Abstract
One of the greatest challenges in the commercialization of graphene and derivatives is production of high quality material in bulk quantities at low price and in a reproducible manner. The very limited control, or even lack of, over the synthesis process is one of the main problems of conventional approaches. Herein, we present a microwave plasma-enabled scalable route for continuous, large-scale fabrication of free-standing graphene and nitrogen doped graphene sheets. The method’s crucial advantage relies on harnessing unique plasma mechanisms to control the material and energy fluxes of the main building units at the atomic scale. By tailoring the high energy density plasma environment and complementarily applying in situ IR and soft UV radiation, a controllable selective synthesis of high quality graphene sheets at 2 mg/min yield with prescribed structural qualities was achieved. Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Near Edge X-ray-absorption fine-structure spectroscopy were used to probe the morphological, chemical and microstructural features of the produced material. The method described here is scalable and show a potential for controllable, large-scale fabrication of other graphene derivatives and promotes microwave plasmas as a competitive, green, and cost-effective alternative to presently used chemical methods.
Highlights
Carbon-based 2D nanostructures have attracted an outstanding research interest due to their extraordinary properties[1, 2] which make them desirable in numerous scientific and engineering disciplines
Multiple processes have been reported for graphene synthesis, including mechanical exfoliation of natural or synthetic graphite[1, 3], wet chemistry reduction techniques that employ graphite oxide (GO)[3, 16], liquid-phase exfoliation[17] and chemical vapour deposition (CVD)[18, 19]
Pure graphene sheets collected at background argon flow of 1200 sccm, power of 2 kW and ethanol flow of 30 sccm are produced at a rate of 2 mg/min
Summary
A waveguide-surfatron based setup was used to create a surface wave (SW) induced microwave plasma at atmospheric pressure conditions (Supplementary material)[45, 46]. The transport of plasma generated carbon atoms/molecules into colder zones (outside of the vaporization boundary) of the reactor results in formation of solid carbon nuclei that are gradually withdrawn in the outlet plasma stream where kinetic processes of assembly and growth of “flowing” carbon nanostructures take place. As well as larger densities of building units, foster supersaturation conditions in the environment and promote the synthesis of plenty nuclei and amorphous structures are more likely to be created. The estimations demonstrate that the rotational temperature measured at fixed background Ar flux (1200 sccm) and precursor fluxes in the range 15–30 sccm, remains nearly constant in the central “hot” zone with variation from about 4000 K to 3000 K It should be mentioned, that this temperature is associated with the axis of the “hot” plasma column, since the radiation collected originates mainly from this region. The temperature demonstrates sharp decrease in the section with expanding radius and reaches nearly room temperature at about 30 cm away from the launcher
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