Efficient Separation of Terephthalate and Phthalate Anions by Selective Ion-Exchange Intercalation in the Layered Double Hydroxide Ca₂Al(OH)₆·NO₃·2H₂O

Abstract

The brucite-like Ca 2+ /Al 3+ layered double hydroxide (LDH), Ca 2 Al(OH) 6 ·NO 3 ·2H 2 O, was synthesized using the coprecipitation method. The dicarboxylate anion 1,4-benzenedicarboxylate can be selectively intercalated into the layered double hydroxide Ca 2 Al(OH) 6 ·NO 3 ·2H 2 O from an aqueous solution containing an equimolar mixture of the 1,2- and 1,4-benzenedicarboxylates. Time-resolved in situ energy-dispersive X-ray diffraction studies of the competitive intercalation reaction reveal that initially both the 1,2- and the 1,4-benzenedicarboxylates are intercalated in the LDH, followed by replacement of the 1,2-benzenedicarboxylate by the 1,4-isomer as the reaction proceeds. The final thermodynamic product is Ca 2 Al(OH) 6 ·[1,4-C 8 H 4 O 4 ] 0.5 · x H 2 O.