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To ensure the long-term sustainable development of nuclear energy as well as the prevention and control of uranium pollution, new materials that can simultaneously detect and separate uranium are still urgently needed. Herein, a new fluorescent covalent organic polymer (COP), namely HT-COP-AO, was synthesized andemployed as both the fluorescent probe and absorbent for simultaneous uranium detection and separationconsidering its excellent fluorescence property and strong uranium coordination ability. The results showed that the fluorescence of HT-COP-AO was quickly quenched by uranium within 2 min, and the limit of detection was 0.23 µM (3σ/K). Further studies implied that uranium was coordinated with the amidoxime groups of HT-COP-AO through U-N and O = U = O bonds, which resulted in electron transfer from uranium to HT-COP-AO and quenching the fluorescence of HT-COP-AO consequently. Meanwhile, HT-COP-AO exhibited excellent absorption ability towards uranium, and the maximum absorption capacity (q max  = 401.3 mg/g) was higher than most reported amidoxime modified materials. The HT-COP-AO also showed high selectivity for both uranium detection and separation which makes it a great promising for uranium monitoring in real water samples., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Nanozymes are nanomaterials with enzyme-mimetic activity. It is known that DNA can interact with various nanozymes in different ways, enhancing or inhibiting the activity of nanozymes, which can be used to develop various biosensors. In this work, we synthesized a photosensitive covalent-organic framework (Tph-BT) as a nanozyme, and its oxidase and peroxidase activities could be reversely regulated by surface modification of single-stranded DNA (ssDNA) for the colorimetric detection of UO 2 2+ . Tph-BT exhibits excellent oxidase activity and weak peroxidase activity, and it is surprising to find that the UO 2 2+ -specific DNA aptamer can significantly inhibit the oxidase activity while greatly enhancing the peroxidase activity. The present UO 2 2+ interacts with the DNA aptamer to form secondary structures and detaches from the surface of Tph-BT, thereby restoring the enzymatic activity of Tph-BT. Based on the reversed regulation effects of the DNA aptamer on the two types of enzymatic activities of Tph-BT, a novel "off-on" and "on-off" sensing platform can be constructed for the colorimetric analysis of UO 2 2+ . This research demonstrates that ssDNA can effectively regulate the different types of enzymatic activities of single COFs and achieve the sensitive and selective colorimetric analysis of radionuclides by the naked eye.

Uranium is a key element in the nuclear industry and also a global environmental contaminant with combined highly toxic and radioactive. Currently, the materials based on post-modification of amidoxime have been developed for uranium detection and adsorption. However, the affinity of amidoxime group for vanadium is stronger than that of uranium, which is the main challenge hindering the practical application of amidoxime-based adsorbents. Herein, we synthesized a fluorescent covalent organic framework (TFPPy-BDOH) through integrating biphenyl diamine and pyrene unit into the π-conjugated framework. TFPPy-BDOH has an excellent selectivity to uranium due to the synergistic effect of nitrogen atom in the imine bond and hydroxyl groups in conjugated framework. It can achieve ultra-fast fluorescence response time (2 s) and ultra-low detection limit (8.8 nM), which may be attributed to its intrinsic regular porous channel structures and excellent hydrophilicity. More excitingly, TFPPy-BDOH can chemically reduce soluble U (VI) to insoluble U (IV), and release the binding site to adsorb additional U (VI), achieving high adsorption capacity of 982.6 ± 49.1 mg g -1 . Therefore, TFPPy-BDOH can overcome the challenges faced by current amidoxime-based adsorbents, making it as a potential adsorbent in practical applications., (Copyright © 2021 Elsevier B.V. All rights reserved.)

2D covalent organic frameworks (2D COFs) have been recognized as a novel class of photoactive materials owing to their extended π-electron conjugation and high chemical stabilities. Herein, a new covalent organic framework (Tph-BDP) is facilely synthesized by using a porphyrin derivative and an organic dye BODIPY derivative (5,5-difluoro-2,8-diformyl-1,3,7,9-tetramethyl-10-phenyl-5H-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazabori-nin-4-ium-5-uide) as monomers for the first time, and their unique photosensitive properties endow them excellent simulated oxidase activity under 635 nm laser irradiation that can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Further findings demonstrate that the presence of uranium (UO 2 2+ ) can coordinate with imines of the oxidation products of TMB, thus modulating the charge transfer process of the colored products accompanied with intensive aggregation and remarkable color fading. This research provides a preparation strategy for COFs with excellent photocatalytic properties and nanozyme activity, and broadens the applications of the simple colorimetric methods for sensitive and selective radionuclide detection., (© 2021 Wiley-VCH GmbH.)

