel sonochemical method for the direct preparation of anatase nanocrystalline TiO 2 was reported by Guo et al. [128]. Nanocrystalline TiO 2 was synthesized
by the hydrolysis of titanium tetrabutyl in the presence of water and ethanol under
high-intensity ultrasonic irradiation (20 kHz, 100 W cm
À2 at 363 K for 3 h.). The
structure and particle sizes of the product were dependent upon the reaction temperature, the acidity of the medium, and the reaction time. The TEM images
showed that the particles of TiO 2 were columnar in shape and the average sizes
were ca. 3 nm  7 nm. The sonochemical formation mechanism of nanocrystalline
TiO 2 is as follows: The hydrolytic species of titanium tetrabutyl in water condensed
to form a large number of tiny nuclei, which aggregated to form larger clusters.
Ultrasound irradiation generated many local hot spots within the gel, and the
crystal structural unit was formed near the hot spots with decrease in the gel nuclei, which led to the formation of nanocrystal particles.
A process has been developed for the formation of titania whiskers and nanotubes with the assistance of sonication [129]. Titanate whiskers are obtained as a
slender sheet with length about 1 mm and width 60 nm; arrays of titania whiskers
with diameter 5 nm are prepared from the titanate whiskers; titania nanotubes (see
Figure 6.7) with diameter about 5 nm, and length 200–300 nm are also synthesized.
The application of ultrasound dramatically increases the rate of exfoliation of
H x Ti 2Àx=4 O 4 ÁyH 2 O in the presence of aqueous tetrabutylammonium (TBA) hydroxide [130]. The effect of ultra sonication power and processing time on particle
size distributions are evaluated. Applied powers of 60–300 W and reaction times of
2–30 min effectively reduce the HaTi particle size to <100 nm. Both particle size
distribution analysis and UV–Vis spectroscopy were used to study the effect of the
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
144
as-prepared a-cobalt hydroxide in the form of a free ion state. b-Cobalt hydroxide
has also been prepared and formed as crystallized thin hexagonal platelets with a
diameter of 100 nm. Pure cobalt oxyhydroxide with a particle size of 10–30 nm has
also been obtained.
6.1.2.9 Sonochemical Preparation of Nanosized Titania
Because of its many applications, a few attempts are known in which ultrasonic
waves have been applied for the synthesis of nanosized titania. Yu and coworkers
[126] discovered a novel method for preparing highly photoactive nano-sized TiO 2
photocatalysts with anatase and brookite phases. The method has been developed
by hydrolysis of titanium tetraisopropoxide in pure water or a 1:1 EtOH:H 2 O solution under ultrasonic irradiation; the photocatalytic activity of TiO 2 particles prepared by this method exceeded that of Degussa P25.
Huang, in a similar reaction [127], found a way to selectively prepare anatase
or rutile as well as their mixtures. This was achieved by using various precursors
and employing ultrasound irradiation. The products, the particle sizes of which are
nanometric (<9 nm), are dependent both upon the reaction temperature and the
precursor used; a substantial reduction in reaction time, as well as reaction temperature is observed, as compared to the corresponding hydrothermal processes.
A novel sonochemical method for the direct preparation of anatase nanocrystalline TiO 2 was reported by Guo et al. [128]. Nanocrystalline TiO 2 was synthesized
by the hydrolysis of titanium tetrabutyl in the presence of water and ethanol under
high-intensity ultrasonic irradiation (20 kHz, 100 W cm
À2 at 363 K for 3 h.). The
structure and particle sizes of the product were dependent upon the reaction temperature, the acidity of the medium, and the reaction time. The TEM images
showed that the particles of TiO 2 were columnar in shape and the average sizes
were ca. 3 nm  7 nm. The sonochemical formation mechanism of nanocrystalline
TiO 2 is as follows: The hydrolytic species of titanium tetrabutyl in water condensed
to form a large number of tiny nuclei, which aggregated to form larger clusters.
Ultrasound irradiation generated many local hot spots within the gel, and the
crystal structural unit was formed near the hot spots with decrease in the gel nuclei, which led to the formation of nanocrystal particles.
A process has been developed for the formation of titania whiskers and nanotubes with the assistance of sonication [129]. Titanate whiskers are obtained as a
slender sheet with length about 1 mm and width 60 nm; arrays of titania whiskers
with diameter 5 nm are prepared from the titanate whiskers; titania nanotubes (see
Figure 6.7) with diameter about 5 nm, and length 200–300 nm are also synthesized.
The application of ultrasound dramatically increases the rate of exfoliation of
H x Ti 2Àx=4 O 4 ÁyH 2 O in the presence of aqueous tetrabutylammonium (TBA) hydroxide [130]. The effect of ultra sonication power and processing time on particle
size distributions are evaluated. Applied powers of 60–300 W and reaction times of
2–30 min effectively reduce the HaTi particle size to <100 nm. Both particle size
distribution analysis and UV–Vis spectroscopy were used to study the effect of the
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
144