Novel Carbon-Based Nanoadsorbents for Removal of Synthetic Textile Dyes from Wastewaters - Green Chemistry for Dyes Removal from Wastewater - page 41

two-dimensional honeycomb network (Figure 2.3) [48]. It is the thinnest,
yet strongest material known to man, being both brittle and ductile simul-
taneously [49,50]. In its purest form, graphene is impermeable to even the
smallest gas molecules, including Helium. This one-atom-thick allotrope
of carbon can be viewed as the basic structural unit of other carbon allo-
tropes. It can be wrapped into zero-dimensional fullerenes, rolled into
one-dimensional CNTs, or can be stacked into three-dimensional graphite
(Figure 2.4) [51].
A hexagonal unit cell of graphene comprises two equivalent sub-lattices
of carbon atoms, joined together by σ bonds with a carbon-carbon bond
length of 0.142 nm [52]. Each carbon atom in the lattice has a π orbital
that contributes to a delocalized network of electrons, making graphene
sufficiently stable compared to other nanosystems [53]. Theoretical and
experimental studies have proved that graphene offers a unique combina-
tion of high three-dimensional aspect ratio and large specific surface area,
superior mechanical stiffness and flexibility, remarkable optical transmit-
tance, exceptionally high electronic and thermal conductivities, as well as
many other supreme properties, as shown in Table 2.1. Because of these
fascinating properties, it is not surprising that graphene has the potential
to be used in a plethora of applications across many fields. The wide range
Figure 2.3 Representation of the honeycomb lattice of graphene and its unit cell
(indicated by the dashed lines). The unit cell contains two atoms, each one belonging to a
different sub-lattice.