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A series of mesoporous carbon nitride (MCN) with tunable specific surface area, pore volume, and nitrogen content has been prepared by using SBA-15 as template and ethylenediamine (EDA) and carbon tetrachloride (CTC) as precursors, respectively. The composition and structural properties of the obtained materials were characterized by FT-IR, XRD, SEM, TEM, N adsorption-desorption, zeta potential, and elemental analysis. Results revealed that the largest special surface area could reach up to 667 m cm and specific pore volume to 0.496 cm g, and the nitrogen content of MCN could be controlled by adjusting the EDA to CTC weight ratio. It was demonstrated for the first time that the synthesized MCN exhibited excellent adsorptive capability toward methylene blue (MB) and the adsorption capacity was attributed to the large specific surface area and surface functional groups. The effects of parameters, including pH, initial concentration, contact time, and temperature, were investigated in batch static adsorption experiments. Besides, the adsorption process of MB onto MCN is fitted to the Langmuir isotherm and pseudo-second-order kinetic models, and the maximum adsorption amounts of MB on MCN were 360.8 mg g. Moreover, the thermodynamic analysis showed that the adsorption was endothermic and spontaneous. MCN remained to have high adsorption capacity after five times of recycling test. All these results demonstrated that MCN is a promising material for adsorbing cationic dye in aqueous solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • A metal coordination polymer Zn-Vlm 6 enriched with imidazole was synthesized to remove iodine. • The imidazole group and the free counter anion NO 3 – in Zn-Vlm 6 play a vital role in the I 2 /I 3 − adsorption. • In the presence of excess competing anions, Zn-Vlm 6 exhibited excellent selective removal of I 3 −. • Zn-Vlm 6 could remove I 3 − in the actual aqueous environment (e.g., lake water, seawater). Rationally designing a new adsorbent with highly selective and high adsorption capacity for removing I 3 − from water is still a significant challenge. Herein, we report an imidazole group-rich coordination polymer (CP) named Zn-Vlm 6 , which was constructed by the reaction of the 1-vinylimidazole (Vlm) and Zn2+ ions. Zn-Vlm 6 showed excellent thermal and chemical stability (1 M HCl and 0.1 M NaOH). The abundance of positively charged imidazole groups and the free anti-anion NO 3 − in the backbone of Zn-Vlm 6 results in strong electrostatic interactions and ion exchange between the material and the guest, in return, a high adsorption capacity for I 3 − (1680.7 mg g−1). In addition, the kinetics of I 3 − adsorption on Zn-Vlm 6 followed the pseudo-second-order kinetic model and reached adsorption equilibrium within 3 min. More importantly, Zn-Vlm 6 can selectively capture I 3 − in the presence of competing anions and selectively remove high up to 96.4% of I 3 − from different environments (e.g., lake water, seawater). Moreover, Zn-Vlm 6 can also adsorb gaseous iodine up to 2470 mg g−1. This study shows that Zn-Vlm 6 has promising applications for removing iodine in the gaseous state and from different aqueous phases. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D cationic covalent organic framework (TFAM-BDNP) was synthesized via Zincke reaction. • TFAM-BDNP exhibits high adsorption capacity and extremely fast exchange kinetic for ReO 4 −. • TFAM-BDNP demonstrates remarkable selectivity for ReO 4 −. • TFAM-BDNP has outstanding removal efficiency of ReO 4 − from simulated Hanford flow sample. Due to the long half-life and high environmental mobility, the selective and efficient capture of TcO 4 − from nuclear effluents is very important, but it is still very challenging. Herein, we design and synthesize a novel three-dimensional (3D) cationic covalent organic framework (TFAM-BDNP) via Zincke reaction for selective capture of TcO 4 −/ReO 4 −. TFAM-BDNP exhibits high adsorption capacity (998 mg g−1) and extremely fast exchange kinetic (60 s) for ReO 4 − (the non-radioactive alternative to TcO 4 −), attributing to the open 3D hydrophobic channels, abundant active sites, and high chemical stability. More importantly, TFAM-BDNP shows good adsorption performance for ReO 4 − in the presence of significant excess competing anions with a wide pH value range of 2 to 12. Under complex simulated Hanford flow sample, TFAM-BDNP has outstanding removal efficiency of ReO 4 −. The adsorption mechanism of ReO 4 − is mainly caused by anion exchange process. This study provides a novel adsorbent for efficient capture of TcO 4 −/ReO 4 − in complex environmental systems and exploits an effective strategy for broadening the types of 3D COFs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Indium-based MOF is synthesized for the efficient removal of iodine from both the vapor and aqueous. • In-MOF exhibits high hydrostability even in seawater for 30 days. • In-MOF shows high selectivity and adsorption capacity for I 3 -. • In-MOF shows high-efficiency removal for iodine in seawater. The highly efficient removal of radioactive iodine from nuclear accident-polluted seawater is of great significance for the purpose of environmental protection. Herein, we report an indium-based metal–organic framework, named In-MOF, for highly efficient removing iodine from seawater. In-MOF is constructed by In3+ ions coordinated with tris (4-(1H-imidazol-1-yl) phenyl) amine and exhibits high chemical stability even under seawater for 30 days. Due to the flexible one-dimensional linear structure and high-density charged imidazolium groups, In-MOF possesses a high adsorption capacity (1138 mg/g) for iodine in water. Furthermore, it exhibits high selectivity in the presence of competitive ions, due to forming the unique I-π interactions between iodine and the In-MOF. Notably, these excellent adsorption features endowed In-MOF successfully remove iodine from seawater with a high removal rate of 93.86%. These results are of fundamental importance to understanding iodine uptake and designing materials with high adsorption capacity. [ABSTRACT FROM AUTHOR]

Effective and selective removal of 99TcO 4 -, one of the most nuisance radionuclides in nuclear waste, is highly desirable but remains a significant challenge. Herein, two isostructural MOFs, NCU-3-X (X = Cl, Br) were constructed by ZnX 2 coordinated to nitrogen-containing neutral ligand tri(4-(1H-imidazole-1-l) phenyl) amine for efficient adsorption ReO 4 -/TcO 4 -. Owning to the twofold interpenetrating structure, both of them exhibit strong alkaline resistance. Consequently, NCU-3-Br exhibited superior adsorption performances with a maximum capacity as high as 483 mg/g, which is 2.23 times larger than that of NCU-3-Cl. The primary reasons accounting for the enhanced adsorption performances of NCU-3-Br are that compared to chlorine atoms, the smaller electronegativity of bromine atoms as halogen bonds donor can facilitate the formation of σ-holes, enhance positively charged skeleton, and reduce the adsorption energy associated with ReO 4 -/TcO 4 -. In addition, the one-dimensional hydrophobic channels in the NCU-3-Br framework enable NCU-3-Br to have highly selective toward ReO 4 -, which has a low relative charge density against interfering ions. The SRS simulation removal experiment further confirmed the excellent adsorption capacity of NCU-3-Br to ReO 4 -/TcO 4 -. This work illustrated that the halogenated new strategy incorporated different halogen atoms into MOF skeletons can dramatically modulate the adsorption performances for ReO 4 -/TcO 4 -. [Display omitted] • Two halogens isostructural MOFs were designed and synthesized for efficient removal of TcO 4 -/ReO 4 -. • The high alkaline resistance was due to the twofold interpenetrating structure of NCU-3-X. • Halogenation in MOFs plays a critical role in modulating the adsorption capacity for ReO 4 -. • NCU-3-Br showed high-efficiency removal for ReO 4 -/TcO 4 - in simulated wastes. [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]

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]

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]