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

Abstract

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), N₂ 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 industrial applications.