Hydrothermal Intercalation Reaction of Nickel Hydroxide into Layered Manganese Oxides

A series of Ni(OH) 2 −manganese oxide (NMO) compounds with a mixed layered structure were synthesized by inserting nickel hydroxide into layered manganese oxides, Na−birnessite (NaBir) and Ni−birnessite (NiBir), under hydrothermal conditions. The hydrothermal intercalation reaction and the NMO compounds were investigated by pH titration, XRD, IR, SEM, TG-DTA, and chemical composition analysis. Ni(OH) 2 is preferentially formed in the interlayer space of the birnessites. The mixed layered NMO with Ni(OH) 2 content up to Ni/Mn = 1/2 can be obtained by using the hydrothermal intercalation method. Ni(OH) 2 was more easily inserted into NiBir than into NaBir under the hydrothermal conditions. A mechanism of topotactic insertion reaction was proposed for the formation of the mixed layered compounds. The mixed layered NMO can be also prepared by hydrothermal treatment of NaBir in Ni(Ac) 2 solution below 250 °C. The NMO compounds were stable up to 300 °C in air, and transformed to other phases over this temperature.