74
A. S. Kazemi and M. A. Abdol
studies. Only recently, Kohler et al. [212] employed MD simulations to explore the
flocculation as a prominent factor in desalination through nano-porous graphene
and MoS 2 membranes. Although there are some insights now on the ideal size and
distribution of nanopores on the free-standing membranes regarding mechanical
robustness, there is no precise protocol with a clear definition of size and distribution
of the pores available to experimentalists.
Experimental gaps: Unlike simulations, experimental efforts towards realizing
nano-porous graphene membranes for RO technology, have confronted us with the
reality of this approach. With all the fascinating properties of 2D materials and
indeed graphene, there are some crucial experimental challenges we need to focus
on. Fabrication of industrial-scale continuous monolayer graphene without intrinsic
or extrinsic defects is at the forefront. With all the advances in perforation techniques,
we are still lacking a technology that creates well-defined pores ~1 nm in diameter.
Pore density is also an important factor for controlling the water permeability of
membranes based. Is the predicted pore density 10
12 pores/cm
2 an ideal number?
Likewise, the chemistry and geometry of pores can significantly impact the water
flux [26]. What about the support layer? There are few studies focused on the impact
of the support layer but there is no conclusion on the ideal type, thickness, porosity,
chemical and physical properties of this layer. No comprehensive experimental work
is yet reported on fouling challenges of nano-porous graphene membranes while
fouling mitigation is the most fundamental reason that motivates replacement of
the current RO membranes with nano-porous atomically thin membranes. Excessive
fouling deteriorates membrane performance and demands chemical cleaning which
results in short membrane life and increases energy consumption and consequently
the operating costs [63, 213]. Production at appropriate scale and cost, packaging into
modules that minimize concentration, and demonstration of long-term performance
under realistic conditions is essential [20]. These require further investigation to
achieve enhanced performance, toward a reduction of operating costs for desalination
plants.
6 Conclusions
Unique properties of pristine graphene such as atomic thickness, extreme flatness
and mechanical robustness, have motivated theoreticians and experimentalists to
exploit it for a new generation of membrane-based materials in water purification
and desalination technologies. Latest findings at the atomic level by MD simulations,
and experimental advancements in the fabrication of large-area free-standing nanoporous membrane was reviewed, the physical interplay of nanopores across graphene
membranes with ion transport was investigated and the challenges, prospects and gaps
were highlighted. Nano-porous graphene membranes represent tremendous potential
for advancing membrane technology and are likely to endure into the future.
A. S. Kazemi and M. A. Abdol
studies. Only recently, Kohler et al. [212] employed MD simulations to explore the
flocculation as a prominent factor in desalination through nano-porous graphene
and MoS 2 membranes. Although there are some insights now on the ideal size and
distribution of nanopores on the free-standing membranes regarding mechanical
robustness, there is no precise protocol with a clear definition of size and distribution
of the pores available to experimentalists.
Experimental gaps: Unlike simulations, experimental efforts towards realizing
nano-porous graphene membranes for RO technology, have confronted us with the
reality of this approach. With all the fascinating properties of 2D materials and
indeed graphene, there are some crucial experimental challenges we need to focus
on. Fabrication of industrial-scale continuous monolayer graphene without intrinsic
or extrinsic defects is at the forefront. With all the advances in perforation techniques,
we are still lacking a technology that creates well-defined pores ~1 nm in diameter.
Pore density is also an important factor for controlling the water permeability of
membranes based. Is the predicted pore density 10
12 pores/cm
2 an ideal number?
Likewise, the chemistry and geometry of pores can significantly impact the water
flux [26]. What about the support layer? There are few studies focused on the impact
of the support layer but there is no conclusion on the ideal type, thickness, porosity,
chemical and physical properties of this layer. No comprehensive experimental work
is yet reported on fouling challenges of nano-porous graphene membranes while
fouling mitigation is the most fundamental reason that motivates replacement of
the current RO membranes with nano-porous atomically thin membranes. Excessive
fouling deteriorates membrane performance and demands chemical cleaning which
results in short membrane life and increases energy consumption and consequently
the operating costs [63, 213]. Production at appropriate scale and cost, packaging into
modules that minimize concentration, and demonstration of long-term performance
under realistic conditions is essential [20]. These require further investigation to
achieve enhanced performance, toward a reduction of operating costs for desalination
plants.
6 Conclusions
Unique properties of pristine graphene such as atomic thickness, extreme flatness
and mechanical robustness, have motivated theoreticians and experimentalists to
exploit it for a new generation of membrane-based materials in water purification
and desalination technologies. Latest findings at the atomic level by MD simulations,
and experimental advancements in the fabrication of large-area free-standing nanoporous membrane was reviewed, the physical interplay of nanopores across graphene
membranes with ion transport was investigated and the challenges, prospects and gaps
were highlighted. Nano-porous graphene membranes represent tremendous potential
for advancing membrane technology and are likely to endure into the future.