SOL-GEL SYNTHESIS OF LAYERED BIRNESSITE-TYPE MANGANESE OXIDES

Layered birnessite-type manganese oxides have been synthesized by sol- gel reactions involving KMnO4 or NaMnO4 with glucose. These microporou s manganese oxides are designated as octahedral layer materials, K-OL- 1 and Na-OL-1, because their layered structure consists of edge-shared MnO6 octahedra. The interlayer regions are occupied by alkali metal c ations and water molecules. K-OL-1 and Na-OL-1 have been characterized by elemental analysis, powder X-ray diffraction, scanning electron mi croscopy, FT-IR spectroscopy, and Auger electron spectroscopy The empi rical formula of K-OL-1 has been determined to be K0.28MnO1.96(H2O)(0. 19) An interlayer spacing of 7 Angstrom, typical of natural and synthe tic birnessites, has been measured by X-ray diffraction. The sol-gel s ynthesis of K-OL-1 is carried out with concentrated aqueous solutions of glucose and KMnO4 in a 1.5:1 mole ratio. Diluted reaction mixtures produce flocculent gels or precipitates which yield other manganese ox ide phases such as cryptomelane and Mn2O3. The synthesis appears to be general for reactions of KMnO4 with a variety of sugars as well as ot her polyalcohols such as ethylene glycol, glycerol, and poly(vinyl alc ohol). Reactions between NaMnO4 and glucose yield two related Na-OL-1 products. A procedure analogous to the K-OL-1 synthesis generates laye red sodium birnessite materials with 5.5 and 7 Angstrom interlayer dis tances. The 7 Angstrom Na-OL-1 is obtained exclusively by hydrating th e mixture of products. The 5.5 Angstrom Na-OL-1 is prepared by calcini ng the Na-OL-1 xerogel at 800 degrees C instead of the typical 400 deg rees C temperature. Both K-OL-1 and Na-OL-1 undergo significant yet in complete cation extraction and ion exchange with monovalent and divale nt cations.