Graphene nanosheets reduced by a multi-step process as high-performance electrode material for capacitive deionisation

We employed a novel three-step reduction of graphite oxide (GO) to obtain graphene nanosheets with high specific surface area and good dispersion in aqueous solution. Iron powder, as a mild and environmentally friendly reducing agent, was used at first in partial-reduction of GO and then, sulphonic functional groups (-SO3-) were introduced on the surface of partially reduced GO. The negatively charged -SO3- units can effectively prevent the graphitic sheets from aggregating and enhance specific surface area of graphene nanosheets after further reduction by hydrazine. The resulting graphene nanosheets exhibited a high specific surface area of 464 m ²/g with mean pore size of 3.3 nm and specific capacitance of 149.8 F/g. Electrodes based on this kind of graphene nanosheets achieved a NaCl removal efficiency of 83.4% and specific electrosorptive capacity of 8.6 mg/g with outstanding regeneration capability, demonstrating great potential in application of graphene-based materials in capacitive deionization process for water desalination.