Preparation of hollow carbon nanocages by iodine-assisted heat treatment

Carbon nanocages (CNCs) with a hollow structure and high degrees of graphitization and purity have wide applications. However, preparation of such material is still a great challenge. In this study, we report a general strategy for the preparation from iron/graphite core-shell nanoparticles. The core-shell nanoparticles are synthesized by the pyrolysis of acetylene with iron carbonyl. In order to remove the metallic core, rather than using the conventional acid oxidation, the nanoparticles are heat treated in the presence of iodine. It is found that the entrapped iron particles can be completely eliminated and hollow CNCs with good graphitization and high purity can be obtained. The purification process may involve the diffusion of iron atoms out from CNCs and their reaction with iodine molecules in the surrounding atmosphere. The reaction product FeI₂ is soluble in ethanol and could thus be easily removed. As an example of a potential application, the CNCs are demonstrated to be a superb material for supporting the Pt catalyst used in low-temperature fuel cells. The present method could be applied to the production of graphitic carbon in large scale, and the resultant material could prove to be practically relevant for fuel cell and many other technologies.