Recyclable Fe₃O₄@UiO-66-PDA core-shell nanomaterials for extensive metal ion adsorption: Batch experiments and...

With the ever-increasing challenge of heavy metal pollution, the imperative for developing highly efficient adsorbents has become apparent to remove metal ions from wastewater completely. In this study, we introduce a novel magnetic core-shell adsorbent, Fe₃O₄@UiO-66-PDA. It features a polydopamine (PDA) modified zirconium-based metal-organic framework (UiO-66) synthesized through a simple solvothermal method. The adsorbent boasts a unique core-shell architecture with a high specific surface area, abundant micropores, and remarkable thermal stability. The adsorption capabilities of six metal ions (Fe³⁺, Mn²⁺, Pb²⁺, Cu²⁺, Hg²⁺, and Cd²⁺) were systematically investigated, guided by the theory of hard and soft acids and bases. Among these, three representative metal ions (Fe³⁺, Pb²⁺, and Hg²⁺) were scrutinized in detail. The activated Fe₃O₄@UiO-66-PDA exhibited exceptional adsorption capacities for these metal ions, achieving impressive values of 97.99 mg/g, 121.42 mg/g, and 130.72 mg/g, respectively, at pH 5.0. Moreover, the adsorbent demonstrated efficient recovery from aqueous solution using an external magnet, maintaining robust adsorption efficiency (>80%) and stability even after six cycles. To delve deeper into the optimized adsorption of Hg²⁺, density functional theory (DFT) analysis was employed, revealing an adsorption energy of -2.61 eV for Hg²⁺. This notable adsorption capacity was primarily attributed to electron interactions and coordination effects. This study offers valuable insights into metal ion adsorption facilitated, by magnetic metal-organic framework (MOF) materials.