Preparation of graphene by exfoliation of graphite using wet ball milling

Wet ball milling was used to exfoliate graphite platelets into graphenes in a liquid medium. Multi-layered graphite nanosheets with a thickness of 30 to 80 nm were dispersed into N,N-dimethylformamide (DMF) and exfoliated by shear-force-dominated ball milling carried out in a planetary mill. After high-speed centrifugation, irregular shaped single- and few-layer graphene sheets (<= 3 layers) having a thickness around 0.8-1.8 nm were found from the supernatant. The graphenes were identified and characterized using transmission and scanning electron microscopy, electron diffraction, atomic force microscopy and Raman spectroscopy. The electrical conductivity of the graphene powder was similar to 1.2 x 10(3) S m(-1) at room temperature.