An imidazolyl hydrogen-bonded organic framework (HOF-T) with outstanding thermal and water stability was constructed by C–H⋯N hydrogen bonding and C–H⋯π interactions. UO22+ can be selectively captured by the imidazole group of HOF-T and rapidly reduced to UO2 under visible light irradiation, realizing exceptional uranium removal with high capacity and fast kinetics. [ABSTRACT FROM AUTHOR]

Extracting uranium from real water samples remains a great challenge due to low uranium concentration, concentrated competing ions and volumes of water. The design and preparation of uranium adsorbents with high efficiency and affinity are still difficult. Herein, we presented a facile one‐pot strategy to obtain a novel metal organic framework (denoted as Mn‐NDISA) for stable and efficient trapping of low concentration uranium. Mn‐NDISA with a built‐in hydrophobic cavity can boost the absorption affinity to 1.99 × 106 mL g−1 through the cooperative capture composed of electrostatic interaction, coordination force and hydrogen binding. Owing to the coordination‐available oxygen sites in flexible framework, a rapid kinetic equilibrium was achieved in just 25 min. Moreover, these exceptional adsorption features enabled Mn‐NDISA to successfully capture the naturally occurring uranium traces (~ppb) in wastewater samples, making it one of the most influential absorbents toward UO22+ ever reported. The experimental and theoretical studies revealed that the electrostatic attraction came from the surface negatively charged Mn‐NDISA and the positively charged UO22+. The coordination originated from Lewis basic hydroxyl, carbonyl groups, and Lewis acid UO22+, while hydrogen bonds further reinforced the as‐formed uranium binding complex. This research offered a promising cooperative capture strategy to improve the uranium affinity of the pristine MOF for trace contaminants removal in environmental remediation fields. [ABSTRACT FROM AUTHOR]

The type of reactions and the availability of monomers for the synthesis of sp2-c linked covalent organic frameworks (COFs) are considerably limited by the irreversibility of the C=C bond. Herein, inspired by the Claisen-Schmidt condensation reaction, two propenone-linked (C=C–C=O) COFs (named Py-DAB and PyN-DAB) are developed based on the base-catalyzed nucleophilic addition reaction of ketone-activated α-H with aromatic aldehydes. The introduction of propenone structure endows COFs with high crystallinity, excellent physicochemical stability, and intriguing optoelectronic properties. Benefitting from the rational design on the COFs skeleton, Py-DAB and PyN-DAB are applied to the extraction of radionuclide uranium. In particular, PyN-DAB shows excellent removal rates (>98%) in four uranium mine wastewater samples. We highlight that such a general strategy can provide a valuable avenue toward various functional porous crystalline materials. The synthesis of sp2 carbon-conjugated covalent organic frameworks is limited to a few reactions and monomers due to the poor irreversibility of carbon double bonds. Here the authors synthesize propenone-linked covalent organic frameworks for the removal of radionuclide uranium from mine wastewater samples. [ABSTRACT FROM AUTHOR]

Extracting uranium from seawater offers opportunities for sustainable nuclear fuel supply, but the task is quite challenging due to the low uranium concentration (∼3 ppb) in seawater. Here, based on the Knoevenagel condensation reaction of aldehyde and acetonitrile groups, a novel stable sp2 carbon-linked three-dimensional covalent organic framework (3D COF), TFPM-PDAN-AO was prepared as a porous platform for uranium extraction from seawater. The TFPM-PDAN-AO designed with regular 3D pore channel of 7.12 Å provides a specific channel for uranyl diffusion, which exhibits high selectivity and fast kinetics for uranium adsorption. Meanwhile, the superior stability and optoelectronic properties enable it an excellent porous platform for uranium electroextraction. By applying alternating voltages between −5 and 0 V, uranyl ions can rapidly migrate and enrich into the porous structure of TFPM-PDAN-AO, then inducing the electrodeposition of uranium compounds to form the charge neutral species (Na2O(UO3H2O)x) with an unprecedentedly high adsorption capacity of 4,685 mg g−1. This work not only expands the application prospects of functionalized 3D COFs, but also provides a technical support for the electrodeposition adsorption of uranium from seawater. [ABSTRACT FROM AUTHOR]

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA‐TN‐AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA‐TN‐AO with a high anti‐biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed UVI to insoluble UIV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA‐TN‐AO to uranium in seawater reaches 6.07 mg g−1, which is 1.33 times of that in dark. The NDA‐TN‐AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater. [ABSTRACT FROM AUTHOR]

