Spatial Engineering Direct Cooperativity between Binding Sites for Uranium Sequestration

Preorganization is a basic design principle used by nature that allows for synergistic pathways to be expressed. Herein, a full account of the conceptual and experimental development from randomly distributed functionalities to a convergent arrangement that facilitates cooperative binding is given, thus conferring exceptional affinity toward the analyte of interest. The resulting material with chelating groups populated adjacently in a spatially locked manner displays up to two orders of magnitude improvement compared to a random and isolated manner using uranium sequestration as a model application. This adsorbent shows exceptional extraction efficiencies, capable of reducing the uranium concentration from 5 ppm to less than 1 ppb within 10 min, even though the system is permeated with high concentrations of competing ions. The efficiency is further supported by its ability to extract uranium from seawater with an uptake capability of 5.01 mg g-1, placing it among the highest-capacity seawater uranium extraction materials described to date. The concept presented here uncovers a new paradigm in the design of efficient sorbent materials by manipulating the spatial distribution to amplify the cooperation of functions.

Construction of covalent organic framework with unique double-ring pore for size-matching adsorption of uranium

The separation and recovery of key nuclides such as uranium and plutonium from effluents related to nuclear industry is of great significance for alleviating the shortage of nuclear energy resources and protecting the environment and human health. However, the high temperature, strong acidity and radioactivity of the nuclear effluents pose a severe challenge to the separation materials used in such conditions. The diversity of structure, flexibility of design, and excellent physicochemical stability of covalent organic framework materials (COFs) provide the possibility for the directional design and preparation of adsorbents for use under harsh conditions. Herein, three COFs with similar structure, different pore sizes and connecting modules were synthesized. The ingenious structure predesign enables Dp-COF to have three carboxyl groups oriented toward the pore center and laid out in appropriate spatial positions, which builds hydrogen-bonding bridges between carboxycarbonyl and hydroxyl groups, and thus constructs for the first time a unique COF material with a double-ring pore. The inner pore size of the "double-ring" is slightly larger than the diameter of uranyl hydrate, which leads to a size-matching adsorption of uranium by Dp-COF, thus greatly reducing the effect of protonation. Even in the simulated spent fuel reprocessing liquid with pH = 1.0, the adsorption capacity of Dp-COF for uranium can reach 66.3 mg g^-1, and the adsorption capacity reaches 317.3 mg g^-1 at pH = 4.5, which is very rare among the reported COFs. More excitingly, the removal rate for uranium reaches up to an unprecedented 99.8% due to the size-matching effect, more than any analogous adsorbents. This study not only proposes new ideas for the design and regulation of the microscopic configuration of COF materials, but also provides an alternative approach for the preparation of efficient uranium adsorbents.

In Vivo Uranium Sequestration using a Nanoscale Metal-Organic Framework

An agent for actinide sequestration with fast uranium uptake kinetics and efficient in vivo uranium removal using a nanoscale metal-organic framework (nano-MOF) is proposed. UiO-66 nanoparticles post-synthetically functionalized with carboxyl groups, UiO-66-(COOH)₄ -180, exhibit the fastest uranium uptake kinetics reported with more than 65 % of uranyl in fetal bovine serum (FBS) removed within 5 min. Moreover, the in vivo bio-distribution studies show that the material partially accumulates in kidneys and femurs where uranium mainly deposits facilitating the in vivo sequestration of uranium. The results of the in vivo uranium decorporation assays with mice show that UiO-66-(COOH)₄ -180 could successfully reduce the amounts of uranyl deposited in kidneys and femurs by up to 55.4 % and 36.5 %, respectively, and is significantly more efficient than the commercial actinide decorporation agent, ZnNa₃ -DTPA.

