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[Display omitted] • A covalent organic framework (DANT-BTT) with a D-A structure was synthesized based on naphthalimide. • DANT-BTT exhibits excellent chemical stability and photocatalytic properties. • Protonated DANT-BTT with superior photocatalytic capability and higher selectivity for uranium. • DANT-BTT has excellent removal efficiency for uranium at pH 1. Efficient removal of UO 2 2+ from radioactive wastewater under strong acid conditions remains a significant challenge due to the competition of excess H+ for adsorption and reduction sites. Here, covalent organic framework with complete charge separation and protonation properties (DANT-BTT) was synthesized for efficient removal of UO 2 2+ under strong acids. The DANT-BTT with strong electron-deficient naphthalimide significantly extended light absorption and enhanced intramolecular charge transfer, which significantly improve the separation efficiency of electrons and holes. Additionally, the auxiliary coordination of hydroxyl groups after protonation provides unparalleled selectivity for UO 2 2+ in strong acids, effectively preventing the competition of H+ for adsorption sites. Protonation of nitrogen atoms and ketones also extends light absorption and store electrons, further enhancing the photocatalytic performance of DANT-BTT. Consequently, DANT-BTT can achieve 71 % photoreduction UO 2 2+ efficiency (pH 1) after 60 min irradiation, where dark adsorption accounts for 43 %. This work provides a strategy for the efficient reduction of U(VI) under strong acids. [ABSTRACT FROM AUTHOR]

We report the first example of covalent organic framework (DHBD-TMT) linked by unsubstituted olefin-linkages for selective loading, chemical reduction and photocatalytic reduction of uranium. The unique structures of DHBD-TMT possess all the characteristics to be well suited as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium, thus exhibiting a groundbreaking uranium capture capacity (2640.8 mg g-1). [Display omitted] • Covalent organic framework (DHBD-TMT) as a uranium adsorbent through three synergistic mechanisms. • This is the first example of covalent organic framework for selective adsorption, chemical reduction and photocatalytic reduction of uranium. • DHBD-TMT is very suitable as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium. • DHBD-TMT exhibited a groundbreaking uranium capture capacity. Herein, we report the first example of covalent organic framework (DHBD-TMT) linked by unsubstituted olefin-linkages for selective loading, chemical reduction and photocatalytic reduction of uranium. The unique structures of DHBD-TMT possess all the characteristics to be well suited as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium, thus exhibiting a groundbreaking uranium capture capacity (2640.8 mg g-1). In the dark, DHBD-TMT can effectively adsorb uranium through the hydroxyl groups laced on the skeleton and reduce UVI to UIV in situ, leading to a higher adsorption capacity and selectivity of uranium. At the same time, the synergistic effect of the hydroquinone and triazine units in the extended π-conjugated skeleton significantly improve the photocatalytic activity of DHBD-TMT, and an additional UVI photocatalytic reduction mechanism can occur under visible light irradiation, allowing significantly higher the capacity and faster adsorption kinetics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phosphate functionalized COF/rGO was synthesized using post-synthetic modification. • Tb-BD-P/rGO exhibited excellent physicochemical stability and rapid uranyl mass transfer ability. • TB-BD-P/rGO enabled photoelectrothermal synergistic photocatalytic reduction of uranium. • Tb-BD-P/rGO performed excellent removal rates (>95 %) in actual strong acid nuclear wastewater. Photocatalytic reduction is becoming an effective method to remove UVI from uranium mine wastewater. Herein, 1,3,5-benzotrialdehyde (Tb) and 4,4′-diaminobiphenyl (BD) used as monomers of covalent organic framework (COF) are in situ growth on graphene oxide (GO) surfaces to obtain Tb-BD/rGO. Then, Tb-BD/rGO is converted into Tb-BD-P/rGO by asymmetric hydrogen phosphorylation, which is served as a new material for photocatalytic reduction of uranium via photoelectrothermal synergy. Benefiting from the transformation of dynamic imine bonds into irreversible carbon–nitrogen single bonds, Tb-BD-P/rGO expresses remarkable chemical and thermal stability. The introduction of phosphate groups improve the electronegativity and hydrophilicity of Tb-BD-P/rGO, which contribute to rapid transportation of uranium. In addition, the introduction of rGO achieves excellent photothermal conversion, accelerating the adsorption kinetics of uranium. Meanwhile, the π-π interaction between Tb-BD-P and rGO promotes inter-interfacial electron transfer and reduces the complexation of electron-hole pairs during the photocatalytic process, further improving photocatalytic performance. Therefore, Tb-BD-P/rGO demonstrates exceptional removal uranium rates (>95 %) in uranium mine wastewater by synergistically photoelectrothermal integration, offering a pathway for developing multifunctional and integrated photocatalysts. [ABSTRACT FROM AUTHOR]

