Hydrothermal Soft Chemical Process for Synthesis of Manganese Oxides with Tunnel Structures

A soft chemical process is used for the synthesis of manganese oxides with tunnel structures. This process comprises two steps: the first step is the preparation of a precursor with layered structure and insertion of templates (structure-directing agents) into its interlayer space by a soft chemical reaction [1], and the second step is the transformation of the template-inserted precursor into a tunnel structure by hydrothermal treatment. The usefulness of this process was demonstrated by synthesizing six kinds of tunnel manganese oxides from a birnessite-type manganese oxide with layered structure. The transformation reactions from layered structure to tunnel structures were investigated by X-ray, DTA-TG, and chemical analyses, and IR spectroscopy. Spinel-, hollandite-, romanechite-, and todorokite-type manganese oxides, which have (1^×3), (2^×2), (2^×3), and (3^×3) tunnel structures, can be obtained by using Li⁺, K⁺, Ba²⁺, and Mg²⁺ ions as the templates, respectively. Pyrolusite- and ramsdellite-type manganese oxides with (1^×1) and (1^×2) tunnel structures can be obtained in acidic solutions. The size of the resulting tunnels correspond to the size of the templates.