Synthesis of Few-Layer Graphene by Peeling Graphite Flakes via Electron Exchange in Solution Plasma

Abstract

Compared with conventional graphene, few-layer graphene is an easy-to-use material because of its interesting mechanical and chemical properties. Meanwhile, solution plasma (SP) represents a nonequilibrium discharge, which induces electron exchange similar to a catalyst. Thus, SP serves as an electron donor and acceptor between organic molecules and graphite flakes in a solution. Finally, electron exchange leads to the formation of few-layer graphene by peeling graphite flakes. Furthermore, CN-functionalized few-layer graphene (f-FLG) exhibits excellent stability and dispersibility because of the balance of attractive and repulsive forces, i.e., the van der Waals force between the planes and the electrostatic force of the nitrile functional groups on the edges. In this study, f-FLG was successfully synthesized by peeling graphite flakes via electron exchange induced by SP in an aqueous solution containing an ionic liquid (IL) (1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA)). X-ray diffraction measurements revealed that the intensity of the 002 diffraction of graphite and the crystallite size along the [001] direction decreased to about 5 nm after SP treatment, indicating the progress of graphite flake peeling. Furthermore, the purified product comprised three layers with a crystallite size along the basal plane of about 80 nm evaluated by the deconvolution of the Raman 2D band. X-ray photoelectron spectroscopy confirmed that the synthesized f-FLG contains 7.7 atom % nitrogen, and the IR spectrum revealed the presence of the CN functional group. To understand the peeling mechanism, the ionization potential (I P ) and electron affinity (E A ) of the IL in water, and the averaged electron excitation temperature (T e ) in plasma were estimated by ab initio molecular orbital calculations, cyclic voltammetry, and optical emission spectroscopy. An energy diagram of I P , E A , and T e shows that SP served to pump electrons for their circulation via EMIM-DCA and to remove electrons from graphite flakes and inject into f-FLG.

Plasma–Solution Junction for the Formation of Carbon Material

“…Raman spectroscopic measurements were also employed to carry out the degree of detailed structural disorder from the samples, as shown in Figure 4b. The characteristic peaks were observed, including the D band (~1340 cm −1 ), G band (~1580 cm −1 ), and 2D band (~2710 cm −1 ) [17,18,37]. The pronounced G peaks are attributed to the E 2g mode, which represents the stretching of carbon bonds from a pair of sp 2 lattice carbon atoms.…”

Electronic, transport, magnetic, and optical properties of graphene nanoribbons and their optical sensing applications: A comprehensive review

“…The exfoliation of bulk graphite can be done in different forms such as graphene flakes, graphene nanoribbons, and planar graphene sheets. [221][222][223][224][225][226] The classification is done on the basis of the dimension of different structural forms. For example, flakes have the dimension ranging from several nanometers to micrometers, and the planar sheets have the dimensions in the macroscopic range.…”

Functionalization and exfoliation of graphite with low temperature pulse plasma in distilled water

“…The obtained materials, however, show a significant number of defects, need further treatments to reduce them, and are more often composed of a few layers of graphene (between 2 and 5 layers) than pure graphene. 21 These defects degrade the properties of graphene flakes, such as the electrical conductivity. 17 Methods able to produce large quantities of graphene without defects are still a challenge.…”