Assessing the effect of calcination on adsorption capability of Mg/Al layer double hydroxides (LDHs)

The present study was carried out to prepare and characterize calcined Mg/Al layer double hydroxides (LDHs) used in the adsorption of methyl orange in an aqueous solution as an anionic dye in a batch system. Synthesis of LDHs using coprecipitation method with Mg/Al ratio of 3:1 and obtained material was treated by hydrothermal treatment for 4 h in 400 °C. The result showed that hydrothermal treatment on the synthesis of Mg/Al LDHs yielded the formation of mixed metal oxide from magnesium oxide and aluminum oxide on calcined LDHs were shown on a wide diffraction pattern, while infrared spectrum showed that NO 3 − and CO 3 2− as balancing anions disappeared after calcination process. The optimum condition for calcined layer double hydroxides (CLDH) and LDHs were in pH 4 (40.61 mg g −1 ) and pH 3 (36.29 mg g −1 ) for methyl orange adsorption. The equilibrium time for CLDH and LDHs respectively were 3 h and 5 h where the initial time started rapidly. The kinetic study described pseudo-second-order fitted for methyl orange adsorption with R 2  = 0.9998 and 0.9996 for CLDH and LDH. The best isotherm was shown by Freundlich model with R 2  = 0.9957 and 0.9721 for CLDH and LDH and. The results suggested that calcined LDHs were efficient adsorbents for methyl orange remediation of relatively high concentrations.