Calcined graphene/MgAl-layered double hydroxides for enhanced Cr(VI) removal

Graphene/MgAl-layered double hydroxides (G–MgAl-LDH) nanocomposite was prepared by urea-hydrolyzed hydrothermal reaction of Al(NO3)3·9H2O, Mg(NO3)2·6H2O, and graphene oxide (GO) and its structure was well characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometer (EDX). Urea could effectively reduce GO and simultaneously induce the nucleation and in situ growth of LDH crystallites on the nanosheets of graphene. Both LDH and graphene layers were exfoliated in the nanocomposite. The calcined G–MgAl-LDH was easily prepared by heating G–MgAl-LDH at higher temperature and used as a potential nanoadsorbent to remove hexavalent chromium from the aqueous solution. Compared to virgin MgAl-LDH, calcined G–MgAl-LDH exhibited higher adsorption efficiency with lower dosage in removing Cr(VI) from aqueous solution. Maximum adsorption capacity of approximately 172.55 mg/g with 1.0 g/L dosage of calcined G–MgAl-LDH was achieved. The results about the adsorption kinetics, isotherms and thermodynamics indicated that adsorption mechanism of Cr(VI) involved the surface adsorption of graphene and memory effect of calcined LDH and synergistic contribution from each components in calcined G–MgAl-LDH enhanced Cr(VI) adsorption capacity. The as-prepared product could act as a highly-effective nanoadsorbent in heavy metal removal from the wastewater.

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► Uncalicined and calcined G–MgAl-LDH nanocomposites are prepared and well characterized.
► Low dosage of calcined G–MgAl-LDH (1.0 g/L) exhibits high adsorption capacity of Cr(VI) (172.55 mg/g).
► The removal enhancement comes from the synergetic effect of the component of G–MgAl-LDH.