We report the first example of vinylene-linked covalent organic framework (Tp-TMT) with enhanced uranium adsorption through combined selective ligand binding, chemical reduction and photocatalytic reduction. The dense hydroxyl functional groups on the Tp-TMT framework had good selectivity and excellent chemical reduction performance for U(VI). Meanwhile, the synergistic effect of hydroxyl groups and triazine unit significantly enhanced the photocatalytic reduction activity. Thus Tp-TMT exhibited incredible adsorption kinetics and capacity for uranium. [Display omitted] • COFs effectively capture uranium through three coordinated mechanisms. • Tp-TMT has excellent visible light conversion efficiency and low band gap. • Tp-TMT enhances uranium adsorption through selective ligand binding and reduction. • Tp-TMT exhibits incredible adsorption kinetics and capacity for uranium. So far, it remains a challenge to synthesize uranium adsorbents with robust stability, high adsorption capacity, excellent photocatalytic activity and easy regeneration. Herein, we report the first example of vinylene-linked covalent organic framework (Tp-TMT) with enhanced uranium adsorption through combined selective ligand binding, chemical reduction and photocatalytic reduction. The unique structure and excellent photocatalytic activity of Tp-TMT make it very suitable for photo-enhanced uranium adsorption through three synergistic mechanisms, thus exhibiting an outstanding uranium adsorption capacity (2362.4 mg g−1). In the dark, a large number of hydroxyl groups in the Tp-TMT framework serve as selective binding sites for uranium, and reduce part of U(VI) to U(IV), thereby greatly improving the adsorption capacity. Meanwhile, the synergistic effect of the triazine units and hydroxyl groups in the highly conjugated framework greatly decreases the optical band gap of Tp-TMT, and an additional U(VI) photocatalytic reduction process can occur under light irradiation, further increasing the adsorption kinetics and capacity. This work explored the structural and functional design of covalent organic frameworks for the adsorption and reduction of uranium in nuclear industry wastewater. [ABSTRACT FROM AUTHOR]

Plasmonic photocatalysis is an effective strategy to solve radioactive uranium hazards in wastewater. A plasmonic photocatalyst Bi/Bi 2 O 3−x @COFs was synthesized by in-situ growth of covalent organic frameworks (COFs) on Bi/Bi 2 O 3−x surface for the U(VI) adsorption and plasmonic photoreduction in rare earth tailings wastewater. The presence of oxygen vacancy in Bi/Bi 2 O 3−x and Schottky potential well formed by Bi and Bi 2 O 3−x interface increased the number of free electrons, which induced localized surface plasmon resonance (LSPR) and enhanced the light absorption performance of composites. In addition, oxygen vacancy improved the Fermi level of Bi/Bi 2 O 3−x , leading to another potential well between Bi 2 O 3−x and COFs interface. The electron transport direction was reversed, thus increasing the electron density of COFs layer. COFs was an N-type semiconductor with specific binding U(VI) groups and suitable band structure, which could be used as an active reaction site. Bi/Bi 2 O 3−x @COFs had 1411.5 mg g−1 removal capacity and high separation coefficient for U(VI) due to the synergistic action of photogenerated electrons and hot electrons. Moreover, the removal rate of uranium from rare earth tailings wastewater by regenerated Bi/Bi 2 O 3−x @COFs was over 93.9%. The scheme of introducing LSPR and Schottky potential well provides another way to improve the photocatalytic effect. [Display omitted] • Bi/Bi 2 O 3−x @COFs with core-shell structure was synthesized in-situ. • Oxygen vacancies in Bi 2 O 3−x induced LSPR and increased light absorption. • The double Schottky potential well increased the electron density of COFs. • U(VI) was reduced by the synergistic action of photogenerated and hot electrons. • Regenerated Bi/Bi 2 O 3−x @COFs had high cyclic stability. [ABSTRACT FROM AUTHOR]