▎ 摘　　要

Graphene oxide (GO) made from graphite oxidation by Hummer's method is a mixture of GO sheets with different size and thickness. Previous work has shown that these GO sheets have different electrophoretic properties and can be separated via capillary electrophoresis according to their surface charge U. Zhao et al., Anal. Chem. 83 (2011) 9100-9106). Herein, the GO sheets were separated by density gradient centrifugation to achieve preparation of bulk GO materials. GO sheets were separated by their thicknesses and the as-obtained sheets were characterized for their spectroscopic, electronic and electrochemical properties. After treated by hydrazine, GO was derivatized with N element and become active toward oxygen reduction reaction. The thin layer GO sheets incorporated with more hydrazine and the atomic ratio of N/C was higher than thick layer GO sheets. This work suggested that the physicochemical properties of GO sheets were N of layer related and it is necessary to separate GO sheets to prepare suitable materials for device fabrication or catalysts use. (C) 2013 Elsevier B.V. All rights reserved.