Hydrothermal synthesis of nano-sized iron oxide crystals in the cavity of carbon nanotubes

Highly crystallized iron oxide nanorods were fabricated by hydrothermal synthesis in the cavity of carbon-coated nanochannels with a diameter of 25 nm. The carbon-coated nanochannels were prepared by uniform carbon coating on the inner walls of the straight nanochannels of an anodic aluminum oxide film. Iron nitrate was loaded in the nanochannels by impregnation method and then subjected to hydrothermal treatment with NaOH aqueous solution in an autoclave. Upon the treatment, the aluminum oxide template was dissolved to leave carbon nanotubes, in which highly crystallized nanorods of α-Fe₂O₃ were formed. Then, the carbon nanotubes were completely removed by high temperature oxidation and the nanorods were liberated from carbon nanotubes as a result. This study demonstrates that the carbon-coated anodic alumina film can be used as a template even under severe reaction conditions such as hydrothermal treatment.