Synthesis of LiAl₂(OH)₆⁺ intercalated montmorillonite by a hydrothermal soft chemical reaction

A LiAl₂(OH)₆⁺ intercalated montmorillonite was prepared from a montmorillonite by using a hydrothermal soft chemical process. As a first step, lithium aluminium hydroxide complex ions (Li(x)Al(n)(OH)m(z+)) were inserted into the interlayer space of the montmorillonite by an ion-exchange reaction. In the second step, the ion-exchanged montmorillonite was hydrothermally treated to polymerize the complex ions in the interlayer space, forming a sandwich-like layered compound. The mechanism of formation of the sandwich layered structure was investigated by XRD, TG-DTA, chemical analyses and FTIR spectroscopy. Na⁺ and Ca²⁺ ions in the interlayer space of the montmorillonite were first exchanged with Li(x)Al(n)(OH)(m)(z+) complex ions, and during this process the basal spacing of the montmorillonite increased from 1.6 to 2.0 nm after the ionexchange. Two types of reactions of the ion-exchanged montmorillonite were observed under the hydrothermal conditions. In the temperature range 100-150 °C, the basal spacing changed from 2.0 to 1.7 nm, corresponding to polymerization of Li(x)Al(n)(OH)(m)(z+) complex ions to LiAl₂(OH)₆⁺ layers between the silicate layers. At temperatures over 200 °C, Li⁺ ions of LiAl₂(OH)₆⁺ layers probably migrated into the octahedral sheets of silicate layers, accompanied by a decrease of the basal spacing from 1.7 to 1.4 nm. The Li(x)Al(n)(OH)(m)(z+) complex ion was also used for pillaring montmorillonite, and a pillared montmorillonite with a basal spacing of 1.5 nm was obtained by heat treatment of this Li(x)Al(n)(OH)(m)(z+) ion-exchanged montmorillonite in air at 500 °C.