**1. Introduction**

Graphene is a 2D material, which was firstly discovered by Geim and Novoselov in 2004. They won Nobel Prize in Physics by synthesizing graphene including of sp2 carbon bonds via Scotch-tape method in 2010 [1, 2]. Graphene is a thin nanoplatelet, which can be produced by cleaving of graphite. Graphite can be downed into the single graphene sheet level [3]. Graphene is a one atomic layer having 0.34 nm thicknesses. Graphene is a single layer of carbon atoms organized in a honeycomb lattice [4]. It is the block of graphite that is used in pencil tips, but graphene is an extraordinary matter with a multitude of astounding specialties that named it as wonder material [5]. It is a hexagonal shaped plane consisting of sp2 -carbon atoms [6, 7]. Graphene can be seemed as either uncoiled single-walled carbon nanotubes or a wide atomic sheet of graphite. Graphene has superior mechanical strength, thermal

conductivity, optical transparency, high mobility, room temperature quantum Hall effect and great electronic properties like Dirac-particles having a linear dispersion, transport energy gap and simply absorption coefficient of lights, thus it will become the favorable prospect after the silicon time [8, 9]. It is the thinnest substance at one atom thick, and also fabulously strong around 200 times stronger than steel [5]. Apart from that, graphene is a superb conductor of heat and electricity and has exciting light absorption capabilities. It is truthfully a material with wide potential for integrating in nearly any industry.

Graphene is a highly varied material and can be merged with other materials (involving gases and metals) to synthesize various materials with different exceptional qualities. Researchers proceed to examine its unexplored properties and possible applications such as touchscreens (for LCD or OLED displays), computer chips, transistors, batteries, supercapacitors, energy production, DNA sequencing, water filters, antennas, solar cells, and spintronics. This new 2D material has a prominent importance in present day. It is a quickly developing subject that flourishing novel concepts at incredible speed [10]. Graphene is extensively used substance in electronic industry such as field-effect transistor, transparent electrode, etc. The recent developments in surface area, optical, magnetic, and mechanical properties of functionalized graphene and the unique electronics have arisen new attitude of green technology and creative discovery for present complications such as photonic and electronic usages for ultrahigh-frequency graphene-based apparatus, anode for Li-ion battery, material science, ceramics, light natural gas tanks, medical science, sensors to identify sickness, supercapacitor, solar cell, desalination of seawater, smartphones, computers, satellites, planes, cars, building materials, obtaining protective coatings and rust free cars, nuclear clean up, transistors, sensors, electron microscopy, and bionics.

Graphene molecular structure includes of sp2 hybrid carbon atoms that were presented in **Figure 1a**. Sp2 hybrids supply σ bonds with adjacent carbon atoms. Each of σ bonds has the length of 1.42 A°. Excellent mechanical characteristics of graphene are obtained under favor of σ bonds.

Graphene gathers much interest particularly after Geim and Novoselov win the 2010 Nobel Prize in physics by obtaining it in 2004. To produce high-quality graphene in high amount is not easy and affordable. Most companies are using chemical vapor deposition (CVD) based processes. Also, mechanical and chemical exfoliation and chemical synthesis are the most preferred ways today. Other methods are unzipping of a nanotube and microwave irradiation [11].

In graphene synthesis, starting material is usually graphite. But different starting materials are also used in literature such as; rice husks [12], fenugreek seeds [13], hibiscus flower petals [14], camphor [15], alfalfa plants [16], petroleum asphalt [17]. Graphene synthesis ways are primarily separated under two main groups entitling as bottom-up and top-down methods as seen as in **Figure 2** [11].

**Figure 1.**

*(a) sp2 hybrids carbon atoms in graphene (b) sp2 hybrids of graphene carbon atoms connected to adjacent ones.*

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*Investigation of Alternative Techniques for Graphene Synthesis*

*Flow chart for available methods for synthesis of graphene sheets.*

In top-down approach, graphene is synthesized by using graphite or graphiteoxide with the help of different methods. In this method, carbon materials such as graphite, carbon nanotubes are starting substances, and they are peeled by using chemical, electrochemical or physical ways [18]. Main top-down techniques are micromechanical exfoliation, cleavage of graphite intercalated compounds (GICs), unzipping of carbon nanotubes (CNTs), arc discharge, cleavage of graphene oxide,

Liquid phase exfoliation is an efficient and productive way for synthesizing of single and few layered graphene. It has been considered as one of the most feasible approach for industrial production of graphene due to its scalability and low cost. Solvent – carbon source suspension was first sonicated for preparation of exfoliation. Due to not having defects and oxide groups in the graphene products synthesized by LPE, they are more suitable for use in the electronics industry than that are

