Controllable synthesis of carbon coils and growth mechanism for twinning double-helix catalyzed by Ni nanoparticle

A simple approach using 90 nm Ni nanoparticles to tune the growth of carbon fibers is developed basing on the bottom-up regulation in this study. By adjusting the preparing temperature and atmospheric composition, the nickel-containing catalysts with specific sizes and shapes are alternately prepared from 90 nm to 500 nm. The straight carbon nanofibers and three kinds of carbon coils (single-helix carbon nanocoils, single-helix carbon microcoils and twinning double-helix carbon microcoils) with the coil diameter ranging from 150 nm to 3 mu m are achieved by using the as-prepared catalyst. The relationship between the carbon coil and catalyst particle, and the growth mechanism for different kinds of helices are discussed in details. The results suggest that catalytic anisotropy come from growing tendency and rate of carbon deposition on the facets, edges and vertices of catalyst grain. The twinning structure exists in each fiber of the double-helix carbon microcoils regardless of circular or flat fiber, which is separated by the tip of the catalyst particle due to the different rate of carbon deposition at edge and vertex. (C) 2013 Elsevier Ltd. All rights reserved