Ionic liquid-assisted exfoliation and dispersion: stripping graphene and its two-dimensional layered inorganic counterparts of their inhibitions
Research on graphene—monolayers of carbon atoms arranged in a honeycomb lattice—is proceeding at a relentless pace as scientists of both experimental and theoretical bents seek to explore and exploit its superlative attributes, including giant intrinsic charge mobility, record-setting thermal conductivity, and high fracture strength and Young's modulus. Of course, fully exploiting the remarkable properties of graphene requires reliable, large-scale production methods which are non-oxidative and introduce minimal defects, criteria not fully satisfied by current approaches. A major advance in this direction is ionic liquid-assisted exfoliation and dispersion of graphite, leading to the isolation of few- and single-layered graphene sheets with yields two orders of magnitude higher than the earlier liquid-assisted exfoliation approaches using surface energy-matched solvents such as N-methyl-2-pyrrolidone (NMP). In this Minireview, we discuss the emerging use of ionic liquids for the practical exfoliation, dispersion, and modification of graphene nanosheets. These developments lay the foundation for strategies seeking to overcome the many challenges faced by current liquid-phase exfoliation approaches. Early computational and experimental results clearly indicate that these same approaches can readily be extended to inorganic graphene analogues (e.g., BN, MoX2 (X = S, Se, Te), WS2, TaSe2, NbSe2, NiTe2, and Bi2Te3) as well.