Filtration Membranes Containing Nanoparticles of Hydrated …
759
The hydrophilicity of GO is mainly provided by functional groups: hydroxyl (C–
OH), epoxy groups (C–O–C), carboxyl (–COOH). Oxygen-containing functional
groups at the edges and in the plane of the graphene oxides are capable of both
covalent and ionic interaction with different species [47]. Theoretical calculations of
the specific surface area give a value of ≈2600 m
2 g
−1 . The experimental magnitudes,
which were obtained with a method of standard contact porosimetry involving water
or octane as working liquids [48–50], are 2200–2400 m
2 g
−1 [51–54].
Filtration of GO suspension through macroporous support allows one to obtain a
mechanically stable layer, which possesses ion sieving ability [55]. This layer is socalled “GO-membrane.” Its stability is provided by the metal contaminants that are
introduced during the synthesis and processing of GO nanosheets [56]. In fact, they
are cross-linked with multivalent ions, particularly alumina (this metal is released
from the porous filter during filtration of GO suspension in acid). Reduced GO and
carbon quantum dots also support mechanical stability of “GO membrane” [57].
Titanium dioxide was purposefully inserted to GO suspension: the layer rejects dye
molecules [58]. Another way is to fix GO in the volume [59, 60] or on the surface
of polymer membranes [61]. However, embedding GO additions to the polymer
matrix causes enlargement of its pores deteriorating rejection. Moreover, GO can be
removed from the membrane pores during pressure-driven separation. The GO layer
attached to the outer surface can be easily damaged.
The solution of these problems is embedding of GO-containing nanocomposite
based on inorganic ion exchanger directly to the pores of the polymer. The inorganic
ion exchanger will provide both binding and rejection functions. The secondary
porosity of the membranes caused by the nanocomposite will ensure the retention of
colloidal particles. The location of the nanocomposite in the pores of the active layer
of membranes will provide mechanical properties and resistance against organic
fouling due to the enhanced hydrophilicity.
2 Preparation of Composite Membranes
Commercial spectrally pure graphite was purchased from “Zaporizhskii graphit” Ltd.
Polymer ultrafiltration membranes were synthesized at the Institute of Physical
Organic Chemistry of the National Academy of Sciences of the Republic of Belarus.
The materials included the active PAN layer fixed at the macroporous substrate made
of non-woven ‘lavsan’ (polyethylene terephthalate). This combination provides the
necessary complex of membrane characteristics. The membranes were marked as
PAN-2, PAN-3, and PAN-4.
The membrane characteristics are listed in Table 1, where J is the flux of deionized
water at 1 bar, rejection corresponds to polyvinylpyrrolidone (40 kDa, the aqueous
solution contained 3 g dm
-3 of this substance).
Sol of insoluble zirconium hydroxocomplexes containing 1 M Zr(IV) was
prepared similar to [33, 34]. Globular primary nanoparticles (6 nm) and their aggregates dominated in sol [34]. The sol was stable: the particle size did not change over
759
The hydrophilicity of GO is mainly provided by functional groups: hydroxyl (C–
OH), epoxy groups (C–O–C), carboxyl (–COOH). Oxygen-containing functional
groups at the edges and in the plane of the graphene oxides are capable of both
covalent and ionic interaction with different species [47]. Theoretical calculations of
the specific surface area give a value of ≈2600 m
2 g
−1 . The experimental magnitudes,
which were obtained with a method of standard contact porosimetry involving water
or octane as working liquids [48–50], are 2200–2400 m
2 g
−1 [51–54].
Filtration of GO suspension through macroporous support allows one to obtain a
mechanically stable layer, which possesses ion sieving ability [55]. This layer is socalled “GO-membrane.” Its stability is provided by the metal contaminants that are
introduced during the synthesis and processing of GO nanosheets [56]. In fact, they
are cross-linked with multivalent ions, particularly alumina (this metal is released
from the porous filter during filtration of GO suspension in acid). Reduced GO and
carbon quantum dots also support mechanical stability of “GO membrane” [57].
Titanium dioxide was purposefully inserted to GO suspension: the layer rejects dye
molecules [58]. Another way is to fix GO in the volume [59, 60] or on the surface
of polymer membranes [61]. However, embedding GO additions to the polymer
matrix causes enlargement of its pores deteriorating rejection. Moreover, GO can be
removed from the membrane pores during pressure-driven separation. The GO layer
attached to the outer surface can be easily damaged.
The solution of these problems is embedding of GO-containing nanocomposite
based on inorganic ion exchanger directly to the pores of the polymer. The inorganic
ion exchanger will provide both binding and rejection functions. The secondary
porosity of the membranes caused by the nanocomposite will ensure the retention of
colloidal particles. The location of the nanocomposite in the pores of the active layer
of membranes will provide mechanical properties and resistance against organic
fouling due to the enhanced hydrophilicity.
2 Preparation of Composite Membranes
Commercial spectrally pure graphite was purchased from “Zaporizhskii graphit” Ltd.
Polymer ultrafiltration membranes were synthesized at the Institute of Physical
Organic Chemistry of the National Academy of Sciences of the Republic of Belarus.
The materials included the active PAN layer fixed at the macroporous substrate made
of non-woven ‘lavsan’ (polyethylene terephthalate). This combination provides the
necessary complex of membrane characteristics. The membranes were marked as
PAN-2, PAN-3, and PAN-4.
The membrane characteristics are listed in Table 1, where J is the flux of deionized
water at 1 bar, rejection corresponds to polyvinylpyrrolidone (40 kDa, the aqueous
solution contained 3 g dm
-3 of this substance).
Sol of insoluble zirconium hydroxocomplexes containing 1 M Zr(IV) was
prepared similar to [33, 34]. Globular primary nanoparticles (6 nm) and their aggregates dominated in sol [34]. The sol was stable: the particle size did not change over