64
A. S. Kazemi and M. A. Abdol
at the atomistic scale. Some of these atomistic simulations have been used to predict
the contact angle of water on different surfaces [144, 145]. The contact angle value
depends on the chemical nature of the surface and other parameters, such as roughness
and chemical heterogeneity, which have been much less investigated from this theoretical approach. Another way for estimating solid—liquid interactions is to compute
the solid—liquid interfacial tension. Thermodynamic definitions of the interfacial
tension were used to compute the solid—liquid interfacial tension for graphene—
water systems [146]. Water transport mechanisms including velocity, viscosity and
slip length have also been studied in nano-porous atomically graphene membranes.
Since water structure, is confined in the radial direction and layered in the axial
direction of the pore, water viscosity and slip length increase with a decrease in the
pore radius [127].
4 Experimental Work on Nano-porous Graphene
Membranes
Practical attainment of nano-porous atomically thin membranes in RO systems
involves the following: (1) synthesis of a continuous large layer of the material,
(2) engineer of nanopores in terms of size and distribution and (3) the ability to
handle the materials using suitable porous supports. The latest achievements at the
experimental level in these fields are discussed in the following subsections.
4.1 Fabrication of Large-Area Graphene
CVD has emerged as a tunable and versatile method for producing continuous layers
of 2D materials over large areas [24, 147] and holds promise in RO membrane
fabrication. The CVD method for graphene synthesis was first reported in 2006 on a
Ni substrate [148]. Later in 2009, Li et al. [149] demonstrated large-area CVD growth
of monolayer graphene on copper, followed by roll-to-roll transfer of 0.76 m sheets
of CVD graphene by Samsung in 2010 [150]. Kobayashi et al. [151] from SONY
exhibited roll-to-roll synthesis and transfer of 100 m long graphene-coated films in
2013. Other techniques developed in recent years for the fabrication of graphene
sheets including micromechanical cleavage, liquid-phase exfoliation, and epitaxial
growth on SiC, result in high quality, small flakes, and low yield. Other methods like
self-assembly, electrochemical exfoliation, unzipping of carbon nanotubes (CNTs)
and reduction of graphene oxide either produce very small flakes or flakes of low
quality. Overall, apart from CVD and epitaxial growth, all the other methods lack
appropriate control over the number of layers [20, 27, 147, 152–155]. Figure 7
summarizes the main fabrication methods of graphene in terms of sheet area and cost.
A. S. Kazemi and M. A. Abdol
at the atomistic scale. Some of these atomistic simulations have been used to predict
the contact angle of water on different surfaces [144, 145]. The contact angle value
depends on the chemical nature of the surface and other parameters, such as roughness
and chemical heterogeneity, which have been much less investigated from this theoretical approach. Another way for estimating solid—liquid interactions is to compute
the solid—liquid interfacial tension. Thermodynamic definitions of the interfacial
tension were used to compute the solid—liquid interfacial tension for graphene—
water systems [146]. Water transport mechanisms including velocity, viscosity and
slip length have also been studied in nano-porous atomically graphene membranes.
Since water structure, is confined in the radial direction and layered in the axial
direction of the pore, water viscosity and slip length increase with a decrease in the
pore radius [127].
4 Experimental Work on Nano-porous Graphene
Membranes
Practical attainment of nano-porous atomically thin membranes in RO systems
involves the following: (1) synthesis of a continuous large layer of the material,
(2) engineer of nanopores in terms of size and distribution and (3) the ability to
handle the materials using suitable porous supports. The latest achievements at the
experimental level in these fields are discussed in the following subsections.
4.1 Fabrication of Large-Area Graphene
CVD has emerged as a tunable and versatile method for producing continuous layers
of 2D materials over large areas [24, 147] and holds promise in RO membrane
fabrication. The CVD method for graphene synthesis was first reported in 2006 on a
Ni substrate [148]. Later in 2009, Li et al. [149] demonstrated large-area CVD growth
of monolayer graphene on copper, followed by roll-to-roll transfer of 0.76 m sheets
of CVD graphene by Samsung in 2010 [150]. Kobayashi et al. [151] from SONY
exhibited roll-to-roll synthesis and transfer of 100 m long graphene-coated films in
2013. Other techniques developed in recent years for the fabrication of graphene
sheets including micromechanical cleavage, liquid-phase exfoliation, and epitaxial
growth on SiC, result in high quality, small flakes, and low yield. Other methods like
self-assembly, electrochemical exfoliation, unzipping of carbon nanotubes (CNTs)
and reduction of graphene oxide either produce very small flakes or flakes of low
quality. Overall, apart from CVD and epitaxial growth, all the other methods lack
appropriate control over the number of layers [20, 27, 147, 152–155]. Figure 7
summarizes the main fabrication methods of graphene in terms of sheet area and cost.