Abstract
An experimental and theoretical investigation on microwave plasma-based synthesis of free-standing N-graphene, i.e., nitrogen-doped graphene, was further extended using ethanol and nitrogen gas as precursors. The in situ assembly of N-graphene is a single-step method, based on the introduction of N-containing precursor together with carbon precursor in the reactive microwave plasma environment at atmospheric pressure conditions. A previously developed theoretical model was updated to account for the new reactor geometry and the nitrogen precursor employed. The theoretical predictions of the model are in good agreement with all experimental data and assist in deeper understanding of the complicated physical and chemical process in microwave plasma. Optical Emission Spectroscopy was used to detect the emission of plasma-generated ‘‘building units’’ and to determine the gas temperature. The outlet gas was analyzed by Fourier-Transform Infrared Spectroscopy to detect the generated gaseous by-products. The synthesized N-graphene was characterized by Scanning Electron Microscopy, Raman, and X-ray photoelectron spectroscopies.
Highlights
The existing variety of carbon structures is due to the ability of the carbon atom to form different hybridizations, such as tetrahedral sp3 -(diamond), sp2 -trigonal, or linear sp-(carbyne) [1]
One approach is based on controlling the type of conductivity and carrier concentration, which can be achieved by doping with foreign atoms
The previously developed chemical kinetics model was updated with nitrogen-containing species and the corresponding rate coefficients
Summary
The existing variety of carbon structures is due to the ability of the carbon atom to form different hybridizations, such as tetrahedral sp3 -(diamond), sp2 -trigonal (graphite, fullerene, nanotubes), or linear sp-(carbyne) [1]. Doping levels as high as 25 at % of N can be reached using the post-treatment plasma approach, but with the doping occurring predominantly on the surface, i.e., not homogeneously Such high doping levels lead to the formation of different carbon–nitride structures [29]. Until recently, obtaining free-standing graphene or N-graphene sheets was considered impossible, since the thermodynamic analyses, computing the fluctuations in the positions of carbon atoms in the graphene lattice, indicated that free-standing 1D and 2D crystals are unstable [30,31] These analyses were conducted under simplified assumptions, including the harmonic approximation and the formation of completely flat 2D crystalline structures. Materials 2020, 13, x FOR PEER REVIEW involved in the formation of N-graphene structures For this purpose, the previously developed chemical kinetics model was updated with nitrogen-containing species and the corresponding rate coefficients.
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