▎ 摘　　要

Graphene sheets were prepared from the raw graphite by 67-70% HNO3 oxidation under refluxing at 140 degrees 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 (XI'S). 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. (C) 2011 Elsevier B.V. All rights reserved.