Dehydration-rehydration behaviour of layered double hydroxides: a study by X-ray diffractometry and MAS NMR spectroscopy

MgAl and ZnAl double hydroxides were synthesized and their dehydration-rehydration behaviour was studied by X-ray diffractometry and 27Al magic-angle spinning (MAS) NMR spectroscopy. On dehydration the layered structure collapsed, but treatment in water resulted in partial reconstitution of the original structure. On heat treatment part of the octahedrally coordinated aluminium, typical of layered double hydroxides, became tetrahedrally coordinated. On rehydration some of the tetrahedral aluminium became octahedrally coordinated again.