Liquid phase exfoliation of graphite into few-layer graphene by sonication and microfluidization

A novel and practical method to exfoliate natural graphite powder into few-layer graphene (FLG) using a sequence of sonication and microfluidization in a mixture of N-methyl-2-pyrrolidone and NaOH has been demonstrated. The exfoliation process was examined with a variety of characterization techniques, including UV/Vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results show that the natural graphite was successfully exfoliated into graphene sheets after sonication and microfluidization process. The lateral size of the flakes is in the range of 0.5-2 mu m. The maximum achieved FLG concentration is 0.47 mg/ml, and the thickness of most of the obtained products is less than 5 layers. The value of ID/IG for the FLG is 0.59, which suggests a low number of defects and a high graphitic degree. Moreover, the obtained graphene dispersion was stable for more than 6 months.