After the discovery of carbon-based nanostructures, two-dimensional (2D) graphene has attracted intensive research
attention because of its unique properties. Mono layer graphene with remarkable properties such as high thermal conductivity
of the order of 5000 W m-1K -1, large specific surface area of 2630 m2 g-1,
high intrinsic mobility of 2 × 105 cm2 V-1 s-1,
Young’s modulus of 1.0 TPa, and high electrical conductivity have high potential for different high tech applications. Owning
to its unique properties such as low flake resistance and good transmittance, graphene was applied in different electronic
devices including the organic light emitting diodes and touch screen displays. Note that the outstanding mechanical and
chemical stability of 2D graphene make it unique and exclusive to rigid indium tin oxide (ITO). In addition, possessing
comprehensive absorption ranging from ultraviolet to infrared and ultrafast response, graphene could be used in different
photodetectors and various optical modulators. Graphene has also illustrated superior potential for fabricating highly
effective storage devices, such as solar cells, supercapacitors, and lithium-ion batteries. Due to the numerous applications
of graphene, there is a need to develop a commercially viable method for mass production of high-quality graphene. This is a
critical issue if different industries are to use novel 2D graphene material for large scale applications. To date, some
methods have been reported for mass production of mono layer graphene, such as chemical vapor deposition (CVD), chemical
exfoliation, exfoliation methods by micromechanical cleavage, and liquid-phase ultrasonic exfoliation. Among these methods,
the CVD has been used extensively for production of graphene. In order to synthesize mono- and few-layered graphene sheets
with CVD method, precursors react on transition metal substrates at high temperature. The CVD is able to synthesize mono-
or few-layered graphene with superior quality; however, the approach requires stringent manufacturing conditions such as high
vacuum and high temperature. Note that the CVD method is also size-limited, which is the major problem of this method. In
addition, in CVD the transfer procedure from the surface of metal to target substrates may induce some defects, leading to
low-quality graphene and associated deteriorating performance. The bulk graphite as a layered material possesses strong
in-plane chemical bonds and weak out-of-plane interactions, which correspond to the van der Waals forces. Therefore,
exfoliation of bulk graphite to thin graphene flakes with thickness of nanometer is possible. To take advantage of this
idea, micromechanical cleavage was introduced. However, the micromechanical cleavage has shown very low performance and
can produce extremely low amount of few-layered graphene. As a low-cost and highly scalable method, chemical exfoliation
was suggested for synthesizing mono- or few-layered graphene, in some cases with exfoliation yield of ~100%. This method
comprises of synthesizing graphene oxide (GO) through chemical oxidation of graphite and subsequent exfoliation via
ultrasonic. Obviously, the presence of structural defects restricts the applications of graphene in electronic and optical
devices. Liquid-phase exfoliation refers to a group of approaches that exfoliate bulk graphite into thin graphene
(mono- or few-layered graphene) directly in the liquid media. The lack of chemical oxidation is an advantage of this method.
Liquid-phase exfoliation includes:
i) Various ultrasonic exfoliation techniques such as liquid phase exfoliation by surfactants, organic solvents, ionic liquids,
and salts.
ii) Electrochemical exfoliation in different liquid media.
iii) Shear exfoliation methods such as high shear mixing, wet ball milling, microfluidization and homogenization.
iv) In situ Functionalization and Exfoliation