Highly efficient removal of humic acid from aqueous solutions by Mg/Al layered double hydroxides–Fe3O4 nanocomposites

The Mg/Al-layered double hydroxides and iron oxide (LDHs-Fe3O4) nanocomposites were synthesized via a facile two-step wet chemistry route. The fabricated samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), N-2 adsorption-desorption analysis, and thermogravimetric analysis (TGA). The resulting Fe3O4 nanoparticles possess unique magnetic properties for LDHs-Fe3O4 separation and the LDHs-Fe3O4 nanocomposites were applied to remove natural organic macromolecular compound (humic acid, HA) from contaminated groundwater. The results indicate that HA adsorption on LDHs-Fe3O4 is strongly dependent on pH and weakly dependent on ionic strength. The adsorption of HA onto LDHs-Fe3O4 occurs by ion exchange with both the intercalated and surface anions of the LDHs. The magnetite nanoparticles could provide extra adsorption sites for HA removal. In addition, the adsorption isotherm of HA on LDHs-Fe3O4 can be well fitted by the Freundlich model and the maximum adsorption capacity of HA onto LDHs-Fe3O4 reaches 353.82 mg g(-1), displaying higher efficiency for HA removal than previously reported adsorbents. This is attributed to the synergistic effect of LDHs and Fe3O4 for HA adsorption. Experimental results demonstrate that HA can be completely and quickly removed by the LDHs-Fe3O4 nanocomposites. Our prepared LDHs-Fe3O4 nanocomposites are expected to become potential and suitable materials for the HA removal from large volumes of water in