Why Do Carbonate Anions Have Extremely High Stability in the Interlayer Space of Layered Double Hydroxides? Case Study of Layered Double Hydroxide Consisting of Mg and Al (Mg/Al = 2)

Layered double hydroxides (LDHs) are promising compounds in a wide range of fields. However, exchange of CO32– anions with other anions is necessary, because the CO32– anions are strongly affixed in the LDH interlayer space. To elucidate the reason for the extremely high stability of CO32– anions intercalated in LDHs, we investigated in detail the chemical states of CO32– anions and hydrated water molecules in the LDH interlayer space by synchrotron radiation X-ray diffraction, solid-state NMR spectroscopy, and Raman spectroscopy. We found the rigidity of the network structure formed between the CO32– anions, hydrated water molecules, and the hydroxyl groups on the metal hydroxide layer surface to be a crucial factor underlying the stability of CO32– anions in the LDH interlayer space.