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 template s (structure-directing agents) into its interlayer space by a soft chemical reaction [1], and the second step is the transformation of the template-in serted precursor into a tunnel structure by hydrothermal treatment. The use fulness of this process was demonstrated by synthesizing six kinds of tunne l manganese oxides from a birnessite-type manganese oxide with layered stru cture. The transformation reactions from layered structure to tunnel struct ures were investigated by X-ray, DTA-TG, and chemical analyses, and IR spec troscopy. Spinel-, hollandite-, romanechite-, and todorokite-type manganese oxides, which have (1 x 3), (2 x 2), (2 x 3), and (3 x 3) tunnel structure s, can be obtained by using Li+, K+, Ba2+, and Mg2+ ions as the templates, respectively. Pyrolusite- and ramsdellite-type manganese oxides with (I x 1 ) and(l x 2) tunnel structures can be obtained in acidic solutions. The sit e of the resulting tunnels correspond to the size of the templates.