Rapid Room-Temperature Preparation of Hierarchically Porous Metal-Organic Frameworks for Efficient Uranium Removal from Aqueous Solutions

The effective removal of uranium from an aqueous solution is a highly valuable process for the environment and health. In this study, we developed a facile and rapid method to synthesize hierarchically porous Cu-BTC (RT-Cu-BTC) using a cooperative template strategy. The as-synthesized RT-Cu-BTC exhibited hierarchically porous structure and excellent thermostability, as revealed by X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Compared with conventional metal-organic frameworks (MOFs) and zeolites, the obtained RT-Cu-BTC exhibited enhanced adsorption capacity (839.7 mg·g-1) and high removal efficiency (99.8%) in the capture of uranium (VI) from aqueous solutions. Furthermore, the conditions such as adsorbent dose, contact time, and temperature in adsorption of uranium (VI) by RT-Cu-BTC were investigated in detail. The thermodynamics data demonstrated the spontaneous and endothermic nature of the uranium (VI) adsorption process. The Langmuir isotherm and pseudo-second-order models could better reflect the adsorption process of uranium (VI) onto RT-Cu-BTC. In addition, the as-synthesized RT-Cu-BTC showed excellent stability in removing uranium (VI) from an aqueous solution. This work provides a facile and rapid approach for fabricating hierarchically porous MOFs to realize a highly efficient removal of uranium (VI) from aqueous systems.

Simultaneous removal of U(VI) and Re(VII) by highly efficient functionalized ZIF-8 nanosheets adsorbent

The simultaneously efficient removal of cationic and anionic radionuclides is an important and challenging topic for nuclear waste remediation as well as environmental protection. Herein, monoclinic ZIF-8 nanosheets modified with ethyleneimine polymer (denoted as ZIF-8/PEI) was achieved and used to determine the capture behaviors of both U(VI) oxycations and Re(VII) oxyanions from aqueous solution. ZIF-8/PEI assemblies showed a maximum U(VI) and Re(VII) uptake capacity of 665.3 (pH 5.0) and 358.2 mg/g (pH 3.5), respectively. Experimental, spectroscopic and theoretical calculation results directly unraveled that U(VI) adsorption onto ZIF-8/PEI assemblies was mainly ascribed to the coordination with abundant amino groups and weakly due to the Zn terminal hydroxyl groups, while anion exchange mechanism contributed predominantly to the Re(VII) sequestration. This work not only sheds light on the interaction mechanisms of simultaneous capture of U(VI) and Re(VII) but also highlights the versatile material design of cationic and anionic radionuclide immobilization in radioactive wastewater remediation.

Rational Construction of Porous Metal-Organic Frameworks for Uranium(VI) Extraction: The Strong Periodic Tendency with a Metal Node

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO₂²⁺ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me₂NH₂⁺, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.

Bio-inspired antibacterial cellulose paper-poly(amidoxime) composite hydrogel for highly efficient uranium(vi) capture from seawater

A bio-inspired cellulose paper-poly(amidoxime) composite hydrogel is explored via UV-polymerization. This hydrogel has a highly efficient uranium capture capacity of up to 6.21 mg g^-1 for W_U/W_dry gel and 12.9 mg g^-1 for W_U/W_{poly(amidoxime)} in seawater for 6 weeks, due to its enhanced hydrophilicity, good hydraulic/ionic conductivity and broad-spectrum antibacterial performance.

Grafting functional groups in metal–organic frameworks for U(vi) sorption from aqueous solutions

Recent highlights of the organic groups-functionalized MOFs for uranium extraction from aqueous solution are discussed.

Synergistic effects of MOF-76 on layered double hydroxides with superior activity for extractive catalytic oxidative desulfurization

The combination of MOF-76 with an LDH provides a completely new route for the synthesis of MOF–LDH advanced functional materials.

Assorted functionality-appended UiO-66-NH2 for highly efficient uranium(vi) sorption at acidic/neutral/basic pH

Eight assorted functionalities were anchored on UiO-66-NH₂via PSM strategy displaying MOFs with similar framework but variable uranyl binding affinities. The excellent sorption capacity of UiO-66-PO-Ph makes it efficient uranium sorbent material.

Selective Th(iv) capture from a new metal–organic framework with O− groups

New MOF adsorbent with functional N⁺–O⁻ groups was designed. The material shows fast adsorption of Th(iv) and high removal efficiency, and is selective over La(iii), Sm(iii), Ho(iii), Cd(ii), Pb(ii) and K(i) ions.

