Defect engineering in β-ketoenamine-linked covalent organic frameworks for high-efficiency uranium extraction

Abstract

In view of energy and the environment, the development of suitable adsorbents for high-efficiency uranium extraction is highly desired. However, most reported adsorbents showcase poor stability, terrible anti-biofouling activity and dissatisfactory adsorption capacity. Herein, we designed and prepared three β-ketoenamine-linked COFs (Tp-DAAQ, Tp-AD and Tp-DAQ) with varying anthraquinone conjugated units for uranium extraction. Compared to Tp-DAQ, Tp-DAAQ and Tp-AD exhibited higher uranium adsorption capacities of 738.4 and 834.4 mg g⁻¹ at pH = 6, which may be ascribed to their high specific surface areas and abundant uranium-binding sites. In addition, defect engineering was creatively introduced into the DAAQ-COFs and AD-COFs to enhance the uranium adsorption performance by exposing more active sites. Notably, the experimental results revealed that the defective COFs possessed higher U-uptake capacities in the same conditions, demonstrating the paramount role of defective sites for uranium extraction. More importantly, good anti-biofouling activity was observed in all these COFs under visible light irradiation conditions, indicating that they can serve as proper candidates for uranium extraction from complex water environments. This work paves a new way for uranium extraction application by rationally designing the bridging units and introducing defect engineering.