Uranyl Research Articles

Engineering shrinkage resistance of nano-structured hydrogels in seawater for fast uranium capture

Synthetic hydrogels, which are 3D networks composed of crosslinked hydrophilic polymer chains, have been created using various crosslinked ways for uranium capture due to full exposure of chelate functional groups. However, the conventional honeycomb-like hydrogels exhibit non-connected micropore structure, which locks abundant water molecules and hence is unfavorable for mass transfer. Herein, we demonstrate a simple synthesis of the nano-structured hydrogel with activated nanogels as nano-crosslinkers (denoted as PGP hydrogel), and probe into the relationship between hydrogel structural parameters and uranium adsorption kinetics. It is found that the PGP hydrogel with a low crosslinking density of ∼0.02 mol/m3 possesses interconnected micropores, thereby facilitating diffusion of uranyl ions (UO22+) in 3D polymeric networks. Furthermore, a freeze-assisted soaking strategy is proposed to endow PGP hydrogel (denoted as target hydrogel) with strong shrinkage resistance in natural seawater, resulting in a ∼40 % increase in water permeance to reach 369 Lm−2h−1MPa−1. Correspondingly, the adsorption equilibrium time is shortened to ∼11 days. Although the uranium uptake capacity of PGP hydrogels with and without freeze-assisted soaking treatment remain basically unchanged (∼9.73 mg-U/g-Ads), a high uranium adsorption rate of 0.88 mg/g/d for the target hydrogel surpasses most currently available polymer adsorbents. The presented strategy is generalizable to a broader range of applications involving the adsorption of economically valuable ions in seawater or brine lake.

In situ Raman monitoring of studtite formation under alpha radiolysis in 18O-labeled water

Studtite [(UO2)(O2)(H2O)2]·2(H2O) is a secondary phase precipitating during the alteration of uranium-bearing materials. The mechanistic link between the formation of uranyl and peroxide bonds in the solid and the nature of the oxidizing species produced by water radiolysis remains to be elucidated. In order to improve our understanding of these mechanisms, an original experimental methodology in the presence of 18O isotopes and Raman spectroscopy has been developed. It appears that there is a direct chemical relationship between the peroxo ligands inside studtite and the peroxide entities of H2O2 molecule into the solution. The link between H2O2 formation mechanism in solution by the radiolysis of water, the nature of the radiation and the isotopy of the peroxo ligands inside studtite has been described thanks to a coherent set of experimental data. For the uranyl UO22+ ions, the characterization of its isotopy allows to specify the mechanism of oxidation at the UO2 /water interface. The isotopic configurations observed for the uranyl ion inside studtite, can be explained by assuming an oxidation mechanism of UO2 involving both a simple transfer of electrons by interaction with H2O2 and the incorporation of oxygen atoms from the solution into the fluorite structure via OH° radicals.

Uptake and coordination behaviour of uranyl on functionalised silica

The safe decommissioning of nuclear reactors is a complex process, requiring a range of technological options for it to be done effectively. It has become more important in recent years, with the substantial number of reactors entering the decommissioning phase. This paper details the use of functionalised silica for the recovery of uranium from aqueous hydrochloric acid solutions, a potential agent for the treatment of steel reactor components during nuclear reactor decommissioning. Silica functionalised with either phosphonic acid, bistriazine, or bistriazinylbipyridine ligands was shown to extract uranium, with the commercially available phosphonic acid functionality being the most effective. Extractions of 100 % were observed at [H+] ≤ 0.24 M, further the phosphonic acid functionality also had the highest loading capacity. Increasing [H+] has a suppressive effect on uranyl recovery, which was more pronounced for the in-house synthesized silica, and was attributed to protonation of the extracting moiety. Extended x-ray absorption fine structure spectroscopy was also used to determine the uranium coordination environments on the functionalised silica, and gain insights into the extraction mechanism. The uranyl cation was bound by two phosphonic acid groups, two bis-triazine groups, and one bistriazinylbipyridine group, respectively on each respective extractant. Uranyl was found to be penta-coordinate in the equatorial plane for all systems, with oxygen and/or chloride always present in the first coordination sphere. Evaluation of the mechanism indicated that uranyl must be loading onto the phosphonic acid functionality via multiple mechanisms, to both the phosphonic acid and silica related surface groups, although preferential binding of uranyl to the phosphonic acid groups was observed.

