96
Y. S. Dzyazko et al.
hydrated zirconium oxide (Fig. 1b, c). Thus, isolated aggregates are observed in
TEM images. Since the GO nanosheets are distributed on the particle surface, oxide
nanoparticles cannot be recognized clearly. However, it is possible to suggest that
their size is smaller in comparison with pure zirconium oxide. When the content of
GO is rather small, the composite has been found to contain some regions, which
are free from GO. Since GO tends to aggregation, its aggregates are also present
in the composite. They are observed as traces. Carbon is chemically transformed
under the action of accelerated electrons of microscope. As a result, degradation of
GO structure occurs. Then carbon is reprecipitated on copper substrate. Nanosized
bubbles are formed in this manner (they are visible as white spots).
Heterogeneity of the composite can be also caused by neutrality of zirconiumcontaining complexes ([Zr 4 (OH) 16 (H 2 O) 8 ] n [35]). Moreover, sol is strongly acidic
medium, where functional groups of GO are not dissociated. It means there is no electrostatic interaction of the complexes with GO surface. Regarding weakly charged
particles, such as quartz sand, their interaction with GO is sufficient at pH > 4 [36].
However, the support nanoparticles can be easily obtained, namely, from sol.
The GO-containing composite based on hydrated zirconium dioxide is effective
for adsorption of toxic Pb
2+ ions as well as organic compounds, such as phenol and
lactose.
The effect of loosening of oxide structure was also observed for rGO-containing
composite that was used for adsorption of elemental mercury [37]. Manganese oxide
(Mn x O y ), which contained Mn 2 O 3 and MnO 2 phases, was used as a support. It was
obtained by precipitation from an Mn(NO 3 ) 2 solution. During synthesis, Mn
2+ ions
were bound with O atoms of the negatively charged oxygen-containing functional
groups of the GO sheets via electrostatic forces. Further Mn x O y nanoparticles were
deposited in situ on the GO nanosheets, and then GO was reduced with a hydrothermal
method. Thus, the rGO-containing composite was obtained via GO.
TEM image shows that pure Mn x O y consists of elongated rod-like formations
(the diameter of their cross section is more than 100 nm) and particles, a shape of
which is close to spherical (about 500 nm and even larger). The globular particles are
characterized by uneven serrated surface. It means, they are aggregates of primary
particles, which cannot be recognized exactly. Smaller Mn x O y particles (10−20 nm)
have been found for the composite; they are clearly visible due to weak aggregation.
As suggested, most of the rGO sheets are embedded in the Mn x O y . However, no
confirmation of this suggestion is given (Fig. 2).
Magnetic properties of GO-containing composite adsorbents are achieved by a
combination of the carbon materials with Fe 3 O 4 [38–44]. The materials are obtained
using mainly hydrothermal synthesis. This is necessary to provide transformation of
Fe(II)/Fe(III) hydroxides to magnetic oxide and to avoid GO degradation. In order
to enhance adsorption properties of Fe 3 O 4 , additional functionalization is carried
out: particularly EDTA [38] or amines [44] are used for this purpose. Different
types of functionalizing agents are considered in [40]. For obtaining rather large
beads, magnetic GO nanoparticles are supported, for instance, by β-cyclodextrin/poly
(l-glutamic acid) [41] or chitosan [43].
Y. S. Dzyazko et al.
hydrated zirconium oxide (Fig. 1b, c). Thus, isolated aggregates are observed in
TEM images. Since the GO nanosheets are distributed on the particle surface, oxide
nanoparticles cannot be recognized clearly. However, it is possible to suggest that
their size is smaller in comparison with pure zirconium oxide. When the content of
GO is rather small, the composite has been found to contain some regions, which
are free from GO. Since GO tends to aggregation, its aggregates are also present
in the composite. They are observed as traces. Carbon is chemically transformed
under the action of accelerated electrons of microscope. As a result, degradation of
GO structure occurs. Then carbon is reprecipitated on copper substrate. Nanosized
bubbles are formed in this manner (they are visible as white spots).
Heterogeneity of the composite can be also caused by neutrality of zirconiumcontaining complexes ([Zr 4 (OH) 16 (H 2 O) 8 ] n [35]). Moreover, sol is strongly acidic
medium, where functional groups of GO are not dissociated. It means there is no electrostatic interaction of the complexes with GO surface. Regarding weakly charged
particles, such as quartz sand, their interaction with GO is sufficient at pH > 4 [36].
However, the support nanoparticles can be easily obtained, namely, from sol.
The GO-containing composite based on hydrated zirconium dioxide is effective
for adsorption of toxic Pb
2+ ions as well as organic compounds, such as phenol and
lactose.
The effect of loosening of oxide structure was also observed for rGO-containing
composite that was used for adsorption of elemental mercury [37]. Manganese oxide
(Mn x O y ), which contained Mn 2 O 3 and MnO 2 phases, was used as a support. It was
obtained by precipitation from an Mn(NO 3 ) 2 solution. During synthesis, Mn
2+ ions
were bound with O atoms of the negatively charged oxygen-containing functional
groups of the GO sheets via electrostatic forces. Further Mn x O y nanoparticles were
deposited in situ on the GO nanosheets, and then GO was reduced with a hydrothermal
method. Thus, the rGO-containing composite was obtained via GO.
TEM image shows that pure Mn x O y consists of elongated rod-like formations
(the diameter of their cross section is more than 100 nm) and particles, a shape of
which is close to spherical (about 500 nm and even larger). The globular particles are
characterized by uneven serrated surface. It means, they are aggregates of primary
particles, which cannot be recognized exactly. Smaller Mn x O y particles (10−20 nm)
have been found for the composite; they are clearly visible due to weak aggregation.
As suggested, most of the rGO sheets are embedded in the Mn x O y . However, no
confirmation of this suggestion is given (Fig. 2).
Magnetic properties of GO-containing composite adsorbents are achieved by a
combination of the carbon materials with Fe 3 O 4 [38–44]. The materials are obtained
using mainly hydrothermal synthesis. This is necessary to provide transformation of
Fe(II)/Fe(III) hydroxides to magnetic oxide and to avoid GO degradation. In order
to enhance adsorption properties of Fe 3 O 4 , additional functionalization is carried
out: particularly EDTA [38] or amines [44] are used for this purpose. Different
types of functionalizing agents are considered in [40]. For obtaining rather large
beads, magnetic GO nanoparticles are supported, for instance, by β-cyclodextrin/poly
(l-glutamic acid) [41] or chitosan [43].