Controllable and large-scale synthesis of metal-free carbon nanofibers and carbon nanocoils over water-soluble NaxKy catalysts

Through the pyrolysis of acetylene at 450 °C, large quantities of carbon nanocoils or carbon nanofibers can be synthesized selectively by controlling the Na:K molar ratio of water-soluble NaxKy catalysts. We found that the temperature adopted for pyrolysis is an important factor for selectively obtaining the different kinds of products. Because the NaxKy catalysts are water-soluble, they can be easily removed, and the nanocarbon materials can be harvested undamaged in high purity. The process is simple, inexpensive, and environment-benign, giving a product yield matching those of the transition-metal catalysts. Based on the results, we conducted discussion on the role of catalyst, effect of pyrolysis temperature, and formation mechanism of the nanomaterials.