1.6.2 Properties and Structure of Graphene
Graphene is a zero band-gap semiconductor, and its unique electronic properties
show a low absorption ratio of 2.3% of light and an unpredictably high cloudiness of
atomic monolayer (Kuzmenko et al. 2008). Fundamentally, graphene shows fascinating properties, such as high charge carrier mobility (100,000 cm
2 V
À1 s
À1 ), large
surface area (2630 m
2 g
À1 ), Young’s modulus (~1100 GPa), high thermal conductivity (2000–5000 W m K
À1 ), large electric current density (10
8 A cm
À2 ), and superb
mechanical strength (2.4 Æ 0.4 TPa) (Upadhyay et al. 2014). These unique properties makes graphene an interesting material for several applications in liquid crystal
devices, solar cells, capacitors, sensors, batteries, and water treatment (Upadhyay
et al. 2014). Graphene is the basic building blocks for several C allotropes, such as
fullerenes (0 D), graphite (3 D), and carbon nanotubes (1 D) (Fu and Wang 2011a).
Two sub-lattices of C atoms in the graphene lattice are linked with the s and p
orbitals of each C atom in the lattice, and this contributes to the electron delocalization network. Graphene’s structure is defect-free since similar types of atoms are
bonded by flexible and strong bonds, which contributes to the extraordinary properties of graphene.
1.6.3 Synthesis of Graphene
Using a Scotch tape, graphene was initially prepared using the manual mechanical
cleavage of graphite (Novoselov et al. 2004), and since then several synthetic
techniques have been reported (Allen et al. 2009). These techniques are the
bottom-up and top-down methods (Allen et al. 2009). The bottom-up method is
the direct fabrication of graphene from molecules or atoms through chemical
reactions. Some typical examples of the bottom-up methods includes chemical
vapor deposition (CVD) on the surface of metal foil, solvothermal, organic synthesis, and epitaxial growth on single crystals of silicon carbide (Emtsev et al. 2009).
However, the bottom-up approaches are not broadly used owing to their high cost
and complexity of the substrates. Currently, high-quality GR sheet with a distinct
molecular structure has been fabricated by the top-down approaches, such as electrochemical synthesis (Guo et al. 2009), unzipping of carbon nanotubes (Jiao et al.
2010), chemical exfoliation of graphite (Park et al. 2009), arc discharge
(Subrahmanyam et al. 2009), micromechanical cleavage (Schedin et al. 2007), liquid
phase exfoliation of graphite (Zhou et al. 2014a), thermal exfoliation (McAllister
et al. 2007), electrostatic deposition (Tung et al. 2009), and chemical reduction of
graphene oxides (Compton and Nguyen 2010). The synthesis techniques of
graphene for environmental remediation application must be simple, efficient on a
large scale, and cost-effective. However, not all these techniques are possible for
water/wastewater treatment. Up to now, there have been a few reports on the
fabrication of pristine graphene for water/wastewater treatment. Through a facial
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
11
Graphene is a zero band-gap semiconductor, and its unique electronic properties
show a low absorption ratio of 2.3% of light and an unpredictably high cloudiness of
atomic monolayer (Kuzmenko et al. 2008). Fundamentally, graphene shows fascinating properties, such as high charge carrier mobility (100,000 cm
2 V
À1 s
À1 ), large
surface area (2630 m
2 g
À1 ), Young’s modulus (~1100 GPa), high thermal conductivity (2000–5000 W m K
À1 ), large electric current density (10
8 A cm
À2 ), and superb
mechanical strength (2.4 Æ 0.4 TPa) (Upadhyay et al. 2014). These unique properties makes graphene an interesting material for several applications in liquid crystal
devices, solar cells, capacitors, sensors, batteries, and water treatment (Upadhyay
et al. 2014). Graphene is the basic building blocks for several C allotropes, such as
fullerenes (0 D), graphite (3 D), and carbon nanotubes (1 D) (Fu and Wang 2011a).
Two sub-lattices of C atoms in the graphene lattice are linked with the s and p
orbitals of each C atom in the lattice, and this contributes to the electron delocalization network. Graphene’s structure is defect-free since similar types of atoms are
bonded by flexible and strong bonds, which contributes to the extraordinary properties of graphene.
1.6.3 Synthesis of Graphene
Using a Scotch tape, graphene was initially prepared using the manual mechanical
cleavage of graphite (Novoselov et al. 2004), and since then several synthetic
techniques have been reported (Allen et al. 2009). These techniques are the
bottom-up and top-down methods (Allen et al. 2009). The bottom-up method is
the direct fabrication of graphene from molecules or atoms through chemical
reactions. Some typical examples of the bottom-up methods includes chemical
vapor deposition (CVD) on the surface of metal foil, solvothermal, organic synthesis, and epitaxial growth on single crystals of silicon carbide (Emtsev et al. 2009).
However, the bottom-up approaches are not broadly used owing to their high cost
and complexity of the substrates. Currently, high-quality GR sheet with a distinct
molecular structure has been fabricated by the top-down approaches, such as electrochemical synthesis (Guo et al. 2009), unzipping of carbon nanotubes (Jiao et al.
2010), chemical exfoliation of graphite (Park et al. 2009), arc discharge
(Subrahmanyam et al. 2009), micromechanical cleavage (Schedin et al. 2007), liquid
phase exfoliation of graphite (Zhou et al. 2014a), thermal exfoliation (McAllister
et al. 2007), electrostatic deposition (Tung et al. 2009), and chemical reduction of
graphene oxides (Compton and Nguyen 2010). The synthesis techniques of
graphene for environmental remediation application must be simple, efficient on a
large scale, and cost-effective. However, not all these techniques are possible for
water/wastewater treatment. Up to now, there have been a few reports on the
fabrication of pristine graphene for water/wastewater treatment. Through a facial
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
11