Siderophore-inspired chelator hijacks uranium from aqueous medium

Siderophores and metallophores: Metal complexation weapons to fight environmental pollution

Siderophores are small molecules of organic nature, released by bacteria to chelate iron from the surrounding environment and subsequently incorporate it into the cytoplasm. In addition to iron, these secondary metabolites can complex with a wide variety of metals, which is why they are commonly studied in the environment. Heavy metals can be very toxic when present in large amounts on the planet, affecting public health and all living organisms. The pollution caused by these toxic metals is increasing, and therefore it is urgent to find practical, sustainable, and economical solutions for remediation. One of the strategies is siderophore-assisted bioremediation, an innovative and advantageous alternative for various environmental applications. This research highlights the various uses of siderophores and metallophores in the environment, underscoring their significance to ecosystems. The study delves into the utilization of siderophores and metallophores in both marine and terrestrial settings (e.g. bioremediation, biocontrol of pathogens, and plant growth promotion), such as bioremediation, biocontrol of pathogens, and plant growth promotion, providing context for the different instances outlined in the existing literature and highlighting their relevance in each field. The study delves into the structures and types of siderophores focusing on their singular characteristics for each application and methodologies used. Focusing on recent developments over the last two decades, the opportunities and challenges associated with siderophores and metallophores applications in the environment were mapped to arm researchers in the fight against environmental pollution.

Achieving ultrahigh uranium/vanadium selectivity of poly(amidoxime) via coupling MXene-enabled strong intermolecular interaction and separated photothermal interface

Poly(amidoxime) (PAO) has been recognized as the most potential candidate for extracting uranium from seawater, owing to its merits of outstanding uranium affinity, low cost, and large-scale production. Despite remarkable achievements, existing PAO sorbents suffer from unsatisfactory uranium extraction efficiency and selectivity, as imposed by the inherently sluggish uranium adsorption kinetics and inevitable spatial configuration transition of amidoxime, which diminishes uranium affinity. Herein, we discover a facile and integrated design to elaborate a PAO/MXene nanocomposite that delivers ultrahigh and durable uranium/vanadium (U/V) selectivity. The key to our design lies in harnessing MXene-enabled strong intermolecular interactions to PAO to minimize the spatial configuration transition of amidoxime and stabilizing its superior uranium affinity, as well as creating a separated photothermal interface to maximize temperature-strengthened affinity for uranium over vanadium. Such a synergetic effect allows the nanocomposite to acquire over a 4-fold improvement in U/V selectivity compared to that of pure PAO as well as an unprecedented distribution coefficient of uranium compared to most state-of-the-art sorbents. We further demonstrate that our nanocomposite exhibits durable U/V selectivity with negligible attenuation and good antibacterial ability even in long-term operation. The design concept and extraordinary performance in this study bring PAO-based sorbents a step closer to practical uranium extraction from seawater.

Development of 225Ac-doped biocompatible nanoparticles for targeted alpha therapy

Targeted alpha therapy (TAT) relies on chemical affinity or active targeting using radioimmunoconjugates as strategies to deliver α-emitting radionuclides to cancerous tissue. These strategies can be affected by transmetalation of the parent radionuclide by competing ions in vivo and the bond-breaking recoil energy of decay daughters. The retention of α-emitting radionuclides and the dose delivered to cancer cells are influenced by these processes. Encapsulating α-emitting radionuclides within nanoparticles can help overcome many of these challenges. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles are a biodegradable and biocompatible delivery platform that has been used for drug delivery. In this study, PLGA nanoparticles are utilized for encapsulation and retention of actinium-225 ([225Ac]Ac3+). Encapsulation of [225Ac]Ac3+ within PLGA nanoparticles (Zave = 155.3 nm) was achieved by adapting a double-emulsion solvent evaporation method. The encapsulation efficiency was affected by both the solvent conditions and the chelation of [225Ac]Ac3+. Chelation of [225Ac]Ac3+ to a lipophilic 2,9-bis-lactam-1,10-phenanthroline ligand ([225Ac]AcBLPhen) significantly decreased its release (< 2%) and that of its decay daughters (< 50%) from PLGA nanoparticles. PLGA nanoparticles encapsulating [225Ac]AcBLPhen significantly increased the delivery of [225Ac]Ac3+ to murine (E0771) and human (MCF-7 and MDA-MB-231) breast cancer cells with a concomitant increase in cell death over free [225Ac]Ac3+ in solution. These results demonstrate that PLGA nanoparticles have potential as radionuclide delivery platforms for TAT to advance precision radiotherapy for cancer. In addition, this technology offers an alternative use for ligands with poor aqueous solubility, low stability, or low affinity, allowing them to be repurposed for TAT by encapsulation within PLGA nanoparticles.

