Production of ready-to-use few-layer graphene in aqueous suspensions

Graphene has promising physical and chemical properties such as high strength and flexibility, coupled with high electrical and thermal conductivities. It is therefore being incorporated into polymer-based composites for use in electronics and photonics applications. A main constraint related to the graphene development is that, being of a strongly hydrophobic nature, almost all dispersions (usually required for its handling and processing toward the desired application) are prepared in poisonous organic solvents such as N-methyl pyrrolidone or N,N-dimethyl formamide. Here, we describe how to prepare exfoliated graphite using a ball mill. The graphene produced is three to four layers thick and ∼500 nm in diameter on average, as measured by electron microscopy and Raman spectroscopy; can be stored in the form of light solid; and is easily dispersed in aqueous media. Our methodology consists of four main steps: (i) the mechanochemical intercalation of organic molecules (melamine) into graphite, followed by suspension in water; (ii) the washing of suspended graphene to eliminate most of the melamine; (iii) the isolation of stable graphene sheets; and (iv) freeze-drying to obtain graphene powder. This process takes 6-7 or 9-10 d for aqueous suspensions and dry powders, respectively. The product has well-defined properties and can be used for many science and technology applications, including toxicology impact assessment and the production of innovative medical devices.