Sol-gel synthesis of birnessite from KMnO4 and simple sugars

Birnessite is a naturally occurring manganese oxide that has been identified as a major constituent of deep sea manganese nodules. The mineral consists of layers of edge- and corner-linked MnO{sub 6} octahedra with water molecules and alkali-metal cations in the interlayer voids. A generalized elemental composition of birnessite is A{sub x}MnO{sub 2{plus_minus}y}{sm_bullet}zH{sub 2}O, in which A represents an alkali-metal cation. Natural and synthetic birnessites with an octahedral layered (OL) structure have attracted significant interest because of their potential as heterogeneous catalysts and materials for secondary batteries. Birnessites are also precursors for tunnel structure manganese oxides such as cryptomelane and todorokite. Sol-gel processing of birnessites potentially offers numerous advantages over traditional methods of synthesis such as high-purity, particle-size homogeneity, and film-casting capability. However, very few sol-gel routes have been developed for materials with near-MnO{sub 2} stoichiometry such as birnessite. Early reports of manganese oxide gels described {open_quotes}MnO{sub 2} jellies{close_quotes} formed from reactions of KMnO{sub 4} with simple sugars. However, until now these systems remained poorly characterized. The authors have reinvestigated these manganese oxide gels and in the process discovered a new sol-gel method of preparing birnessite with interlayer potassium cations, K-OL-1. 26 refs., 3 figs.