Graphene oxides as sorbents for liquid purification and separation: a physicochemical study

The features of sorption properties of oxidized graphite materials with respect to polar and non-polar liquids are considered. A direct comparison of sorption properties was carried out between a material with a high oxidation state - graphene oxide synthesized by the improved Hummers method, and weakly oxidized thermally expanded graphite. Differences in a number of physicochemical parameters were confirmed by X-ray phase analysis, infrared spectroscopy, X-ray photoelectron spectroscopy and differential scanning calorimetry. Graphene oxide, synthesized by the Hummers method, with a C/O ratio of $\approx$ 2.5 sorbs only polar liquids. Thermally expanded graphite, obtained by heat treatment of electrochemically oxidized graphite, with a C/O of $\approx$ 9.5 sorbs both polar and non-polar liquids. Differential scanning calorimetry has shown that the sorption values of polar liquids are comparable within the error limits for materials that differ significantly in oxidation states. It has been shown that sorption of water by materials based on thermally expanded graphite does not lead to their swelling. The ability to maintain a constant interplanar distance when interacting with aqueous media can make thermally expanded graphite a promising material for the manufacture of membranes capable of removing impurities from water.