Membrane-supported 1D MOF hollow superstructure array prepared by polydopamine-regulated contra-diffusion synthesis for uranium entrapment

This work reports the architecture of a novel class of membrane-supported 1D MOF hollow superstructures, by using the bio-inspired polydopamine (PDA) mediated contra-diffusion synthetic strategy, for facile and efficient separation of uranium in a flow-through mode. PDA chemistry was firstly employed to modify the inner surfaces of the cylindrical pore channels of polycarbonate track-etched membrane (PCTM), thereby regulating the heterogeneous nucleation and interfacial growth of ZIF-8 crystals. ZIF-8 hollow superstructures embedded in membrane matrix with well-defined 1D channels were obtained. These membrane-supported MOF hollow superstructures then, for the first time, served as integrated chromatographic micro-column arrays for effective entrapment of uranium from aqueous solutions. It is highlighted that the PCTM supported ZIF-8 superstructures exhibited outstanding uranium entrapment ability in both traditional batch mode (capacity 62.3 mg/g) and fast flow-through mode (removal rate over 90% for 3 level). Moreover, new insights into the interaction between ZIF-8 and uranyl ions were obtained, suggesting that an ion-exchange mechanism involved synergistic effect was responsible for uranium binding, especially in a long-term exposure. The membrane-supported 1D MOF hollow superstructures developed in this work represent a new category of organic-inorganic composite membrane. And, it is envisioned that the methodology established in this work would be versatile for preparing more MOF superstructures with deployable form for separation applications. In summary, a novel class of membrane-supported ZIF-8 hollow superstructure was fabricated for effective separation of uranyl ions.

In situ Preparation of Chitosan/ZIF-8 Composite Beads for Highly Efficient Removal of U(VI)

With the rapid growth of nuclear power generation and fuel processing, the treatment of nuclear industry wastewater has become a major problem, and if not handled properly, it will pose a potential threat to the ecological environment and human health. Herein, a chitosan (CS)/ZIF-8 composite monolithic beads with ZIF-8 loading up to 60 wt% for U(VI) removal was prepared, which can be easily removed after use. It possesses a very high adsorption capacity of 629 mg•g⁻¹ at pH = 3 for U(VI) and a well recyclability is demonstrated for at least four adsorption/desorption cycles. X-ray photoelectron spectroscopy (XPS) was carried out to study the adsorption mechanism between uranium and adsorbent, and the chelation of U(VI) ions with imidazole, hydroxyl, and amino groups was revealed. This work shows that CS/ZIF-8 composite can be used as an effective adsorbent for uranium extraction from aqueous solution, and has a potential application value in wastewater treatment.

Ammoniating Covalent Organic Framework (COF) for High-Performance and Selective Extraction of Toxic and Radioactive Uranium Ions

An ideal porous adsorbent toward uranium with not only large adsorption capacity and high selectivity but also broad applicability even under rigorous conditions is highly desirable but still extremely scarce. In this work, a porous adsorbent, namely [NH4]+[COF-SO3 -], prepared by ammoniating a SO3H-decorated covalent organic framework (COF) enables remarkable performance for uranium extraction. Relative to the pristine SO3H-decorated COF (COF-SO3H) with uranium adsorption capacity of 360 mg g-1, the ammoniated counterpart of [NH4]+[COF-SO3 -] affords ultrahigh uranium uptake up to 851 mg g-1, creating a 2.4-fold enhancement. Such a value is the highest among all reported porous adsorbents for uranium. Most importantly, a large distribution coefficient, K d U, up to 9.8 × 106 mL g-1 is observed, implying extremely strong affinity toward uranium. Consequently, [NH4]+[COF-SO3 -] affords highly selective adsorption of uranium over a broad range of metal ions such as SU/Cs = 821, SU/Na = 277, and SU/Sr = 124, making it as effective uranium adsorbent from seawater, resulting in amazing uranium adsorption capacity of 17.8 mg g-1. Moreover, its excellent chemostability also make it an effective uranium adsorbent even under rigorous conditions (pH = 1, 8, and 3 m acidity).

