Direct production of highly conductive graphene with a low oxygen content by a microwave-assisted solvothermal method

Few-layer graphene (FLG) with a low oxygen content has been synthesized by a two-step process using expanded graphite (EG) as a starting material. EG was subjected to solvothermal treatment, followed by microwave radiation. The FLG had an average thickness in the range of 1.8-2 nm with a lateral size of 3-10 mu m. Both Raman spectroscopy and high resolution TEM measurements showed that the sizes of sp(2) carbon domains in graphene oxide (GO) and FLG were estimated to be about 2-5 nm and 10-16 nm, respectively. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy spectra revealed that the FLG consisted of several peaks similar to those of EG, which were not observed in GO, indicating the effectiveness of the solvothermal reduction method in lowering the oxygen level. The electrical conductivity of the as-synthesized FLG is measured to be 165 S/m, which is much higher than that of the GO (1.2 x 10(-4) S/m), possibly due to the larger sp(2) carbon domain size, lower oxygen content, and fewer structural defects. In contrast to the Hummer method, the method is simple, inexpensive, and does not generate toxic gas. This simple method could provide the synthesis of high quality FLG on a large scale. (C) 2013 Elsevier B.V. All rights reserved.