Liquid-phase Exfoliation Of Graphite Into Graphene Utilizing Ionic Liquid Crystals And Polyoxometalate

Recent progress about the preparation of graphene has been summarized in the present dissertation.Based on the past research,liquid-phase exfoliation of graphite in the presence of ionic liquid crystals([C12min]BF4)and polyoxometalate was employed to produce monolayer/few layer graphene sheets and two kinds of electrically-conductive composites were prepared by subsequent polymerization or hybridization.Molecular mechanism of exfoliating graphite into graphene was systematically investigated.This work creates a new methodology of fabricating high quality,large area,highly stable dispersion and defect-free graphene sheets.First,graphite powder was dispersed into a midazolium-based[C12min]BF4 through grinding,stirring and microwave treatment.The resultant black suspension was then subjected to hydrothermal treatment at temperature over the clear point of thermotropic[C12min]BF4 upon heating.Above clear point,[C12min]BF4 changed into the isotropic liquid state with low viscosity,which made graphite easily exfoliated to give a stable dispersion due to the fact that the inter-graphene layers in graphite were intercalated by liquid molecules through cation-?,and ?-? interactions.On the othe hand,[C12min]BF4 was recovered at low temperature to give an increased viscosity.The newly exfoliated graphene sheets were stabilized and separated by the viscous resistance and steric hindrance arising from the local molecular alignment of[C12min]BF4.Mono-and few-layer graphene sheets were finally obtained by centrifugation and filtration of graphene suspersions.Second,a thienyl imidazolium(Th-imi)monomer was successfully synthesized and dissolved in water.The as-formed an aqueous lyotropic liquid crystal was mixed graphite under ultrasonication.Th-imi molecules were intercalated into the inter-layer of graphite through cation-?,and ?-? interactions to produce mono-/few-layer graphene sheets covered by Th-imi molecules.After chemically oxidative polymerization of Th-imi,polymer chains were assembled into nanopins that were uniformly stacked on the surface of graphene sheets.Third,graphite was dispersed into an aqueous solution of polyoxometalate under ultrasonication,and graphene sheets with large area were thus achieved by an intercalation-exfoliation mechanism due to the presence of nano-sized polyoxometalate.