Hydrothermal Soft Chemical Reaction for Formation of Sandwich Layered Manganese Oxide

Lithiophorite with a sandwich layered structure, which consists of stacked MnO 6 octahedral sheets and LiAl 2 (OH) 6 octahedral sheets, was prepared from a birnessite-type sodium manganese oxide with a layered structure, by using a hydrothermal soft chemical process. In the first step, lithium−aluminum hydroxide complex ions (Li x Al n (OH) m z + ) were inserted into the interlayer space of the manganese oxide layers by an ion-exchange reaction. In the second step, the ion-exchanged manganese oxide was hydrothermally treated to polymerize the complex ions in the interlayer space, forming the sandwich layered structure. The formation reaction of the sandwich layered structure was investigated by XRD, TG-DTA, chemical analyses, and FT-IR spectroscopy. Li x Al n (OH) m z + can be formed by dropping a LiOH solution into an Al(NO 3 ) 3 solution with Li/Al mole ratio = 2, at 60 °C. A mixed layered phase of manganese oxide with basal spacings of 0.72 and 0.95 nm was obtained after the ion-exchange treatment of the birnessite-type manganese oxide with Li x Al n (OH) m z + solution. The mixed layered phase transforms to a 0.95-nm layered phase which corresponds to lithiophorite, with a sandwich-layered structure, under hydrothermal conditions. If a Keggin ion (Al 13 O 4 (OH) 24 7+ ) solution was used instead of the Li x Al n (OH) m z + solution, the pure 0.95-nm phase cannot be obtained. In the formation reaction of the sandwich layered structure, the layered structure of the manganese oxide acts as a template under hydrothermal conditions for the two-dimensional polymerization of Li x Al n (OH) m z + to a LiAl 2 (OH) 6 octahedral sheet in the interlayer space.