Growth mechanisms of carbon nanofilaments on Ni-loaded diamond catalyst

摘要

Nickel-loaded oxidized powdered diamond (Ni/O-Dia) was used for the synthesis of carbon nanofibers (CNFs). CNFs grown at 400 deg C, from both CH4 and C_2H_6 over Ni/O-Dia, had herring-bone type graphene sheets and those grown at 600 deg C had tube type graphene sheets. The amount of CNFs was greatly affected by the growth temperature in both CH_4 and C_2H_6. In all the cases, Ni particle was found on the tip end of the grown CNFs. No carbon formation was observed at 650 deg C or higher temperature from both CH4 and C_2H_6, because Ni particles on O-Dia were covered with graphene sheets. Termination of the growth of CNFs was ascribed to the rapid decomposition of hydrocarbons on active Ni surface as compared to the dissolution and diffusion of the carbon on Ni surface into bulk Ni particle to give CNFs on the opposite side of active Ni surface.