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Top1. Introduction
Graphene is a two-dimensional material with a conducting mono atomic layer of carbon atoms arranged into benzene rings (Wallace, 1947; Novoselov et al., 2004; Geim & Novoselov, 2007), and Graphene Oxide (GO) is its insulating disordered analogue. GO was first discovered by Oxford chemist Benjamin Brodie in 1859; the experiment conducted for exfoliation of graphite via oxidation produces atomically thin GO sheets that are easily dispersible in organic and aqueous solvents. There have been various works to optimize the procedure for GO synthesizes with fewer defects and efficient oxidation in its basal plane (Cecilia et al., 2009; Wu et al., 2013).
GO has procured diverse applications in sensors (Koppens et al., 2014), optoelectronic devices (Bonaccorso et al., 2010), transparent electrodes (Kim et al., 2009) and as a transparent conducting layer for photovoltaic cells (Pospischil et al., 2014). Due to its low cost, it has a wide range of applications in flexible and stretchable textile (Yun et al., 2013). These wide applications motivated researchers to keep on searching for better ways for the synthesis of Graphene Oxide (GO) and reduced Graphene Oxide (rGO). Several synthesis (oxidation-reduction) mechanisms are available in literature such as Staudenmaier's, Hofmann's, Hummer's, modified Hummer's, improved Hummers', mild oxidation methods, etc. for oxidation and thermal, chemical, hydrothermal, etc. for reduction (Chen et al., 2013; Dreyer et al., 2010; Singh et al., 2011; Poh et al., 2012; Khan et al., 2017; Zhu et al., 2010; Kim et al., 2015). The atomically thin sheets of GO contain sp2 and sp3 hybridized carbon atoms, also abundant oxygen functional groups attached to its surface make it insulating and desirable for flexible electronics devices (Jung et al., 2008; Venugopal et al., 2012; Alam et al., 2017). The investigations by various research groups manifest that through chemical/thermal reduction of GO, electrical properties can be engineered (Baladin, 2008; Gomez-Navarro et al., 2010). Predominantly the chemical/thermal reduction process employs GO as a precursor for rGO. The rGO flakes obtained generally constitutes highly disordered regions of attached oxygen functional groups and is composed of nano-meter size conducting crystalline sp2 domains (Gomez-Navarro, et al., 2008). It affects the transport mechanism of rGO which results in high charge carrier mobility. Mayorov et al. (2011) reported > 105cm2v-1s-1charge carrier mobility of rGO quite high from that of pristine graphene.
Thus, comprehension of charge transport mechanism of rGO is imperative to optimize rGO based device applications. However, the research work reported so far lacks a clear understanding of the structural and electrical properties of rGO. In this study, different characterization tools like XRD, FTIR, Raman Spectroscopy and SEM analysis have been used to investigate the structure and morphology of GO and rGO films (Kim, 2016). This paper uses a mild oxidation method for graphene oxidation as it avoids evolution of toxic gases (Kumar et al., 2015) and chemical reduction for rGO using sodium borohydride. Withal the charge transport mechanism in GO and rGO film is analyzed by monitoring the variation of electrical conductivity with temperature. The methodology representation of tattered graphite synthesis to the product is shown in Figure 1.
Figure 1. Flowchart of GO synthesis and characterization methodology