Highly effective and selective recovery of Gd(III) from wastewater by defective MOFs-based ion-imprinted polymer: Performance and mechanism

Developing a high-performance adsorbent for the recovery of Gd(III) from wastewater is of great environmental and economic significance. Metal organic frameworks (MOFs) functionalized with mixed-linker defect strategy hold huge potential for use as adsorbents for removing heavy metal ions from wastewater. However, the defective MOFs still show a relative low selectivity to target metal ions. Herein, we propose the combination of surface-imprinting and defect engineering strategies to synthesize Gd(III) ion-imprinted polymers (G-IIPs) based on mixed-linker Zr-MOFs, and apply them for capturing Gd(III) ions from wastewater. It is worth noting that 2-hydroxyphosphonoacetic acid not only served as monodentate ligand to in-situ induce ligand vacancies and form hierarchical pores on UiO-66-NH2, but also as high-efficient functional monomer in imprinted layer to provide the strong coordination ability towards Gd(III). Benefiting from its abundant binding sites and hierarchical pore structure, the as-prepared G-IIP-3 with rich defects displays a high adsorption capacity of 181.75 mg·g−1 and a short equilibration time of 30 min for Gd(III). In addition, G-IIP-3 presents highly selective capture of Gd(III) over interfering ions. Furthermore, density functional theory calculation demonstrates that both phosphate group and Zr-O cluster play key roles in the Gd(III) adsorption process. Thus, this work provides an effective method to develop high-performance materials for Gd(III) recovery by organically combining the advantages of surface-imprinting and defect engineering strategies.