Reconstruction of Built-in Electric Field in Covalent Organic Frameworks through Defect Engineering for Photocatalytic Reduction of Uranium

Covalent organic frameworks (COFs) featuring periodic skeletons and extended pi-conjugated structures have emerged as a promising class of photocatalytic materials. However, inadequate charge separation and fast photogenerated carriers' recombination in COFs severely limits their photocatalytic activities. Herein, a defect TADH-COF-COOH with carboxylic acid groups introduced in situ was synthesized by selecting 4,4 ',4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine as the amino building block and 4 '-formyl-[1,1 '-biphenyl]-4-carboxylic acid as the aldehyde component. Compared to the intrinsic COF (TADH-COF) and the single-defect COF (TADH-COF-H), TADH-COF-COOH significantly enhances the local built-in electric field due to the presence of carboxyl groups, thereby improving the separation of the photogenerated charges and effectively mitigating the nonradiative recombination issue commonly observed in COFs used as photocatalysts. Benefiting from the introduction of highly polar carboxyl groups and defect engineering design on the COFs skeleton, TADH-COF-COOH exhibits superior performance in the photocatalytic removal of uranium from actual nuclear wastewater. These findings highlight the great potential of using simple defect engineering strategy to induce enhanced built-in electric field in customizing porous materials to improve photocatalytic efficiency.