Plasma-Based Direct Methane Conversion into Multi-layer Graphene: A Microwave Plasma Torch Approach

Multi-layer graphene (MLG) was synthesized via direct methane conversion using a newly developed microwave plasma torch, which enables carbon-deposition-free and continuous growth. TEM clearly resolved the layered morphology and defect structures of MLG, while Raman spectroscopy exhibited a low defect density (I_D/I_G ≈ 0.3) and a distinct 2D band. XRD confirmed graphitic ordering with an interlayer spacing of ~ 0.343 nm. XPS verified high carbon purity (> 99 at.% C) with only minor C–H contributions. Electrical conductivity reached ~ 85 S/cm, with a compressed density of 5.94 g/cm³. A simple water dispersion test revealed strong hydrophobicity and poor suspension stability in aqueous media, characteristic of pristine MLG. These findings demonstrate that plasma-based direct methane conversion is an effective and scalable route for producing high-purity, structurally ordered MLG with strong potential for catalytic, electrochemical, and composite applications.