published in Chemistry – A European Journal [96]. We will therefore repeat briefly
our early findings and introduce some new results.
The report demonstrates that ultrasound radiation can also be used for the
preparation of MSP materials. MSP silica, MCM-41 [97], MSP titania [98], and
YSZ (yittria stabilized zirconia) [99] were all prepared by this method. In addition,
straight-extended layered mesostructures based on transition metal (Fe, Cr) and
rare earth (Y, Ce, La, Sm, Er) oxides were also synthesized sonochemically [100].
The synthetic processes reproduced in most cases the already published sol–gel
synthesis [101]. The main advantage of the sonication method is the short irradiation time. In most cases the reaction time was 3 h. The longest sonication period
was 6 h. It was applied for the synthesis of MSP YSZ and caused the transformation of the product from a layered to a hexagonal mesostructure due to this
prolonged irradiation time. A second advantage of the sonochemical synthesis is
that the walls of the sonochemical product were thicker than those obtained conventionally (see Table 1, [97]). The thicker walls are responsible for the MCM-41
obtained sonochemically being more stable than MCM-41 prepared by conventional hydrothermal methods [102]. This was demonstrated when our product was
treated with pure water, and its crystallinity changed only a little after heating
under reflux for 6 h, and decreased by approximately 65% after heating under reflux for 12 h. In the literature [102] the MCM-41 prepared by using conventional
hydrothermal methods became amorphous after refluxing for 12 h.
During the formation of the framework, despite the agitation of the ultrasound,
which helps to disperse the small silica oligomers more homogeneously in the
mixture, the formation of hot spots within the surfactant–silicate interface may
accelerate the silica polymerization, which is slow and rate limiting under normal
conditions. Thus, the fabrication of the meso-structure can be achieved more efficiently. On the one hand, acoustic cavitation etches the surfactant–silicate micelles
on the surface; this results in a coarse outer surface or even the fragmentation of
the micelles. An additional factor is that hot spots accelerate the condensation of
surface silanol groups among micelles; in this way ultrasound radiation accelerates
the formation of the MCM-41 framework and the growth of particles.
The discovery of MSP materials led immediately to the development of many
experimental methods for the deposition of materials, especially catalysts, into the
mesopores. We have deposited Mo oxide, and Co/Mo oxides into MCM-41 as well
as into the pores of Al-MCM-41 [103]. We have also anchored Fe 2 O 3 into the mesopores of titania [104]. A large variety of nanoparticles has been introduced into
many MSP materials. This work, however, has not been published. In addition to
the characterization studies of the composite catalyst-mesoporous product, catalytic
studies have also been conducted.
The typical sonochemical reaction is performed as follows: a slurry of the MSP
material, for example, Al-MCM-41, in decalin containing dissolved Mo(CO) 6 and/
or Co(CO) 3 NO, is sonicated. The sonication is carried out under ambient air at
room temperature. The solid product is separated by centrifugation, thoroughly
washed with dry pentane, and dried in vacuum at room temperature. The chemical
composition of the solid phase was determined by EDAX to probe whether the
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
138
our early findings and introduce some new results.
The report demonstrates that ultrasound radiation can also be used for the
preparation of MSP materials. MSP silica, MCM-41 [97], MSP titania [98], and
YSZ (yittria stabilized zirconia) [99] were all prepared by this method. In addition,
straight-extended layered mesostructures based on transition metal (Fe, Cr) and
rare earth (Y, Ce, La, Sm, Er) oxides were also synthesized sonochemically [100].
The synthetic processes reproduced in most cases the already published sol–gel
synthesis [101]. The main advantage of the sonication method is the short irradiation time. In most cases the reaction time was 3 h. The longest sonication period
was 6 h. It was applied for the synthesis of MSP YSZ and caused the transformation of the product from a layered to a hexagonal mesostructure due to this
prolonged irradiation time. A second advantage of the sonochemical synthesis is
that the walls of the sonochemical product were thicker than those obtained conventionally (see Table 1, [97]). The thicker walls are responsible for the MCM-41
obtained sonochemically being more stable than MCM-41 prepared by conventional hydrothermal methods [102]. This was demonstrated when our product was
treated with pure water, and its crystallinity changed only a little after heating
under reflux for 6 h, and decreased by approximately 65% after heating under reflux for 12 h. In the literature [102] the MCM-41 prepared by using conventional
hydrothermal methods became amorphous after refluxing for 12 h.
During the formation of the framework, despite the agitation of the ultrasound,
which helps to disperse the small silica oligomers more homogeneously in the
mixture, the formation of hot spots within the surfactant–silicate interface may
accelerate the silica polymerization, which is slow and rate limiting under normal
conditions. Thus, the fabrication of the meso-structure can be achieved more efficiently. On the one hand, acoustic cavitation etches the surfactant–silicate micelles
on the surface; this results in a coarse outer surface or even the fragmentation of
the micelles. An additional factor is that hot spots accelerate the condensation of
surface silanol groups among micelles; in this way ultrasound radiation accelerates
the formation of the MCM-41 framework and the growth of particles.
The discovery of MSP materials led immediately to the development of many
experimental methods for the deposition of materials, especially catalysts, into the
mesopores. We have deposited Mo oxide, and Co/Mo oxides into MCM-41 as well
as into the pores of Al-MCM-41 [103]. We have also anchored Fe 2 O 3 into the mesopores of titania [104]. A large variety of nanoparticles has been introduced into
many MSP materials. This work, however, has not been published. In addition to
the characterization studies of the composite catalyst-mesoporous product, catalytic
studies have also been conducted.
The typical sonochemical reaction is performed as follows: a slurry of the MSP
material, for example, Al-MCM-41, in decalin containing dissolved Mo(CO) 6 and/
or Co(CO) 3 NO, is sonicated. The sonication is carried out under ambient air at
room temperature. The solid product is separated by centrifugation, thoroughly
washed with dry pentane, and dried in vacuum at room temperature. The chemical
composition of the solid phase was determined by EDAX to probe whether the
6 Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles
138