Decarbonating layered double hydroxides using a carbonated salt solution

Abstract

Layered double hydroxides (LDHs) intercalated with tunable anionic species are finding increasingly wide applications. While LDHs with intercalated CO₃²⁻ anions (LDH-CO₃) are usually synthesized to achieve high crystallinity, the substitution of the intercalated CO₃²⁻ with other desired anions is rather difficult because of the ultra-high affinity of CO₃²⁻ 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 CO₃²⁻ 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 CO₃²⁻ anions. It is shown that carbonic acid H₂CO₃ in the salt solution reacts with intercalated CO₃²⁻ 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.