Aqueous two-phase extraction of graphene oxides

Graphene oxide (GO) is widely used as a graphene conversion material for transparent electrodes and conductive films via reduction treatment. However, GOs are typically provided as mixtures that include various chemical structures and oxidation degrees, including strongly damaged ones. Since the contamination of these defective GOs decreases the conductivity of the resulting reduced GOs (rGOs), purification methods to concentrate low-defect GOs are required. In this study, we successfully separated GOs via aqueous two-phase extraction using a combination of polyethylene glycol (PEG) and octylphenol ethoxylate (OPE). Based on the difference in hydrophobicity caused by the number of carboxy groups, low-defect GOs and defective GOs were extracted into the hydrophobic PEG-rich phase and the hydrophilic OPE-rich phase, respectively. The low-defect GOs were then converted into rGOs, which exhibited higher conductivity than the non-extracted pristine GOs. © 2020 The Japan Society of Applied Physics.