Synthesis of Todorokite at Atmospheric Pressure

3 × 3 tunnel-structured manganese oxide, todorokite, or MnO6 octahedral molecular sieve (OMS-1), was synthesized at atmospheric pressure by a refluxing process from birnessite, 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 and extended. Intergrowth of different widths of tunnels commonly occurred in a disorderly manner, with a triple octahedral chain width being the most predominant. Such morphological and intergrowth characteristics were similar to those of natural todorokites and a hydrothermally synthesized todorokite. When refluxing time was increased, the crystallinity of OMS-1-R was promoted and small scale twinning in morphology became a relatively large and coarse twinning. However, there was no other crystalline phase produced. The OMS-1R24, 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 the surface was predominantly mesoporous with the BJH adsorption average pore diameter of 14 nm.