Metal organic framework (La-PDA) as an effective adsorbent for the removal of uranium(VI) from aqueous solution

A two-dimensional lanthanum(III) porous coordination polymer was prepared, characterized and applied as an efficient adsorbent for the removal of uranium from aqueous solution. Lanthanum(III) was the metal center of MOFs, and the deprotonated anions of pyridine-2,6-dicarboxylic acid (H2PDA), PDA2− was the organic ligand, this MOF was name as La-PDA, which was synthesized by hydrothermal reaction method. Scanning electron microscope (SEM), Fourier transform infrared (FTIR), powder X-ray diffraction (PXRD) and thermal gravimetric (TG) analysis were used for characterization, and the results indicated that the La-PDA composites were successfully prepared. Compared with traditional adsorbents of uranium, La-PDA showed excellent adsorption properties. The adsorption capacity was 247.6 mg g−1 at 298 K and pH 4.0. The adsorption equilibrium achieved within 120 min, and the adsorption process was exothermic and spontaneous. The absorption mechanism of La-PDA was also explored, from the XPS spectra, the pyridine-like nitrogen atoms (C=N–C) and carboxyl oxygen atoms (–COO–) contributed to the adsorption of uranium. The results suggested that PDA2− was a potential ligand of uranium adsorption, La-PDA composites were effective adsorbents for the removal of uranium from aqueous solution.

Two-dimensional copper-based metal-organic frameworks nano-sheets composites: One-step synthesis and highly efficient U(VI) immobilization

In this study, a new kind of thin 2D MOFs nano-sheets (MNS) was successfully prepared through complexation between 2-methylimidazole and Cu(II) by a one-step, and cost-effective route. The structural morphologies can be tuned by adjusting the ratio of MeOH/H₂O. The synthesized MNS (MNS-1, MNS-2, MNS-3 and MNS-4) were fully characterized and the results indicated that the synthesized MNS were freestanding and possess micro-sized lateral dimensions and nanoscale thickness of sub-25 nm. All the obtained MNS display great performance with the adsorption capacity hierarchy of MNS-2 (591.79 mg·g^-1) > MNS-3 (409.49 mg·g^-1) > MNS-4 (387.07 mg·g^-1) > MNS-1 (384.84 mg·g^-1) at pH ˜ 6.0, and 298 K. The thermodynamic parameters indicated the exothermic and spontaneous nature of U(VI) immobilization. The U(VI) immobilization mechanism was achieved through the complexation between U(VI) and C-N(H) /-OH groups. This work supplies a facile and purposeful approach for developing 2D MOFs nano-sheets toward a highly efficient immobilization of U(VI), and it also promotes the preparation of structure-based design of nanomaterials for radionuclide-containing-medium pretreatment.

A Universally Applicable Strategy for Construction of Anti-Biofouling Adsorbents for Enhanced Uranium Recovery from Seawater

The ocean reserves 4.5 billion tons of uranium and amounts to a nearly inexhaustible uranium supply. Biofouling in the ocean is one of the most severe factors that hazard uranium extraction and even cause the failure of uranium extraction. Therefore, development of uranium adsorbents with biofouling resistance is highly urgent. Herein, a strategy for constructing anti-biofouling adsorbents with enhanced uranium recovery capacity in natural seawater is developed. This strategy can be widely applied to modify currently available carboxyl-contained adsorbents, including the most popular amidoxime-based adsorbent and carboxyl metal organic framework adsorbent, using a simple one-step covalent cross-link reaction between the antibacterial compound and the adsorbent. The prepared anti-biofouling adsorbents display broad antibacterial spectrum and show more than 80% inhibition to the growth of marine bacteria. Benefitting from the tight covalent cross-link, the anti-biofouling adsorbents show high reusability. The modified amidoxime-based adsorbents show enhanced uranium recovery capacity both in sterilized and bacteria-contained simulated seawater. The anti-biofouling adsorbent Anti-UiO-66 constructed in this study exhibits 24.4% increased uranium recovery capacity, with a uranium recovery capacity of 4.62 mg-U per g-Ads, after a 30-day field test in real seawater, suggesting the strategy is a promising approach for constructing adsorbents with enhanced uranium extraction performance.

