Introduction
3
a
b
Fig. 2 a Stacking of GO nanosheets in the lamellar membrane and b nanoporous graphene
membrane. Here C: black, H: white, O: red, K + : blue, Na + : purple, Mg 2+ : orange and Cl − : cyan.
Figure is reproduced with permission from the Royal Society of Chemistry [11]
and reduced GO (rGO) which have been used for membrane fabrications. The freestanding graphene-family-based membranes mainly appear in two forms, (a) lamellar
membranes, formed by stacking of GO/rGO, and (b) nanoporous graphene membrane
where pore is generated using oxygen plasma, ion bombardment, etc. (Fig. 2).
As shown in Fig. 2a, water molecules typically permeate through the fabricated
nanochannel between each GO/rGO layer/sheets, while hydrated salt ions/pollutants
are blocked. On the other hand, water molecules could pass through the artificially
created desired nanopores in the graphene (called nanoporous membrane) to hinder
the permeation of large hydrated salt ions (Fig. 2b). Therefore, they have the potentiality for size-selective transport through the graphene nanopores. These membranes
significantly outperform the commercial polymeric membranes in terms of high water
flux and solute selectivity [12]. However, most of the GO-based membranes have a
tendency to be swelled in presence of water, compromising with solute selectivity
and have shown poor lifelong stability.
After tremendous efforts for graphene production, very recently, researchers are
motivated to synthesize its iso-structural form called hexagonal boron nitride (h-BN).
Similar to graphene, h-BN has good mechanical and thermal conductivity. In contrast,
h-BN has high thermal and chemical stabilities and a wide bandgap (5.5–5.9 eV) [14].
H-BN is also a layered 2D material, consisting of equal numbers of boron (B) and
nitrogen (N) atoms in an alternative way in a hexagonal lattice. Compared to carbon
in graphite, B-atoms are situated directly above or below corresponding N atoms as
shown in Fig. 3a, and the interlayer distance is almost 0.33 nm. Compared to C-C bond
in graphene, B-N bond in h-BN is partially ionic and therefore, would have good
interaction property for solutes. Despite having these leapfrogging properties, the
application of h-BN in separation science is sparsely reported. Recently, Chen et al.
fabricated amino-functionalized h-BN lamellar membrane as depicted in Fig. 3b–d
which retains solutes based on size-exclusion (molecular sieving) mechanism [13].
Very recently, transition metal disulfides (TMDS) that mainly include tungsten
disulfide (WS 2 ) and molybdenum disulfide (MoS 2 ) have found tremendous research
3
a
b
Fig. 2 a Stacking of GO nanosheets in the lamellar membrane and b nanoporous graphene
membrane. Here C: black, H: white, O: red, K + : blue, Na + : purple, Mg 2+ : orange and Cl − : cyan.
Figure is reproduced with permission from the Royal Society of Chemistry [11]
and reduced GO (rGO) which have been used for membrane fabrications. The freestanding graphene-family-based membranes mainly appear in two forms, (a) lamellar
membranes, formed by stacking of GO/rGO, and (b) nanoporous graphene membrane
where pore is generated using oxygen plasma, ion bombardment, etc. (Fig. 2).
As shown in Fig. 2a, water molecules typically permeate through the fabricated
nanochannel between each GO/rGO layer/sheets, while hydrated salt ions/pollutants
are blocked. On the other hand, water molecules could pass through the artificially
created desired nanopores in the graphene (called nanoporous membrane) to hinder
the permeation of large hydrated salt ions (Fig. 2b). Therefore, they have the potentiality for size-selective transport through the graphene nanopores. These membranes
significantly outperform the commercial polymeric membranes in terms of high water
flux and solute selectivity [12]. However, most of the GO-based membranes have a
tendency to be swelled in presence of water, compromising with solute selectivity
and have shown poor lifelong stability.
After tremendous efforts for graphene production, very recently, researchers are
motivated to synthesize its iso-structural form called hexagonal boron nitride (h-BN).
Similar to graphene, h-BN has good mechanical and thermal conductivity. In contrast,
h-BN has high thermal and chemical stabilities and a wide bandgap (5.5–5.9 eV) [14].
H-BN is also a layered 2D material, consisting of equal numbers of boron (B) and
nitrogen (N) atoms in an alternative way in a hexagonal lattice. Compared to carbon
in graphite, B-atoms are situated directly above or below corresponding N atoms as
shown in Fig. 3a, and the interlayer distance is almost 0.33 nm. Compared to C-C bond
in graphene, B-N bond in h-BN is partially ionic and therefore, would have good
interaction property for solutes. Despite having these leapfrogging properties, the
application of h-BN in separation science is sparsely reported. Recently, Chen et al.
fabricated amino-functionalized h-BN lamellar membrane as depicted in Fig. 3b–d
which retains solutes based on size-exclusion (molecular sieving) mechanism [13].
Very recently, transition metal disulfides (TMDS) that mainly include tungsten
disulfide (WS 2 ) and molybdenum disulfide (MoS 2 ) have found tremendous research