Hybrid Strategy for In Situ Shaping of Zeolite-Imidazolate-Frameworks into Polymeric Macrocapsule: Toward Practical Applications of Rare Earth Element Recovery

Abstract

The efficient recovery of rare earth elements (REEs) from secondary sources is an urgent global challenge. Although zeolite-imidazolate-framework-8 (ZIF-8) has unique advantages for REE recovery, its nanopowder form poses a significant obstacle to its practical application. Herein, the study proposes a novel in situ strategy for shaping ZIF-8 into hierarchical 3D center-radial channels of a polymeric macrocapsule (PMC) via a hybrid approach. Core？shell-type ZIF-8-PMC hybrids (ZIF-8@PMC) with the intrinsic physicochemical properties of ZIF-8 are synthesized by combining counter-diffusion-based in situ growth and phase transformation, enabling unprecedented REE recovery of 463.6 and 580 mg g？1 for Nd3+ and Dy3+, respectively, which are superior to that of traditional encapsulating protocols. Moreover, ZIF-8@PMC exhibits good applicability in the simulated permanent magnet leachate with recovery efficiencies of 92.5% (Nd3+) and 81.8% (Dy3+), after five repetitive cycles because of its protective nanoporous shell layer that prevents the release of in situ-shaped ZIF-8 to the exterior and invasion of external particulates into the PMC. Overall, these findings demonstrate the suitability of PMC as an ideal platform for the in situ shaping of ZIF-8 and the application of the newly proposed protocol as a promising approach to expand the applicability of ZIF-8 in various fields.