Carboxylate-functionalized organic nanocrystals for high-capacity uranium sorbents

Carboxylate-functionalized organic nanocrystals (ONCs) derived from perylene diimide or naphthalene diimide were synthesized and carefully characterized as novel high-capacity uranium (U(VI)) sorbents. Adsorption studies using uranyl ions demonstrated that the carboxyl and hydroxyl groups on the surface of the ONCs play pivotal roles in U(VI) adsorption. ONCs formed from the condensation of perylene dianhydride and aminoisophthalic acid exhibit very high U(VI) adsorption capacities of 1393 mg g^-1 comparable to the highest capacity ever reported. The adsorption kinetics of the ONCs were found to obey the second-order model, indicating that chemisorption is the rate-determining step for U(VI) adsorption by these materials. Furthermore, the perylene-based ONC containing imidazole exhibited no pH dependency upon the U(VI) adsorption and the naphthalene-based ONC was able to remove up to 97.5% U(VI) from simulated nuclear industrial effluent containing many competing elements. These findings will facilitate the development of high-performance organic U(VI) sorbents with high densities of adsorption sites.

Fully phosphorylated 3D graphene oxide foam for the significantly enhanced U(VI) sequestration

Efficient sequestration of U(VI) from complex aqueous solution is of vital importance for environmental remediation. In this work, the fully phosphorylated graphene oxide foam (phos-GOF) was synthesized via a facile hydrothermal method and the as-prepared 3D phos-GOF was served as an adsorbent to capture U(VI) from aqueous solution. The introduction of abundant phosphorus-containing groups via phytic acid endows phos-GOF good hydrophilia and excellent affinity for U(VI). The adsorption performance of phos-GOF for U(VI) was carefully evaluated under different environments. phos-GOF shows rapid and high efficiency for U(VI) adsorption. The maximum adsorption capacity of phos-GOF for U(VI) is ∼483 mg/g, which is much higher than that of pristine graphene oxide foam (GOF). In addition, the spent 3D phos-GOF can be easily regenerated by a simple and low-cost desorption process using 0.02 mol/L HNO₃. The interaction mechanism between phos-GOF and U(VI) is mainly attributed to the inner-sphere complexation between phosphoric functional groups and U(VI) based on a series of spectroscopic analyses. The 3D phos-GOF exhibits favorable sequestration performance towards U(VI) which can be used as a potential candidate in uranium-bearing wastewater treatment and disposal.

Novel sensing platform based on gold nanoparticle-aptamer and Fe-metal-organic framework for multiple antibiotic detection and signal amplification

The development of a feasible antibiotic detection method is important in water quality analysis. In this study, we developed a metal-organic framework (MOF)-aptamer-3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂-based sensing platform composed of the reaction variable of TMB catalytic oxidation as the label (from colorless to blue) and aptamer as the target recognition element for antibiotic detection. The platform works by calculating the relation between the antibiotic concentration and the resultant decrease in MOF's catalytic activity. Basing from the comparison of typical iron-based MOF materials (Fe-MIL-53, Fe-MIL-88A, and Fe-MIL-100), we selected Fe-MIL-53 to obtain an improved signal amplification effect. The outstanding performance of the Fe-MIL-53-based sensing platform can be attributed to its topological flexibility and small electron transfer impedance. In addition, a signal increment of up to 86% was obtained with an intensified gold nanoparticle (AuNP)-supported aptamer. The inhibitory catalytic activity stemmed from the coating of antibiotic-(AuNP-aptamer) conjugates onto the outer surface of the MOF material, which increased the impedance and decreased the electron transfer efficiency. Validation results indicated that the platform showed high selectivity and sensitivity (i.e., wide linearity range of 50-200 nM, detection limit up to 8.1 ng/mL, and recovery rate of 106%-110%) for chloramphenicol detection and universal applicability for other antibiotics, including ampicillin, tetracycline, and oxytetracycline. In general, the detection reliability and easy operation of this platform render it a promising candidate for antibiotic detection in future water quality monitoring practices.

Metal–organic framework-based materials for the recovery of uranium from aqueous solutions

This review focuses on the recent progress in MOFs and MOF-based materials as superior adsorbents for the efficient removal of uranium from aqueous solutions.

Hollow cobalt sulfide for highly efficient uranium adsorption from aqueous solutions

The preparation of hollow Co₃S₄nanostructures by ZIF-67 guarantees high uranium adsorption performance in aqueous solutions.

An anionic manganese(ii) metal–organic framework for uranyl adsorption

A robust MOF that can rapidly and selectively adsorb uranyl in a seawater system is reported.