Abstract
1) TQY-COF, a nitrogen–oxygen rich pyrazine-connected covalent–organic framework (COF) designed for efficient uranium extraction through photocatalytic processes, overcoming limitations posed by the scarcity of adsorption sites in traditional COFs.
2) The material features a preorganized bisnitrogen–bisoxygen donor configuration that matches the geometric coordination of hexavalent uranyl ions, offering high affinity and tetra-coordination.
3) TQY-COF demonstrates an exceptional luminous time of 99.8% uranium removal from actual uranium mine wastewater under light conditions, and a separation coefficient of 1.73 × 10^6 mL g–1 in the presence of multiple metal ions, outperforming previous works.

Background
1) Industry Problems: The photocatalytic extraction of uranium is hindered by the limited number of adsorption sites on semiconductor materials, preventing effective capture of uranyl ions.
2) Scholarly Solutions: Previous research has explored adsorbent–photocatalyst hybrid systems but faced challenges with complex modification processes and lack of photocatalytic functionality in sorbent components.
3) Innovative Ideas by Authors: The authors propose a COF with multiple redox sites (C═N/C═O) to facilitate rapid charge transfer pathways and exhibit strong affinity toward uranyl ions, addressing the need for multifunctional photocatalysts.

Experimental Details
1) Synthesis of TQY-COF and TY-COF: The authors synthesized TQY-COF and TY-COF using a dual condensation reaction, with TQY-COF incorporating dual redox-active sites for enhanced uranium extraction.
2) Theoretical Predictions: ESP and ELF calculations were performed to predict the coordination behavior and electron affinity of UO22+, indicating TQY-COF's superior electron transport ability and ion chelating ability.
3) Characterization and Optical Performance: FT-IR, XPS, PXRD, Raman spectroscopy, and UV–vis DRS were utilized to characterize the synthesized COFs, confirming their crystallinity, surface area, porosity, and optoelectronic properties.

Test and Analysis
1) Adsorption Photocatalytic Performance: Batch uranium experiments were conducted to evaluate the uranium removal efficiency of TQY-COF and TY-COF under different pH conditions and light irradiation.
2) Selectivity and Practical Applications: The selectivity of TQY-COF for uranium in the presence of competing ions was tested, followed by real-world application tests using actual uranium mine wastewater.
3) Mechanistic Analysis: EDS, XPS, FT-IR, and DFT calculations were employed to investigate the interaction mechanism of uranium with COF and the role of redox-active sites in photocatalytic adsorption.

Conclusion
1) TQY-COF demonstrated a high removal efficiency of 99.8% for uranium from real wastewater and a superior separation coefficient, highlighting the effectiveness of the incorporated redox-active sites.
2) The study elucidates the coordination mechanism of uranium with TQY-COF, showing the necessity of N/O atoms in photocatalytic adsorption and the role of electron transport channels in enhancing uranium reduction.
3) The research provides a strategy that combines precise adsorption with enhanced photocatalysis, offering a pathway to improve uranium extraction and address challenges in radioactive waste management.
4) Further research is needed on the long-term stability and recyclability of TQY-COF under continuous operation 


Construction of a Bifunctional Redox-Site Conjugated Covalent–Organic Framework for Photoinduced Precision Trapping of Uranyl Ions
Xiao-Juan Chen, Cheng-Rong Zhang, Yuan-Jun Cai, Hao-Xuan He, Cheng-Peng Niu, Jia-Xin Qi, Jin-Lan Liu, Zheng Xia, Ru-Ping Liang*, and Jian-Ding Qiu*
DOI: 10.1021/acs.inorgchem.4c01649
Link: https://pubs.acs.org/doi/10.1021/acs.inorgchem.4c01649