First Structured Uranium‐Based Monoliths Produced via Vat Photopolymerization for Nuclear Applications

AbstractUranium plays an unquestionable role in the framework of nuclear physics, biology, and radiopharmacy. Moreover, uranyl ion UO22+ offers an immense variety of applications due to the unique photosensitivity of its complexes. The excited state of uranyl cation is indeed accessible under ultraviolet‐visible (UV–vis) light, readily producing radical species UO22+* upon light irradiation. Herein, an innovative synthesis protocol is presented to explore the use of uranyl cations as photocatalyst systems for photocurable sol–gel‐based formulations, coupling the photochemical reactions of uranyl cations with photopolymerization‐based additive manufacturing processes. Additive manufacturing has nowadays revolutionized the production of complex structures with arbitrary geometries and has opened up enticing opportunities for innovative technological breakthroughs and highly tailorable systems. The fabrication of micro‐architected components is shown via vat photopolymerization, namely, the Digital Light Processing technique, and ‐3D) printed parts are converted into uranium dicarbide (UC2)/carbon nanocomposite upon carbothermal reduction. This uranyl‐mediated additive manufacturing process constitutes the first application of the synergistic role of uranyl motifs in a photopolymer platform, demonstrating for the first time the possibility to directly pattern uranium‐based materials in complex structures.

Bifunctional hyper-cross-linked polymer with phosphorylated-amidoximated groups for efficient uranium extraction from water

Designing and developing a uranium adsorbent with high adsorption capacity and good selectivity is highly significant. We synthesized a novel hyper-cross-linked polymer adsorbent with bifunctional groups, (PHCP-4-AO), such as phosphate and amidoxime groups, via simple Scholl reaction and subsequent functionalization for the first time highly efficient extraction of U(VI) from aqueous solution. Due to its unique molecular structure design, it can enhance the selectivity and adsorption capacity of uranium by using two different functional groups. The maximum uranium adsorption capacity of PHCP-4-AO was 424.33 mg/g, which was higher than the single-functional group phosphorylated (PHCP-4) (315.43 mg/g) and amidoximated (HCP-4-AO) (260.38 mg/g) adsorbents. The combination of phosphate and amidoxime groups improves the adsorption effect. PHCP-4-AO has good selectivity and affinity for uranyl ions. In simulated wastewater, the Kd of PHCP-4-AO for uranium was 7266.3 mL/g, which was more than 15 times that of other ions. After three adsorption–desorption cycles, the adsorption capacity of PHCP-4-AO can still be maintained above 300.00 mg/g. Through XPS analysis, it is speculated that the sorption of uranium by PHCP-4-AO is owing to the lone pair electrons found on the oxygen atom of the phosphate groups, as well as the oxime oxygen and amino nitrogen atoms of the amidoxime groups entering the uranium’s empty orbit to form the coordination bonds. These findings demonstrated that this new hyper-cross-linked polymer could be considered as a valuable material in the extraction and recovery of uranium from uranium-containing aqueous solutions.

Construction of a Bifunctional Redox-Site Conjugated Covalent-Organic Framework for Photoinduced Precision Trapping of Uranyl Ions.

