On the plasma-based growth of ‘flowing’ graphene sheets at atmospheric pressure conditions

Abstract

A theoretical and experimental study on atmospheric pressure microwave plasma-based assembly of free standing graphene sheets is presented. The synthesis method is based on introducing a carbon-containing precursor (C 2 H 5 OH) through a microwave (2.45 GHz) argon plasma environment, where decomposition of ethanol molecules takes place and carbon atoms and molecules are created and then converted into solid carbon nuclei in the 'colder' nucleation zones. A theoretical model previously developed has been further updated and refined to map the particle and thermal fluxes in the plasma reactor. Considering the nucleation process as a delicate interplay between thermodynamic and kinetic factors, the model is based on a set of non-linear differential equations describing plasma thermodynamics and chemical kinetics. The model predictions were validated by experimental results. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the 'hot' plasma zone. Raman spectroscopy, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) techniques have been applied to analyze the synthesized nanostructures. The microstructural features of the solid carbon nuclei collected from the colder zones of plasma reactor vary according to their location. A part of the solid carbon was deposited on the discharge tube wall. The solid assembled from the main stream, which was gradually withdrawn from the hot plasma region in the outlet plasma stream directed to a filter, was composed by 'flowing' graphene sheets. The influence of additional hydrogen, Ar flow rate and microwave power on the concentration of obtained stable species and carbon−dicarbon was evaluated. The ratio of sp 3 /sp 2 carbons in graphene sheets is presented. A correlation between changes in C 2 and C number densities and sp 3 /sp 2 ratio was found.

Nanosize carbon products formed in microwave discharge in liquid alkanes

“…Graphene was synthesized in MW discharge at atmospheric pressure in the mixtures of argon with methane and argon with ethanol . At the same time it is known that the rates of chemical processes in the MW discharge in liquids are much higher than those in the conventional gas discharges .…”

“…At the same time it is known that the rates of chemical processes in the MW discharge in liquids are much higher than those in the conventional gas discharges . Therefore, the fact of detection of graphene in the discharge in liquid hydrocarbons is interesting, because the conditions in such a discharge differ significantly from those described in ref . Further study of this task requires research of influence the discharge parameters on the quality of graphene.…”

“…Graphene was synthesized in MW discharge at atmospheric pressure in the mixtures of argon with methane [40] and argon with ethanol. [41] At the same time it is known that the rates of chemical processes in the MW discharge in liquids are much higher than those in the conventional gas discharges. [14][15][16] Therefore, the fact of detection of graphene in the discharge in liquid hydrocarbons is interesting, because the conditions in such a discharge differ significantly from those described in ref.…”

“…[14][15][16] Therefore, the fact of detection of graphene in the discharge in liquid hydrocarbons is interesting, because the conditions in such a discharge differ significantly from those described in ref. [40,41] Further study of this task requires research of influence the discharge parameters on the quality of graphene.…”

Direct synthesis of hydrogenated graphene via hydrocarbon decomposition in plasmas

“…Earlier, we investigated the possibility of synthesizing free graphene by means of high-power plasma torch at the pressure of 150 -710 Torr [11,12]. Analysis of the processes in the carbon nucleation zone of the plasma jet generated by the plasma torch indicates high concentration of the atomic hydrogen and of the C 6 H 6 -like compounds; these substances, according to [13][14][15][16], might promote the graphene formation. Additionally, it is common knowledge that application of the DC plasma torches makes it possible to synthesize high-quality pure carbon nanomaterials from inexpensive precursors [17], thus reducing the requirements to the carbon source, its cost and the final product cost.…”