Partic. vol. 8 no. 3 pp. 212-220 (June 2010)
doi: 10.1016/j.partic.2010.03.004

Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

Hong Yan^a, Min Wei^a,*, Jing Ma^b, Xue Duan^a

weimin@mail.buct.edu.cn

Abstract

A density functional theory (DFT) study has been carried out for [Zn_n−1Al(OH₂)_n+6(OH)_2n−2]³⁺ (n = 3–6) and [Zn_n−1Al(OH₂)_2n−2(OH)_2n−2]³⁺ (n = 7) clusters, which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides (LDHs) with Zn/Al molar ratio (R) in the range 2–6, in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs. Based on systematic calculations of the geometric parameters and formation energies of the cluster models, it was found that it is possible for Zn²⁺ and Al³⁺ cations to replace Mg²⁺ isomorphously in the brucite-like structure with different R values, resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs. Analysis of the geometry and bonding around the trivalent Al³⁺ or divalent Zn²⁺ cations reveals that Al³⁺ plays a more significant role than Zn²⁺ in determining the microstructure properties, formation and bonding stability of the corresponding ZnRAl clusters when R < 5, while the influence of Zn²⁺ becomes the dominant factor in the case of R ≥ 5. These findings are in good agreement with experiments. This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.

Keywords

Layered double hydroxide; Zn/Al molar ratio; Density functional calculation; Microstructure; Formation and bonding stability