High-capacity uranium extraction from seawater through constructing synergistic multiple dynamic bonds

Abstract

Seawater is the largest uranium reserve in the world, and the efficient extraction of uranium from seawater could facilitate the sustainable development of the nuclear industry for thousands of years. However, conventional extraction processes must suffer the dissociation of CO32− ions from [UO2(CO3)3]4− anions to bind the uranyl core, which has a high energy barrier, resulting in poor selectivity and long working times. Here we combine a molecular templating strategy to synthesize several hydroxy-rich covalent organic frameworks with tunable nanopore sizes. In the 1.2-nm-sized covalent organic framework cavity, hydroxyl groups coupled with the hydrogen-bonded NH4+ cations selectively bind uranyl tricarbonate ions via synergistic electrostatic and hydrogen-bonding interactions. This framework exhibits high uranium extraction capability with a removal ratio of > 99.99% in 400 min (initial concentration of 5 ppm at 298 K, pH = 8–9). Notably, a record uranium adsorption uptake is achieved with a capacity of 23.66 mg g−1 in seven days from natural seawater, surpassing that of classical amidoxime-based adsorbents by a factor of 350%. The synthesis of covalent organic frameworks with a multiple-dynamic-bonds strategy realizes selective extraction of uranyl tricarbonate anions from ultra-low concentrations and multiple interfering ions.