Synthesis and Applications of Manganese Oxide Nanotubes

Metal oxide nanotubes can be classified into single-crystal nanotubes and polycrystalline nanotubes. In the most cases, the single-crystal nanotubes have layered structure, where the metal oxide elementary layer of the layered structure is rolled into the nanotubular structure. This suggests that if a metal oxide can form layered compounds easily, its single-crystal nanotube could be expected. For the manganese oxide, many kinds of layered compounds have been reported, and the layered manganese oxides show excellent host-guest reactivities [1]. Their host-guest reactions have been applied to the development of new soft chemical processes for the preparation of new compounds and nanomaterials [2]. For the synthesis of the single-crystal nanotubes with layered structure, two types of processes have been reported. One is direct synthesis process; in which the nanotubes are prepared under the conditions where the layered structure is to be formed easily. The other is the soft chemical process, in which a layered compound is used as a precursor and is transformed to the nanotubular structure using the host-guest reactions. For the synthesis of polycrystalline metal oxide nanotubes, porous templates, e.g., porous anodic alumina and porous silicon, and one-dimensional templates, e.g., nanofiber and carbon nanotube, are used usually. This section describes the synthesis of single-crystal manganese oxide nanotubes by soft chemical process and direct synthesis process, synthesis of polycrystalline manganese oxide nanotubes by porous template process; and properties of the manganese oxide nanotubes prepared using these methods.