16.3 Synthesis of Graphene

Analogous to all other nanomaterial synthesis procedures, graphene can also be syn­

thesized by top-down and bottom-up approaches. The synthetic approaches adopted for

the synthesis of graphene are schematically represented in Figure 16.2. The top-down

synthetic strategy involves breaking down the starting materials into graphene layers and

is a destructive technique.

The major top-down approaches adopted for the synthesis of graphene include ex­

foliation of graphite and graphite derivatives creating nano-sized graphene sheets [4].

Other top-down approaches adopted for the synthesis of graphene are mechanical ex­

foliation, liquid-phase exfoliation, arc discharge, oxidative exfoliation, reduction, and

unhooking of carbon nanotubes (CNTs) [25–27]. Top-down approaches were adopted for

the synthesis of graphene isolates and split the graphite layers into single, bi-, tri-, and

multilayers of graphene. The major disadvantages encountered in the top-down synthetic

strategy are its poor yields and uneven properties, which are related to the quality of the

precursors adopted during the synthesis.

Another synthetic method is known as the bottom-up technique, which customs atomic-

sized carbon precursor rather than graphite to nurture graphene and its derivatives and is

regarded as the construction technique of graphene synthesis. In the bottom-up method,

the assembly of graphene was produced from minor carbonaceous materials. Graphene can

be generally synthesized utilizing numerous bottom-up methods, namely, chemical vapor

deposition (CVD) substrate-free gas-phase synthesis (SFGP), epitaxial growth, template

route, and total organic synthesis [28]. The advantages of the bottom-up technique over

the top-down approach include the production of uniform and perfect graphene layers

possessing a high surface area. Bottom-up synthetic methods were relatively expensive

compared to the top-down approach.

Diverse materials can be employed as precursors towards the synthesis of graphene,

with variable gradations of success. Solid forms are the widely studied and conventional

precursors used for the synthesis of graphene, but liquid and gas precursors were also

found to be effective. The ideal precursors suitable for the synthesis of graphene were

found to be renewable resources but these materials should be systematically estimated,

and the environmental impacts connected with the renewable resource should be thor­

oughly investigated. The precursors chosen can be of various types, ranging from con­

ventional precursors to advanced starting materials such as carbon nanotubes. Figure 16.3

describes the potential precursors adopted for the synthesis of graphene.

FIGURE 16.2

Schematic representation of the synthetic approaches adopted for graphene.

Source: (Reproduced from Nanotechnology Reviews 2020; 9: 1284–1314: licensed under creative commons attri­

bution 4.0).

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