| Abstract
| - A 3 × 3 tunnel-structured manganese oxide, todorokite, or MnO6 octahedral molecularsieve (OMS-1), was synthesized at atmospheric pressure by a refluxing process frombirnessite, the layer-structured precursor. The todorokite synthesized by the refluxing process(named as OMS-1-R) consisted of fibers with various lengths and platy trilling patterns,made of fiber crystals twinned with each other at 120°, from which the fibers matted andextended. Intergrowth of different widths of tunnels commonly occurred in a disorderlymanner, with a triple octahedral chain width being the most predominant. Such morphological and intergrowth characteristics were similar to those of natural todorokites and ahydrothermally synthesized todorokite. When refluxing time was increased, the crystallinityof OMS-1-R was promoted and small scale twinning in morphology became a relatively largeand coarse twinning. However, there was no other crystalline phase produced. The OMS-1-R24, synthesized after 24 h of refluxing, with a chemical composition of Mg0.17MnO2.10(H2O)0.88, was stable up to 400 °C. The BET surface area was found to be 77 m2/g, and thesurface was predominantly mesoporous with the BJH adsorption average pore diameter of14 nm.
- The (0 0 1) plane HRTEM image of the 3 × 3 tunnel-structured manganese oxide, todorokite, synthesized by the refluxing process at atmospheric pressure, exhibited the predominant triple chain width (1 nm) along the a axis and the disorderly intergrowth of different widths of tunnels, the characteristics of which were similar to those of the natural or hydrothermally synthesized samples.
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