Direct Synthesis of Unilamellar MgAl-LDH Nanosheets and Stacking in Aqueous Solution

Two-dimensional (2D) materials, such as graphene, inorganic oxides, and hydroxides, are one of the most extensively studied classes of materials due to their unilamellar crystallites or nanosheet structures. In this study, instead of using the universal exfoliation method of the bulky crystal precursor, 2D crystals/nanosheets of MgAl-layered double hydroxides (LDHs) were synthesized in formamide. We propose that the obtained crystals are unilamellar according to the XRD, TEM, and AFM observations. The HRTEM and fast Fourier transform images confirm that the crystal structures are the same as those of the exfoliated MgAl-LDH nanosheets. The directly synthesized sheets can stack into a 3D crystal structure, which is the same as that of typical LDHs except for the disordered orientation of the a-/b- crystal axis of each sheet. This result provides not only a novel approach to the preparation of 2D crystals but also insight into the formation mechanism of LDHs.