Different dye removal mechanisms between monodispersed and uniform hexagonal thin plate-like MgAl-CO₃^2--LDH and its calcined product in efficient removal of Congo red from water

Monodispersed and uniform hexagonal thin plate-like magnesium-aluminum layered double hydroxide intercalated with CO₃^2- (MgAl-CO₃^2--LDH) is synthesized by an ethanol-water mediated solvothermal method. The maximum adsorption capacities of the as-synthesized and calcined MgAl-CO₃^2--LDH are 129.9 and 143.27 mg g^-1, respectively, which are higher than those of the other metal oxide nanostructures reported to date. More importantly, although N₂ adsorption-desorption analysis indicates that the BET surface area changed from 24.74 m² g^-1 for the as-synthesized MgAl-CO³_2--LDH to 165.07 m² g^-1 for the calcined MgAl-CO³_2--LDH, the as-synthesized and calcined hexagonal thin plate-like MgAl-CO³_2--LDH structures show similar adsorption capacity of Congo red (CR) from aqueous solution. The adsorption mechanism for the as-prepared LDH is anion exchange while adsorption mechanism for the calcined LDH is reconstruction. Our study opens a new insight for understanding and preparing high-performance adsorbents for organic dye removal.