Uranium is a key element in the nuclear industry, but its unintended leakage has caused health and environmental concerns. Here we report a sp2 carbon-conjugated fluorescent covalent organic framework (COF) named TFPT-BTAN-AO with excellent chemical, thermal and radiation stability is synthesized by integrating triazine-based building blocks with amidoxime-substituted linkers. TFPT-BTAN-AO shows an exceptional UO22+ adsorption capacity of 427 mg g−1 attributable to the abundant selective uranium-binding groups on the highly accessible pore walls of open 1D channels. In addition, it has an ultra-fast response time (2 s) and an ultra-low detection limit of 6.7 nM UO22+ suitable for on-site and real-time monitoring of UO22+, allowing not only extraction but also monitoring the quality of the extracted water. This study demonstrates great potential of fluorescent COFs for radionuclide detection and extraction. By rational designing target ligands, this strategy can be extended to the detection and extraction of other contaminants. Porous materials for uranium capture have been developed in the past, but materials for simultaneous uranium capture and detection are scarce. Here the authors develop a stable covalent organic framework capable of adsorbing and detecting uranyl ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu-based metal covalent organic framework (Cu-TMT) was prepared for the extraction of uranium. • Cu-TMT has unsaturated Cu centers that serve as chemical reduction sites. • Cu-TMT has excellent visible light conversion efficiency and low band gap. • Cu-TMT reduced uranium by chemical reduction and photocatalytic reduction reached 1438.8 mg g−1. The reduction of hexavalent uranium to tetravalent uranium is an effective strategy for controlling uranium contamination in wastewater. Herein, a C C bonded metal-covalent organic framework (Cu-TMT) was synthesized via the Aldol condensation reaction by using the metal cluster Cu 3 (PyCA) 3 and 2,4,6-trimethyl-1,3,5-triazine (TMT) for the chemical and photocatalytic synergistic reduction of uranium. In the Cu-TMT, the low-valent Cu in the metal clusters provides the framework with numerous distributed redox sites being capable of chemically reducing UVI. Meanwhile, the encapsulating Cu clusters in long-range ordered frameworks can provide fast transport channels for intramolecular charge transfer and effectively inhibit electron/hole complexation, making Cu-TMT suitable for photocatalytic reduction of uranium. The chemical reduction of uranium by Cu-TMT was verified under light-avoidance conditions, reaching 659.5 mg g−1. After exposure of Cu-TMT to light, the amount of reduced uranium further increases to 1438.8 mg g−1 with 98.1 % removal rate of actual uranium containing wastewater. This study not only expands the range of applications of variable valence metal covalent organic frameworks, but also provides unique insights into the effective combination of chemical and photocatalytic reduction strategies for removing UVI in a single material. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cocrystals based on I-, Br-based halogen-bond donors and N-based halogen-bond acceptor were constructed. • Strength and density of σ-hole could affect degree of electron-hole separation and charge carrier transport. • Tuning photoelectric response of halogen-bonded cocrystals can be achieved employing the σ-hole effect. • Halogen-bonded cocrystals are enable to effectively photocatalytic reduce U(VI) of uranium contamination. The mechanism of how the internal composition of halogen-bonded cocrystals affecting photoelectric properties is ambiguous. Herein, we report a series of stable halogen-bonded cocrystals containing I-, Br-based halogen bond donors and N-based halogen bond acceptor. The halogen bonds served an intrinsic hub, and the two parts (donor and acceptor) were spliced into a highly ordered periodic network with a tight electronic configuration. The charge transfer within lattice induced by the σ-hole effect activates disparate photoelectric phenomena. The results uncover that the degree of photoelectric response of cocrystals can be adjusted rationally by manipulating the intensity and density of σ-holes with an atomic precision at the molecular level. The experimental and theoretical studies of the σ-hole effect pave the way to simplify the design principle of functional cocrystals. Eventually, benefiting from the fascinating photoelectric activity, halogen-bonded cocrystals exhibited excellent photocatalytic reduction ability of radionuclide uranium. [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]

The increasing uranium containing wastes generated during uranium mining and finishing pose a huge threat to the environment and human health, and thus robust strategies for on-site monitoring of uranium pollutant are of great significance for environmental protection around uranium tailings. Herein, a facile "turn-on" colorimetric platform that can achieve uranium detection by spectrometry and naked eyes was developed based on the uranium-enhanced nanozyme activity of covalent organic framework (JUC-505). Thanks to the extended π-conjugated skeleton and donor-acceptor (D-A) structure, JUC-505 exhibited superior photo-activated nanozyme activity, which would be prohibited when the cyano group in JUC-505 skeleton was transformed to the amidoxime group. Further results elucidated that the coordination of uranium with amidoxime groups led to the electron transfer between uranium and the JUC-505-AO skeleton, and thus significantly restored the nanozymatic activity of JUC-505-AO with the subsequent remarkable color changes. Moreover, the uranium concentrations in uranium tailing wastewater detected by the present "turn-on" colorimetric method were well agreed with those by ICP-MS, demonstrating a high accuracy of the present method in real samples. The D-A structured JUC-505 with superior photocatalytic property and nanozymatic activity was applied to facilitate colorimetric detection of uranium, which displays the advantages of low detection limit, excellent selectivity, fast response and simple operation for uranium detection in real samples, and shows a great potential in on-site monitoring of uranium pollutant around uranium tailings as well as nuclear power plant. [Display omitted] • A facile "turn-on" colorimetric platform was developed for on-site uranium detection by the nanozymatic activity of JUC-505. [ABSTRACT FROM AUTHOR]

