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A major challenge of uranium extraction from seawater (UES) is to effectively block the biofouling without destroying the ecological balance, especially prevent the attachment of macroalgae on the surface of the adsorbent. Herein, a robust montmorillonite-polydopamine/polyacrylamide nanocomposite hydrogel is reported by a two-step method, including PDA intercalation MMT and further free radical polymerization with AM monomers. The interpenetrating structure of hydrogel lead to high water permeability with the swelling ratio of 51, which could fully facilitate the internal accessible sites exposure and increase the uranium diffusion. As a result, a high adsorption capacity of 44 mg g -1 was achieved in lab-scale dynamic adsorption. Most importantly, the prepared anti-biofouling hydrogel adsorbents display excellent anti-adhesion ability towards Nitzschia after 8 days contact. The adsorption capacity of uranium can reach 2130 μg g -1 in algae-contained simulated seawater. This hydrogel also exhibited a long service life of acceptable mechanical strength and adsorption capacity after at least 6 adsorption-desorption cycles. This new anti-biofouling nanocomposite hydrogel shows great potential as a new generation adsorbent for UES., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Effectively extracting uranium (VI) [U(VI)] from seawater requires efficient adsorbents. Generally, there are two major factors that affect the adsorption efficiency of adsorbents, including the biofouling around the adsorbents and the relative density of adsorption active sites. To enhance the practical application value of powdered polyamidoxime-based materials, macro-braidable and hierarchical porous bamboo strips (BS) with antibacterial properties are selected to synthetize polyamidoximized bamboo strips (PAOBS) by in-situ polymerization methods. On the one hand, natural BS have a bamboo quinone structure, and their intrinsic structure is not destroyed during the reaction process, which endows PAOBS with excellent antibacterial properties. In addition, PAOBS retains the hierarchical porous structure of BS, providing channels for the adsorption process, which is beneficial to achieve the maximum utilization of adsorption active sites. On the other hand, PAOBS increases the relative density of amidoxime functional groups, and its adsorption capacity (233 mg g−1) is approximately 2.14 times higher than that of pure PAO at pH= 6.0, including electrostatic effect and chelation mechanism. After PAOBS is floated in the Yellow Sea Basin for 30 days, its adsorption capacity for U(VI) reaches 1.03 mg g−1. Importantly, the addition of BS increases the coordination modes with the uranyl ion, and the single coordination mode of CH(NH 2)= N - O H from PAO is translated to the three mixed coordination modes of CH(NH 2)= N - O H, CH(N H 2)=N - O H, and CH(N H 2)=N - OH and adjacent CH(N H 2)=N - OH from PAOBS. Construction of PAOBS plays a role in the design of novel adsorbents with high relative density of adsorption active sites and biofouling-resistant, laying the steady foundation for further realizing sustainable U(VI) extraction from seawater. [Display omitted] • PAOBS was synthetized by in-situ polymerization method for the first time. • The outstanding anti-biofouling ability of PAOBS was due to bamboo quinone itself. • Compared with PAO, the adsorption capacity of PAOBS was increased by 2.1 times. • PAOBS was floated in Yellow Sea for 30 d to solve the issue from pure powder PAO. [ABSTRACT FROM AUTHOR]

• A hyperbranched structure with multi-active sites on PAN fibers was constructed. • The adsorption amount reached 1.3 mg/g in dynamic simulated seawater. • The adsorption amount reached 0.6 mg/g in real marine environment. • The adsorption mechanism is chemisorption and N forms a coordination with U(VI). • The branched structure increased the molecular chain rigidity and h →. With the depletion of terrestrial uranium deposits, a large amount of uranium(VI) (U(VI)) in seawater has attracted the attention of researchers and energy suppliers. However, the extremely low concentration of U(VI) and the complex environment enhance the difficulty of extracting U(VI) from seawater. In this study, a multi-active polyacrylonitrile (PAN) adsorbent was constructed to extract