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[Display omitted] • The effect of hydration shells on uranium adsorption kinetics is deeply investigated. • The external diffusion can be facilitated due to fast water exchange. • The increasing temperature would reduce the apparent friction during mass transfer. • The adsorption equilibrium time can be shortened from 32 days down to 18 days. Identifying mass transfer is essential for boosting adsorption kinetics. The internal and external diffusions serve as rate-limiting steps. The liquid film diffusion is commonly identified as external diffusion, while the mass diffusion across the ubiquitous hydration shell is generally ignored. Charged functional groups can bind water molecules strongly via electrostatically induced hydration. Herein, three representative polar polymers, including cation polymer (PDMAPAA), anion polymer (PSS) and zwitterion polymer (PSBMA), are crosslinked with polyamioxime (PAO) to synthesize radially aligned PAO-PDMAPAA, PAO-PSS, PAO-PSBMA, respectively, by a bidirectional freeze-casting. We focus on the effect of hydration structure and hydration dynamics on marine uranium extraction performance. It is found that the external diffusion in PAO-polar polymer adsorbents can be facilitated due to fast water exchange in dynamic hydration shell, leading to a reduced adsorption equilibrium time compared with the pristine PAO. However, the high hydration degree causes strong viscous shear and high dehydration barrier, which impede the complexation of UO 2 2+ with binding sites of PAO. Although the hydration degree follows the order of PAO-PSBMA > PAO-PDMAPAA > PAO-PSS, PAO-PDMAPAA delivers the shortest equilibrium time required. In addition, the increasing temperature would weaken viscous shear in static hydration shell, which equivalently reduces the apparent friction of hydrated uranyl ions. Consequently, light-irradiated GO@PAO-PDMAPAA adsorbent, in which GO acts as a photothermal mediator, yields a shorter equilibrium time (∼18 days) than PAO-PDMAPAA together with a high uranium adsorption capacity of 12.24 mg-U/g-Ads in natural seawater. These findings provide valuable guidance for enhancing uranium adsorption kinetics associated with hydration shell. [ABSTRACT FROM AUTHOR]

With the continuous research and development of amidoxime (AO)‐based adsorbents, industrialization production of uranium from seawater gradually becomes a reality. However, the currently available AO‐based adsorbents still suffer from low adsorption rate and poor selectivity. Herein, vertically aligned polyamioxime–graphene oxide (VA‐PG) sheet membrane is fabricated by directional freeze casting. The run‐through microchannels contribute to the free diffusion of uranyl ions (UO22+), leading to the fast adsorption kinetics. Furthermore, partially reduced graphene oxide allows high photothermal conversion efficiency and rapid in‐plane heat transfer, resulting in the fast temperature rise under simulated sunlight irradiation. Because of the endothermic behavior of UO22+, light‐irradiated VA‐PG can simultaneously satisfy the requirements of high adsorption capacity (13.63 mg‐U g‐Ads−1), high adsorption rate (0.43 mg g−1 day−1), and excellent selectivity toward U(VI) over V(V) (U/V = 1.24) in natural seawater, indicating the right direction for a breakthrough in the field of uranium extraction from seawater. [ABSTRACT FROM AUTHOR]

UiO‐66‐NH2/black phosphorus quantum dots (MOF/BPQDs) heterojunctions are anchored on the carboxyl cellulose nanofiber (CNF) aerogel with high porosity (>98%) to fabricate high‐efficiency uranium adsorbents (BP@CNF‐MOF). CNF aerogels possess abundant carboxyl groups, which can serve as nucleation centers to in situ synthesize UiO‐66‐NH2 with smaller crystal size, high mass loading, and good adhesion. BP@CNF‐MOF demonstrates good mechanical flexibility and minimal MOF loss from the CNF aerogel, both of which result from the mutual physical interactions and entanglements of CNFs as well as strong binding interactions between MOF crystals and CNF aerogel. Owing to the excellent heterogeneous photocatalytic activity of MOF/BPQDs, on one hand, marine bacteria can be effectively destroyed by reactive oxygen species (ROS). On the other hand, the photocatalytic U(VI) reduction to insoluble