title: Non-oxidative intercalation and exfoliation of graphite by Brønsted acids.
abstract: Graphite intercalation compounds are formed by inserting guest molecules or ions between sp(2)-bonded carbon layers. These compounds are interesting as synthetic metals and as precursors to graphene. For many decades it has been thought that graphite intercalation must involve host-guest charge transfer, resulting in partial oxidation, reduction or covalent modification of the graphene sheets. Here, we revisit this concept and show that graphite can be reversibly intercalated by non-oxidizing Brønsted acids (phosphoric, sulfuric, dichloroacetic and alkylsulfonic acids). The products are mixtures of graphite and first-stage intercalation compounds. X-ray photoelectron and vibrational spectra indicate that the graphene layers are not oxidized or reduced in the intercalation process. These observations are supported by density functional theory calculations, which indicate a dipolar interaction between the guest molecules and the polarizable graphene sheets. The intercalated graphites readily exfoliate in dimethylformamide to give suspensions of crystalline single- and few-layer graphene sheets.
authors.affiliation: Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Nina I
authors.initials: NI
authors.lastname: Kovtyukhova
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Yuanxi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Ayse
authors.initials: A
authors.lastname: Berkdemir
authors.affiliation: Research Center for Exotic Nanocarbons, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Cruz-Silva
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Terrones
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Vincent H
authors.initials: VH
authors.lastname: Crespi
authors.affiliation: 1] Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA [2] Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA [3] Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Mallouk