Chapter 17 - Assembly Chemistry of Anion-intercalated Layered Materials

Abstract

Layered double hydroxides (LDHs) are a group of anion-intercalated inorganic functional materials, which are also known as hydrotalcite-like compounds or anionic clays. In LDHs, positively charged metal hydroxide host layers stack alternately with interlayer anions to form a sandwich structure. The metal ions in the host layer are octahedrally coordinated divalent MII and trivalent MIII cations, whereas the interlayer anions interact with the host layers by ionic bonding, hydrogen bonding, and van der Waals forces. Much of the interest in LDHs arises from their wide range of possible compositions which give rise to the possibility of tailoring the properties of the material in several different ways to realize the microscopic controllability of layer chemical composition, the microscopic controllability of the nature and amount of interlayer anions, and the mesoscopic controllability of crystallite size and size distribution. Great efforts have been focused on detailed studies of the structure of LDHs including the possible range of stoichiometry and composition, the extent of ordering of metal cations within the layers, the stacking arrangement of the layers, and the distribution of interlayer anions and water molecules. In the lattice of LDHs, trivalent MIII cations substitute some of the Mg2+ in the brucite layers resulting in positively charged host layers, and the interlayer An- anions are located in hydrated interlayer galleries, whereas the host layers stack on top of one another to form a three-dimensional structure.