Preparation and physicochemical properties of nitrogen-doped graphene inks

Nitrogen-doped graphene ink is still not perfect for printing because of its low concentration, many defects, and easy agglomeration, limiting its use in functional printing devices. To solve these problems, nitrogen-doped graphene (NG) was prepared from nature flake graphite by a combined chemical oxidation-reduction and solvothermal method. It was dispersed in water with a help of a surfactant to prepare stable NG inks with a high NG content. Results indicate that the NG has a nitrogen content of 8.58 at% and an electrical conductivity of 257.2 S•m^-1. The stability of the dispersion of aqueous NG inks is regulated by controlling the mass ratio of the surfactant, sodium dodecyl sulfonate (SLS), sodium dodecyl sulfate (SDS), or sodium alkylbenzene sulfonate (SDBS), to NG. The physicochemical properties of the stable NG inks in water can be regulated by adding SLS, SDS, or SDBS in different proportions. The zeta potentials range from -50 to -90 mV, viscosities from 1 to 3 mPa•s and surface tensions from 30.8 to 71.9 mN/m. A uniform NG line with a width of 250 μm is printed by uniform droplet spraying with an optimized NG ink. The NG in the line is uniformly distributed to form an excellent film. This work suggests a simple method for the production of stable NG inks, which might pave the way for preparing NG-based functional devices.