Controllable synthesis of Co-Al layered double hydroxides with different anionic intercalation layers for the efficient removal of methyl orange.

In order to investigate the effect of the types of interlayer anions on the adsorption performance of LDHs, herein, we synthesized three cobalt-aluminum layered double hydroxides (CoAl-LDHs) with different interlayer anions (NO/Cl/CO). The experimental results demonstrate that the CoAl-LDH (Cl) exhibited high adsorption capacity of 1372.1 mg/g at room temperature and the fastest adsorption rate on methyl orange (MO), mainly attributed to the excellent ion exchange capacity and high specific surface area and pore volume. Furthermore, the ion exchange driven by electrostatic interaction, hydrogen bonding, and surface complexation might be the main mechanisms for MO adsorption on CoAl-LDH (Cl) and CoAl-LDH (NO). However, the MO adsorption on CoAl-LDH (CO) was strongly pH-dependent and the optimal pH value was about 3.5. Additionally, the supramolecular structure of CoAl-LDHs-MO was formed through electrostatic interaction, hydrogen bonding, and surface complexation between the host hydroxide layers and the guest MO after adsorption equilibrium. An in-depth understanding of the differences in the adsorption performance of three anion-intercalated CoAl-LDHs will provide opportunities for further improvement of the adsorption capacity and exhibit a bright future for the design and optimization of efficient nano-adsorbents shortly.