Ultratrace Uranium Removal by Covalent Organic Frameworks on an In-Situ-Decorated Sponge as Integral Materials

Herein, a sulfonated covalent organic framework (COF-SO₃H) is prepared in situ on melamine sponge (MS) to produce MS@COF-SO₃H as integral materials by a one-pot synthesis in water at room temperature, for facile deep removal of trace uranium-containing wastewater. The -SO₃H on the COFs is able to form complexation with UO₂²⁺ through strong coordination interactions, and MS@COF-SO₃H is therefore highly selective for UO₂²⁺ (K_d = 52603 mL g^-1). The adsorption efficiency of MS@COF-SO₃H-3 can reach 97.9% and 87.5% when the initial UO₂²⁺ concentration is 100 and 5 μg L^-1, respectively, and the minimum residual UO₂²⁺ concentration is as low as 0.478 μg L^-1, far lower than that in previous reports. In addition, MS@COF-SO₃H exhibits excellent durability as an adsorbent, and its adsorption efficiency for UO₂²⁺ is still as high as 92.4% even after 5 cycles of recycling. The mild preparation conditions and excellent performance of MS@COF-SO₃H make it quite promising as a highly efficient adsorbent for uranium removal. This work provides an important clue to prepare adsorbents facilely for nuclear wastewater deep treatment.