Surface engineering: binary Mg,Fe-LDH·xFe3O4 nanocomposites for improved magnetic solid-phase extraction of pharmaceuticals from aqueous solution

Abstract

In this work, binary Mg,Fe-LDH·xFe₃O₄ (x = 0 to 2.0) nanocomposites were prepared via the in situ growth of Mg,Fe-layered double hydroxides (LDHs) onto magnetite nanoparticles and applied for the removal of diclofenac motives. These materials were prepared by a simple prolonged sonication method and systematically characterized by several techniques (e.g. XRD, VRM, SEM, FTIR, TEM, etc.). The XRD patterns of the magnetic nanocomposites confirm the formation of both LDHs and magnetic phases. The intricate surface functional groups of the starting components played pivotal roles in the formation of magnetic composites, according to FTIR spectra. The hexagonal plate-like morphology of the Mg,Fe-LDHs and Mg,Fe-LDH·xFe₃O₄ samples is evident from TEM data. The Mg,Fe-LDH·1.0Fe₃O₄ nanocomposite exhibited high agglomeration of the magnetite nanoparticles, which broke their layered structure. Various influencing factors (e.g., concentration, pH medium, and contact time) that are known to influence the adsorption properties of materials were systematically studied to clarify the mechanism of the adsorption process. To assess the safety of the adsorbents, the effect of the adsorbed DCF on the release of metal ions from the LDHs structure was also monitored. Moreover, the Mg,Fe-LDH·xFe₃O₄ (x = 0.1 to 1.0) nanocomposites can be quickly separated from the 400 mL solution by an external NdFeB magnet before and after the magnetic solid-phase extraction process. The capacity of the magnetic nanocomposites to adsorb diclofenac increased with increasing solution pH. At 25 °C and pH = 7.5, the maximum adsorption capacities for Mg,Fe-LDH·0.1Fe₃O₄ and Mg,Fe-LDH·0.3Fe₃O₄ were 153.2 mg g⁻¹ (0.48 mmol g⁻¹) and 143.2 mg g⁻¹ (0.45 mmol g⁻¹), respectively, which do not exceed the capacities for the starting Mg,Fe-LDHs (158.1 mg g⁻¹). Further results indicated that the adsorption isotherm for diclofenac anion retention could be fitted to the Langmuir equation. The FTIR and XRD data indicate that organic molecules are adsorbed on the obtained materials by electrostatic and complex-forming processes without significant anion-exchange reactions. Moreover, after 3 regeneration cycles, the magnetic nanocomposites still retained a highly ordered structure and morphology with a magnetic response.