Excellent adsorption of Acid Flavine 2G by MgAl-mixed metal oxides with magnetic iron oxide

Abstract Background Most of synthetic dyes that appear in wastewaters may pose aesthetic problem even at a very low concentration. Adsorption is an important method for dye removal. Layered double hydroxides (LDHs) and calcined layer double hydroxide (CLDH) as adsorbents have received wide attention, which combined with magnetic iron oxide, would be better for LDHs/CLDH separation and recycle. Methods Co-precipitation method was used to prepare the composites of LDHs and magnetic iron oxide (Fe/LDHs). Then Fe/LDHs were calcined at 450 °C for 4 h to obtain Fe/CLDH. The prepared materials were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption measurements, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Batch adsorption experiments were carried out to investigate the removal of Acid Flavine 2G (AF 2G) from aqueous solution by using Fe/CLDH as the adsorbent. Results Fe/LDHs and Fe/CLDH were successfully prepared. The adsorption process could be well described by the pseudo-second order kinetic model and fitted well with the Langmuir isotherm model. The values of thermodynamic parameters (ΔH, ΔS and ΔG) indicated that the adsorption process was endothermic and spontaneous. Competitive adsorption experiments showed that competing anions strongly affected the adsorption process. The adsorption of AF 2G occurred only on external surface of the LDH. After 5 cycles of magnetic separation, regeneration and calcination, the removal efficiency of AF 2G was still above 85%. Conclusions Fe/CLDH could be used as a low-cost and alternative sorbent for the removal of dyes from wastewaters.