Photoreduction of highly toxic U(VI) to less toxic U(IV) is crucial for mitigating radioactive contamination. Herein, a CoWO 4 /TpDD p-n heterojunction is synthesized, with TpDD serving as the n-type semiconductor substrate and CoWO 4 as the p-type semiconductor grown in situ on its surface. The Fermi energy difference between TpDD and CoWO 4 provides the electrochemical potential for charge-hole separation. Moreover, the Coulombic forces from the distinct carrier types between the two materials synergistically facilitate the transfer of electrons and holes. Hence, an internal electric field directed from TpDD to CoWO 4 is established. Under photoexcitation conditions, charges and holes migrate efficiently along the curved band and internal electric field, further enhancing charge-hole separation. As a result, the removal capacity of CoWO 4 /TpDD increases from 515.2 mg/g in the dark to 1754.6 mg/g under light conditions. Thus, constructing a p-n heterojunction proves to be an effective strategy for remediating uranium-contaminated environments. [Display omitted] • CoWO 4 /TpDD heterojunction was formed by CoWO 4 in situ grown on the TpDD surface. • The differences in energy levels and carrier types facilitate carrier separation. • The electric field and energy band facilitate the photogenerated carrier separation. • Photogenerated electrons moving to TpDD contribute to the photoreduction of U(VI). • DFT and in-situ XPS confirm the mechanism of carrier transfer in heterojunction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti-MOF@DATp was developed by using Ti-MOF as core and in-situ growing DATp shells on its surface. • A Z-Scheme heterojunction was created through covalent bonds between Ti-MOF and DATp. • The Ti-MOF@DATp enables tetracycline passing through the DATp shell while selectively capturing U(VI). • Ti-MOF serves as the site for photooxidation tetracycline, while DATp serves as the site for photoreduction U(VI). Uranium and antibiotics coexisting in natural water bodies pose a significant threat to the environment and human health. Herein, Ti-MOF@DATp was developed by using a metal–organic framework (Ti-MOF) as the core and in-situ growing covalent organic framework (DATp) shells on its surface for simultaneous photocatalytic reduction U(VI) and oxidation tetracycline. The staggered energy levels between Ti-MOF and DATp create a Z-Scheme heterojunction through covalent bonds between them, promoting the charge and holes transfer with enhancing the photocatalytic performance. The Ti-MOF@DATp enables tetracycline passing through the DATp shell while selectively capturing U(VI), then Ti-MOF functions as the site for photooxidation tetracycline, while DATp serves as the site for photoreduction U(VI). The oxidation and reduction of sites can be effectively separated, improving the utilization efficiency of photogenerated electrons and holes. Hence, Ti-MOF@DATp can effectively accomplish the simultaneous photocatalytic removal of 96% U(VI) and 90% tetracycline of their mixture. In comparison to the removal efficiency of 89% for U(VI) and 77% for tetracycline when removal alone, a notable enhancement in performance is observed. Particularly, the removal rate constant of the U(VI) and tetracycline mixture is 55 times higher than that of U(VI) alone and 4 times higher than that of tetracycline alone. Therefore, bifunctional photocatalysts offer an effective approach to tackling complex environmental challenges. [ABSTRACT FROM AUTHOR]

