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Structural and morphological evolution of β-MnO 2 nanorods during hydrothermal synthesis

2009; IOP Publishing; Volume: 20; Issue: 5 Linguagem: Inglês

10.1088/0957-4484/20/5/055610

1361-6528

Tao Gao, Helmer Fjellvåg, Poul Norby,

Polyoxometalates: Synthesis and Applications

β-MnO2 nanorods were synthesized via a redox reaction of (NH4)2S2O8 and MnSO4 under hydrothermal conditions. In situ and ex situ x-ray diffraction and scanning electron microscopy were employed to follow the structural and morphological evolution during growth. It was found that the crystallization of β-MnO2 nanorods proceeds through two steps: γ-MnO2 nanorods form first via a dissolution–recrystallization process and then transform topologically into β-MnO2 with increasing temperature. The phase transformation was associated with a short-range rearrangement of MnO6 octahedra. Vibrational spectroscopic studies showed that the β-MnO2 nanorods had four infrared absorptions at 726, 552, 462 and 418 cm−1 and four Raman scattering bands at 759 (B2g), 662 (A1g), 576 (Ramsdellite impurity) and 537 (Eg) cm−1, which are in agreement with Mn–O lattice vibrations within a rutile-type MnO6 octahedral matrix.