Growth of graphene sheets under an oxyacetylene flame without a catalyst

High quality graphene sheets that had a low I_D/I_G and a high 2D intensity in Raman spectra were prepared by a catalyst-free acetylene flame method. The sheets were grown vertically on the surface of carbon particles to form a petal-like morphology. A high temperature, high pressure and short residence time of the flame intensified the decomposition and cyclization reactions of acetylene, leading to the formation of graphene sheets in the gas phase. The turbulent flame and the gases released during the formation of the graphene sheets from carbon nuclei could be responsible for their petal-like morphology instead of an onion-like structure.