Preparation of protonic layered manganates and their intercalation behavior

The Na+ extraction of alpha-NaMnO2 upon acid leaching and subsequent intercalation of hexylamine were examined. The acid treatments using 0.01-1 M HCl solutions produced a protonic layered manganate HxMnO2.yH(2)O (x = 0.1-0.3, y similar to 0.6). The oxidation state of Mn was dependent on the HCl concentration. The change in oxidation state was attributed to the competition of redox extraction and ion-exchange reaction of Na ions: the redox extraction involved disproportionation, 2 Mn-III(s) --> Mn-IV(s) + Mn2+ (aq). The disproportionation reaction deteriorated the crystallinity of a protonic form of alpha-NaMnO2. On the other hand, the slow acid treatment and the pre-oxidized starting materials remarkably improved crystallinity of the protonic products of alpha-NaMnO2. These protonic manganates underwent intercalation with hexylamine, inducing interlayer expansion to 1.8 or 2.1 nm. Their intercalation compounds showed that crystallinity was dependent on their original protonic phases. (C) 2002 Elsevier Science B.V. All rights reserved.