Enhanced uranium extraction from seawater: from the viewpoint of kinetics and thermodynamics

Uranium extraction from seawater (UES) is recognized as one of the seven pivotal chemical separations with the potential to revolutionize global paradigms. The forthcoming decade is anticipated to witness a surge in UES, driven by escalating energy demands. The oceanic reservoirs, possessing uranium quantities approximately 1000-fold higher than terrestrial mines, present a more sustainable and environmentally benign alternative. Empirical evidence from historical research indicates that adsorption emerges as the most efficacious process for uranium recovery from seawater, considering operational feasibility, cost-effectiveness, and selectivity. Over the years, scientific exploration has led to the development of a plethora of adsorbents with superior adsorption capacity. It would be efficient to design materials with a deep understanding of the adsorption from the perspective of kinetics and thermodynamics. Here, we summarize recent advancements in UES technology and the contemporary challenges encountered in this domain. Furthermore, we present our perspectives on the future trajectory of UES and finally offer our insights into this subject.

Solar-powered simultaneous highly efficient seawater desalination and highly specific target extraction with smart DNA hydrogels

Obtaining freshwater and important minerals from seawater with solar power facilitates the sustainable development of human society. Hydrogels have demonstrated great solar-powered water evaporation potential, but highly efficient and specific target extraction remains to be expanded. Here, we report the simultaneous highly efficient seawater desalination and specific extraction of uranium with smart DNA hydrogels. The DNA hydrogel greatly promoted the evaporation of water, with the water evaporation rate reached a high level of 3.54 kilograms per square meter per hour (1 kilowatt per square meter). Simultaneously, uranyl-specific DNA hydrogel exhibited a high capture capacity of 5.7 milligrams per gram for uranium from natural seawater due to the rapid ion transport driven by the solar powered interfacial evaporation and the high selectivity (10.4 times over vanadium). With programmable functions and easy-to-use devices, the system is expected to play a role in future seawater treatment.

Design and Modulation of Selectivity toward Vanadium(V) and Uranium(VI) Ions: Coordination Properties and Affinity of Hydroxylamino-Triazine Siderophores

Based on the strong binding and high selectivity properties of 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) for [UVIO2]2+, novel binucleating ligands (BLs) N,N',N″,N‴-((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis(N-methylhydroxylamine) (H4qtn), N1,N4-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (H4pdl), and N1,N2-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (H4enl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with H4qtn are thermodynamically more stable than their mononuclear analogues with H2bihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either H4qtn or H4pdl or H4enl with [UVIO2]2+ and [VVO2]+ resulted in the isolation of the binuclear complexes [(UVIO2)2(μ-qtn)(H2O)4] (1), [(VVO2)2(μ-qtn)][PPh4]2[PPh4] (2), [(UVIO2)2(μ-pdl)(H2O)2(MeOH)2] (3), [(VVO2)2(μ-pdl)][PPh4]2 (4), [(UVIO2)2(μ-enl)(H2O)4] (5), and [(VVO2)2(μ-enl)][PPh4]2 (6). The binuclear complexes 1-6 were characterized by single-crystal X-ray diffraction analysis in solid state and by NMR and ESI-MS in solution. The comparison of the coordination ability of the BLs with either pyridine-2,6-dicarboxylic acid (H2dipic) or H2bihyat or CO32- toward [UVIO2]2+ and [VVO2]+ was investigated by NMR and UV-vis spectroscopies and DFT theoretical calculations, revealing a superior performance of BLs. The selectivity of the BLs for [UVIO2]2+ over [VVO2]+ is decreased compared to that of H2bihyat but increases considerably at pH > 9 values. Formation of the mixed-metal binuclear species [UVIO2(μ-O)VVO2] influences the selectivity and dynamics of the reaction of H4qtn for [UVIO2]2+ and [VVO2]+ in aqueous solution. The results of this study provide crucial information for the ligand design and the development of stronger and more selective systems.

How does chemistry contribute to circular economy in nuclear energy systems to make them more sustainable and ecological?

While one should be aware that its zero CO₂ emission is actually achievable only when electric power is generated, nuclear power is one of the most viable and proven "carbon-free" energy sources to provide baseload electricity to the current energy-demanding society. Even after the power generation, the major part of spent nuclear fuels still consists of recyclable nuclear fuel materials such as U and Pu, promising circular economy of nuclear energy systems in principle. However, actual situations are not very simple due to the following issues: (1) resource security of nuclear fuel materials, (2) issues of depleted uranium, and (3) treatment and disposal of high-level radioactive wastes. In this Perspective, I discussed how chemistry can contribute to resolving these problems and what task academic research in fundamental chemistry should take on there.

Uranium extraction from seawater: material design, emerging technologies and marine engineering

Uranium extraction from seawater (UES), a potential approach to securing the long-term uranium supply and sustainability of nuclear energy, has experienced significant progress in the past decade. Promising adsorbents with record-high capacities have been developed by diverse innovative synthetic strategies, and scale-up marine field tests have been put forward by several countries. However, significant challenges remain in terms of the adsorbents' properties in complex marine environments, deployment methods, and the economic viability of current UES systems. This review presents an up-to-date overview of the latest advancements in the UES field, highlighting new insights into the mechanistic basis of UES and the methodologies towards the function-oriented development of uranium adsorbents with high adsorption capacity, selectivity, biofouling resistance, and durability. A distinctive emphasis is placed on emerging electrochemical and photochemical strategies that have been employed to develop efficient UES systems. The most recent achievements in marine tests by the major countries are summarized. Challenges and perspectives related to the fundamental, technical, and engineering aspects of UES are discussed. This review is envisaged to inspire innovative ideas and bring technical solutions towards the development of technically and economically viable UES systems.

