Abstract
Aerosol formation of novel carbons offers potential for scale and purity unmatched by condensed phase processes. A microwave driven plasma drives decarbonization of methane to form solid carbon as an aerosol. Dependent upon gas mixture, different forms of carbon are produced: 2D nanographene and a 3D graphitic carbon black analogue. TEM reveals the morphological differences and nanostructure. The ability to tune the dominant form is demonstrated by control of the CH4/Ar ratio. TGA plots reveal the change in products with feed gas composition and quality by oxidation temperature shift. Corresponding Raman analysis illustrates control of graphene content and lamellae quality by peak ratios. To test the origins of the graphitic particles and nanographene, a commercial carbon black was seeded into the microwave reactor, demonstrating a path for graphitic nanostructure evolution and confirming the molecular growth origins for the nanographene.
Highlights
High current plasmas are versatile vehicles for synthesis of novel carbon forms given their high energy density, energetic species and abundant radical concentrations
With this study conducted as a categorical survey across test conditions, results from two reactant to argon ratio of order 1:1. These two cases are designated as low ratio (LR) and high ratio (HR)
Results are rather insensitive to gas composition, as results may be categorized as methane to argon ratio of order 1:1
Summary
High current plasmas are versatile vehicles for synthesis of novel carbon forms given their high energy density, energetic species and abundant radical concentrations. One study of graphene nano-flake synthesis in a non-thermal plasma process found that increasing the hydrogen to carbon (H/C) molar ratio promoted the morphological transformation of carbon nanomaterials from spherical carbon nanoparticles (SCNs) to graphene nanoflakes (GNFs), improving the quality of GNFs and reducing the stacking of graphite layers [20,21]. A microwave plasma offers the unique features of atmospheric pressure operation and high electron concentration [11,27] The former offers ease of processing while the latter ensures a high radical concentration and non-thermal chemistry. Such features are manifested in the direct formation of the free-standing (aerosol) form of nanographene, as reported previously [28]. Its crystallite structure is atypical for a nascent aerosol carbon; it resembles that of an annealed carbon black
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