carried out separately, both with and without the use of a triblock copolymer.
Without thermal treatment, mesoporous TiO 2 was formed by the agglomeration of
monodispersed TiO 2 sol particles. The use of ultrasound irradiation assisted in the
formation of the brookite phase. As the content of the brookite phase increased,
the pore size and the crystalline sizes of anatase and brookite became larger when
the triblock copolymer was used in the synthesis. Both as-prepared samples exhibited better activities than the commercial photocatalyst P25 in the degradation
of n-pentane in air. The degradation rate of mesoporous TiO 2 synthesized in the
presence of triblock copolymer was about two times greater than that of P25. The
high activities of the mesoporous TiO 2 with a bicrystalline framework can be attributed to the combined effect of three factors: high brookite content, high surface
area, and the existence of mesopores.
Two other MSP oxides were recently reported by Srivastava [114, 115]. Both
preparations used the alkoxides of the metals as the inorganic precursor and CTAB
as the template. The first report details the preparation of MSP SnO 2 [114]. The
porous tin oxide prepared in this way was used in dye-sensitized solar cells.
The second paper [115] describes the synthesis of mesoporous iron oxide. Iron
(III) ethoxide was used as an inorganic precursor and CTAB as an organic structure directing agent. After sonication, the surfactant was removed by calcination
and solvent extraction methods. FTIR spectra demonstrated the removal of the
surfactant from the pores of the mesoporous iron oxide. The surface area after
solvent extraction is found to be 274 m
2 g
À1 . The as-prepared amorphous Fe 2 O 3
shows paramagnetic behavior, but after calcination at 350
C it changes to g-Fe 2 O 3
with good magnetic properties. The catalytic activity of mesoporous iron oxide was
studied in the reaction of cyclohexane oxidation under mild conditions. The mesoporous Fe 2 O 3 catalyst showed 36% conversion of cyclohexane into cyclohexanone
and cyclohexanol, with a high selectivity. This is the highest conversion percentage
ever reported for the oxidation of cyclohexane. The oxidation was conducted under
1 atm of O 2 at 70
C.
MSP titania was also used to make electrodes, which were tested in a dyesensitized solar cell [116]. The short-circuit photocurrent, open-circuit photovoltage
and fill factor increased with increasing sintering temperature, having a performance threshold at 450
C, showing that the more ordered structures are required
for high solar cell conversion efficiencies.
Rana [117] has recently demonstrated that ultrasound radiation can be employed
for the formation of vesicular mesoporous silica. The dimension of the vesicles
ranged from 50–500 nm. If the synthesis is compared with a previous work on the
synthesis of MSP silica vesicles [118], the advantages of the sonochemical synthesis are as follows: (1) It employs the commonly used CTAB as a surfactant, instead
of Gemini surfactant, C n H 2nþ1 NH(CH 2 ) 2 NH 2 ; (2) the sonochemical reaction takes
1 h as compared with 48 h; (3) the reaction is conducted at 25–35
C instead of
100
C; and (4) a higher surface area is obtained, 940, as compared with 280–
520 m
2 g
À1 . The special role of the bubbles in the formation of the vesicle is also
explained.
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
142
Without thermal treatment, mesoporous TiO 2 was formed by the agglomeration of
monodispersed TiO 2 sol particles. The use of ultrasound irradiation assisted in the
formation of the brookite phase. As the content of the brookite phase increased,
the pore size and the crystalline sizes of anatase and brookite became larger when
the triblock copolymer was used in the synthesis. Both as-prepared samples exhibited better activities than the commercial photocatalyst P25 in the degradation
of n-pentane in air. The degradation rate of mesoporous TiO 2 synthesized in the
presence of triblock copolymer was about two times greater than that of P25. The
high activities of the mesoporous TiO 2 with a bicrystalline framework can be attributed to the combined effect of three factors: high brookite content, high surface
area, and the existence of mesopores.
Two other MSP oxides were recently reported by Srivastava [114, 115]. Both
preparations used the alkoxides of the metals as the inorganic precursor and CTAB
as the template. The first report details the preparation of MSP SnO 2 [114]. The
porous tin oxide prepared in this way was used in dye-sensitized solar cells.
The second paper [115] describes the synthesis of mesoporous iron oxide. Iron
(III) ethoxide was used as an inorganic precursor and CTAB as an organic structure directing agent. After sonication, the surfactant was removed by calcination
and solvent extraction methods. FTIR spectra demonstrated the removal of the
surfactant from the pores of the mesoporous iron oxide. The surface area after
solvent extraction is found to be 274 m
2 g
À1 . The as-prepared amorphous Fe 2 O 3
shows paramagnetic behavior, but after calcination at 350
C it changes to g-Fe 2 O 3
with good magnetic properties. The catalytic activity of mesoporous iron oxide was
studied in the reaction of cyclohexane oxidation under mild conditions. The mesoporous Fe 2 O 3 catalyst showed 36% conversion of cyclohexane into cyclohexanone
and cyclohexanol, with a high selectivity. This is the highest conversion percentage
ever reported for the oxidation of cyclohexane. The oxidation was conducted under
1 atm of O 2 at 70
C.
MSP titania was also used to make electrodes, which were tested in a dyesensitized solar cell [116]. The short-circuit photocurrent, open-circuit photovoltage
and fill factor increased with increasing sintering temperature, having a performance threshold at 450
C, showing that the more ordered structures are required
for high solar cell conversion efficiencies.
Rana [117] has recently demonstrated that ultrasound radiation can be employed
for the formation of vesicular mesoporous silica. The dimension of the vesicles
ranged from 50–500 nm. If the synthesis is compared with a previous work on the
synthesis of MSP silica vesicles [118], the advantages of the sonochemical synthesis are as follows: (1) It employs the commonly used CTAB as a surfactant, instead
of Gemini surfactant, C n H 2nþ1 NH(CH 2 ) 2 NH 2 ; (2) the sonochemical reaction takes
1 h as compared with 48 h; (3) the reaction is conducted at 25–35
C instead of
100
C; and (4) a higher surface area is obtained, 940, as compared with 280–
520 m
2 g
À1 . The special role of the bubbles in the formation of the vesicle is also
explained.
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
142