Fractionation and characterization of graphene oxide by oxidation extent through emulsion stabilization

The conversion of graphite to graphite oxide (GO) is an effective and widely used method for solubilizing and exfoliating graphite. The oxidation is not uniform however, and wide variations in the degree of oxidation exist between and within batches of GO. In this article we introduce an approach to both quantify the global degree of oxidation in GO and to separate GO into fractions with more uniform extents of oxidation. Using the formation of GO stabilized oil-in-water emulsions, GO is separated into an emulsion fraction and a water fraction. We find GO sheets that stabilize the emulsion droplets are less oxidized than sheets suspended in water as shown by XRD, Raman spectroscopy, FTIR, elemental analysis and electrical conductance. The use of successive fractionation allows not only for the preparation of GO fractions with more narrowly defined properties, but also provides a method for characterizing GO batches. This promises to provide the field with a critical missing piece: a straightforward and standard method for the global characterization and comparison of GO made by different procedures and by different investigators. (C) 2015 Elsevier Ltd. All rights reserved.