U(VI) from seawater. Poly(amido)amine (PAMAM) with hyperbranched topology was grown onto the surface of PAN fiber by a multi-step method, forming a swollen layer in water. The highest adsorption capacity of the material reached 555.5 mg/g. Importantly, during a continuous 50-day simulated seawater dynamic adsorption process, the material reached an adsorption equilibrium in 15 days, with the adsorption amount of 1.3 mg/g. The ocean test in the Yellow Sea of China showed that the adsorption capacity of the material was 0.6 mg/g in 34 days in seawater environment. The effect of molecular chain conformation and swelling behavior on adsorption properties were investigated. The study on the adsorption mechanism of the material shows that the lone pair of electrons of the N atom coordinates with U(VI). [ABSTRACT FROM AUTHOR]

Highlights • Hollow MOFs were first applied into seawater uranium extraction. • Uranium could be efficiently extracted from aqueous solution by DAMN functionalized double-shelled MIL-101 material. • The maximum adsorption capacity is 601 mg g−1, exceeding all known amino groups grafted onto MIL-101 adsorbents. • Hollow properties play a key role in the adsorption of materials. • The adsorbent shows high selectivity and great adsorption rate in simulated seawater. Abstract Hollow metal-organic frameworks (MOFs) have attracted wide interest because of their unique core-shell structure. As a novel uranium adsorbent, diaminomaleonitrile (DAMN) functionalized double-shelled hollow (DSHM) metal-organic framework of chromium(III) terephthalate was prepared by a post-synthetic method of grafting amino group onto coordinatively unsaturated sites (CUS). TEM, XRD, nitrogen sorption and FT-IR spectrometry were used to characterize the obtained DAMN functionalized hollow MOF. The maximum capacity of uranium adsorption is 601 mg g−1, which exceeds all known functionalized MIL-101 uranium adsorption materials. The optimal adsorption pH is 8 which is close to the pH of seawater. Furthermore, the high selectivity of uranium and high adsorption rate in simulated seawater provide a promising prospect to introduce DSHM-DAMN for the extraction of uranium from seawater. In this work, we first applied hollow MOF for uranium adsorption, which greatly improves the uranium adsorption performance of MOF materials; we also explored the practical application of hollow MOF materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • SN-ACP nanofiber membranes were first presented by electrospinning method. • SN-ACP nanofiber membranes exhibited both adsorption and photocatalytic performance. • SN-ACP nanofiber membranes have excellent stability and selectivity. • Reasonable synergistic uranium extraction mechanism was suggested. Developing a uranium extraction material from seawater with high performance and sustainable use is still challenging. Herein, a dual regulation strategy was proposed to prepare AO-CS/CdS-porous few-layer g-C 3 N 4 nanofiber membrane (SN-ACP) with a visible light response by electrospinning technology. SN-ACP has both adsorption and photocatalytic uranium extraction properties. ACP nanofiber membrane can solve the shortcomings of SN nanoparticles, which are easy to agglomerate and challenging to recover, while SN nanoparticles can further improve the uranium extraction capacity and selectivity of ACP nanofiber membrane. More importantly, SN-ACP showed good antibacterial properties under both dark and light conditions, which could effectively resist membrane fouling caused by marine fouling organisms during real seawater applications. In addition, the synergy of SN and ACP significantly improved the uranium extraction performance, with a 6 % SN-ACP nanofiber membrane exhibiting 1.74 times higher uranium extraction capacity than the ACP nanofiber membrane. Moreover, the SN-ACP nanofiber membrane also has excellent selectivity and stability. This work not only provides a method of uranium extraction combined with adsorption and photocatalysis but also provides a new idea for developing a new generation of multifunctional nanofiber membranes. [ABSTRACT FROM AUTHOR]

