High-Efficiency Photoenhanced Extraction of Uranium from Natural Seawater by Olefin-Linked Covalent Organic Frameworks

Extracting uranium from seawater with a chemically stable adsorbent is one of the most promising strategies for challenges originating from sustainable nuclear energy industries. Covalent organic frameworks (COFs) featuring highly stable and regular porous network structures possess practical advantages compared to other adsorbents such as metal–organic frameworks. We are interested in designing rational monomers to achieve novel COFs and understanding structure–property relationships to improve the performance of natural seawater uranium extraction. In particular, biofouling is a critical issue for long-term uranium extraction in natural seawater, where it would cause a severe decrease in extraction capacity and high costs for adsorbent recycling. On the basis of the fully planar conjugated feature and photoelectric effect of triazine units, we successfully prepared a highly stable two-dimensional COF (named PT-BN-AO) that is based on triazine as central planar units and bridged by an olefin linkage with prominent antibiofouling activity and greatly enhanced uranium extraction capacity. On the basis of the superior photocatalytic performance of PT-BN-AO, it can generate biotoxic reactive oxygen species to sterilize bacteria effectively. Meanwhile, the photoelectric effect of PT-BN-AO promotes the reduction of U(VI) to U(IV) by photoelectrons, thus greatly improving the adsorption capacity of uranium. On the basis of the excellent photocatalytic and photoelectric properties, the extraction capacity of PT-BN-AO for uranium in natural seawater reached 5.78 mg g–1, which is 1.42 times that without light irradiation. The excellent performance of PT-BN-AO makes it an advanced material for the practical extraction of uranium from seawater.