Structural and tribological characterization of fluorinated graphene with various fluorine contents prepared by liquid-phase exfoliation

The high strength and noble inertness of fluorinated graphene (FG) indicate very promising properties for its application in tribological applications to reduce friction and save energy, yet few works refer to its tribological performance, mostly due to the lack of an effective synthesis method and limited knowledge of FG. In this work, fluorinated graphene (FG) sheets with various fluorine contents are prepared from fluorinated graphite (FGi) by means of controllable chemical reaction with ethylenediamine (EDA) and liquid-phase exfoliation with N-methyl-2-pyrrolidone (NMP) in a one-pot synthesis. Transmission electron microscopy and atomic force microscopy analyses show that the obtained FG sheets possess large lateral size and ultrathin thickness (1.8-4.0 nm). Chemical characterizations indicate the C/F ratio can be readily tuned by adjusting the reaction temperature with EDA, which leads to defluorination and also substitution of a small amount of fluorine atoms by alkylidene amino groups. The tribological performance of FG samples as novel lubricant additives in base oil of polyalphaolefin-40 with different concentrations (0.1-0.4 mg mL(-1)) is investigated. The tribological tests suggest that the addition of FG at optimum concentration can greatly improve the anti-wear property of the base oil and there exists a strong proportional relationship between anti-wear ability and fluorine content.