Control on the Stacking Mode in a Sulfonic Covalent Organic Framework Enabling a Precise Uranyl-Identified Pocket for Ultrahigh-Capacity Uranium Extraction from Seawater.

Designing a precise uranyl-identified motif in materials to meet the planar coordination nature of uranyl ion is highly important for uranium extraction from seawater but remains a challenging issue. Herein, we find that the control on the stacking mode in sulfonic-COF (covalent organic framework) can be used to create a precise uranyl-identified motif. The AB stacking in sulfonic COF leads to the formation of a uranyl-identified pocket that can execute an exact recognition toward uranyl through a planar four coordination, thus allowing for not only a high affinity toward uranyl with a Kd value of 10 × 109 mL/g but also a high U/V selectivity up to 103. More attractively, in natural seawater, sulfonic-COF in the AB stacking mode affords an ultrahigh extraction capacity of 31.5 mg/g in just 1 day and 37.1 mg/g in 7 days, creating a record in this field. At the same time, the uptake of other ions such as Fe, Cu, Zn, and V is extremely low (less than 2 mg/g), suggesting the superior potential of the sulfonic-COF in AB stacking for acquiring uranium from seawater.