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.