• TFHH-POM was developed by using amino-modified polyoxometalates embedded in covalent organic framework pores. • The covalent bond connection between TFHH and POM improves the stability of POM. • Covalent bonding and internal confined improve the mass transfer from TFHH to POM. • TFHH-POM exhibits a notably elevated photoreduction capacity of U(VI). To achieve sustainable nuclear energy and environmental protection, capturing uranium from mining wastewater is imperative. Herein, as an extraction composite of U(VI), TFHH-POM was developed by using a highly conjugated polyaromatic ether-based covalent organic framework (TFHH) as the carrier with amino-modified polyoxometalates (POM) embedded in its pores through amide bonds. The highly conjugated structure of TFHH facilitates charge transport, and in combination with the charge density contrast between POM and TFHH, along with the constraining effect of POM within TFHH channels, jointly enhances charge separation efficiency. As a result, the photoreduction efficiency of U(VI) is substantially increased. Simultaneously, the oxygen-containing groups in POM and carboxyl groups in TFHH could selectively adsorb U(VI), while Mo(V) in POM effectively reduces U(VI) to U(IV), synergistically promoting U(VI) capture. Hence, TFHH-POM exhibits remarkable U(VI) extraction efficiency through enhanced mass transfer, improved diffusion, and introduced chemical reduction. The U(VI) extraction capacity of TFHH-POM reaches 489.2 mg/g, surpassing those of POM and TFHH by 3.2 and 1.6 times, respectively. The reduced U(IV) remains stable after 30 days of storage with no reoxidation observed. Moreover, TFHH-POM demonstrates selective U(VI) capture from mining wastewater, highlighting its vast potential for environmentally sustainable uranium mining. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bi-functional COF based heterostructure (NH 2 -Ti 3 C 2 T x @COF) was developed in situ. • The Schottky interface realizes efficient carrier separation and solar utilization. • NH 2 -Ti 3 C 2 T x @COF has excellent photocatalytic activity without sacrificial agents. • NH 2 -Ti 3 C 2 T x @COF exhibits multiple-in-one advantage for photoreduction U(VI). Reduction of soluble U(VI) to insoluble U(IV) is considered as a promising strategy to avoid uranium contamination. Herein, a bi-functional covalent organic framework based heterojunction (NH 2 -Ti 3 C 2 T x @COF) was constructed on the amino-modified Ti 3 C 2 T x MXene for efficient photoreduction U(VI) without additional sacrificial agents. Schottky interface with electronic unidirectional channel is established by the formation of local electrophilic/nucleophilic region due to the introduction of reductive COF with alkynyl group, resulting in efficient photogenerated carrier separation and solar energy utilization. More importantly, NH 2 -Ti 3 C 2 T x with negative charge served as electron collector and transfer channel can effectively surmount the low photocatalytic activity caused by high polarization of imine-linked COFs. Thus, the tailored-made design of NH 2 -Ti 3 C 2 T x @COF exhibits excellent photocatalytic activity, fast reaction kinetics (removal of 97.8 % in 60 min) and high adsorptive capability (1557.2 mg/g) under the light condition. This multiple-in-one advantage makes well-designed NH 2 -Ti 3 C 2 T x @COF as a promising capture platform. This work will provide some new insight and inspiration to COF based heterojunctions for enhancing U(VI) capture. [ABSTRACT FROM AUTHOR]

[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]

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]

