Effects of quenching rate on the plasma gas-phase synthesis of graphene: Insight from the experiments and ReaxFF studies

This investigation analysed the effects of quenching rate on the plasma gas-phase synthesis of graphene. The quenching rate was modulated by the flowrate/type of radial gas whish was injected in the plasma downstream. The experimental results showed that the plasma pyrolysis of acetylene produced spherical carbon nanoparticles. The content graphene flakes in the products increased with the quenching effect, and the layer number of graphene decreased accordingly. Further characterisation confirmed that a high quenching rate increased the crystallinity of the product, reduced the amorphous carbon content, and resulted in better oxidation resistance. The graphene formation pathway was carried out by the molecular dynamics simulations (ReaxFF), focusing on the effect of the quenching rate on graphene growth. As the quenching rate increased, the decrease in the time for surface reactions lowered the generation of five- and seven-membered rings, reducing the possibility of edge growth bending. Besides, an increased quenching rate rapidly lowered the growth temperature and thus retarded the C–H bond breakage at the edges of the carbon clusters. The C–H bonds terminated C–C bond formation at the edges of the carbon clusters, preventing edge growth bending of the carbon clusters, and thus contributing to the growth of lamellar structure. These results suggested that increasing the quenching rate is an effective method for regulating the plasma gas-phase synthesis of graphene.