Elsevier

Materials Letters

Volume 70, 1 March 2012, Pages 181-184
Materials Letters

Facile preparation of graphene sheets from synthetic graphite

https://doi.org/10.1016/j.matlet.2011.12.002Get rights and content

Abstract

Graphene sheets were prepared from the raw graphite by 67–70% HNO3 oxidation under refluxing at 140 °C for 4 h, followed by the treatment with KOH powder in an automatic mortar at room temperature for 1 h and subjecting to the 1-methyl-2-pyrrolidinone (NMP) solution for exfoliation. The obtained graphene sheets were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, atom force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The KOH in the process was found to play a key role in the preparation of the graphene sheets and can be regarded as a reducing agent.

Highlights

► A facile method for preparation of graphene sheets was developed. ► The KOH was found to play a key role in preparation of graphene sheets. ► The KOH in the process can be regarded as a reducing agent.

Introduction

Graphene, a one-atom-thick with sp2-hydridized carbon structure and two-dimensional individual sheet morphology which resulting in its extraordinarily remarkable electronic, thermal and mechanical properties, has been received growing number of attentions [1]. Many efforts have been devoted to prepare the graphene with individual or few layers, including micromechanical exfoliation of highly ordered pyrolytic graphite oxide [2], epitaxial growth [3], chemical vapor deposition [4], [5], thermal exfoliation [6], bottom–up assembly [7], electrostatic deposition[8], liquid phase exfoliation of graphite [9], [10], [11], arc-discharging [12] and solvothermal method [13]. Among these methods, micromechanical cleavage is currently the most effective and reliable method to produce high-quality graphene sheets. However, it is unsuitable for large scale production of graphene sheets because of its low productivity. Therefore, working with chemically modified forms of graphene may provide a powerful solution. It is demonstrated that exfoliation of graphite oxide either by rapid thermal expansion or ultrasonic dispersion has been one of the best approaches to obtain graphene in bulk. Herein, in this letter, we present a facile method by liquid phase exfoliation of synthetic graphite to prepare graphene sheets from raw graphite.

Section snippets

Experimental

The synthesis of graphene sheets was carried out by oxidation of 1.0 g synthetic graphite (purchased from Aldrich) in 100 mL 67–70% HNO3 at 140 °C by refluxing for 4 h. Then, the reaction solution was cooled down to room temperature. The graphite powder was filtered, washed, and dried in an oven. After that, 0.5 g dried graphite powder was ground with 3.5 g KOH powder (RDH) in an automatic mortar at room temperature for 1 h. Then, the mixed graphite powder and KOH were put into 200 mL distilled water

Results and discussion

As shown in Fig. 1a, the raw synthetic graphite exhibits an irregular morphology with a stack of carbon layers. The size of the graphite is about 1 μm. And we found that the flakes are dark, thick and large, showing the original graphite structure. The inset of the Fig. 1a is the selected area electron diffraction pattern of the graphite. The clearly diffraction rings corresponded to its typical crystal structure of raw graphite. Fig. 1b shows the obtained dispersions upon ultrasonication and

Conclusions

In conclusion, we have demonstrated an effective and facile liquid phase exfoliation of graphite oxide to make graphene sheets. The KOH was found to be a key reactant to produce the graphene sheets and make the graphene reduced. We believe in that this effective synthetic method presented here may provide the way for successfully employing graphene for microelectronics, photovoltaic, composites and energy storage and conversion applications.

Acknowledgement

The authors would like to thank for the support from “The Fundamental Research Funds for the Central Universities”.

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