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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]

• G-AOBS is synthetized by chemical cross-linking and acid-base neutralization reactions. • G-AOBS has outstanding anti-biofouling and superhydrophilic characteristics. • Compared with AOBS, the adsorption capacity of G-AOBS is increased by 1.38 times. • Three "bridges hydrogen bonds" are used to form the most stable chelation mode. Uranium adsorption from seawater can provide a sustainable development path for the future raw material supply of nuclear energy. However, in the process of uranium extraction from seawater, biofouling adheres to the surface of the adsorbent, wasting the adsorption sites and seriously affecting the adsorption capability of the adsorbent. Herein, inspired by the superanti-biofouling property of guanidine groups, a superantibacterial and knitted adsorbent with guanidine and amidoxime groups cografted on natural bamboo strips (G-AOBS) is synthesized to adsorb uranium from simulated seawater. The intrinsic structure of bamboo is not destroyed by the whole grafting process, and G-AOBS still maintains the porous and cellulose crystalline structure. The grafting of guanidine groups improves the hydrophilicity and significantly enhances the anti-biofouling performance, thereby increasing the adsorption capacity for uranium (q e = 201.4 ± 13.23 mg g−1 at pH = 4 with C 0 = 100 mg L−1 and q e = 1.04 ± 0.12 mg g−1 in simulated seawater with C 0 = 500 μg L−1). According to the results of DFT, the guanidine and amidoxime groups can not only replace one carbonate in uranyl tricarbonate alone to form a more stable coordination structure but also have a synergistic effect between the two, that is, using three "bridging hydrogen bonds" to form the most stable chelation mode with uranyl dicarbonate. [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]

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]

If U(VI) in seawater (unconventional uranium resource) can be extracted efficiently, it can provide important supplies and guarantees for the stable development of nuclear power. In this study, a mixing melting method without condensation agent was proposed to prepare ultra-high flexibility and different proportions DAMN modified EAA resin film (EAA-DAMN) through the condensation reaction between -COOH and -NH 2 and the uniform mixing of liquid EAA and DAMN. In addition, the dense film structure and -C N of EAA-DAMN were transformed into multiple pores structure and amidoxime groups of the amidoximated EAA (AO-EAA) by amidoxime reaction. The AO-EAA-3 showed the most excellent adsorption performance (q e =146.40 mg g−1) at pH = 5, which was 2.33 times that of EAA. Moreover, a hypothesis was proposed for the first time that -NH 2 in the material could combine with H+ ionized by water to form -NH 3 +, and then adsorbed NO 3 - in the solution through electrostatic attraction, and O element from NO 3 - adsorbed on the surface and N-O from amidoxime groups of material as the adsorption active sites performed coordination with U(VI), thereby improving the adsorption performance of AO-EAA. [Display omitted] • The AO-EAA were synthesized by a mixed melting method without condensation agent. • The synthesis mechanism included the condensation reaction and liquid mixing. • The AO-EAA-3′s adsorption capacity was 5.30 μg g−1 in 3 μg L−1 simulated seawater. • The O from NO 3 - and N-O from amidoxime groups acted as adsorption sites. [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]

