Boosted capture of trace Cd(II) with a magnetic dual metal-organic-framework adsorbent

Abstract

The microcrystalline powders of metal-organic frameworks (MOFs) are usually difficult to be separated and reused, restricting their applications for cadmium ions (Cd(II)) removal from water. Thus, it is imperative to develop the magnetic adsorbents with high adsorption performances and excellent recoverability. Herein, a novel type of magnetic dual MOFs composite for Cd(II) capture has been successfully synthesized with (ZIF-67)-on-(PMA@MIL-125-NH2) as the adsorption mainstay and Fe3O4 nanoparticle as the magnetic component. The advantages of the combination and its synergistic effect are achieved through the self-assembly process. Owing to the associate effect of abundant adsorption sites and high porosity, (ZIF-67)-on-(PMA@MIL-125-NH2@Fe3O4) exhibits a significant adsorption capacity (152 ​mg ​g−1) and rapid adsorption rate (20 ​min) towards Cd(II). The adsorption data are well fitted by the Freundlich and pseudo-second-order kinetic models. The adsorption mechanism involves the critical contributions of π-π interaction, Lewis's acid-base, surface adsorption, electrostatic attraction, etc. Moreover, the adsorbent could be easy obtained from liquid through Fe3O4 magnetism, exhibiting a good reusability. This work provides a new perspective on the synthesis of high-efficiency adsorbents for the Cd(II) capture from water.