Metal-assisted Microwave Induction Method for Constructing Basal Plane and End-face Nanostructures of High-quality Graphene
Abstract
Most commercial graphene is prepared by exfoliation, redox processes, chemical vapor deposition (CVD), etc. Although some methods have been featured for high-quality graphene or massive productivity, they require high-energy cost treatment or environmentally unfriendly chemicals, which may lead to defective structures or low yields. Here, we describe the use of metal-assisted microwave induction (MAMI) to generate high-energy density plasma to effectively remove the remaining functional groups of the carbon source material in seconds. The removal step is followed by the peeling off single-layer material to reorder basal plane and end surface, establishing a sequential crystal structure. To our knowledge, in this study, the world-record for the highest graphene Raman spectroscopy of 2D/G band intensity ratio (~12) via proposed method is achieved for microwave-irradiated carbon black (MICB). Meanwhile, a world-record low-intensity D/G band (0.0034) in Raman spectroscopy is revealed, suggesting that MICB contains ultralow defect concentrations, clearly proving the turbostratic structure in the microwave-irradiated carbon materials. The strong interlayer interaction in turbostratic graphene layers significantly strengthens intervalley resonance scattering, attributing to the mirror symmetry of the valence and conduction bands relative to the Fermi level near the Dirac point in the Brillouin zone, result in a notable increase of the 2D peak intensity. The almost perfect single Lorentzian line shape fitting of 2D peak indicates either only single layer graphene or turbostratic graphene where 2-dimensional structure generated while the defect density is calculated to be ~7.5×108 cm-2 according to D/G band ratio. The conductivity can increase when the functional groups are eliminated followed by decreased D peak. Consequently, highly reproducible and excellent quality materials synthesized from low-cost carbon source materials such as bamboo, coconut shell, rice shell, wood via MAMI can be used for universal preparations and applications of graphene. The electric energy consumed is estimated to be ~0.6 kilojoules per gram.