Synthesis of thin-walled carbon nanocages and their application as a new kind of nanocontainer

Carbon nanocages (CNCs) with a hollow core and a thin wall of a few graphitic layers have a wide range of applications. However, the preparation of such a material remains a great challenge. In this study, we report the preparation of thin-walled CNCs through the pyrolysis of a mixture composed of pyridine and liquid iron pentacarbonyl, subsequent heat treatment in the presence of NH4Cl at a low temperature, and finally washing and filtering in water. The finding that pyridine is completely mutually soluble with liquid iron pentacarbonyl in any proportion stands out to be a crucial advantage for reducing the thickness of the graphitic wall formed on a metal core. To obtain hollow CNCs, heat-treatment proves to be simple and effective in removing the metal core and, more importantly, maintaining the thin graphitic wall when compared with conventional boiling in a strong oxidant, such as HNO3. The thin-walled hollow CNCs are demonstrated to be suitable nanocontainers for encapsulating iodine, as iodine can easily get into and out of the CNCs when it is heated at a relatively low temperature. Considering the large internal space and thin graphitic wall, the hollow CNCs could be widely used in many fields, such as biology, medicine and chemistry.