The LPE can form a stable dispersion of monolayer or few-layer defect-free graphene, which only involves the exfoliation of natural graphite via high-shear mixing or sonication [19]. Prepared graphene dispersion was stabilized by used solvent. Solvent type has also importance in productivity of the graphene dispersion [20]. Solvent ensures both the stability of synthesized graphene mixture and its productiveness. Tetrahydrofuran (THF) and N,N-dimethyl-formamide (DMF) are advantageous solvents to get high quality of graphene merely they are poisonous and show low efficiency. Dibasic ester (DBE) is an a nontoxic and environmentalfriendly solvent and it was used for cleavage of graphite by Jiang et al. Its surface

Graphite can be exfoliated in liquid medium exploiting sound waves to form single layer, **Figure 3** [21]. Basically, exfoliation of carbon materials is a relatively

The exfoliation step of the LPE can be conducted by the sonication of graphite in different solvents. There are two types of sonication: tip and bath sonication. In this study, tip sonication treatment was applied to the graphite-solvent dispersions. Epoxy/graphene composite shows better mechanical properties due to direct ultrasonication of tip sonication, that generates higher sound pressures and intensity compared to bath sonication which is indirect ultrasonication [23, 24]. The direct sonication of graphite in a solvent having similar surface energy to graphite enables a

tension is 35.6 mJ/m−2 and solubility parameter is 9.7 [20].

economical and easy way to produce graphene [22].

*DOI: http://dx.doi.org/10.5772/intechopen.94153*

and liquid phase exfoliation.

**Figure 2.**

**2. Liquid phase exfoliation**

produced by other techniques.

**Figure 2.**

*Novel Nanomaterials*

for integrating in nearly any industry.

conductivity, optical transparency, high mobility, room temperature quantum Hall effect and great electronic properties like Dirac-particles having a linear dispersion, transport energy gap and simply absorption coefficient of lights, thus it will become the favorable prospect after the silicon time [8, 9]. It is the thinnest substance at one atom thick, and also fabulously strong around 200 times stronger than steel [5]. Apart from that, graphene is a superb conductor of heat and electricity and has exciting light absorption capabilities. It is truthfully a material with wide potential

Graphene is a highly varied material and can be merged with other materials (involving gases and metals) to synthesize various materials with different exceptional qualities. Researchers proceed to examine its unexplored properties and possible applications such as touchscreens (for LCD or OLED displays), computer chips, transistors, batteries, supercapacitors, energy production, DNA sequencing, water filters, antennas, solar cells, and spintronics. This new 2D material has a prominent importance in present day. It is a quickly developing subject that flourishing novel concepts at incredible speed [10]. Graphene is extensively used substance in electronic industry such as field-effect transistor, transparent electrode, etc. The recent developments in surface area, optical, magnetic, and mechanical properties of functionalized graphene and the unique electronics have arisen new attitude of green technology and creative discovery for present complications such as photonic and electronic usages for ultrahigh-frequency graphene-based apparatus, anode for Li-ion battery, material science, ceramics, light natural gas tanks, medical science, sensors to identify sickness, supercapacitor, solar cell, desalination of seawater, smartphones, computers, satellites, planes, cars, building materials, obtaining protective coatings and rust free cars,

nuclear clean up, transistors, sensors, electron microscopy, and bionics.

Each of σ bonds has the length of 1.42 A°. Excellent mechanical characteristics of

Graphene gathers much interest particularly after Geim and Novoselov win the 2010 Nobel Prize in physics by obtaining it in 2004. To produce high-quality graphene in high amount is not easy and affordable. Most companies are using chemical vapor deposition (CVD) based processes. Also, mechanical and chemical exfoliation and chemical synthesis are the most preferred ways today. Other methods are

In graphene synthesis, starting material is usually graphite. But different starting materials are also used in literature such as; rice husks [12], fenugreek seeds [13], hibiscus flower petals [14], camphor [15], alfalfa plants [16], petroleum asphalt [17]. Graphene synthesis ways are primarily separated under two main groups entitling as bottom-up and top-down methods as seen as in **Figure 2** [11].

hybrid carbon atoms that were

 *hybrids of graphene carbon atoms connected to adjacent ones.*

hybrids supply σ bonds with adjacent carbon atoms.

Graphene molecular structure includes of sp2

unzipping of a nanotube and microwave irradiation [11].

graphene are obtained under favor of σ bonds.

 *hybrids carbon atoms in graphene (b) sp2*

presented in **Figure 1a**. Sp2

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**Figure 1.** *(a) sp2*

*Flow chart for available methods for synthesis of graphene sheets.*

In top-down approach, graphene is synthesized by using graphite or graphiteoxide with the help of different methods. In this method, carbon materials such as graphite, carbon nanotubes are starting substances, and they are peeled by using chemical, electrochemical or physical ways [18]. Main top-down techniques are micromechanical exfoliation, cleavage of graphite intercalated compounds (GICs), unzipping of carbon nanotubes (CNTs), arc discharge, cleavage of graphene oxide, and liquid phase exfoliation.