The performance of covalent-organic frameworks (COFs) for the photocatalytic extraction of uranium is greatly limited by the number of adsorption sites. Herein, inspired by electronegative redox reactions, we designed a nitrogen-oxygen rich pyrazine connected COF (TQY-COF) with multiple redox sites as a platform for extracting uranium via combining superaffinity and enhanced photoinduction. The preorganized bisnitrogen-bisoxygen donor configuration on TQY-COF is entirely matched with the typical geometric coordination of hexavalent uranyl ions, which demonstrates high affinity (tetra-coordination). In addition, the presence of the carbonyl group and pyrazine ring effectively stores and controls electron flow, which efficaciously facilitates the separation of e-/h+ and enhances photocatalytic performance. The experimental results show that TQY-COF removes up to 99.8% of uranyl ions from actual uranium mine wastewater under the light conditions without a sacrificial agent, and the separation coefficient reaches 1.73 × 106 mL g-1 in the presence of multiple metal ions, which realizes the precise separation in the complex environment. Importantly, DFT calculations further elucidate the coordination mechanism of uranium and demonstrate the necessity of the presence of N/O atoms in the photocatalytic adsorption of uranium.

One-dimensional nanostructure arrays with Schottky Junction enhanced charge separation for the photoelectrocatalytic selective removal of Uranium from wastewater

The photoelectrocatalytic reduction of soluble U(VI) to relatively insoluble U(IV) is a promising method for uranium wastewater treatment. However, the strong reliance on sacrificial agents and an inert atmosphere due to the rapid charge reorganization remains a great challenge. The construction of an inner electrical field at a heterojunction interface accompanied by an external electric field provides a promising strategy for enhancing charge transfer. Herein, a photoelectrode was proposed by in-situ coating nano-TiO2 cone arrays (NTCA) on a titanium mesh, and used for uranium removal from complex effluents under air conditions without sacrificial agents. The enhanced spatial charge separation driven by the Schottky junction built-in electric field and an external bias voltage, coupled with rapid fluid diffusion, granted the photoelectrode an outstanding photoelectrocatalytic uranium removal performance with photocurrent densities of up to 3 mA cm−2 at −0.55 VAg/AgCl. The impressive uranium removal performance was maintained in a wide range of chemical conditions, as well as in real seawater and industrial wastewater. Theoretical calculation revealed that uranyl ions were confined on the NTCA surface as [UO2(H2O)5]2+, further reduced to UO2. This work demonstrated a viable route for uranium separation from aqueous solutions with inexhaustible solar energy and minimal electrical energy.

Iron-carbon composite as flow electrode active material for highly efficient electrosorption of uranium from radioactive wastewater

A kind of iron-carbon composite for efficient electrosorption of uranium from radioactive wastewater was prepared by simply carbonization of cellulose and ferric nitrate, and the uranium electrosorption performance and behavior of the iron-carbon composite as flow electrode active material were investigated for low-concentration (below 50 mg/L) uranium-containing wastewater. By regulating the experimental conditions such as cellulose particle sizes, the mass ratio of cellulose/Fe(NO3)3, liquid flow rate, pH, and electric field strength, it was found that under the optimized conditions, the uranium removal ratios were 66.8, 81.92, 95.2, and 97.75 % for initial concentrations of 0.1, 0.5, 5.0, and 50.0 mg/L, respectively. The uranium concentration could be reduced from 0.1 mg/L to 0.0332 mg/L (the emission standard is 0.05 mg/L in China, GB 8798–1996) within 180 min of treatment. In addition, the material maintained an average salt removal rate of 26.27 μg cm−2 min−1 after 36 cycles of electrosorption. It achieved a uranium removal ratio of 87 %, and the upper limit of the electrosorption capacity was still not reached. Combined with X-ray photoelectron spectroscopy (XPS) analysis, the results indicated that the uranyl ion (UO22+) was firstly adsorbed on the surface of the active material after entering the flow electrode. Then, parts of the UO22+(Ⅵ) were reduced to uranium dioxide [UO2(Ⅳ)] under the synergistic action of zero-valent iron (ZVI) and cathodic electro-reduction and were finally immobilized on the electrode surface. This study proposed an innovative application of iron-carbon composite as flow electrode active material in FCDI for the treatment of uranium-containing wastewater with low-concentration (below 50 mg/L).

