Numerous single-layer graphene sheets prepared from natural graphite by non-chemical liquid-phase exfoliation

A simple method was used to produce a high concentration of single-layer graphene sheets in a single organic solvent system, without using any surfactants. In this experiment, the concentration of single-layer graphene sheets dispersed in solution increased as the sonication time increased, but damage occurred after performing sonication for 120 min. The concentration of single-layer graphene sheets was 0.915 mg/ml after sonication for 60 min. According to a transmission electron microscope image, the length of the single-layer graphene sheets was ~2-3 μm, and the width was 0.5-1 μm. The perfect single-layer graphene sheets and the defective single-layer graphene sheets were distinguished using selected-area electron diffraction. X-ray diffraction determined that the two-theta angle of the numerous single-layer graphene sheets on a (002) plane was 25.57°, but the `one layer´ graphene sheets produced no peak along the (002) plane. According to the Raman spectra, the ratio of I_D/I_G was 0.3, which indicated that the graphene sheets contained few defects.