758
L. Rozhdestvenska et al.
When solutions contain organic molecular and colloidal species as well as
microorganisms, rapid clogging and fouling of membranes occur [8, 12–15]. Organic
impurities are accumulated inside the membrane pores deteriorating the membrane
elasticity [16]. In order to remove them, aggressive reagents are required for cleaning
[15, 17–20]. Their usage reduces a lifetime of polymer membranes. Another fouling
type is the adhesion of organic substances to the membrane surface, the cakes can be
easily removed by backwashing with permeate enhanced by air flux [21]. Accumulation of organic impurities is explained by the hydrophobicity of polymer materials
[22–24].
Modifying the outer surface of commercially available membranes with polymer
hydrophilic constituents allows one to prevent fouling and, as a result, to reduce the
operation costs of separation processes [25–28]. However, the protecting layer is
not always mechanically stable. Another way is to insert nanoparticles of inorganic
ion exchangers to the polymer matrix. Nanocomposite polysulfone membrane was
designed with 5% of Al 2 O 3 nanoparticles (20 nm, the modifier was in a form of
hydrated oxide) [29]. The contact angle was found to reach 56°. The rejection degree
toward BSA was 99%. In the case of larger particles (80 nm), the rejection was 96%.
Considerable BSA rejection was found also for microfiltration membrane modified
with hydrated zirconium dioxide (HZD) [30–32]. This ion exchanger forms smaller
nanoparticles comparing with zirconium hydrophosphate [31, 32]. Thus, it is precipitated directly in the active layer of the membrane. HZD was also applied to modifying ceramic [33, 34] or polymer [35] membranes for electrodialysis. As opposed,
zirconium hydrophosphate is precipitated in the macroporous support: the composite
membrane shows mush lower rejection, particularly during filtration of corn distillery
[31, 32, 36]. However, nanoparticles of this ion exchanger were obtained, when
the deposition inside ion exchange polymer occurs [35, 37, 38]. Other inorganic
modifiers for polymer filtration membranes are TiO 2 [39], silica [40]. Even Ag [41]
and CuO coupled with carbon nitride [42] have been proposed that the composite
membranes demonstrate antibacterial properties.
Now, carbon nanomaterials (one-dimensional nanotubes, CNT, and twodimensional graphene oxide, GO) are considered as prospective modifiers. The
fullerenes of CNTs provide a higher pore size on the membrane surface as well as
empty space called porosity in membrane structures [43]. However, the hydrophobicity of CNTs deteriorates their distribution in polymers, since they tend to agglomerate with each other. This leads to a decrease in the dispersion ability in a polymercontaining solvent during membrane preparation, and, as a result, a decline in the
compatibility of a membrane structure. The effect of synthesis conditions on nanotube
aggregation was examined in [44]. Functionalization of CNTs is expected to solve
those problems. The addition of 0.00084–0.0048% of nanotubes to polymers gives
a possibility to vary the transport properties of the hollow fibrous membranes in a
wide range [45]. Polyvinylpyrrolidone–polysulfone membrane modified with CNTs
was tested to estimate the possibility of its usage in hemodialysis [46]. The liquid
flux through the membrane was 0.72 dm m
−2 h
−1 , the rejection was found to achieve
56, 55, and 28% of urea, creatinine, and lysozyme, respectively.
L. Rozhdestvenska et al.
When solutions contain organic molecular and colloidal species as well as
microorganisms, rapid clogging and fouling of membranes occur [8, 12–15]. Organic
impurities are accumulated inside the membrane pores deteriorating the membrane
elasticity [16]. In order to remove them, aggressive reagents are required for cleaning
[15, 17–20]. Their usage reduces a lifetime of polymer membranes. Another fouling
type is the adhesion of organic substances to the membrane surface, the cakes can be
easily removed by backwashing with permeate enhanced by air flux [21]. Accumulation of organic impurities is explained by the hydrophobicity of polymer materials
[22–24].
Modifying the outer surface of commercially available membranes with polymer
hydrophilic constituents allows one to prevent fouling and, as a result, to reduce the
operation costs of separation processes [25–28]. However, the protecting layer is
not always mechanically stable. Another way is to insert nanoparticles of inorganic
ion exchangers to the polymer matrix. Nanocomposite polysulfone membrane was
designed with 5% of Al 2 O 3 nanoparticles (20 nm, the modifier was in a form of
hydrated oxide) [29]. The contact angle was found to reach 56°. The rejection degree
toward BSA was 99%. In the case of larger particles (80 nm), the rejection was 96%.
Considerable BSA rejection was found also for microfiltration membrane modified
with hydrated zirconium dioxide (HZD) [30–32]. This ion exchanger forms smaller
nanoparticles comparing with zirconium hydrophosphate [31, 32]. Thus, it is precipitated directly in the active layer of the membrane. HZD was also applied to modifying ceramic [33, 34] or polymer [35] membranes for electrodialysis. As opposed,
zirconium hydrophosphate is precipitated in the macroporous support: the composite
membrane shows mush lower rejection, particularly during filtration of corn distillery
[31, 32, 36]. However, nanoparticles of this ion exchanger were obtained, when
the deposition inside ion exchange polymer occurs [35, 37, 38]. Other inorganic
modifiers for polymer filtration membranes are TiO 2 [39], silica [40]. Even Ag [41]
and CuO coupled with carbon nitride [42] have been proposed that the composite
membranes demonstrate antibacterial properties.
Now, carbon nanomaterials (one-dimensional nanotubes, CNT, and twodimensional graphene oxide, GO) are considered as prospective modifiers. The
fullerenes of CNTs provide a higher pore size on the membrane surface as well as
empty space called porosity in membrane structures [43]. However, the hydrophobicity of CNTs deteriorates their distribution in polymers, since they tend to agglomerate with each other. This leads to a decrease in the dispersion ability in a polymercontaining solvent during membrane preparation, and, as a result, a decline in the
compatibility of a membrane structure. The effect of synthesis conditions on nanotube
aggregation was examined in [44]. Functionalization of CNTs is expected to solve
those problems. The addition of 0.00084–0.0048% of nanotubes to polymers gives
a possibility to vary the transport properties of the hollow fibrous membranes in a
wide range [45]. Polyvinylpyrrolidone–polysulfone membrane modified with CNTs
was tested to estimate the possibility of its usage in hemodialysis [46]. The liquid
flux through the membrane was 0.72 dm m
−2 h
−1 , the rejection was found to achieve
56, 55, and 28% of urea, creatinine, and lysozyme, respectively.