Interaction between Uranyl Cations and Layered Double Hydroxide Nanoparticles: Implications for Nuclear Wastewater Management

Interaction between Uranyl Cations and Layered Double Hydroxide Nanoparticles: Implications for Nuclear Wastewater Management

Dual‐Site Trigger Electronic Communication Effects to Accelerate H2O2 Activation for Colorimetric Sensing of Uranyl Ions in Seawater

AbstractEfficient activation of hydrogen peroxide (H2O2) through biomimetic catalysis still faces a major challenge. In this work, inspired by the catalytic pocket of natural peroxidase, Cu single atom (CuSA) and AuCu nanoparticles (AuCuNPs) anchored on nitrogen‐doped carbon skeleton (CuSA‐AuCuNPs/NC) serve as dual active sites that significantly accelerate the charge transfer process and thus achieve efficient H2O2 activation. Meanwhile, the experimental and theoretical calculations show that the well‐established electronic communication effect between CuSA and AuCuNPs results in moderate electronic modifications to CuSA, which promotes the heterolysis of H2O2 and the timely desorption of H2O. As a proof of concept, CuSA‐AuCuNPs/NC show remarkable performance in detecting uranyl ions in seawater. This work provides new insights into the H2O2 activation for colorimetric sensing.

Understanding the Complexation of Alkyl-Substituted Nitrilotriacetamides with Uranium: A Study by Absorption Spectroscopy and Microcalorimetry.

Complexation thermodynamics of UO22+ ions with a series of alkyl-substituted nitrilotriacetamides (NTA) was investigated by absorption spectroscopy and microcalorimetry. The hexamethyl derivative of NTA (HMNTA) forms the weakest two successive complexes with UO22+ ions with stability constants of log β11 = 3.5 ± 0.1 and log β12 = 6.1 ± 0.1. The formation constant values increased linearly with increasing alkyl chain length of the substituents from hexamethyl NTA to hexabutyl NTA (HBNTA) and to hexahexyl NTA (HHNTA). The complexation with each ligand was both enthalpy and entropy driven with exothermic enthalpy changes of ΔH11 = -14.7 ± 1.0 kJ/mol, ΔH12 = -10.2 ± 0.8 kJ/mol for HMNTA, ΔH11 = -19.2 ± 1.2 kJ/mol, ΔH12 = -16.4 ± 1.1 kJ/mol for HBNTA, and ΔH11 = -21.3 ± 1.4 kJ/mol, ΔH12 = -19.4 ± 2.3 kJ/mol for HHNTA. Similarly, the positive entropy changes with each ligand were ΔS11 = 18.1 ± 2.7 J/mol/K, ΔS12 = 82.9 ± 3.8 J/mol/K for HMNTA, ΔS11 = 14.4 ± 1.2 J/mol/K, ΔS12 = 87.2 ± 4.2 J/mol/K for HBNTA, and ΔS11 = 16.1 ± 2.4 J/mol/K, ΔS12 = 92.6 ± 3.1 J/mol/K for HHNTA. Structural features of the complex suggest the participation of two ligands coordinating in a bidentate mode via the carbonyl oxygens. The [UO2L2]2+ complexes appear to be noncentrosymmetric with two ligands and one water molecule occupying the equatorial plane of the dioxo uranyl cation. The structure of the complex was confirmed by 1H NMR titration, EXAFS measurements, and DFT calculations.

