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Uranium is a critical element of the nuclear industry, and while extracting it from seawater is considered the most promising way to meet the growing demand for uranium, there are still some problems that still need to be solved. This work designed a UiO-66(Ce)-CdS/PEI-modified chitosan composite sponge (USPS) with an adsorption-photocatalytic synergistic effect to extract uranium efficiently. On the one hand, the drawback that the powder material is difficult to be recycled is solved. On the other hand, the uranium extraction capacity of the substrate sponge is improved. Compared with the unmodified PCS sponge, the uranium extraction capacity of the USPS-4 composite sponge is 1.63 fold higher than that of the PCS sponge. In addition, the USPS-4 composite sponge exhibits excellent selectivity and regenerability. The mechanism of uranium extraction can be summarized as the coordination chelation of uranium with active functional groups in the adsorption process and the reduction of hexavalent uranium by photogenerated electrons in the photocatalytic process. This study provides a new strategy for designing and preparing a novel material with high uranium extraction performance, easy separation, and recovery., 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 © 2023. Published by Elsevier B.V.)

Uranium is an important fuel for nuclear power, with 4.5 billion tons of it stored in the oceans, 1,000 times more than on land. Polymer membrane materials are widely used in the marine resources fields, due to their convenient collection, good separation and can work continuously. Herein, a poly(amidoxime)-polyacrylonitrile blend membrane (PCP) with high flux, excellent antibacterial properties and uranium adsorption performance has been prepared by using the phase inversion method, and the prepared membrane was used for highly efficient uranium extraction from seawater. In static adsorption experiments, the PCP membrane reached adsorption equilibrium after 48 h, and the adsorption capacity was 303.89 mg/g (C 0 =50 mg/L). In dynamic adsorption experiments, it was found that the lower flow rate and higher number of membrane layers were favorable for dynamic adsorption. In addition, the water flux of the PCP membrane was 7.4 times higher than that of the PAN membrane. The adsorption mechanism can be attributed to the chelation between amino and hydroxyl groups in CS, amidoxime group in poly(amidoxime) and uranyl ions. The simple preparation process coupled with the excellent adsorption performance indicated that the PCP membrane would be a promising material for the uranium extraction from seawater., 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.)

The preparation of powder adsorbent into microsphere adsorbent is one of the effective methods for the industrialization of uranium extraction from seawater. Herein, a MOF-derived Co-Ni layered double hydroxides/polyethyleneimine modified chitosan micro-nanoreactor (DNPM) was prepared by a simple method in this work. The microstructure and chemical structure of DNPM were comprehensively characterized. The pH value, adsorption time, initial solution concentration, temperature, competitive ions, regeneration performance, and bed column heights were investigated for the adsorption performance of DNPM by batch adsorption and fixed-bed column continuous adsorption experiments. When the contact time was 8 h, the initial concentration was 150 mg/L, and the pH value was 6, the adsorption capacity of DNPM was 334.67 mg/g. The uranium adsorption by DNPM fits with the pseudo-second-order kinetic and Langmuir models, which was a spontaneous and endothermic process. In addition, DNPM has good adsorption selectivity and reusability. The fixed-bed column continuous adsorption experiment shows that the adsorption capacity increased with the increase of bed column height. The adsorption mechanism can be attributed to coordination chelation and electrostatic interaction. In general, this work provides an effective strategy for developing environmentally friendly uranium adsorbent that can be industrially used. [Display omitted] [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]

[Display omitted] • Porous few-layer g-C 3 N 4 was prepared by a facile bottom-up method. • Ultrathin TFC composite exhibits excellent uranium extraction performance. • Schottky junction and built-in electric field promoted charge carriers separation. • Plausible synergistic uranium extraction mechanism was suggested. Photocatalytic reduction towards hexavalent uranium has been considered as one of the most promising strategies for uranium extraction from seawater because of its good selectivity, high efficiency and environment friendliness. Of metal-free photocatalysts, graphitic carbon nitride (g-C 3 N 4) is an attractive candidate. However, its practical application has been limited due to the low photogenerated electron-hole pair separation efficiency and poor electronic conductivity. In this respect, porous few-layer C 3 N 4 (PFC) was prepared by a simple bottom-up method, and its combination with Ti 3 C 2 via electrostatic assembly constructed a 2D/2D heterojunction structure, marked as TFC. The TFC composite exhibit remarkable uranium extraction performance, which is 4.9 times higher than bulk C 3 N 4. Moreover, the sample bears good selectivity and stability. The simple preparation process and excellent uranium extraction capability make TFC-3 composite has a promising application prospect for uranium extraction from seawater. [ABSTRACT FROM AUTHOR]

