Cation exchange by anion-exchanging clays: the effects of particle aging

We have observed the effects of exposure to aqueous transition metal cations of freshly prepared, and thermally aged, layered double hydroxides (LDHs) of type Mg2Al(OH)6Cl·xH2O. For M(II) = Co(II), Ni(II), or Zn(II), freshly prepared material undergoes complete reconstitution to give products of composition (M(II)Mg)2Al(OH)6Cl, while thermally aged LDH undergoes surface adsorption of a small amount of M(II) cations. Infrared spectroscopy shows that the former represents a distinct phase, different from both the parent and the M(II)2Al(OH)6Cl, which we prepared for comparison. The same appears true for M(II) = Mn(II), although facile air oxidation complicates the picture. With Cu(II), as might be expected from its high acidity, more extensive changes occur with destruction of the LDH lattice. The results from both types of parent LDH suggest a significant difference in reaction pathways.