Hydrated layered manganese dioxide: Part I. Synthesis and characterization of some hydrated layered manganese dioxides from α-NaMnO2

Hydrated layered manganese dioxides with the birnessite structure (monoclinic Na-birnessite, hexagonal Na-birnessite and hexagonal K-birnessite) were synthesized from the ternary phase α-NaMnO2. The synthesis of monoclinic Na-birnessite was carried out through hydrolysis in air. Hexagonal Na-birnessite was prepared by oxidation of monoclinic Na-birnessite with excess Br2, 6 M NaOH, while hexagonal K-birnessite was prepared by oxidation of monoclinic Na-birnessite with K2S2O8. The characterization of the synthesized samples was carried out using chemical analysis, X-ray diffraction (XRD) measurement, IR and ion exchange. Samples were found to possess the layered structure with good crystallinity and reversible changes of the interlayer distance. Moreover, type and amount of the guest ion affect the lattice symmetry. IR spectra of the hydrated phases enhance the presence of at least two types of OH groups.