Cr(VI) removal from aqueous solutions by hydrothermal synthetic layered double hydroxides: Adsorption performance, coexisting anions and regeneration studies

Layered double hydroxide (LDH) materials comprising of Mg/Al, Ni/Al and Zn/Al with molar ratio (M2+/Al3+ = 3) were synthesized via a facile hydrothermal route. The microstructures, morphologies and textural properties of the LDH materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption–desorption techniques. It was found that the three LDHs with different divalent metal cations were constructed from nanosheets with well-defined shapes and sizes. Adsorption rates and isotherms of the LDH adsorbents for Cr(VI) were investigated in batch experiments. Desorption behaviors and regeneration of Cr(VI)-adsorbed LDHs at the solid liquid interface were also studied. The ZnAl-LDH exhibited excellent sorption capacity (68.07 mg/g) for Cr(VI) and good regeneration performance. The effect of coexisting anions on the adsorption performance revealed that the anions (CO32−, HCO3−) greater impact on the adsorption process due to their larger laminate binding energy and closer affinity for hydrotalcite material.