Decarbonating layered double hydroxides using a carbonated salt solution

Layered double hydroxides (LDHs) intercalated with tunable anionic species are finding increasingly wide applications. While LDHs with intercalated CO₃^2- anions (LDH-CO₃) are usually synthesized to achieve high crystallinity, the substitution of the intercalated CO₃^2- with other desired anions is rather difficult because of the ultra-high affinity of CO₃^2- to LDHs' main plates. Herein, we report a novel and facile method to overcome this difficulty. LDH-CO₃ is decarbonated via submerging in a carbonated NaCl solution with CO₂ bubbling. Complete deintercalation of CO₃^2- is achieved quickly without damaging the main plates, i.e., the hydroxide layers, even in the case of Mg₂Al-LDH-CO₃ having the most stable CO₃^2- anions. It is shown that carbonic acid H₂CO₃ in the salt solution reacts with intercalated CO₃^2- to form bicarbonate (HCO₃^-), which exhibits a much lower affinity to the main plates and thus is easily substituted by chloride ions (Cl^-) from the salt solution.