Facile hydrothermal synthesis of ultra-long manganese oxyhydroxide nanorods and their transformation into MnO2 and Mn2O3 nanorods

Single-crystal manganese oxyhydroxide (MnOOH) nanorods with high aspect ratios have been successfully prepared employing a simple hydrothermal route based on the redox between potassium permanganate (KMnO₄) and polyvinyl pyrrolidone (PVP). By adjusting the reaction temperature, reaction time and the mass ratio of PVP/KMnO₄, MnOOH nanorods with lengths up to 20 μm and diameters in the range of 100-400 nm could be facilely prepared in high yield. The as-prepared MnOOH nanorods were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Fourier transformed infrared spectroscopy. The formation mechanism of MnOOH nanorods was preliminarily discussed based on the Ostwald´s ripening process. Furthermore, MnO₂ and Mn₂O₃ nanorods with high aspect ratios were synthesised by calcination of MnOOH nanorods.