Converting Mn/Al layered double hydroxide anion exchangers into cation exchangers by topotactic reactions using alkali metal sulfate solutions

Layered double hydroxides (LDHs), traditional anion exchangers, can be converted into cation exchangers by topotactic reactions using aqueous solutions of alkali metal sulfates. LDHs with the composition [Mn2Al(OH)(6)](A(n-))(1/n)center dot yH(2)O (A(n-) = Cl- or NO3-, CO32-) were reacted with aqueous solutions of Na2SO4. The anion carbonate could only be partially replaced by sulfate.