114
S. Pakdel et al.
colloidal stability in water, nanopores’ generation, and excellent mechanical behavior
[13, 14]. GO is an oxidized form of graphene that is considered to be the thinnest
and strongest material with an extended one-atom sheet of sp
2 -bonded carbon atoms
[15–17]. Moreover, reduced GO (rGO) is another important derivative of graphene,
with similar properties as GO that has been used in membrane separation technology
[18]. The structure of the GO is supposed to be a network of sp
2 -hybridized –C–C–
atoms, with approximately 55% of sp
3 C–O bonds in the form of carboxyl, hydroxyl,
or epoxy groups [19]. These polar oxygen units facilitated aqueous dispersion and
also brought positive consequences in terms of declining sheet conductivity. Hence,
an effective removal of these oxygen species from GO for production of rGO is
important in many applications, such as linear and non-linear conductive polymer
nanocomposite fabrication [20–23].
Alternatively, GO is a better candidate for constructing free-standing and
polymer–GO hybrid membranes for water separation processes because of the wide
availability of reactive surface sites and the layered structure. GO nanosheets display
great antifouling capacity that is a significant desired property in the field of water
desalination processes [24, 25]. GO-based thin membranes display promising qualities in the field of water-permeable membrane to be employed in the desalination
procedure [26, 27]. GO has also revealed to be effective in allowing the permeation of
water, while subsequently blocking penetration of other liquids, vapors, or gases [28].
Ideally, the membranes should be mechanically and chemically stable against high
pressures over a long period of operation, while maintaining their desired water flux
and ion rejection characteristics. The manufacturing processes of thin-film composite
(TFC) membranes, which consist of a substrate and an interfacial polymerized skin
layer, have been developed for water purification [29–31]. In these membranes, GO
can be used as nanofillers to improve the membrane permselectivity [32].
The nanofillers such as graphene, GO, and rGO have strong interaction with the
polymer chain as well as monotonic good dispersion in the polymer matrix. This
results in increasing the mechanical strength and thermal stability of the membrane.
Moreover, the hydrophilic functional groups bound onto GO improve the wetting
properties of the hydrophobic polymer membrane [33]. The GO sheets as twodimensional (2D) nanofillers can effectively modify the physicochemical properties
of the polymer matrix due to their large surface area and functional groups as well as
their intrinsic mechanical and thermal stability [34, 35]. However, pristine graphene
is not compatible with organic polymers, GO sheets containing epoxide, hydroxyl,
diol, carboxyl, and ketone functional groups are known to modify the interactions
of GO sheets and polymer matrix and consequently make them compatible [36]. In
the past 5 years, numerous studies have been carried out to fabricate polymer–GO
nanocomposite membranes [37–40]. Alternatively, several approaches to preparing
stacked graphene-based nanosheets or graphene-based polymer nanocomposites
have been discovered for their potential applications in the water treatment area.
One of these methods is to coat ultrathin, a few-layered graphene/GO/rGO sheets
on polymeric substrates [24, 41–43]. The manufactured composite membranes all
displayed upgraded filtration performance. For instance, Han et al. [41] synthesized
ultrathin graphene nanofiltration (NF) membrane using vacuum filtration of rGO
S. Pakdel et al.
colloidal stability in water, nanopores’ generation, and excellent mechanical behavior
[13, 14]. GO is an oxidized form of graphene that is considered to be the thinnest
and strongest material with an extended one-atom sheet of sp
2 -bonded carbon atoms
[15–17]. Moreover, reduced GO (rGO) is another important derivative of graphene,
with similar properties as GO that has been used in membrane separation technology
[18]. The structure of the GO is supposed to be a network of sp
2 -hybridized –C–C–
atoms, with approximately 55% of sp
3 C–O bonds in the form of carboxyl, hydroxyl,
or epoxy groups [19]. These polar oxygen units facilitated aqueous dispersion and
also brought positive consequences in terms of declining sheet conductivity. Hence,
an effective removal of these oxygen species from GO for production of rGO is
important in many applications, such as linear and non-linear conductive polymer
nanocomposite fabrication [20–23].
Alternatively, GO is a better candidate for constructing free-standing and
polymer–GO hybrid membranes for water separation processes because of the wide
availability of reactive surface sites and the layered structure. GO nanosheets display
great antifouling capacity that is a significant desired property in the field of water
desalination processes [24, 25]. GO-based thin membranes display promising qualities in the field of water-permeable membrane to be employed in the desalination
procedure [26, 27]. GO has also revealed to be effective in allowing the permeation of
water, while subsequently blocking penetration of other liquids, vapors, or gases [28].
Ideally, the membranes should be mechanically and chemically stable against high
pressures over a long period of operation, while maintaining their desired water flux
and ion rejection characteristics. The manufacturing processes of thin-film composite
(TFC) membranes, which consist of a substrate and an interfacial polymerized skin
layer, have been developed for water purification [29–31]. In these membranes, GO
can be used as nanofillers to improve the membrane permselectivity [32].
The nanofillers such as graphene, GO, and rGO have strong interaction with the
polymer chain as well as monotonic good dispersion in the polymer matrix. This
results in increasing the mechanical strength and thermal stability of the membrane.
Moreover, the hydrophilic functional groups bound onto GO improve the wetting
properties of the hydrophobic polymer membrane [33]. The GO sheets as twodimensional (2D) nanofillers can effectively modify the physicochemical properties
of the polymer matrix due to their large surface area and functional groups as well as
their intrinsic mechanical and thermal stability [34, 35]. However, pristine graphene
is not compatible with organic polymers, GO sheets containing epoxide, hydroxyl,
diol, carboxyl, and ketone functional groups are known to modify the interactions
of GO sheets and polymer matrix and consequently make them compatible [36]. In
the past 5 years, numerous studies have been carried out to fabricate polymer–GO
nanocomposite membranes [37–40]. Alternatively, several approaches to preparing
stacked graphene-based nanosheets or graphene-based polymer nanocomposites
have been discovered for their potential applications in the water treatment area.
One of these methods is to coat ultrathin, a few-layered graphene/GO/rGO sheets
on polymeric substrates [24, 41–43]. The manufactured composite membranes all
displayed upgraded filtration performance. For instance, Han et al. [41] synthesized
ultrathin graphene nanofiltration (NF) membrane using vacuum filtration of rGO