Direct Separation of UO 2 2+ by Coordination Sieve Effect via Spherical Coordination Traps.

Molecule sieve effect (MSE) can enable direct separation of target, thus overcoming two major scientific and industrial separation problems in traditional separation, coadsorption, and desorption. Inspired by this, herein, the concept of coordination sieve effect (CSE) for direct separation of UO , different from the previously established two-step separation method, adsorption plus desorption is reported. The used adsorbent, polyhedron-based hydrogen-bond framework (P-HOF-1), made from a metal-organic framework (MOF) precursor through a two-step postmodification approach, afforded high uptake capacity (close to theoretical value) towards monovalent Cs , divalent Sr , trivalent Eu , and tetravalent Th ions, but completely excluded UO ion, suggesting excellent CSE. Direct separation of UO can be achieved from a mixed solution containing Cs , Sr , Eu , Th , and UO ions, giving >99.9% removal efficiency for Cs , Sr , Eu , and Th ions, but <1.2% removal efficiency for UO , affording benchmark reverse selectivity (S ) of >83 and direct generation of high purity UO (>99.9%). The mechanism for such direct separation via CSE, as unveiled by both single crystal X-ray diffraction and density-functional theory (DFT) calculation, is due to the spherical coordination trap in P-HOF-1 that can exactly accommodate the spherical coordination ions of Cs , Sr , Eu , and Th , but excludes the planar coordination UO ion.