Preparation of water-dispersible graphene using N-methylmorpholine N-oxide monohydrate and its application for the preparation of nanocomposites using PEDOT

Solid-state powders of water-dispersible graphene (GPN) were prepared by treatment of methylmorpholine N-oxide monohydrate (NMMOm). Re-dispersion of GPN in water by simple sonication was successfully demonstrated using a highly concentrated aqueous GPN solution (0.284 mg mL−1) after centrifugation at 9000 rpm for 10 min. The produced GPN had the graphitic structure without defects, and its electrical conductivity was 94.7 S cm−1, as measured from a filtered GPN film. The spin-coated thin film from the aqueous GPN solution exhibited a single-layered structure, which was examined using scanning electron microscopy, atomic force microscopy, and scanning transmission electron microscopy (with selective area electron diffraction). The GPN was also dispersible in polar solvents such as dimethyl sulfoxide, dimethylformamide, ethanol, and tetrahydrofuran. The origin of good dispersity of GPN in polar solvents, including water, was discussed with reference to the high polar nature of NMMO. A nanocomposite system with a water-soluble poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was prepared on a glass substrate. A fourfold improvement in the electrical conductivity of PEDOT:PSS without deterioration of transmittance was achieved by adding 1 wt% GPN.