Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

Abstract

A thermal plasma process at atmospheric pressure is an attractive method for continuous synthesis of graphene flakes. In this paper, a magnetically rotating arc plasma system is employed to investigate the effects of buffer gases on graphene flakes synthesis in a thermal plasma process. Carbon nanomaterials are prepared in Ar, He, Ar-H2, and Ar-N2 via propane decomposition, and the product characterization is performed by transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the Brunauer–Emmett–Teller (BET) method. Results show that spherical particles, semi-graphitic particles, and graphene flakes coexist in products under an Ar atmosphere. Under an He atmosphere, all products are graphene flakes. Graphene flakes with fewer layers, higher crystallinity, and a larger BET surface area are prepared in Ar-H2 and Ar-N2. Preliminary analysis reveals that a high-energy environment and abundant H atoms can suppress the formation of curved or closed structures, which leads to the production of graphene flakes with high crystallinity. Furthermore, nitrogen-doped graphene flakes with 1–4 layers are successfully synthesized with the addition of N2, which indicates the thermal plasma process also has great potential for the synthesis of nitrogen-doped graphene flakes due to its continuous manner, cheap raw materials, and adjustable nitrogen-doped content.

Simultaneous Synthesis and Nitrogen Doping of Free-Standing Graphene Applying Microwave Plasma

“…Dependences of the plasma buffer gas, type of the carbon-containing precursor and the arc current on the morphology of the created structures are established. It is interesting to mention that 2D to G intensity line ratio in the present spectra is higher than the one reported in [ 62 , 63 ] of samples synthesized in arc plasma. However, it is unclear if this is a sign for some “mildness” of the conditions of the microwave plasma synthesis compared to the arc plasma synthesis—there are too many parameters that can influence this ratio such as nitrogen content, number of layers in the graphene flake, flake size, etc.…”

“…Analogous results are reported in [ 62 ], were substrate-free graphene flakes are synthesized in arc plasma using different precursors and appropriate process parameters. Dependences of the plasma buffer gas, type of the carbon-containing precursor and the arc current on the morphology of the created structures are established.…”

Distinctive Features of Graphene Synthesized in a Plasma Jet Created by a DC Plasma Torch

“…This formation allows the direct application of synthesized graphene, without additional treatment. Thus, the presence of hydrogen in the graphene flakes demonstrates its key role in graphene synthesis, which is in agreement with a number of researches [43][44][45]. Probably H atoms can effectively cut off ragged carbon bonds creating carbon-hydrogen bonds, and to suppress the formation of spherical structure.…”

Impact of N2 admixture on the synthesis of graphitic carbon nanoparticles using atmospheric-pressure microwave plasma

“…For example, spherical carbon nanoparticles are produced in an argon atmosphere [14,15], carbon nanohorns are produced in a nitrogen atmosphere [15][16][17], and few-layer graphene flakes are produced in a hydrogen atmosphere [15,18,19]. However, few studies have systematically addressed the effect of these buffer gases on carbon nanoparticle synthesis [20].…”

“…Argon has been most commonly used as the plasma buffer gas. However, argon plasma form streamers at high pressures (this phenomenon is called filamentation) [20,23]. Therefore, in this study, we used helium plasma, which does not suffer from filamentation at atmospheric pressure.…”