Hydrothermal synthesis of MnO2 nanowires: structural characterizations, optical and magnetic properties

In this paper, 1D single-crystalline MnO2 nanowires have been successfully synthesized by hydrothermal method using KMnO4 and (NH4)(2)S2O8 as raw materials. X-ray diffraction patterns and high-resolution TEM images reveal pure tetragonal MnO2 phase with diameters of 15-20 nm. Photoluminescence studies exhibited a strong ultraviolet (UV) emission band at 380 nm, blue emission at 452 nm and an extra weak defect-related green emission at 542 nm. UV-visible spectrophotometery was used to determine the absorption behavior of nanostructured MnO2 and a direct optical band gap of 2.5 eV was acquired by Davis-Mott model. The magnetic properties of the products have been evaluated using vibrating sample magnetometer, which showed that MnO2 nanowires exhibited a superparamagnetic behavior at room temperature. The magnetization versus temperature curve of the as-obtained MnO2 nanowires shows that antiferromagnetic transition temperature is 99 K.