Influence of Fe doping on the structural, optical and thermal properties of α-MnO2 nanowires

We report the synthesis of pure and Fe-doped α-MnO2 nanowires by a facile hydrothermal method. The influence of iron with varying doping concentration on structural, optical and thermal properties of crystalline α-MnO2 nanowires is discussed. X-ray diffraction studies indicate that the synthesized nanowires have tetragonal structure and are in crystalline α-MnO2 phase with average crystallites size of 17.36 nm for pure α-MnO2 while 14.59 nm, 14.93 nm and 13.32 nm for 5 mol %, 10 mol % and 15 mol % Fe-doped α-MnO2, respectively. Scanning electron microscopy images show that the synthesized products have nanowire morphology with an average diameter of 38 nm for pure α-MnO2 and 28 nm for 5 mol % Fe-doped α-MnO2. In Fourier transform infrared spectra, the strong absorption band at 501 cm−1 and 699 cm−1 correspond to the bending and stretching vibration of Mn–O bond. Furthermore, Thermal gravimetric analysis indicates that Fe doping in MnO2 leads to the enhancement of its thermal stability. The broad absorption band of the UV–vis spectra appeared at 250 nm to 600 nm for pure α-MnO2 and at 250 nm to 700 nm for Fe-doped α-MnO2 nanowires is assigned to the d-d transition between lower t2g and higher eg of the metallic ions. For the first time we are reporting an indirect optical bandgap energy of 0.30 eV, 0.29 eV and 0.18 eV for different Fe-doped α-MnO2 samples.