Photoreduced Ag+/sodium alginate supramolecular hydrogel as a sensitive SERS membrane substrate for rapid detection of uranyl ions

BackgroundIn the fields of environmental monitoring and nuclear emergency, in order to obtain the relevant information of uranyl-induced environmental pollution and nuclear accident, it is necessary to establish a rapid quantitative analytical technique for uranyl ions. As a new promising technique, surface-enhanced Raman scattering (SERS) is hopeful to achieve this goal. However, uranyl ions are easily desorbed from SERS substrates under acidic conditions, and the structures of SERS substrates will be destroyed in the strong acidic aqueous solutions. Besides, the quantitative detection ability of SERS for uranyl ions needs to be promoted. Hence, it is necessary to develop new SERS substrates for accurate quantitative detection of trace uranyl in environmental water samples, especially in acidic solutions. ResultsIn this work, we prepared silver ions/sodium alginate supramolecular hydrogel membrane (Ag+/SA SMH membrane), and the Ag+ ions from the membrane were transformed into Ag/Ag2O complex nanoparticles under laser irradiation. The Raman signal of uranyl was strongly enhanced under the synergistic interaction of electromagnetic enhancement derived from the Ag nanoparticles and charge transfer enhancement between uranyl and Ag2O. Utilizing the peak of SA (550 cm−1) as an internal standard, a quantitative detection with a LOD of 6.7 × 10−9 mol L−1 was achieved due to a good linear relation of uranyl concentrations from 1.0 × 10−8 mol L−1 to 2 × 10−6 mol L−1. Furthermore, foreign metal ions hardly affected the SERS detection of uranyl, and the substrate could determine trace uranyl in natural water samples. Particularly, the acidity had no obvious effect on SERS signals of uranyl ions. Therefore, in addition to the detection of uranyl ions in natural water samples, the proposed strategy could also detect uranyl ions in strong acidic solutions. Significance and noveltyA simple one-step method was used to prepare an Ag+/SA SMH membrane for rapid quantitative detection of uranyl ions for the first time. The proposed substrate successfully detected uranyl ions under acidic conditions by immobilizing uranyl ion in hydrogel structure. In comparison with the previous studies, a more accurate quantitative analysis for uranyl ions was achieved by using an internal standard, and the proposed strategy could determine trace uranyl in either natural water samples or strong acidic solutions.

Highly sensitive and selective determination of uranyl ions based on Ag/Ag2O–COF composite SERS substrate

Uranium is an essential nuclear material in civilian and military areas; however, its extensive application raises concerns about the potential safety issues in the fields of environmental protection and nuclear industry. In this study, we developed an Ag/Ag2O–COF (covalent-organic framework) composite SERS substrate to detect uranyl ions (UO22+) in environmental aqueous solutions. Herein, the strong SERS effect of uranyl adsorbed in Ag/Ag2O composite and the high adsorption efficiency of COF TpPa-1 were combined to realize the trace detection of uranyl ions. This method displayed a linear range of 10−8 mol L−1 to 10−6 mol L−1 with the detection limit of 8.9 × 10−10 mol L−1 for uranyl ions. Furthermore, common metal cations and oxo-ions hardly affected the SERS detection of uranyl, which is helpful for the trace analysis of uranyl in natural water samples. Although the proposed strategy is deployed for uranyl detection, the reusable and high-efficiency system may be expanded to trace detection of other substance with Raman activity.

Kevlar Aerogel‐Confined Functional Liquid‐Based Composite Membrane Enables Dynamic Uranium Capture

AbstractSolid–liquid composite materials that confine a functional liquid within a porous solid have appeared in a wealth of emerging applications. However, creating dynamic liquid interfaces for efficient ion capture while stably retaining functional liquid in porous confinements is challenging. Here, an aerogel‐confined liquid‐based composite membrane (ALCM) for dynamic and highly efficient uranium capture is reported. As a proof of concept, Kevlar aerogel membrane is selected as the nanoporous solid, and calix[6]arene/tributyl phosphate (C6/TBP) is used as the guest liquid. The obtained ALCMs possess high stability, optimum adhesion between solid‐liquid interface, and high selectivity for uranyl ions (250–6510 times over other competing ions). Different dynamic interface regulating approaches are explored for ALCMs, and uranium extraction efficiency under alternating pressures can be up to 258.48 mg g−1 h−1, outperforming many reported uranium capture materials. This strategy can be applicable to develop a rich family of solid‐liquid composite materials and may spearhead a new paradigm for uranium capture from sustainable seawater resources.

