Stability of polytypes 3R2 Mg-Al Layered Double Hydroxides towards various anions

Polytype 3R2 Mg-Al layered double hydroxides contain tetrahedral aluminates ion in its interlayer. In this research, the possibility of other tetrahedral coordinated ions to mediate the 3R2 layer stacking was investigated in the two-step hydrothermal synthesis at 170 °C. None of the investigated tetrahedrally coordinated ions, such as sulphate, borate or gallate could mediate the formation of the 3R2 stacking in the two step synthesis. Ion exchange of aluminate ions in the interlayer of polytype 3R2 is feasible in the following order of preference: CO32− > SO42− > stearate > C2O42− > Br−. The 3R2 stacking is however not conserved, as the ion exchanged products have 3R1 stacking sequence.

► Ion exchange of polytype 3R2 Mg-Al LDH is accompanied by the formation of boehmite.
► The 3R2 stacking cannot be sustained upon ion exchanged, as it transformed into 3R1.
► The grafted aluminates in polytype 3R2 make it less readily ion exchanged.