Magnetic metal-organic frameworks for efficient removal of cadmium(II), and lead(II) from aqueous solution

Efficient and convenient methods for the removal of toxic heavy metal ions especially Cd(II) and Pb(II) from aqueous solutions is of great importance due to their serious threat to public health and the ecological system. In this study, two magnetic metal-organic frameworks (namely: Fe3O4@ZIF-8, and Fe3O4@UiO-66-NH2) were synthesized, fully characterized, and applied for the adsorption of Cd(II) and Pb(II) from aqueous solutions. The adsorption efficiencies for the prepared nanocomposites are strongly dependent on the pH of the aqueous solution. The maximum adsorption capacities of Fe3O4@UiO-66-NH2, and Fe3O4@ZIF-8 at pH 6.0 were calculated to be 714.3 mg.g(-), and 370 mg.g(-1) for Cd(II), respectively, and 833.3 mg.g(-1), and 666.7 mg.g(-1) for Pb(II), respectively. The adsorption process follows a pseudo-second-order model and fit the Langmuir isotherm model. Moreover, the thermodynamic studies revealed that the adsorption process is endothermic, and spontaneous in nature. A plausible adsorption mechanism was discussed in detail. The magnetic adsorbents: Fe3O4@ZIF-8, and Fe3O4@UiO-66-NH2 showed excellent reusability, maintaining the same efficiency for at least four consecutive cycles. These results reveal the potential use of magnetic Fe3O4@ZIF-8, and Fe3O4@UiO-66-NH2 as efficient adsorbents in removing Cd(II) and Pb(II) from aqueous solutions.

Automated summary

The study synthesized two magnetic metal-organic frameworks and investigated their adsorption capacities for Cd(II) and Pb(II). The adsorption efficiency is strongly dependent on the pH of the solution, and the process follows a pseudo-second-order model and fits the Langmuir isotherm model.