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.