Photocatalytic reduction of UVI to UIV can help remove U from the environment and thus reduce the harmful impacts of radiation emitted by uranium isotopes. Herein, we first synthesized Bi 4 Ti 3 O 12 (B1) particles, then B1 was crosslinked with 6-chloro-1,3,5-triazine-diamine (DCT) to afford B2. Finally, B3 was formed using B2 and 4-formylbenzaldehyde (BA-CHO) to investigate the utility of the D-π-A array structure for photocatalytic UVI removal from rare earth tailings wastewater. B1 lacked adsorption sites and displayed a wide band gap. The grafted triazine moiety in B2 introduced active sites and narrowed the band gap. Notably, B3, a Bi 4 Ti 3 O 12 (donor)-triazine unit (π-electron bridge)-aldehyde benzene (acceptor) molecule, effectively formed the D-π-A array structure, which formed multiple polarization fields and further narrowed the band gap. Therefore, UVI was more likely to capture electrons at the adsorption site of B3 and be reduced to UIV due to energy level matching effects. UVI removal capacity of B3 under simulated sunlight was 684.9 mg g−1, 2.5 times greater than B1 and 1.8 times greater than B2. B3 was still active after multiple reaction cycles, and UVI removal from tailings wastewater reached 90.8%. Overall, B3 provides an alternative design scheme for enhancing photocatalytic performance. [Display omitted] Photocatalytic UVI reduction is one of the most promising methods to reduce radioactive uranium contamination in tailings wastewater. Herein, a Bi 4 Ti 3 O 12 (donor)-triazine (π-electron bridge)-aldehyde benzene (acceptor) crosslinked molecule, named B3, was formed D-π-A array structure for significantly improving photocatalytic UVI removal performance from tailings wastewater. The improved performance of B3 is due to the increased adsorption sites on the triazine and the increased electron push-pull effect of aldehyde group benzene as a weak acceptor for extended electron delocalization, resulting in the formation of multiple polarization fields. The modulation of D-π-A array structure provides an alternative means to improve photocatalytic performance. • Bi 4 Ti 3 O 12 -triazine unit-aldehyde benzene molecule formed D-π-A array structure. • The D-π-A array structure can form multiple polarization fields. • The D-π-A array structure can regulate band gap width and charge transfer. • The modulation of D-π-A structure can improve photocatalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SnS 2 -covalent organic framework van der Waals heterojunction (SnS 2 COF) was constructed. • With good photoelectric properties, SnS 2 COF can realize separation and transfer of electron-hole. • The electron flow path of heterojunction conforms to Z-scheme by experimental study and theoretical calculation. • SnS 2 COF can effectively reduce and remove U (VI) from rare earth tailings wastewater under UV/Vis light. Uranium removal by photocatalytic reduction is one of the most promising methods to reduce radioactive contamination in wastewater. Herein, a Z-scheme van der Waals heterojunction photocatalyst (SnS 2 COF) was synthesized in situ by combining covalent organic frameworks (COF) with semiconductor (SnS 2) for U (VI) reduction in rare earth tailings wastewater. The synthesis method of van der Waals heterojunction is simple and solves the problem of no hanging bond in composite components. In this heterojunction, large areas of van der Waals interaction form high-speed electron transport channels. In addition, it is deduced that SnS 2 COF fits the Z-scheme heterojunction electron transport mode through the theoretical calculation of the ground state and excited state electron density difference and the related band structure. Under the photoexcitation, the direction of electron flow is reversed, which further promotes the separation of the photogenerated electron (e−)-hole (h+) under the action of the built-in electric field, maintains the high reducibility of the conduction band, and avoids the photocorrosion of SnS 2. Compared with inorganic-inorganic heterojunction, SnS 2 COF has a wider light absorption range, more active sites, and higher e−-h+ separation and transfer efficiency. Therefore, it had a higher U (VI) reduction removal capacity, up to 1123.3 mg g−1, far surpassing the SnS 2 and COF counterparts under ultraviolet/visible light. And the U (VI) removal rate reached 98.5 % in rare earth tailings wastewater. The design concept of organic–inorganic heterojunction materials provides an alternative strategy for improving the photocatalytic performance. [ABSTRACT FROM AUTHOR]

It has been considered challenging to develop ideal adsorbents for efficient and lower adsorption time uranium extraction, especially 3D covalent organic frameworks with interpenetrating topologies and tunable porous structures. Here, a "soft" three-dimensional (3D) covalent organic framework (TAM-DHBD) with a fivefold interpenetrating structure is prepared as a novel porous platform for the efficient extraction of radioactive uranium. The resultant TAM-DHBD appears exceptional crystallinity, prominent porosity and excellent chemical stability. Based on the strong mutual coordination between phenolic-hydroxyl/imine-N on the main chain and uranium, TAM-DHBD can effectively avert the competition of other ions, showing high selectivity for uranium extraction. Impressively, the 3D ultra-hydrophilic transport channels and multi-directional uniform pore structure of TAM-DHBD lay the foundation for the ultra-high-speed diffusion of uranium (the adsorption equilibrium can be reached within 60 min under a high-concentration environment). Furthermore, the utilization of lightweight structure not only increases the adsorption site density, but renders the adsorption process flexible, achieving a breakthrough adsorption capacity of 1263.8 mg g-1. This work not only highlights new opportunities for designing microporous 3D COFs, but paves the way for the practical application of 3D COFs for uranium adsorption. [Display omitted] • A three-dimensional covalent organic framework (TAM-DHBD) is prepared for extraction of uranium. • TAM-DHBD can effectively avoid the competition of other ions, showing high selectivity to uranium. • TAM-DHBD possesses superhydrophilic transport channels and multidirectional uniform pore structure. • The lightweight structure increases adsorption site density and makes adsorption process flexible. • TAM-DHBD achieved a breakthrough adsorption capacity of 1263.8 mg g-1. [ABSTRACT FROM AUTHOR]