Extracting uranium from seawater through an effective and economical adsorbent is a challenging task which is limited by (1) the extremely low concentration (∼3.3 ppb), (2) the presence of other metals ions with similar or even higher concentrations than U(VI), (3) the chemical and structural stability in seawater, and (4) implementation and environmental pollution problems. Therefore, it is desirable to develop adsorbents with superior adsorption capacity, excellent selective adsorption, robust chemical/mechanical stability and efficiency for treatment of large amounts of seawater. Herein, an acrylic acid (AA)/polyethyleneimine (PEI) modified Luffa cylindrical (LC) (LC-PAA-PEI) adsorbent, comprising the unique characteristics of PAA (3-D network hydrogel, large numbers of active sites and hydrophilicity), PEI (high adsorbability and selectivity for U(VI)) and LC substrate (3-D network fiber, high mechanical strength, stability, and eco-friendliness), was developed for the adsorption of U(VI) from seawater. The prepared adsorbent exhibited excellent adsorption properties with a maximum capacity of 444.4 mg/g and effective selectivity with a K d value of 16944.4 mL/g for U(VI). Moreover, LC-PAA 5 -PEI 1 displayed superior adsorption at low concentration (3–100 ppb) in simulated seawater. [ABSTRACT FROM AUTHOR]

Schematic representation of AL-PNIPAM hydrogels for uranium adsorption and desorption. [Display omitted] • Aminated lignin-based thermo-responsive hydrogels (AL-PNIPAM) was prepared by radical polymerization to remove uranium. • The maximum uranium adsorption capacity of AL-PNIPAM hydrogels reached 285.5 mg·g−1 at 298 K. • AL-PNIPAM hydrogels had the larger K d value (3.82 × 105 mL·g−1) in the simulated seawater. In this work, triethylenetetramine (TETA) functional lignin (AL) has been prepared, and the aminated lignin-based thermo-responsive (AL-PNIPAM) hydrogels were prepared by radical polymerization. AL-PNIPAM hydrogels exhibited a satisfactory adsorption performance for uranium aqueous solution, with a maximum uranium adsorption capacity of 285.5 mg·g−1 at 298 K. The study of adsorption kinetics showed that the adsorption model of AL-PNIPAM hydrogels was more consistent with pseudo-second-order kinetic equation, confirming the prominent chemical adsorption of the adsorption process. More importantly, it showed high selectivity towards uranium (VI), and the K d was 3.82 × 105 mL·g−1 in simulated seawater. And uranium (VI) can be effectively desorbed, the best desorption was achieved at 15 °C using dilute nitric acid solution with a maximum resolution efficiency of 76 %. Therefore, AL-PNIPAM hydrogels could be considered as a potential candidate in the field of uranium extraction from seawater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The C N (C N , C N hydrolysis and itself) were used to synthesize AOBS. • The flexibility of BS was utilized to woven and shaped. • The AOBS showed ultra-high adsorption capacity and ultra-fast adsorption rate. • The crude U(VI) (m U = 40.45 mg) was recovered by AOBS-M placing in the Yellow Sea. The uranium(VI) (U(VI)) extraction from seawater was crucial for future energy problems such as increasingly depleted fossil fuels and serious environmental pollution, and it could improve the current situation of limited U(VI) reserves on land. In this study, the natural material bamboo strips (BS) were utilized due to the flexibility and richness of various functional groups, and the amidoximized bamboo strips (AOBS) could be directly prepared by a simple one-step method. The amidoximation of materials not only adjusted the optimal adsorption pH from 4 to 6, but also advanced the hydrophilicity, speeded up the reaction rate (adsorption equilibrium within 1 h, about 0.17 times of BS), and increased the adsorption capacity (q e = 268.41 mg g−1 at pH = 6, about 1.7 times of BS). Importantly, the AOBS maintained its initial stitchability through flexibility adjustment, and was woven into a macro-shaped adsorbent (AOBS-M). After being placed in the Yellow Sea basin for 30 days, approximately 44.75 g of crude U(VI) (U(VI) content = 40.45 mg) was obtained (q e = 0.97 mg g−1), and it showed the excellent selectivity for U(VI). The AOBS-M not only overcame the problem that the existing adsorption materials were difficult to achieve macroscopic large-area molding, but also realized the flexibility adjustment during the modification process by controlling the reaction conditions, and promoted the industrial development of U(VI) extraction from seawater. [ABSTRACT FROM AUTHOR]