Mechanistical Insights into the Ultrasensitive Detection of Radioactive and Chemotoxic UO22+ Ions by a Porous Anionic Co-Metal-Organic Framework.

Development of a simple, cost-efficient, and portable UO22+ sensory probe with high selectivity and sensitivity is highly desirable in the context of monitoring radioactive contaminants. Herein, we report a luminescent Co-based metal-organic framework (MOF), {[Me2NH2]0.5[Co(DATRz)0.5(NH2BDC)]·xG}n (1), equipped with abundant amino functionalities for the selective detection of uranyl cations. The ionic structure consists of two types of channels decorated with plentiful Lewis basic amino moieties, which trigger a stronger acid-base interaction with the diffused cationic units and thus can selectively quench the fluorescence intensity in the presence of other interfering ions. Furthermore, the limit of detection for selective UO22+ sensing was achieved to be as low as 0.13 μM (30.94 ppb) with rapid responsiveness and multiple recyclabilities, demonstrating its excellent efficacy. Density functional theory (DFT) calculations further unraveled the preferred binding sites of the UO22+ ions in the tubular channel of the MOF structure. Orbital hybridization between NH2BDC/DATRz and UO22+ together with its significantly large electron-accepting ability is identified as responsible for the luminescence quenching. More importantly, the prepared 1@PVDF {poly(vinylidene difluoride)} mixed-matrix membrane (MMM) displayed good fluorescence activity comparable to 1, which is of great significance for their practical employment as MOF-based luminosensors in real-world sensing application.

Anchoring chitosan/phytic acid complexes on polypyrrole nanotubes as capacitive deionization electrodes for uranium capture from wastewater

Capacitive deionization (CDI) technology holds great potential for rapid and efficient uranyl ion removal from wastewater. However, the related electrode materials still have much room for research. Herein, chitosan/phytic acid complexes were anchored on polypyrrole nanotubes (CS/PA-PPy) to fabricate the electrode for the electrosorption of uranyl ions (UO22+). In this system, polypyrrole nanotubes provided specific channels for ion and electron diffusion, and chitosan/phytic acid complexes offered selective sites for UO22+ binding. The results demonstrated that CS/PA-PPy via electrosorption showed faster kinetics and higher uranium uptake than those via physicochemical adsorption. The maximum adsorption capacity toward UO22+ via electrosorption (1.2 V) could reach 799.3 mg g−1, which was higher than most of the reported CDI electrodes. Electrochemical measurements and experimental characterizations showed that the electrosorption of UO22+ by CS/PA-PPy was a synergistic effect of capacitive process and physicochemical adsorption, in which the capacitive mechanism involved the formation of an electric double layer from hollow polypyrrole nanotubes, whereas the coordination of phosphate, amino and hydroxyl groups with UO22+ was attributed to physicochemical adsorption. With the rational design of material, along with its excellent uranium removal performance, this work exhibited a novel and potential composite electrode for uranium capture via CDI from wastewater.

Design and Construction of the Uranyl Coordination Polymer with Multifunction Stimulus Response: Fluorescent Sensors for Halide Ions and Photochromism.

It can provide ideas for the use of uranium elements in the treatment of spent fuel from nuclear wastewater to explore the application potential of uranium element. Thus, it is necessary to research the structure and properties of a novel uranyl coordination polymer (CP) for uranium recovery and reuse. Herein, we designed and prepared a new uranyl CP U-CMNDI based on UO22+ and H2CMNDI (H2CMNDI = N, N'-bis(carboxymethyl)-1,4,5,8-naphthalenediimide). Structural analysis shows that two uranyl ions are connected by two parallel deprotonated CMNDI ligands to form a discrete uranyl dimer structure. U-CMNDI can act as a potential stimulus-responsive halide ion sensor by a fluorescence "turn on" response in water. The limit of detection for fluoride (F-), bromide (Br-), iodide (I-), and chloride (Cl-) is 5.00, 5.32, 5.49, and 5.73 μM, respectively. The fluorescence "turn on" behavior is based on the photoinduced electron transfer (PET) mechanism between halide ions and electron-deficient NDI cores. In addition, U-CMNDI demonstrates a color response to ultraviolet light, exhibiting reversible photochromic behavior with a notable color change. The color change mechanism can contribute to the PET process and the radical process.

