SYNTHETIC ROUTES TO MICROPOROUS MANGANESE OXIDES

Microporous manganese oxides with layer and tunnel structures have bee n synthesized by methods such as redox precipitation, thermal and hydr othermal alteration, sol-gel processing, and microwave heating. The op en frameworks of these materials are composed of edge and corner share d MnO6 octahedra, with the internal pores being occupied by cations an d water molecules. Birnessite-type (OL-l) manganese oxides have layere d structures with interlayer spacings that depend on hydration. Hollan dites (OMS-2) and todorokites (OMS-1) have tunnel structures that cons ist of respective 2 x 2 and 3 x 3 arrays of MnO6 octahedra. Microporou s manganese oxides are of interest because of potential applications i n heterogeneous catalysis, chemical absorption, and battery technology . This article describes some recent developments in the synthesis of microporous manganese oxides, with particular attention being given to birnessites, hollandites, and todorokites.