Morphological Control of Layered Double Hydroxides Prepared by Co-Precipitation Method

Layered double hydroxides (LDHs) can be used in various popular fields due to their good biocompatibility, easy chemical modification, and high theoretical specific capacity. However, for different applications, there are different requirements for the morphology of LDH nanosheets. In this paper, the crystal morphological control and the exfoliation states of LDHs are investigated. The interlayer spacing of LDH decreases with the increase of intercalating ion affinity, exhibiting difficulty in being exfoliated into nanosheets. The calculated binding energies between LDH laminates and intercalated ions CO32−, Cl−, and NO3− are 0.311 eV, 0.301 eV, and 0.071 eV, respectively. LDH-NO3− with complete hexagonal shape and high crystallinity can be prepared under the condition of Co:Al:urea = 3:1:10, 90 °C, and 48 h. In the preparation of LDH-NO3− with high saturation co-precipitation method, formamide acts as an effective layer growth inhibitor. When the formamide content is 50%, the size of formed LDH nanosheets is significantly reduced by 28.1%, and when the formamide content is up to 100%, it is further reduced by 7.0%. The addition of formamide can also inhibit the generation of byproducts. The addition of NaNO3 leads to a stronger monodispersity of LDH nanosheets. By comparing CoAl-LDH, MgAl-LDH, and ZnAl-LDH, lower standard molar Gibbs free energy results in a larger nanosheet with high saturation co-precipitation method, but the alteration of M2+ exhibits negligible difference in the size and shape by means of homogeneous co-precipitation.