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 , 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.
tunnel manganese oxides soft chemistry hydrothermal reaction metal ion templates