Deintercalation of carbonate ions and anion exchange of an Al-rich MgAl-LDH (layered double hydroxide)

A novel method to deintercalate carbonate ions (CO32−) from a layered double hydroxides (LDHs) with NaCl–HCl solutions was applied to well-crystallized Al-rich LDH2 (LDH with Mg/Al ≈ 2) prepared by using hexamethylenetetramine (HMT). Enhanced deintercalation of the carbonate ions was observed, and the reaction occurred without any morphological changes at 25 °C under proper HCl/NaCl concentration conditions. The optimum decarbonation conditions were the molar ratio [H+]solution/[CO32−]LDH = 1.5–2.0, HCl concentration at around 0.005N, and NaCl concentrations more than 4 mol/L. The decarbonation was affected by the Mg/Al ratio of LDH. LDH2 was more difficult to decarbonate than LDH3 (Mg/Al ≈ 3) probably due to its higher layer charge. The obtained Cl− form of LDH2 (Cl−LDH2) could be converted into organo-LDH2s by normal anion exchange with long chain carboxylates, retaining the crystal morphology.