U(IV) could be facilitated, thereby allowing more binding sites on the MOF crystals for further U(VI) adsorption. Consequently, compared with dark conditions, the adsorption efficiency of the light irradiated BP@CNF‐MOF increases by 55.3%, reaching up to 6.77 mg‐U per g‐Ads after 6 weeks of exposure to natural seawater. The intrinsic instability of BPQDs can be overcome by MOF coating layer simultaneously. The strategy applied in this work could also be applicable to other superior MOF crystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • The incorporation of TCPP(Ni) enhances the visible light absorption of UIO-type MOF. • TCPP(Ni) ligands give rise to the downward LUMO energy level of Zr-oxo cluster. • More mesoporous created by TCPP(Ni) increase utilization of hidden binding sites. • A high U-sorption capacity of 8.95 mg-U/g-Ads is achieved from natural seawater. Integrating multi-functionality into metal–organic frameworks (MOFs) has attracted growing attention as it plays a critical role in realizing the potential of MOFs for a wide variety of applications. Owing to the ultrahigh surface areas and porosity, MOFs have been recognized as potential adsorbents for uranium capture through chemical chelation of uranyl ions (UO 2 2+). As a new type of photocatalyst, however, these MOFs are rarely applied in uranium recovery by photocatalytic reduction of soluble U(VI) to the less soluble U(IV), which is largely due to the limited visible light harvesting as well as the poor separation and transfer of photo-generated carriers. Herein, we present a facile one pot synthetic route to incorporate photo-responsive Ni(II)-centered porphyrin (TCPP(Ni)) ligands into UIO-66-NH 2 (TCPP(Ni) ⊂ MOF) while maintaining the crystal structure and ultrahigh chemical stability. TCPP(Ni) not only provides strong visible light harvesting but also improves the charge transfer from excited ligands to Zr-oxo clusters. Consequently, the mixed-linker strategy boosts the photoreduction of soluble U(VI) to the less soluble U(IV) for uranium immobilization. After optimization, TCPP(Ni) ⊂ MOF-3 presents excellent selective uranium capture from wastewater and natural seawater through combined complexation and photoreduction. Strikingly, after immersing in natural seawater for 25 days, a high uranium sorption capacity of 8.95 ± 0.39 mg-U/g-Ads can be achieved together with good antibacterial ability. This work provides a promising strategy to improve the photoreduction potential of MOF adsorbents for uranium capture. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wood aerogel with run-through microchannel arrays was used for in-situ growth of MOF. • Bilayer MOF architecture was developed to boost the loading content of MOF. • CMPM adsorbents exhibited good reversible compressibility and fragility resistance. • The recycle CMPM exhibited high selective adsorption capacity in natural seawater. Metal-organic frameworks (MOFs) have been widely applied in the recovery of specific guest molecules due to their excellent properties including high porosities, adjustable pore size and abundant chelating functions. However, the granular MOF crystals bring a great challenge to the recycling and reusing from aqueous media, and thus seriously limit their practical application. In this work, MOF bonded wood aerogel prepared by means of in-situ growth strategy was developed for uranium extraction from natural seawater. Eco-friendly and biocompatible wood aerogel possesses run-through microchannel arrays enclosed by aligned cellulose nanofibers (CNFs), contributing to the free and fast diffusion of uranyl ions (UO 2 2+), and thus result in the sufficient coordination with active chelation sites of MOF crystals. To increase the loading content of MOF, bilayer MOF architecture (CMPM) was prepared by using hydroxyl functional groups in CNFs and polydopamine (PDA) coating as nucleation centers of MOF, respectively. The resultant CMPM adsorbents exhibited good reversible compressibility and fragility resistance, which were critical to extend its service life. Moreover, the excellent photothermal conversion capability of PDA enabled CMPM to acquire high temperature under simulated sunlight irradiation. Owing to the apparently endothermic behavior of UO 2 2+, light-irradiated CMPM achieved high adsorption