Highly efficient removal of methyl orange in aqueous solutions by calcined-layered double hydroxides

Zn–Al-layered double hydroxides were firstly prepared and then dehydrated to calcined-layered double hydroxides (c-LDHs) by annealing at elevated temperature. The structure, surface area, and adsorption properties of the prepared samples were studied. The results show that the surface area of the c-LDHs is enlarged compared to their precursors, which is favorable for the adsorption of methyl orange (MO). The optimum pH for the adsorption of MO ranges from 4 to 9. In such conditions, MO can be adsorbed on the surface and inserted into the layers of the adsorbent, thus the c-LDHs possess high adsorption capacity even at low MO concentration. The adsorption process can be well described by the pseudo-second-order kinetic model, and the adsorption isotherm of MO on the c-LDHs follows the Langmuir equation. The adsorption mechanism of MO on the c-LDHs and the recycling adsorption performance of the c-LDHs are also discussed.