nealed at 700
C, longer lifetimes were measured. The shorter lifetimes were attributed to concentration quenching.
This series of experiments was continued and we recently deposited sonochemically a nanolayer of Eu 2 O 3 on submicron-size titania [84]. Ultrasound irradiation of
a slurry of titania, europium nitrate, and ammonia in an aqueous medium for 120
min yielded an Eu 2 O 3 aTiO 2 nanocomposite.
Finally, europium oxide nanorods have been prepared by the sonication of an
aqueous solution of europium nitrate in the presence of ammonia [85]. The particle sizes measured from transmission electron micrographs and HRSEM are about
50 Â 500 nm (W Â L). Sonication of an aqueous solution of europium nitrate in
the presence of ammonia results in the precipitation of europium hydroxide: The
as-prepared material is europium hydroxide, as confirmed by TGA, DSC, XPS, and
Mo ¨ssbauer spectroscopy measurements, as well as by PXRD of the as-prepared
sample assisted by microwave irradiation
Eu
þ3
ðaqÞ þ 3H 2 O ! EuðOHÞ 3ðSÞ þ 3H
þ
ðaqÞ þ NH
þ4
ðaqÞ
ð5Þ
The presence of ammonium ion seems to be important for the formation of particles with morphology usually obtained in the absence of ammonia. In our case
this was confirmed by the absence of precipitate after sonicating a solution of
europium nitrate without addition of ammonia. Regarding the shape of the asprepared product, careful examination of TEM, HRSEM, and HRTEM micrographs reveals that the rod-shaped particles of europium hydroxide consist of a few
spherical particles aligned in one direction. The formation of europium hydroxide
nanorods may be explained as follows. The Eu(OH) 3 particles formed upon collapse of the bubbles adsorb NH 4
þ ions or ammonia on their surfaces, thus forming a monolayer and fusing them by hydrogen bonding. In this way ammonium
ions would be responsible for the observed morphology. This adsorption of NH 4
þ
on the surface of the particles is supported by the results of Sherif et al. [86], who
showed that ammonium nitrate (NH 4 NO 3 ) is adsorbed on the surface of the powder after precipitation. We also evoke in the explanation the microjets mentioned
above, and due to this very high velocity of liquid jets, the Eu(OH) 3 , nanoparticles
are pushed toward each other, forming the nanorods.
6.1.2.4 The Sonohydrolysis of Group 3A Compounds
A detailed study of the sonohydrolysis of Ga, Al, In and Tl was conducted by sonicating the chloride aqueous solutions of these metals. Unlike the sonication of
carbonyls, which resulted in nanophase amorphous products [6, 12], the sonication of inorganic salts such as GaCl 3 , InCl 3 , or TlCl 3 yields crystalline nanophase
products. The sonochemical reaction of an aqueous solution of GaCl 3 led to the
formation of GaO(OH) rolled up in a scroll-like layered structure to give cylinders
of 80–120 nm diameter and 500–600 nm in length [89]. Small amounts of metallic
Ga were incorporated with these tubes. The presence of zero-valent Ga (ca. 1%)
was demonstrated by the DSC spectrum, which displayed an endothermic peak at
29.2
C. The amount of metallic gallium is dependent on the irradiation time:
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
134
C, longer lifetimes were measured. The shorter lifetimes were attributed to concentration quenching.
This series of experiments was continued and we recently deposited sonochemically a nanolayer of Eu 2 O 3 on submicron-size titania [84]. Ultrasound irradiation of
a slurry of titania, europium nitrate, and ammonia in an aqueous medium for 120
min yielded an Eu 2 O 3 aTiO 2 nanocomposite.
Finally, europium oxide nanorods have been prepared by the sonication of an
aqueous solution of europium nitrate in the presence of ammonia [85]. The particle sizes measured from transmission electron micrographs and HRSEM are about
50 Â 500 nm (W Â L). Sonication of an aqueous solution of europium nitrate in
the presence of ammonia results in the precipitation of europium hydroxide: The
as-prepared material is europium hydroxide, as confirmed by TGA, DSC, XPS, and
Mo ¨ssbauer spectroscopy measurements, as well as by PXRD of the as-prepared
sample assisted by microwave irradiation
Eu
þ3
ðaqÞ þ 3H 2 O ! EuðOHÞ 3ðSÞ þ 3H
þ
ðaqÞ þ NH
þ4
ðaqÞ
ð5Þ
The presence of ammonium ion seems to be important for the formation of particles with morphology usually obtained in the absence of ammonia. In our case
this was confirmed by the absence of precipitate after sonicating a solution of
europium nitrate without addition of ammonia. Regarding the shape of the asprepared product, careful examination of TEM, HRSEM, and HRTEM micrographs reveals that the rod-shaped particles of europium hydroxide consist of a few
spherical particles aligned in one direction. The formation of europium hydroxide
nanorods may be explained as follows. The Eu(OH) 3 particles formed upon collapse of the bubbles adsorb NH 4
þ ions or ammonia on their surfaces, thus forming a monolayer and fusing them by hydrogen bonding. In this way ammonium
ions would be responsible for the observed morphology. This adsorption of NH 4
þ
on the surface of the particles is supported by the results of Sherif et al. [86], who
showed that ammonium nitrate (NH 4 NO 3 ) is adsorbed on the surface of the powder after precipitation. We also evoke in the explanation the microjets mentioned
above, and due to this very high velocity of liquid jets, the Eu(OH) 3 , nanoparticles
are pushed toward each other, forming the nanorods.
6.1.2.4 The Sonohydrolysis of Group 3A Compounds
A detailed study of the sonohydrolysis of Ga, Al, In and Tl was conducted by sonicating the chloride aqueous solutions of these metals. Unlike the sonication of
carbonyls, which resulted in nanophase amorphous products [6, 12], the sonication of inorganic salts such as GaCl 3 , InCl 3 , or TlCl 3 yields crystalline nanophase
products. The sonochemical reaction of an aqueous solution of GaCl 3 led to the
formation of GaO(OH) rolled up in a scroll-like layered structure to give cylinders
of 80–120 nm diameter and 500–600 nm in length [89]. Small amounts of metallic
Ga were incorporated with these tubes. The presence of zero-valent Ga (ca. 1%)
was demonstrated by the DSC spectrum, which displayed an endothermic peak at
29.2
C. The amount of metallic gallium is dependent on the irradiation time:
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
134