Novel Olefin-Linked Covalent Organic Framework with Multifunctional Group Modification for the Fluorescence/Smartphone Detection of Uranyl Ion.

Monitoring and purification of uranium contamination are of great importance for the rational utilization of uranium resources and maintaining the environment. In this work, an olefin-linked covalent organic framework (GC-TFPB) and its amidoxime-modified product (GC-TFPB-AO) are synthesized with 3-cyano-4,6-dimethyl-2-hydroxypyridine (GC) and 1,3,5-tris(4-formylphenyl) benzene (TFPB) by Knoevenagel condensation. GC-TFPB-AO results in specificity for rapid fluorescent/smartphone uranyl ion (UO22+) detection based on the synergistic effect of multifunctional groups (amidoxime, pyridine, and hydroxyl groups). GC-TFPB-AO features a rapid and highly sensitive detection and adsorption of UO22+ with a detection limit of 21.25 nM. In addition, it has a good recovery (100-111%) for fluorescence detection in real samples, demonstrating an excellent potential of predesigned olefin-linked fluorescent COFs in nuclear contaminated wastewater detection and removal.

Semiconductive Behavior and Photoconductivity of Uranyl Dithiophosphinate Single Crystal.

Herein, we detail the synthesis, structure, and photoconductivity of the uranyl dithiophosphinate single crystal UO2[S2P(C6H5)2]2(CH3OH)·CH3OH (denoted as U-DPDPP). The formation of bonds between uranyl ions and sulfur-based ligands endows U-DPDPP with a distinct electronic absorption property with a broadband spectrum spanning from 250 to 550 nm, giving rise to a unique semiconductive property. Under X-ray illumination, U-DPDPP displays a distinctive photoconductivity response, with a charge carrier mobility lifetime (μτ) of 2.78 × 10-4 cm2·V-1 achieved, which contradicts the electronic-silence behavior of uranyl nitrate crystal.

Phytic acid-functionalized polyamidoxime/alginate hydrogel for targeted uranium extraction from acidic wastewater

Efficient removal of uranium from radioactive wastewater is crucial for both environmental protection and sustainable development of nuclear energy. However, selectively extracting uranium from acidic wastewater remains a significant challenge. Here we present a phytic acid-functionalized polyamidoxime/alginate hydrogel (PAG) via a facile one-step hydrothermal reaction. The PAG, leveraging the robust binding affinity of phytic acid and the selective coordination of amidoxime for U(VI), exhibited high efficiency and selectivity in adsorbing U(VI) from acidic uranium-containing wastewater. At pH 2.50, U(VI) adsorption equilibrium was achieved within 60 min, showcasing a maximum theoretical adsorption capacity of 218.34 mg/g. Additionally, the PAG demonstrated excellent reusability, maintaining a uranium removal rate exceeding 90 % over five adsorption-desorption cycles. Remarkably, the as-synthesized PAG removed 94.1 % of U(VI) from actual acidic uranium-contaminated groundwater with excellent anti-interference performance, reducing U(VI) concentration from 272.0 μg/L to 16.1 μg/L and making it meet the WHO drinking water standards (30 μg/L). The adsorption mechanism was elucidated through XPS and DFT calculation, revealing that the uranyl ion primarily coordinated with phosphate and amidoxime groups on phytic acid and polyamidoxime, respectively. These findings underscore the promising potential of PAG hydrogel for addressing acidic uranium-containing wastewater from uranium mining and metallurgy.