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

Abstract

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 (LixAln(OH)mz+) 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 LixAln(OH)mz+ complex ions, and during this process the basal spacing of the montmorillonite increased from 1.6 to 2.0 nm after the ion-exchange. 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 LixAln(OH)mz+ 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 LixAln(OH)mz+ 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 LixAln(OH)mz+ ion-exchanged montmorillonite in air at 500°C.