Preparation of protonic layered manganates and their intercalation behavior

The Na+ extraction of α-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·yH2O (x=0.1–0.3, y∼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 MnIII(s)→MnIV(s)+Mn2+(aq). The disproportionation reaction deteriorated the crystallinity of a protonic form of α-NaMnO2. On the other hand, the slow acid treatment and the pre-oxidized starting materials remarkably improved crystallinity of the protonic products of α-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.