Hierarchical MFe₂O₄ Core-shell Layered Double Hydroxide Composites As Magnetic Adsorbents For Anionic Dye Removal For Wastewater （M=Fe, Zn, Co, Ni）

With the rapid development of modem industry, the global industrial water consumption was rapid rising. The industrial water demand headed by the textile industry increased, and the dyes wastewater was the main textile industry wastewater, which caused the dyes wastewater treatment to be a hot and emphasis research project in modern times. As an efficient method to treat dyes wastewater, traditional adsorption methods and its adsorbents have some weakness, such as low seperation efficency, high cost and low adsorption capacity. But a new multi-functional material-Layered Double Hydroxide (LDH) showed many advantages in wastewater treatment, for its "memory effect" and changeability. And the composites connected with LDH and magnetic material could overcome many defects of traditional adsorbents.Through solvothermal reaction, MFe2O4 particles were prepared. And Mg3Al-CO3 LDHs were loaded on the surface of MFe2O4 nanoparticles by co-precipitation method, then the core-shell MFe2O4@MgAl-LDH structure was formed. The factors such as aging time, aging temperature, calcination temperature, ionic strength, pH of solution, dosage of adsorbent and the ratio of methanol/water were tested. The crystal structure, morphology, magnetization and surface area were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and BET. And using Fourier transform infrared spectroscopy (FTIR), visible spectrophotometer and ultraviolet-visible spectrophotometer (UV-Vis) to analyze the process of adsorption.The results indicated that the material was composed of spherical MFe2O4 (300～400 nm) core with a vertically aligned Mg3Al-CO3 LDH shell coating. CoFe2O4 showed the best magnetization and thermol ability. The optimal conditions of aging temperature, aging time, the ratio of methanol/water, adsorption temperature, dosage of adsorbent, pH value, ionic strength, concentration of Mg/Al solution and calcination temperature were found to be:30～90℃,12～48 h,1:1,20～35℃,0.48 gadsorbent/gdye,7.0～9.0,0.001～0.1 mol/L,15 mmol/L and 400℃, respectively. Under these conditions, the adsorption capacity of CoFe2O4@ Mg3Al-CO3 LDH for C.I.Acid Yellow 219 (AY219) reached 2016 mg/g. And after 10 times cycle adsorpiton, the adsorption efficiency was still up to 80% with 1698 mg/g adsorption capacity. It proved that the adsorbent prepared in this study was a high efficiency and environment friendly material, which was easy to seperate under magnetic field with a good adsorption performance. In conclusion, MFe2O4@Mg3Al-CO3 LDH, especially CoFe204@Mg3Al-CO3 LDH, had a better application prospect in the treatment of dye wastewater.