Synthesis of Homogeneous Manganese-Doped Titanium Oxide Nanotubes from Titanate Precursors

We report a novel synthesis route of homogeneously manganese-doped TiO2 nanotubes in a broad concentration range. The scroll-type trititanate (H2Ti3O7) nanotubes prepared by hydrothermal synthesis were used as precursors. Mn2+ ions were introduced by an ion exchange method resulting MnxH2-xTi3O7. In a subsequent heat treatment, they were transformed into MnyTi1-yO2, where y = x/(3 + x). The state and the local environment of the Mn2+ ions in the precursor and final products were studied by the electron spin resonance (ESR) technique. It was found that the Mn2+ ions occupy two positions: the first having an almost perfect cubic symmetry while the other is in a strongly distorted octahedral site. The ratio of the two Mn2+ sites is independent of the doping level and amounts to 15:85 in MnxH2-xTi3O7 and to 5:95 in MnyTi1-yO2. SQUID magnetometry does not show long-range magnetic order in the homogeneously Mn2+-doped nanotubes.