Exfoliation of layered double hydroxides by an electrostatic repulsion in aqueous solution

Ni/Fe layered double hydroxides (Ni/Fe LDHs) with 11-aminoundecanoic acid (AUA) as pillared species (Ni/Fe LDHs-AUA with Ni/Fe = 4) was prepared by a co-precipitation method. The prepared Ni/Fe LDHs-AUA material was successfully delaminated in an aqueous system by a novel host–guest repulsive interaction process. The delaminated LDHs nanosheets were confirmed by XRD, TG-DSC, TEM, AFM, and IR analyses. XRD measurement on the slurry centrifuged from the solution showed an amorphous halo and the crystalline phase of Ni/Fe LDHs-AUA lost its sharp reflections at pH value of 2.0. After freeze-drying the slurry, the broad pattern was converted into a basal diffraction pattern, indicating the restacking of delaminated nanosheets to restore the original stacked form. AFM images showed that a large part of Ni/Fe LDHs-AUA was delaminated into one elementary layer at least, and the delaminated nanosheets had disk-like shapes with a diameter of ca. 100 nm. IR results confirmed the AUA molecules released from the interlayer accompanied with the delamination process and they could not be restacked into the interlayer during freeze-drying the delaminated nanosheets.