chemically induced self-transformation (Qi et al. 2016) method has been used to
synthesize several hierarchical hollow microspheres, such as CaCO 3 , TiO 2 , Al 2 O 3 ,
SnO 2 , and WO 3 . The mechanism of the in situ template-free assembly differs from
the chemically induced self-transformation (Li et al. 2016). The chemically induced
self-transformation involves the creation of hollow interiors through chemical etching of the primary particles, while the in situ template-free assembly involves the
self-assembly of nanosized building blocks around the nuclei (Yu et al. 2006).
1.6 Graphene
Nanomaterials with unique properties can be used to design new technologies, as
well as improving the performance of existing processes due to their nanoscale
dimensions. Nanomaterials have been used to solve major environmental issues,
such as contaminant sensing, energy production, and water treatment (Qu et al.
2013). The latest nanomaterials to capture the interest of researchers is graphene
(GR), which is a two-dimensional (2D) layer of carbon (C) atoms arranged in a
honeycomb crystalline structure (Geim 2009). The interest is due to its unique and
notably exceptionally large surface area, physicochemical properties, excellent
mechanical strength, thermal and electron mobility.
1.6.1 History of Graphene
Graphene is a thin layer hexagonal crystal structure comprising a 2D monolayer
planar sheet of sp
2 -bonded C atoms. Graphene is the building block of graphite with
the π-stacking sheets holding the lamellar graphite structure (Hontoria-Lucas et al.
1995). The interlayer spacing between the sheets was recorded at 3.34 Å (HontoriaLucas et al. 1995). Through a micromechanical cleavage route, graphene was
initially synthesized from graphite (Novoselov et al. 2004). This method permits
easy fabrication of high-quality GR crystallites, which can lead to massive experimental process (Katsnelson 2007). Under ultrahigh vacuum (<1010 torr) and elevated temperatures, monolayer flakes of carbon with graphene structure were
obtained via the epitaxial sublimation of silicon from silicon carbide (SiC) monolayer (Van Bommel et al. 1975). The term “graphene” was described as a singleatom carbon sheet by Boehm et al. (1986). This graphene sheet showed a transparent, flat, and monolayer sheetlike honeycomb structure comprising a single layer of
sp
2 -bonded C atoms with a C–C bond length of 1.42 Å. The 2D crystals of graphene
were thermodynamically unstable under ambient conditions (Yusuf et al. 2015).
However, Novoselov et al. (2004) successfully isolated and characterized a mechanically exfoliated graphene monolayer.
10
F. Opoku et al.
synthesize several hierarchical hollow microspheres, such as CaCO 3 , TiO 2 , Al 2 O 3 ,
SnO 2 , and WO 3 . The mechanism of the in situ template-free assembly differs from
the chemically induced self-transformation (Li et al. 2016). The chemically induced
self-transformation involves the creation of hollow interiors through chemical etching of the primary particles, while the in situ template-free assembly involves the
self-assembly of nanosized building blocks around the nuclei (Yu et al. 2006).
1.6 Graphene
Nanomaterials with unique properties can be used to design new technologies, as
well as improving the performance of existing processes due to their nanoscale
dimensions. Nanomaterials have been used to solve major environmental issues,
such as contaminant sensing, energy production, and water treatment (Qu et al.
2013). The latest nanomaterials to capture the interest of researchers is graphene
(GR), which is a two-dimensional (2D) layer of carbon (C) atoms arranged in a
honeycomb crystalline structure (Geim 2009). The interest is due to its unique and
notably exceptionally large surface area, physicochemical properties, excellent
mechanical strength, thermal and electron mobility.
1.6.1 History of Graphene
Graphene is a thin layer hexagonal crystal structure comprising a 2D monolayer
planar sheet of sp
2 -bonded C atoms. Graphene is the building block of graphite with
the π-stacking sheets holding the lamellar graphite structure (Hontoria-Lucas et al.
1995). The interlayer spacing between the sheets was recorded at 3.34 Å (HontoriaLucas et al. 1995). Through a micromechanical cleavage route, graphene was
initially synthesized from graphite (Novoselov et al. 2004). This method permits
easy fabrication of high-quality GR crystallites, which can lead to massive experimental process (Katsnelson 2007). Under ultrahigh vacuum (<1010 torr) and elevated temperatures, monolayer flakes of carbon with graphene structure were
obtained via the epitaxial sublimation of silicon from silicon carbide (SiC) monolayer (Van Bommel et al. 1975). The term “graphene” was described as a singleatom carbon sheet by Boehm et al. (1986). This graphene sheet showed a transparent, flat, and monolayer sheetlike honeycomb structure comprising a single layer of
sp
2 -bonded C atoms with a C–C bond length of 1.42 Å. The 2D crystals of graphene
were thermodynamically unstable under ambient conditions (Yusuf et al. 2015).
However, Novoselov et al. (2004) successfully isolated and characterized a mechanically exfoliated graphene monolayer.
10
F. Opoku et al.