96
M. H. Köhler et al.
higher than that of pure GO under CO 2 stimulation and, upon removal of CO 2 by
Ar bubbling, a high rejection rate of dye molecules and MgCl 2 is achieved—without
noticeable degradation of the water permeability.
Stability is another critical factor for GO/rGO lamellar membranes. Most of the
studies focus on creating covalent or non-covalent bonds between adjacent GO/rGO
sheets. Different cross-linking molecules and ions, such as polyions, multivalent
cations, dopamine, glutaraldehyde, and diamine can borrow structural stability to
the membrane. Functionalization by Janus particles has also been used to reinforce these structures. The incorporation of asymmetrically functionalized Janus
GO (JGO) sheets in GO films exhibited extraordinary stability in the water at broad
pH values even under agitation [50]. These structures present dual interfaces (i.e.,
hydrophilic and hydrophobic) that interact with the extended π-systems on adjacent
nanosheets. The approach also allows for high molecular retention of charged and
uncharged dye molecules, rhodamine B, and brilliant blue G compounds, while
maintaining water permeability comparable with previously reported GO-based
membranes under osmotic pressure.
In addition to the approaches described above, a new trend to better control the
properties of GO-based membranes is the combination with other materials forming
hybrid structures, aiming to increase both permeability and selectivity. Other 2D
materials such as graphitic carbon nitrides (g-C 3 N 4 ) and MXenes can ideally engage
with GO membranes to produce enhanced nanofiltration devices.
The combination of GO membranes with g-C 3 N 4 aims to improve their antipressure ability and, with the addition of other materials (e.g., metal nanoparticles), add catalytic properties. This approach solves a limitation of the pure GO
membrane, enabling the degradation of molecules of environmental interest. It also
brings forward additional benefits, such as increasing the number of permeable
nanochannels, which allows for a twofold water permeability compared with traditional GO membranes [51]. GO/g-C 3 N 4 hybrid membranes also feature enhanced
stability and rigidity.
Wu et al. [52] developed different GO hybrid membranes with g-C 3 N 4 for
nanofiltration using glycine as a molecular binder. Contrary to expectations, the
carbon nitride group reduced nanochannel dimensions while the glycine led to
expanded channels. The hybrid membranes resulted in faster water transport, without
compromising the retention of dye molecules.
MXenes are a family of 2D materials based on transition metal carbides and
nitrides. Their structure and hydrophilicity allow for fast and selective transport of
water [53]. However, the retention of various molecules, such as dyes, is quite poor,
for the addition of GO/rGO layers can borrow a significant improvement.
A recent study described the preparation of a hybrid GO/MXene (Ti 3 C 2 T x )
membrane through vacuum filtration [54]. The resultant membrane presents a typical
lamellar structure with increased interlayer spacing compared with pristine GO. Both
hydrophilicity and increased space provide these membranes with excellent surface
wettability to water and organic solvents. For instance, high flow for pure solvents,
with emphasis on water (~21 L · m
−2 · h
−1 ), and excellent performance in the retention
of dyes (above 90%) were found for aqueous and organic solutions.
M. H. Köhler et al.
higher than that of pure GO under CO 2 stimulation and, upon removal of CO 2 by
Ar bubbling, a high rejection rate of dye molecules and MgCl 2 is achieved—without
noticeable degradation of the water permeability.
Stability is another critical factor for GO/rGO lamellar membranes. Most of the
studies focus on creating covalent or non-covalent bonds between adjacent GO/rGO
sheets. Different cross-linking molecules and ions, such as polyions, multivalent
cations, dopamine, glutaraldehyde, and diamine can borrow structural stability to
the membrane. Functionalization by Janus particles has also been used to reinforce these structures. The incorporation of asymmetrically functionalized Janus
GO (JGO) sheets in GO films exhibited extraordinary stability in the water at broad
pH values even under agitation [50]. These structures present dual interfaces (i.e.,
hydrophilic and hydrophobic) that interact with the extended π-systems on adjacent
nanosheets. The approach also allows for high molecular retention of charged and
uncharged dye molecules, rhodamine B, and brilliant blue G compounds, while
maintaining water permeability comparable with previously reported GO-based
membranes under osmotic pressure.
In addition to the approaches described above, a new trend to better control the
properties of GO-based membranes is the combination with other materials forming
hybrid structures, aiming to increase both permeability and selectivity. Other 2D
materials such as graphitic carbon nitrides (g-C 3 N 4 ) and MXenes can ideally engage
with GO membranes to produce enhanced nanofiltration devices.
The combination of GO membranes with g-C 3 N 4 aims to improve their antipressure ability and, with the addition of other materials (e.g., metal nanoparticles), add catalytic properties. This approach solves a limitation of the pure GO
membrane, enabling the degradation of molecules of environmental interest. It also
brings forward additional benefits, such as increasing the number of permeable
nanochannels, which allows for a twofold water permeability compared with traditional GO membranes [51]. GO/g-C 3 N 4 hybrid membranes also feature enhanced
stability and rigidity.
Wu et al. [52] developed different GO hybrid membranes with g-C 3 N 4 for
nanofiltration using glycine as a molecular binder. Contrary to expectations, the
carbon nitride group reduced nanochannel dimensions while the glycine led to
expanded channels. The hybrid membranes resulted in faster water transport, without
compromising the retention of dye molecules.
MXenes are a family of 2D materials based on transition metal carbides and
nitrides. Their structure and hydrophilicity allow for fast and selective transport of
water [53]. However, the retention of various molecules, such as dyes, is quite poor,
for the addition of GO/rGO layers can borrow a significant improvement.
A recent study described the preparation of a hybrid GO/MXene (Ti 3 C 2 T x )
membrane through vacuum filtration [54]. The resultant membrane presents a typical
lamellar structure with increased interlayer spacing compared with pristine GO. Both
hydrophilicity and increased space provide these membranes with excellent surface
wettability to water and organic solvents. For instance, high flow for pure solvents,
with emphasis on water (~21 L · m
−2 · h
−1 ), and excellent performance in the retention
of dyes (above 90%) were found for aqueous and organic solutions.