• Three-dimensional luminescent covalent organic framework (TAPM-DHBD) for reversible uranium detection and extraction. • This is the first example of three-dimensional fluorescent covalent organic framework for simultaneous uranium detection and extraction. • TAPM-DHBD is suitable for sensitive and on-site monitoring the radioactive uranium contamination of the extracted water. • TAPM-DHBD exhibits an exceptional uranium extraction capacity as well as fast kinetics. Uranium is a key fuel for nuclear reactions, but it also causes serious public health concerns to human beings when leaked into the environment. Exploring new strategies for simultaneous uranium detection and extraction is highly desirable for public health and environmental protection. Herein, a hydroxyl-functionalized 3D covalent organic framework (termed TAPM-DHBD) with strong fluorescence and 3D interconnected pore channels is synthesized and evaluated for uranium detection and extraction. TAPM-DHBD exhibits an exceptional uranium extraction capacity of 955.3 mg g−1 as well as fast kinetics due to the plentiful selective binding sites on the extremely accessible pore channels of 3D interconnected micropore skeleton. Interestingly, due to the signal amplification of the 3D conjugated skeleton, it has a rapid-response time of 2 s and an ultra-low detection limit of 4.08 nM UO 2 2+ suitable for sensitive and on-site monitoring the radioactive uranium contamination of the extracted water. Furthermore, TAPM-DHBD exhibits excellent regenerable performance at least six cycles. This study provides a new strategy for constructing high-performance 3D COFs for radioactive contamination monitoring and strategic nuclides extraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • COFs and CNTs composites were synthesized by in-situ synthesis. • The synergistic effect improved the adsorption capacity and selectivity. • The removal mechanism of samples was clarified through various characteristic modes. • The problem of U (VI) removal from the rare earth tailings wastewater had been solved. The wastewater containing uranium produced in the mining process is harmful to the environment and life safety due to the inherent biotoxicity and radioactivity of uranium. In this paper, 4,4′-diamino-[1,1′-biphenyl]-3,3′-diol and 2,4,6-triformylphloroglucinol were in situ synthesized β -ketoenamine covalent organic frameworks (COFs) on the surface of carbon nanotubes (CNTs) to obtain a composite of CNT/COF-OH for removal uranium in the rare earth tailings wastewater. Grafting COFs with a large number of specific uranium-binding groups and redox-active sites on the surface of CNTs, CNT/COF-OH can effectively enhance the uranium ion selectivity and adsorption capacity. Furthermore, CNTs have good electron transport capacity and π-conjugation properties, electrons can be effectively transferred from CNTs to COFs, which increases the electron density of the adsorption functional groups, resulting in an increase of the adsorption energy and reductive activity for U (VI), thus improving the removal efficiency. In addition, the skeleton of COFs can be supported by CNTs, thus reducing collapse. Through the synergistic effect of composite, CNT/COF-OH had a good uranium adsorption capacity of 518.2 mg g−1. The adsorption capacity of CNT/COF-OH was increased by 390.7 %, 54.6 %, and 84.5 % compared with those of single CNTs, COF-OH, and mixed CNT + COF-OH, respectively. The selective separation coefficient of CNT/COF-OH was 1.6 times higher than that of COF-OH. The experiment of uranium removal was carried out in the rare earth tailings wastewater using CNT/COF-OH, the removal rate reached 96.7 %. The COFs modified CNTs with synergistic effect have important theoretical and practical significance for the safety problems caused by harmful ions in wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • De novo synthesis of novel MOF-based high performance UO 2 2+ recognition motif by direct synthesis. • CaNDI- o OH as artificial design for uranium adsorbent through mimicking the bioreceptors. • Bio-inspired multiple interaction strategy provides a new paradigm compensating for UO 2 2+ affinity. • CaNDI- o OH shows enhanced performance towards uranium enrichment. By mimicking the binding motifs of bioreceptors, we have developed a series of multiple functional uranium adsorbents to meet this criterion: positioning direct chelation sites and hydrogen-bonding sites inside deep hydrophobic cavity of naphthalene diimide MOFs. Benefiting from well-designed specific microenvironment namely the regular spatial structure and an unusual synergy from hydroxyl and carbonyl groups, the easy-prepared and stable MOF shows enhanced comprehensive performance. Representatively, the MOF CaNDI- o OH shows outstanding performance towards uranium enrichment with chemical and radiation stability, exceptional uptake capacity (572 mg g−1), fast kinetics (within 25 min), high anti-interference ability (the concentration of competitive ions exceeds 10 times), excellent reusability (at least 4 circles). Specifically, this adsorbent is able to reduce uranium in uranium-containing water samples to 3.27 ppb within 30 min, highlighting the potential application in radionuclide removal from wastewater. The experiment results and DFT calculation suggest biomimetic multiple interactions are responsible for high performance uranium capture. The cooperative interactions strategy established here reveals a new paradigm in enhanced uranium extraction for pristine MOFs with limited uranium affinity. [ABSTRACT FROM AUTHOR]

