The
first laboratory method which was used to make graphene sheets involved a much
harder and more laborious method of isolating monolayer graphene sheet from
graphite by peeling of graphite. Ever since the first historical discovery of
making graphene large-scale synthetic approaches for the making of graphene has
become a necessity. Further research and methods has been introduced in order to
improve the quality of graphene as well as to increase the cost-efficiency of
it synthesis. The methodology for the synthesis of graphene is based on the
exfoliation of pristine graphite into single layers of graphene sheets by two
pathways, physical and chemical techniques81. The physical method
for the synthesis of graphene include mechanical cleavage of graphite by Scotch
tape protocol, epitaxial growth on silicon carbide substrate/wafer, chemical
vapor deposition (CVD) of graphene on metal, growth of graphene from
metal-carbon melts, exfoliation of graphite by ultrasonication, etc. The major
factor in such techniques is there draw backs in large scale production,
however, researchers has been able to synthesis high-quality graphene
regardless the draw-backs. The CVD is the most effective method for the mass
production of graphene while limiting the number of defects90. Mechanical exfoliation
method is know to have a poor reproducibility and is not amenable to
large-scale fabrication, however it produces graphene of less defects.
Epitaxial based method has little or no defects for every single graphene
island, however, the graphene produced is discontinuous. The total

The
alternative to the physical method is the chemical based method which includes
oxidation of graphite followed by reduction, unzipping of carbon nanotube by
control oxidation, and total organic synthesis of graphene81. The synthesis of GO
was first introduced by Brodie81 and years that followed
Staudenmaier96 was able to modify the
method which resulted in the production of highly oxidized GO in a one-step
reaction process. In the 1950s Hummers reported a more popular method and ever
since researchers has been modifying the Hummers method for the synthesis of
GO. The figure below shows the schematic chemical methods for the synthesis of
GO from 3 different methods.

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