Ultrasound-assisted synthesis of single layer MgAl hydrotalcite for the removal of Cr(VI) in solution and soil

Abstract

The controllability of composition and structure of layered double hydroxide (LDH) is one of the important grounds for their widespread use in removing hexavalent chromium (Cr(VI)) from the environment. In this study, single-layer LDHs were successfully produced through an ultrasound-assisted process in the presence of formamide and characterized by X-Ray diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM) and surface energy. Then LDHs were utilized to remove Cr(VI) in solutions, of which the results demonstrated that delaminated MgAl in formamide with ultrasound (F-U-MgAl) had the highest adsorption efficiency, and the adsorption equilibrium was reached in the first 1 min, with a removal rate of 100%. While the removal rate of Cr(VI) by delaminated MgAl without ultrasound (F-MgAl) and MgAl were only 77% and 12% after 60 min. Based on the XRD patterns and SEM images of samples before and after adsorption, the adsorption mechanisms of F-U-MgAl included anion exchange, surface adsorption and electrostatic attraction.The effects of initial pH, dosage, initial concentration, coexisting anions, and HA were also investigated. In addition, the adsorption in Cr(VI)-containing soil by LDHs was considered, and the results indicated that the single-layer LDHs had a broad application prospect in soil remediation. Besides that, we had also verified the above conclusion through the phytotoxicology tests.