Direct Separation of UO₂²⁺ by Coordination Sieve Effect via Spherical Coordination Traps

Abstract 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 UO₂²⁺, 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 Sr²⁺, trivalent Eu³⁺, and tetravalent Th⁴⁺ ions, but completely excluded UO₂²⁺ ion, suggesting excellent CSE. Direct separation of UO₂²⁺ can be achieved from a mixed solution containing Cs⁺, Sr²⁺, Eu³⁺, Th⁴⁺, and UO₂²⁺ ions, giving >99.9% removal efficiency for Cs⁺, Sr²⁺, Eu³⁺, and Th⁴⁺ ions, but <1.2% removal efficiency for UO₂²⁺, affording benchmark reverse selectivity (S_M/U) of >83 and direct generation of high purity UO₂²⁺ (>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⁺, Sr²⁺, Eu³⁺, and Th⁴⁺, but excludes the planar coordination UO₂²⁺ ion.