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Methods of Graphene Synthesis

In this article, we are going to learn about the methods of Graphene Synthesis that are Hummers method, Chemical Vapor deposition, Chemical Exfoliation of Graphene, Electrochemical Exfoliation.
Submitted by Vandana Sharma, on November 15, 2017

There are several methods of synthesizing graphene and graphene oxide. A number of techniques for preparing graphene sheets have been developed but only a few yield graphene in appreciable quantity. Different methods of graphene synthesis are known for a decade and a long time back. Scientists have tried their best to achieve high-quality graphene. Among these methods, some methods are known for the simpler approach and some for high yields. Various methods like Solution based reduction of graphene oxide, chemical vapor deposition, Micromechanical exfoliation of graphite, electrochemical method and epitaxial growth on electrically insulating surfaces are known for graphene synthesis. Different methods are discussed below which employ the above-stated approaches.

1) Hummers Method

In this method powdered flake of graphite is mixed with NaNo3 and H2SO4. Next KMnO4 is added slowly by maintaining the required temperature. The temperature of the mixture is maintained below 5° C. The suspension is then reacted in an ice bath and stirred before again stirred in a 40° C water bath. The temperature of the mixture is constantly maintained while water is added continuously. Also, DI water is used for frequent treatments. In this method basically, graphite is converted into graphene oxide first and then into graphene. There are several modifications experimented on basic hummers approach in order to achieve modified graphene. However, assist is found that all the approaches are similar to the fundamental approach of producing graphene using hummers method. Some involve more chemicals and some use them at a later stage.

2) Chemical Vapor deposition

High-Quality graphene can be produced potentially on a large scale by employing this method.CVD is a process of depositing gaseous reactants onto a substrate. The gas molecules are combined in a gas chamber, a reaction occurs that creates a material film on the substrate surface. There is an outlet way to pump out the waste gases from the reaction chamber. The vital physical quantity to be controlled here is temperature. The solid compounds are vaporized and then deposited onto the substrate via condensation. This could be low-pressure chemical vapor deposition technique or high-pressure chemical vapor deposition technique, depending upon the requirement of quality of graphene that can be achieved using this method.

3) Chemical Exfoliation of Graphene

Larger quantities of graphene sheets can be formed by employing physical or chemical exfoliation of graphite. The interplanar spacing of graphite is 0.34nm which is not appreciable to have room for organic molecules/ions or other inorganic species. A number of intercalation strategies can be applied to extend the interlayer galleries of graphite from 0.34nm to higher values, which can attain more than 1nm. Graphite intercalation compounds (GICs) are stabilized between the graphene layers through ionic or polar interactions with no alteration of graphene structure. GICs can be formed not only with lithium, potassium, sodium but also with anions like nitrate, bisulfate, or halogens. In this approach solvents like ODCB, NMP and DMF are used in order to exfoliate graphite.

4) Electrochemical Exfoliation

It is one of the simplest and most handy methods for the large-scale production of graphene sheets. Herein, we describe a highly efficient plasma-assisted electrochemical exfoliation method, involving a plasma-generated graphite cathode and a graphite anode, for the production of graphene sheets from electrodes in a basic electrolyte solution in a short reaction time; the production rate of GSs is six times as fast as that from conventional electrochemical methods. In this method, electrolytes such as H2SO4, Na2SO4, KMNO4 and (NH4)2SO4 are used along with platinum wire and graphite rod. Platinum wire is used as cathode and graphite as an anode in this process. The electrochemical exfoliation takes place at different voltages and the fast process takes place.

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