• 3D macroscopic g-C 3 N 4 sponge have been designed by thermal polymerization. • Thermodynamic analysis was best described by Langmuir model. • The maximum adsorption capacity of MFCN-DETA composites was 658.57 mg/g at pH 6. • MFCN-DETA showed selective U(VI) adsorption from simulated seawater. Uranium is the key fuel for nuclear power and there is 4.5 billion tons of uranium in the oceans. However, it is a significant challenge for the current adsorbent with powder form to extract uranium from seawater. In this study, we report a facile method for the synthesis of three-dimensional macroscopic g-C 3 N 4 sponge from melamine-formaldehyde (MFCN) resin by thermal polymerization, which can easily be extracted from aqueous solution. Different organic amino (diethylenetriamine, triethylenetetramine and tetraethylenepentamine) modified g-C 3 N 4 sponge composites (MFCN-DETA, MFCN-TETA and MFCN-TEPA) has been designed by schiff base reaction. The uranium adsorption performance of the products from aqueous solutions and simulated seawater was investigated. MFCN, MFCN-DETA and MFCN-TEPA achieved the maximum adsorption capacity at pH 6 and the optimum pH for MFCN-TETA was 5.0. The results showed that the maximum adsorption capacity of MFCN-DETA composites was 658.57 mg/g at pH 6. Furthermore, the MFCN-DETA composites was effectively regenerated using 0.1 N HNO 3 , which could be reused for enrichment of uranium (VI) and the adsorption efficiency could maintain 83% after 5 cycles of adsorption and desorption. The distribution coefficie(K d) value of uranium was 9.1 × 104 mL g−1 for MFCN-DETA in simulating seawater. Thus, MFCN-DETA composites are believed to have promising potential applications in removal of uranium (VI) from seawater. [ABSTRACT FROM AUTHOR]

Adsorption uranium [U(VI)] from U-containing radioactive wastewater (URW) is a critical strategy for solving the resource shortage and environmental pollution in pace with the sustainable development of nuclear energy. However, the URW universally exhibits acidity and contains co-existing metal ions with high concentration. Herein, the amidoximation ethylene-acrylic acid copolymer balls (EAA-AO) with aciduric and super-high mechanical property were successfully synthesized through grafting diaminomaleonitrile and further treatment of amidoximation. Significantly, the mechanical properties of EAA-AO were not affected by the grafting process and maintained super-high mechanical properties. Furthermore, the –NH 2 and unreacted –C N groups in diaminomaleonitrile adjusted the pK a to make the optimal pH be 4. In addition, the microstructure of EAA-AO was transformed from the original dense to multi-layer porous structure, which promoted the mass transfer process and the contact between uranyl ions (UO 2 2+) and internal adsorption active sites. The adsorption capacity of EAA-AO was about 1.78 times that of EAA at pH = 4, and the adsorption capacity for U(VI) was about 8.17 times that of Ba2+ with the second highest adsorption capacity. Therefore, the EAA-AO exhibited ultra-high adsorption performance (q e = 3.196 mg g−1) in the artificial radioactive wastewater, laying a good foundation for subsequent large-scale industrial adsorption of U(VI) in nuclear industrial wastewater. The amidoximation ethylene-acrylic acid copolymer balls (EAA-AO) with ultra-high mechanical property and multi-layer porous structure was revealed for the first time the modulation of hot alkali ethanol water mixed solution on the structure, and exhibited superior adsorption performance and specific selectivity for U(VI) from radioactive wastewater. [Display omitted] • The EAA-AO were successfully synthetized through two-step approach: the dehydration condensation reaction and amidoximation reaction, and the ultra-high mechanical and aciduric property didn't be destroyed by preparation process. • The hot alkaline ethanol-water mixed solution transformed the original dense structure of EAA into a multi-layer porous structure of EAA-AO, which accelerated the mass transfer process and maximized utilization of adsorption active sites. • The EAA-AO showed superior adsorption performance for U(VI) in radioactive wastewater because -NH 2 and unreacted -C≡N groups from diaminomaleonitrile adjusted the pK a of adsorbents. • Based on -N=C-, -O-N- from amidoxime groups, and unreacted -C≡N groups participating in the chemical coordination process, the EAA-AO exhibited specific selectivity for U(VI) in radioactive wastewater with high concentration interfering metal ion. [ABSTRACT FROM AUTHOR]

• An anti-biofouling and robust MMT-PDA/PAM nanocomposite hydrogel was first proposed. • The interpenetrating network lead to high water permeability and stability. • A high adsorption amount of 44 mg g−1 was achieved in lab-scale dynamic adsorption. • The MMT-PDA/PAM displayed excellent anti-adhesion ability without killing algae. • It also showed superior adsorption capacity in algae-contained simulated seawater. 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. [ABSTRACT FROM AUTHOR]