capacity (5.81 mg-U/g-Ads) together with excellent UO 2 2+ selectivity in natural seawater after 30 days. Therefore, this work provides a feasible solution in promoting the practical application of MOF adsorbents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mussel-inspired photothermal PAO hydrogel adsorbents were successfully fabricated. • PDA contributes to excellent hydrophilicity and photothermal conversion capacity. • Light irradiation yields the high uranium sorption capacity of 12.67 mg-U/g-Ads. • Excellent adsorption selectivity towards U(VI) over V(V) can be obtained. • Fe3+ coordination endows with excellent tensile strength and self-recovery ability. The efficient development of selective adsorbents for uranium extraction from seawater is necessary for their potential application in nuclear power generation. The amidoxime-based adsorbents have been recognized as the potential candidates, whereas they still suffer from a much higher affinity towards V(V) present in the seawater over U(VI), leading to the extremely limited commercial use. In this work, we develop a novel mussel-inspired photothermal polyamidoxime (PAO) hydrogel adsorbent, in which polydopamine (PDA) chains are linked to PAO (PDA-PAO) via Michael addition. Dual-crosslinked Fe@PDA-PAO hydrogel structure is constructed by noncovalent bonds between the catechol of PDA chains (e.g. π-π stacking and hydrogen bonds) as well as ionic coordination of Fe3+. PDA contributes to the improved hydrophilicity and high photothermal conversion efficiency. As a result, after immersing in real seawater for 6 weeks, light-irradiated Fe@PDA-PAO hydrogel delivers high uranium sorption capacity (12.67 mg-U/g-Ads) together with high U/V mass ratios (1.17), which are superior to currently available hydrogel adsorbents. Meanwhile, Fe3+ coordination endows Fe@PDA-PAO hydrogel with excellent tensile strength and self-recovery ability, which are of great significance to withstand the harsh conditions of ocean environment for practical applications. The results presented here reveal that Fe@PDA-PAO hydrogel holds tremendous potential for practical applications in the uranium-selective extraction from seawater. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF-bonded carbon sponge is designed for photothermally enhancing U(VI) adsorption. • The mass loading of UiO-66-NH 2 prepared by in-situ growth can reach up to 85 wt%. • The monolithic MOF adsorbent exhibits favorable elastic and recyclable performance. • The selectivity of U(VI) can be improved when exposure to light irradiation. • Light irradiation yields a 32.37% increase in the U(VI) adsorption amount than dark. Extraction of radioactive uranium from the natural seawater is regarded as one of the most promising ways to address the shortage of uranium resources. As a kind of potential uranium adsorbent, more attention has been paid to metal–organic framework materials (MOFs) due to large specific surface area and high ion selectivity. Currently, however, MOF adsorbents are hardly applied to the real seawater in view of the relatively low uranium adsorption capacity and recyclable issues. Herein, we present the monolithic MOF adsorbent with photothermally enhancing uranium adsorption capacity. Carbon sponge (CS) substrate with macroporous open cell structure was used as excellent photothermal conversion material. Zr-MOF (UiO-66-NH 2) crystals were in situ grown on the fibrils network of polydopamine (PDA) pre-coated CS to obtain UiO-66-NH 2 @CS-PDA adsorbent. It is found that UiO-66-NH 2 coating with perfect coverage and good adhesion has a high mass loading (>85 wt%). As a result, UiO-66-NH 2 @CS-PDA adsorbents exhibited the advantage of high-selectivity, high-affinity and cycling stability. Compared with the dark condition, the uranium adsorption amount was increased by 32.37% after 4 weeks in the natural seawater under simulated solar irradiation, which was mainly ascribed to the endothermic behavior of uranium adsorption process. Moreover, the elasticity attribute of CS was essential for sustenance of volume variation buffering during seawater flow. As a recyclable and favorable elastic large-scale monolithic MOF adsorbent, UiO-66-NH 2 @CS-PDA holds great promise for extracting uranium from the natural seawater. [ABSTRACT FROM AUTHOR]