Anion-Exchange Reactions of Layered Double Hydroxides: Interplay between Coulombic and H-Bonding Interactions

The NO₃⁻- and Cl⁻-containing layered double hydroxides (LDHs) of Mg with Al interact weakly with anions in solution under equilibrated conditions and yield a type V isotherm. The uptake of anions under nonequilibrated conditions varies monotonically with the layer charge when the outgoing anion is NO₃⁻, whereas it goes through a maximum when the outgoing anion is Cl⁻. These observations suggest that Coulombic interactions play a dominant role in Cl⁻-LDHs, whereas weak interactions governing the mode of intercalation of NO₃⁻ ions influence the exchange reactions of NO₃⁻-LDHs. These studies have significant implications for the remediation of insidious anions by LDHs.