ZnO-MgFe2O4/(Mg)- or (Zn)-Al-ldh Composites: Adsorption Efficiency, Kinetics, and Adsorption Isotherm for Congo Red Removal

In this research, ZnO-MgFe2O4/ZnAl-LDH, ZnO-MgFe2O4/MgAl-LDH, ZnO-MgFe2O4, ZnAl-LDH and MgAl-LDH were prepared and characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and FT-IR spectrometer analyses. The samples were synthesized by the co-precipitation method. The efficiency of the samples was investigated for the Congo red dye removal from the aqueous solution. According to the results, a similar efficiency for the LDHs samples and ZnO-MgFe2O4/LDHs composites was observed. The experimental data for the ZnO-MgFe2O4/ZnAl-LDH and ZnO-MgFe2O4/MgAl-LDH composites were analyzed by adsorption isotherm (Langmuir and Freundlich) and kinetic models (pseudo-first-order, pseudo-second-order, and intra-particle diffusion). The results showed that more than >90% of the Congo red dye was removed from the solution after 90 min contact time. The experimental results showed the adsorption process fitted well with the Langmuir isotherm model and pseudo-second-order kinetic model. For the ZnO-MgFe2O4/ZnAl-LDH and ZnO-MgFe2O4/MgAl-LDH samples, the RL value close to zero (0.024 and 0.037) was obtained. This result indicates that the adsorption of the CR dye molecules on the surface of the samples is an almost irreversible process. The low RL value indicates that the interactions between Congo red dye molecules and LDH composites might be relatively strong.