Exfoliation reaction of birnessite-type manganese oxide by a host–guest electrostatic repulsion in aqueous solution

The birnessite-type manganese oxide (BirMO) intercalated with 11-aminoundecanoic acid (AUA) as pillared species (BirMO–AUA) was prepared by an ion-exchange method. The prepared BirMO–AUA material was successfully delaminated in an aqueous system by a novel host–guest repulsive interaction process. The delaminated manganese oxide nanosheets were confirmed by XRD, TEM, AFM, and IR analyses. XRD measurement on the slurry centrifuged from the solution showed an amorphous halo and the crystalline phase of BirMO–AUA lost its sharp reflections at pH = 12. Freeze-drying the slurry, the broad pattern was converted into a basal diffraction pattern, indicating the restacking of delaminated manganese oxide nanosheets. AFM and TEM images showed that a large part of BirMO–AUA material was delaminated into one elementary layer at least, and the delaminated nanosheet had a disk-like shape. IR results confirmed that the AUA molecules released from the interlayer accompanied with the delamination process and they could not be restacked into the interlayer by freeze-drying the delaminated nanosheets. The novel delamination process is favorable for negative inorganic layered materials with high layered charge density.

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