Tuning of fluorine content in graphene: towards large-scale production of stoichiometric fluorographene

Abstract

The availability of well-defined modified graphene derivatives such as fluorographene, graphane, thiographene or hydroxygraphene is of pivotal importance for tuning the resulting material properties in numerous potential applications. A series of fluorinated graphene with various contents of fluorine was synthesized by a simple fluorination procedure in an autoclave with a nitrogen/fluorine atmosphere at different exposure times and temperatures. To investigate the composition, structure and properties all samples were characterized in detail by a number of analytical techniques such as SEM, XRD, EDS, AFM, STEM, combustible elemental analysis, STA, XPS, Raman spectroscopy, UV-VIS spectroscopy and cyclic voltammetry. The fully fluorinated graphene with the overall stoichiometry C1F1.05 had a bright white color indicating a significant change of band-gap. In comparison to other samples such a high concentration of fluorine led to the occurrence of exotic thermal behavior, strong luminescence in the visible spectral region and also the unique super-hydrophobic behavior observed on the material surface. The described tunable fluorination should pave the way to fluorographene based devices with tailored properties.

Simple Synthesis of Fluorinated Graphene: Thermal Exfoliation of Fluorographite

“…[14] Graphene can be also modifiedb yh ydrogenation. [17] Other methods are based on the fluorination of graphene by using variousf luorinating agentss uch as SF 6 ,X eF 2 ,o rf luorine at elevated temperatures and pressures. [15] Analogous to graphane, the fully fluorinated graphene with composition C 1 F 1 is called fluorographene.…”

“…[17] Other methods are based on the fluorination of graphene by using variousf luorinating agentss uch as SF 6 ,X eF 2 ,o rf luorine at elevated temperatures and pressures. [6] It has been also reported that fluorinated graphene is ah igh-quality insulator with high Young's modulus. [19] The bandgapo f fluorographene can be tuned in the range from 0eV( unmodified graphene) to 3.4 eV for stoichiometric fluorographene.…”

Fluorographene: Synthesis and sensing applications

“…[37][38][39][40] It is also shown that the defluorination can be achieved by exposing FG to ultraviolet irradiation for long time in aromatic solvents like toluene and benzene. 23,41 On a different report, the possibilities of defluorination by the solvent based treatment of fluorinated graphene is also discussed, where the semi-ionic C-F bonds were removed from fluorinated graphene upon its treatment with dipolar solvents such as N-methyl-2-pyrrolidinone (NMP) via ultra-sonication. 23 Recently, the authors have demonstrated that the interactions between polar solvents and C-F bond in FG are highly crucial for the solvent assisted defluorination, and even moderately polar solvents such as tetrahydrofuran (THF) can interact with FGO to remove C-F bonds in a day or two without any extensive sonication.…”

“…23,41 On a different report, the possibilities of defluorination by the solvent based treatment of fluorinated graphene is also discussed, where the semi-ionic C-F bonds were removed from fluorinated graphene upon its treatment with dipolar solvents such as N-methyl-2-pyrrolidinone (NMP) via ultra-sonication. 23 Recently, the authors have demonstrated that the interactions between polar solvents and C-F bond in FG are highly crucial for the solvent assisted defluorination, and even moderately polar solvents such as tetrahydrofuran (THF) can interact with FGO to remove C-F bonds in a day or two without any extensive sonication. 40 This method also proves that other oxygen functionalities are kept intact even after 30 days of THF treatment indicating that the reaction is quite selective.…”

“…22 Further, similar to the C/H ratio dependent electrical conductivity of graphane, conductivity of fluorographene is highly dependent on the C/F ratio and it can vary from 0 eV (pure graphene) to 3.4 eV (stoichiometric fluorographene), similar to hydrogenation from 0 eV to 4 eV. 20,23 But the changes in the other physico-chemical properties with fluorination is more drastic than hydrogenation, and hence need to be pursued more vigorously. Furthermore, it is studied that on the heterogeneous electron transfer (HET) kinetics of various halogenated graphene oxides, the electron transfer rates increases with the decrease in atomic number of the doped halogen (transfer rates track the following order, Cl-TRGO .…”