One-step preparation of single-crystalline β-MnO2 nanotubes

Single-crystal beta-MnO2 nanotubes with diameters in the range 200-500 nm and lengths up to several micrometers were successfully prepared by a simple hydrothermal method through oxidizing MnSO4 with NaClO3 in the presence of poly(vinyl pyrrolidone) (PVP). It was found that the formation process of beta-MnO2 nanotubes included two primary evolution stages over time: (1) the MnOOH nanoparticles initially formed in the hydrothermal system and anisotropic growth to nanorods and nanorod aggregates, and (2) the MnOOH nanorods transformed into beta-MnO2 tubular structure and grown into beta-MnO2 nanotubes due to continuous growth through a dissolution-recrystallization process eventually. Based on a series of experimental analysis, the formation mechanism of these nanostructures was discussed briefly. The present study has enlarged the family of nanotubes available and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials.