Reduced graphene oxide (RGO) is an intriguing nanomaterial with tremendous potential for many applications. Although considerable efforts have been devoted to develop the reduction methods, it still needs further improvement, and how to choose an appropriate one for a specific application is a troublesome problem. In this study, RGOs were prepared by six typical reduction methods: N 2 H 4 3 H 2 O, NaOH, NaBH 4 , solvothermal, high-temperature, and two-step. The samples were systematic compared by four aspects: dispersibility, reduction degree, defect repair degree, and electrical conductivity. On the basis of the comparison, a simple evaluation criterion was proposed for qualitatively judging the quality of RGO. This evaluation criterion would be helpful to understand the mechanism of reduction and design more ideal reduction methods.

A simple density gradient ultracentrifuge separation method has been developed for sorting chemically modified graphene (CMG) by sheet size and surface chemistry in just a few minutes. By optimizing the parameters, including the density gradient and centrifugation time, CMG sheets with specific size ranges and optical properties can be targeted selectively. UV-vis absorbance and photoluminescence spectra revealed the properties of separated CMG samples are highly dependent on their sheet size and degree of oxidation. A possible mechanism for the separation is discussed.