Chitosan-based hydrogels have been used as adsorption materials and offered remarkable prospects, due to their abundant, biodegradable, inexpensive features and rich amino and hydroxyl groups. In this work, the structure of chitosan (CS) hydrogel and its adsorption performance toward uranyl species (UO 2 2+ and UO 2 (CO 3) 3 4−) were comprehensively investigated on the basis of various characterizations and theoretical simulation. Systematic experiments show that CS hydrogel bears excellent adsorption performance for low-concentration UO 2 (CO 3) 3 4− solution in column adsorption experiment and the removal efficiency is >99 %. The outer-sphere complexation adsorption has been postulated for the case of UO 2 (CO 3) 3 4−, where intermolecular hydrogen bonds dominate in the adsorption. Differently, the inner-sphere one is attributed for capturing UO 2 2+ species, which is coordinated by C N, -NH 2 and -OH groups of CS hydrogel. Since the 3D network structure of CS hydrogel is prone to couple with water, it is difficult for U(VI) to enter inside the hydrogels, which reduces the adsorption performance. However, this phenomenon has been effectively weakening by using column adsorption experiment, which accomplished the exchange between water and U(VI). These detailed investigation toward adsorption mechanism might open a doorway to gain deeper insights on the design and application of efficient adsorption materials for uranium extraction. [Display omitted] • Inner-sphere mechanism: UO 2 2+ coordinated by C N, -NH 2 and -OH groups. • Outer-sphere mechanism: UO 2 (CO 3) 3 4− interacts with intermolecular hydrogen bonds. • CS hydrogel is beneficial to couple with UO 2 (CO 3) 3 4− and easy to form bound-water. • CS hydrogel has high removal efficiency for UO 2 (CO 3) 3 4− (C 0 = 11.24–101.69 μg/L). [ABSTRACT FROM AUTHOR]

• TiO 2 -polyacrylonitrile photocatalytic membrane was prepared by phase conversion method. • TiO 2 -polyacrylonitrile photocatalytic membrane exhibited good uranium extraction performance. • The mechanism of uranium extraction was reasonably speculated. Uranium, as an important nuclide, has attracted extensive attention because of its high energy density, clean and pollution-free characteristics. Herein, a TiO 2 -polyacrylonitrile photocatalytic membrane (TPM) was prepared by phase conversion method for efficient uranium extraction. TPM photocatalytic membrane is composed of TiO 2 , PAN and conductive carbon cloth, in which TiO 2 is the main active substance in the photoreduction process and PAN is the membrane-forming substrate material. Carbon cloth can improve the conductivity of the polymer substrate and improve the photocatalytic efficiency to a certain extent ((The uranium extraction reaction rate of the carbon cloth-based TPM membrane was 1.35 and 1.41 times higher than that of the non-substrate and non-woven fabric-based membranes, respectively). TPM photocatalytic membrane has excellent photoreduction performance of hexavalent uranium. Under the optimal reaction conditions (C 0 = 100 mg/g, pH = 5), the capacity of uranium extracted is 263.92 mg/g. In addition, TPM photocatalytic membrane also exhibited good reusability (uranium extraction capacity after the fifth cycle is 246.13 mg/g) and selective uranium extraction ability (K dU /K dV = 41.78, and the removal rate of uranium is 74.63 %). The extraction mechanism of uranium can be summarized as the reduction of hexavalent uranium by photogenerated electrons excited in photocatalytic membrane under light condition. In general, this work provides a new strategy for designing simple, low-cost and efficient photocatalytic materials for uranium extraction from seawater. [ABSTRACT FROM AUTHOR]