nuclear energy. [1][2] Generally, selective adsorption of UO 2 2+ was viewed to be one of the best effective methods to achieve UO 2 2+ separation, due to the complicated environment in both spent fuel or seawater that contains a large number of other metal ions except for UO 2 2+ ion. [3] Accordingly, there have paid a long-term and big effort to enhance the selectivity of uranyl over other metal ions (S U/M ) selectivity by designing various adsorption sites via tuning their affinity towards UO 2 2+ such as amidoxime, phosphonic, sulfonic, and carboxylate units. [4][5][6][7][8][9][10][11][12][13][14][15] Although there have obtained a great achievement in this route, however, this two-step route still suffers two inherently scientific and industrial problems. One is coadsorption, viz. while it captures UO 2 2+ ions, it also adsorbs other metal ions. Inevitably, this not only reduces the S U/M selectivity, but also requires further purification. The other is the regeneration of UO 2 2+ from adsorbents by means of desorption, where we commonly use of acid or base as eluent; however, this could not only damage the adsorbent, leading to sharp decrease in adsorption performance and subsequent reusability, but also bring secondary pollution and high cost. [13d] Alternative to this two-step S U/M method, we proposed a direct separation approach by means of coordination sieve effect (CSE) with reverse selectivity (S M/U ), which could theoretically avoid further purification and the use of eluent, representing a more simple, low-cost, and facile counterpart. Although direct separation through MSE has been shown promising potential in gas separation such as C 2 H 2 and C 2 H 4 purification, [16] however, to the best of our knowledge, there is still unknown about direct separation of metal ions through CSE.CSE with S M/U means highly capturing other metal ions, but excluding UO 2 2+ ion. This could be theoretically accessed if designing a unique coordination surrounding to fix other metal ions, except for UO 2 2+ ion. As we know, UO 2 2+ ion owns the unique planar coordination feature, [17] due to the presence of two uranyl oxygen atoms, where the location of adsorption sites is co-plane; by contrast, other metal ions such as monovalent Cs + , divalent Sr 2+ , trivalent Eu 3+ , and tetravalent Th 4+ ions (usually existed in spent fuel or seawater) generally take the spherical coordination character, [18] where the adsorption sites are arranged in a surrounding way. In this regard, 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 2 2+, different from the previously established two-step separation method, adsorption plus desorption is reported. The used adsorbent, polyhedron-based hydrogenbond framework (P-HOF-1), made from a metal-organic framework (MOF) precursor through a...