Synthesis and adsorption properties of nanosized Mg-Al layered double hydroxides with Cl ^-, NO ^- ₃ or SO ² ₄ ^- as interlayer anion

Nanosized Mg-Al layered double hydroxides (LDHs) with Cl ^-, NO ^- ₃ or SO4 as the interlayer anion have been synthesized by a modified coprecipitation method. The obtained LDHs were confirmed to be composed of a single phase and to be highly substituted by Al (Mg/Al ratio ∼1.9). The abilities of the LDHs to adsorb several harmful anions (F ^-, CrO ₄ ^2-, HAsO ₄ ^2- and HSeO ^3-) in aqueous solution were studied. The LDHs exhibit high adsorption abilities. The amount of adsorption onto the LDHs differed between the starting interlayer anions, and decreased in the following order of the interlayer anions: NO ₃ ^- > Cl ^- > SO ₄ ^2-. The NO ₃-formed Mg-Al LDH reached a CrO ₄ ^2- adsorption equilibrium state within only 30 min, much faster than those in previous reports. Thus, the nanocrystallized, highly Al substituted phase of the NO ₃-formed Mg-Al LDH is found to markedly enhance the anion adsorption ability.