Efficient Separation of Adjacent Rare Earths in One Step by Using Ion-microporous Metal–Organic Frameworks

Abstract

High-purity rare earth (REEs) materials are key raw materials for the development of cutting-edge technologies. However, due to similar physical and chemical properties, separating adjacent REEs from actual samples faces a formidable challenge. To overcome this challenge, an ion-microporous metal–organic framework (ATZ-BTC-Zn; MOFs) is designed and synthesized, featuring densely packed nano-trap pockets constructed from non-coordinating carboxyl and amino groups. The synergistic effect of open nano-trap pockets and suitable ions channel in ATZ-BTC-Zn is highly responsive to the size variation of lighter REEs. Notably, the configuration of Zn(H₂O)₆²⁺ counterion in ATZ-BTC-Zn is similar to lanthanide hydrated ions (Ln(H₂O)₆³⁺), facilitating the efficient ion exchange between them in the high-speed ion transport channel. This accelerates the diffusion of REEs within the MOF pores, enhancing the utilization of active adsorption sites and promoting the efficient capture of adjacent REEs by nano-traps. The binary model experiments show high separation factors for adjacent REEs (SF_La/Nd = 908, SF_Ce/La = 543), demonstrating efficient separation by ATZ-BTC-Zn in one step. This capability achieves the selective separation of adjacent REEs in tailings wastewater, providing a strategy to infer the compatibility between MOFs and REEs.