We proposed a strategy to synergistically enhance uranium capture capacity through photothermal desalination, and prepared a COF hydrogel (KTG) through a simple process for the first time. KTG with ideal broadband light absorption capacity could be used as an outstanding photothermal conversion material. Meanwhile, the built-in elastic honeycomb structure endowed the KTG with good mechanical properties and adequate water transport performance that accelerated the diffusion and mass transfer ability of uranyl. Under a simulated sunlight, the adsorption capacity, selectivity, adsorption rate and cycle capacity of uranium could be significantly improved. Moreover, benefiting from the outstanding photocatalytic performance, KTG exhibited a high anti-fouling activity against marine biological entities, thereby achieving long-term efficient uranium adsorption and solar desalination. [Display omitted] • The first example of COF hydrogel for solar desalination and uranium recovery. • COF hydrogel for synergistically enhance uranium capture through photothermal desalination. • COF hydrogel shows a high evaporation rate and exceptional uranium recovery capacity. • COF hydrogel has high anti-biofouling activity and good reusability. Capturing of uranium from the natural seawater is considered to be one of the most promising methods to meet the current demand for nuclear energy. Herein, we prepared a reduced graphene oxide-based (rGO-based) covalent organic framework hydrogel (KTG) with three-dimensional porous structure as a platform for enhancing uranium capture capacity through photothermal desalination. Under light irradiation, the KTG produces a local heat that can be used to generate steam while promoting the rapid diffusion of uranium inside the hydrogel 3D network, thereby increasing the adsorption efficiency and capacity of uranium. KTG can achieve exceptional uranium capture capacity (521.6 mg g−1) under one sun irradiation, which is 42.4% higher than that under dark conditions. In addition, excellent photocatalytic activity and mechanical properties make KTG possess high anti-biofouling activity, good reusability, and achieving continuous uranium capture and solar distillation. [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] • High selectivity imidazole was introduced as linkage in varying degree hydroxylation covalent organic polymers. • Benefiting from the introduction of hydroxyl groups, the uranium adsorption capacities were largely enhanced. • The TpDAB endowed prominent selectivity towards multiple metal ions including vanadium. • The hydroxyl groups significantly influenced the uranium coordination mechanism of imidazole functional group. Highly effective and reliable adsorbents for uranium extraction are vital significant for environmental protection and social development. Herein, inspired by the interaction between imidazole affinity ligand of histidine and uranium, a series of varying degree hydroxylation imidazole linked covalent organic polymers were developed for the first time via one step facile reaction without any post treatment between 2,4,6-triformylphloroglucinol (Tp), 2,4,6-triformylresorcinol (Bd), 2,4,6-triformylphenol (Hb) and 3,3′-diaminobenzidine (DAB), denoted as TpDAB, BdDAB, and HbDAB, respectively. Benefiting from the hierarchical structure of the covalent organic polymer and synergistic effects originating from hydroxyl groups and imidazole linkages, TpDAB, BdDAB, and HbDAB displayed as the promising adsorbents for uranium extraction with high extraction ability and fast capture kinetics. X-ray photoelectron spectroscopy results revealed that both nitrogen atoms in imidazole and oxygen atom in hydroxyl took part in uranium coordination. With the increasing of hydroxyl group amounts, TpDAB achieved highest extraction capacity of uranium. Furthermore, TpDAB with imidazole affinity group possessed eminent selectivity for uranium in the multiple metal ions solution, and especially overcome the unavoidable problem of vanadium interfering with amidoxime adsorption uranium. This work provided a promising uranium extraction strategy with high selectivity and easy preparation for environmental protection and human health. [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]

• Highly stable sp2 carbon-conjugated covalent organic framework (COF-PDAN-AO) was synthesized and characterization. • Acid and radiation resistant COF-PDAN-AO exhibits efficient adsorption of UO 2 2+ from radioactive wastewater. • COF-PDAN-AO possesses short adsorption equilibrium time and selectivity for uranium. • The emission of COF-PDAN-AO was selectively quenched upon adding UO 2 2+. Uranium is an important element in the nuclear industry while the discharge of radioactive wastewater can cause serious damages to the environment. In this work, an ultra-stable sp2 carbon-conjugated covalent organic framework (COF-PDAN-AO) is synthesized with amidoxime-substituted monomers for detection and efficient adsorption of uranium from radioactive wastewater. Abundant amidoxime groups laced on the open 1D channels of COF-PDAN-AO exhibit exceptional accessibility and the regular pores facilitate the mass transfer. Based on these features, COF-PDAN-AO achieves ultra-low detection limit of 6.5 nM, high uranium adsorption capacity (410 mg/g) and selective interaction with uranium. In addition, various spectroscopies verify COF-PDAN-AO possesses excellent radioresistance in acidic solution. Regeneration studies have shown that COF-PDAN-AO maintained good structural stability after seven cycles. These results indicate that our sp2 carbon conjugated COF can be potentially used for practical detection and adsorption of uranium from radioactive wastewater. This strategy can be extended to detection and extraction of other contaminants by designing the target ligand. [ABSTRACT FROM AUTHOR]