Insight into the adsorption mechanisms of aqueous hexavalent chromium by EDTA intercalated layered double hydroxides: XRD, FTIR, XPS, and zeta potential studies

Abstract

To understand the possible mechanisms of hexavalent chromium (Cr(VI)) adsorption on the surface of modified layered double hydroxides (LDHs), we synthesized ethylenediaminetetraacetic acid intercalated MgAl-LDH (LDH-EDTA) and its magnetic product (Mag-LDH-EDTA), and evaluated their adsorption performance for Cr(VI) by batch equilibrium experiments. The characterization analysis proved that the EDTA was intercalated into MgAl-LDH and the adsorbents had an ordered structure and abundant functional groups. The adsorption mechanisms of Cr(VI) by LDH-EDTA and Mag-LDH-EDTA could be attributed as electrostatic attraction, surface complexation, anion exchange, and reduction reaction speculating from the detailed X-ray diffraction patterns (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential analysis. The removal ratio remained above 96% and 79% for 50 mg L⁻¹ Cr(VI) using 0.03 g LDH-EDTA and Mag-LDH-EDTA, respectively. The adsorption process was less influenced by the pH value of the aqueous solution. The pseudo-second-order model and the Langmuir equation well fitted to the adsorption kinetic and isotherm data. Thus, the EDTA intercalated LDH materials had potential applications for Cr(VI) removal in real wastewater treatment.