Adsorption and intercalation of organic pollutants and heavy metal ions into MgAl-LDHs nanosheets with high capacity

Abstract

Hexagonal MgAl layered double hydroxide (MgAl-LDH) materials comprised of nanosheets and microsheets with different precipitants were synthesized via a facile hydrothermal route. XRD, FESEM, TEM and BET were employed to characterize the samples. Structural characterization revealed that MgAl-LDHs nanosheets and microsheets are 100 nm and 2 μm in width, respectively. Furthermore, MgAl-LDHs nanosheets have a higher specific surface area (65.94 m² g⁻¹) than that of microsheets (15.75 m² g⁻¹). Methyl orange and Cr(VI) anion and Ni(II) cation adsorption on the as-synthesized MgAl-LDHs nanosheets and microsheets were systematically assessed by measuring the residual concentration during the adsorption process. The MgAl-LDHs nanosheets showed better adsorption performance than the MgAl-LDHs microsheets for methyl orange and Cr(VI) anions and Ni(II) cations. The adsorption performance versus time for the adsorption of methyl orange by MgAl-LDHs nanosheets has an excellent adsorption quantity (229.82 mg L⁻¹) with high adsorption rate. The adsorption kinetics and adsorption isotherms of Cr(VI) anions and Ni(II) cations of MgAl-LDHs nanosheets can be described by the pseudo-second order kinetic and Langmuir isotherm with saturated adsorption of 63.8 and 92.3 mg g⁻¹, respectively. Combined with results from XRD, FTIR, EDS and XPS experiments, the adsorption mechanisms of MgAl-LDHs nanosheets including precipitation, surface complexation, isomorphic substitution and ion exchange in the interlayer space of MgAl-LDHs nanosheets are discussed in detail. Finally, based on the quick and efficient removal of heavy metal ions by MgAl-LDHs nanosheets, a filtering-type water purification device was constructed.