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 degrees 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.

Automated summary

Layered double hydroxides (LDHs) play an important role in various applications due to their biocompatibility, chemical versatility, and high theoretical capacity. This study investigates the crystal morphology control and exfoliation of LDHs. It is found that the interlayer spacing of LDH decreases with the affinity of intercalating ions, making it more difficult to exfoliate into nanosheets. By adjusting reaction conditions and adding specific compounds, the morphology and size of LDH can be controlled. The addition of formamide inhibits the formation of byproducts and reduces the size of LDH nanosheets. NaNO3 improves the monodispersity of LDH nanosheets. Lower standard molar Gibbs free energy leads to larger nanosheets using high saturation co-precipitation method, while the alteration of M2+ shows negligible difference in size and shape using homogeneous co-precipitation method.