Adsorptive sequestration of noxious uranium (VI) from water resources: A comprehensive review

Groundwater is usually utilized as a drinking water asset everywhere. Therefore, groundwater defilement by poisonous radioactive metals such as uranium (VI) is a major concern due to the increase in nuclear power plants as well as their by-products which are released into the watercourses. Waste Uranium (VI) can be regarded as a by-product of the enrichment method used to produce atomic energy, and the hazard associated with this is due to the uranium radioactivity causing toxicity. To manage these confronts, there are so many techniques that have been introduced but among those adsorptions is recognized as a straightforward, successful, and monetary innovation, which has gotten major interest nowadays, despite specific drawbacks regarding operational as well as functional applications. This review summarizes the various adsorbents such as Bio-adsorbent/green materials, metal oxide-based adsorbent, polymer based adsorbent, graphene oxide based adsorbent, and magnetic nanomaterials and discuss their synthesis methods. Furthermore, this paper emphasis on adsorption process by various adsorbents or modified forms under different physicochemical conditions. In addition to this adsorption mechanism of uranium (VI) onto different adsorbent is studied in this article. Finally, from the literature reviewed conclusion have been drawn and also proposed few future research suggestions.

Effect of Siderophore DFOB on U(VI) Adsorption to Clay Mineral and Its Subsequent Reduction by an Iron-Reducing Bacterium

Uranium mining and nuclear fuel production have led to significant U contamination. Past studies have focused on the bioreduction of soluble U(VI) to insoluble U(IV) as a remediation method. However, U(IV) is susceptible to reoxidation and remobilization when conditions change. Here, we demonstrate that a combination of adsorption and bioreduction of U(VI) in the presence of an organic ligand (siderophore desferrioxamine B, DFOB) and the Fe-rich clay mineral nontronite partially alleviated this problem. DFOB greatly facilitated U(VI) adsorption into the interlayer of nontronite as a stable U(VI)-DFOB complex. This complex was likely reduced by bioreduction intermediates such as the Fe(II)-DFOB complex and/or through electron transfer within a ternary Fe(II)-DFOB-U(VI) complex. Bioreduction with DFOB alone resulted in a mobile aqueous U(IV)-DFOB complex, but in the presence of both DFOB and nontronite U(IV) was sequestered into a solid. These results provide novel insights into the mechanisms of U(VI) bioreduction and the stability of U and have important implications for understanding U biogeochemistry in the environment and for developing a sustainable U remediation approach.

Two Ligands of Interest in Recovering Uranium from the Oceans: The Correct Formation Constants of the Uranyl(VI) Cation with 2,2'-Bipyridyl-6,6'-dicarboxylic Acid and 1,10-Phenanthroline-2,9-dicarboxylic Acid

The ligands BDA (2,2'-bipyridyl-6,6'-dicarboxylic acid) and PDA (1,10-phenanthroline-2,9-dicarboxylic acid) are of interest as functional group types for ion-exchange materials for extracting uranium from the oceans, reported in a previous paper for PDA Lashley, M. A. ( Inorg. Chem. 2016 55 10818 10829). Yang, Y. ( Inorg. Chem. 2019, 58, 6064 6074) have published what they claim to be a more accurate result for the formation of the UO₂²⁺/PDA complex of log K₁ = 22.84 compared with our reported value of log K₁ = 16.5, as well as log K₁ = 21.52 for the BDA complex. The determination of log K₁ for the PDA and BDA complexes with the UO₂²⁺ cation was carried out by Yang et al. using a competition reaction between DTPA (diethylenetriamine pentaacetic acid) and BDA or PDA, monitoring the absorbance due to the BDA and PDA ligands. This competition method using absorbance versus pH titrations was developed for determining the formation constants of the complexes of several polypyridyl ligands plus PDA complexes of metal ions, which were too stable for log K determination by competition with protons. A key feature of such titrations is that in the competition reaction, the displacement of the pyridyl donor ligand (e.g., PDA) by the competing ligand (e.g., DTPA), the absorbance spectrum of the displaced pyridyl donor ligand should be observed. Competing ligands used to date have been EDTA (ethylenediamine tetraacetic acid), DTPA, or the hydroxide ion. In the study of Yang et al., no such displaced PDA or BDA was apparent in the absorbance spectra in their titrations so that their reported log K₁ values have no validity. Their log K₁ values are so much higher than log K₁ for the uranyl DTPA complex (∼13.6) that DTPA could not possibly displace BDA or PDA from the uranyl cation, and a competition reaction could not possibly occur. We report the correct value of log K₁ = 15.4 (ionic strength = zero) for the uranyl BDA complex, to illustrate the correct determination of such a constant by a competition reaction between BDA and hydroxide, showing how the characteristic absorbance spectrum for a BDA complex, here the UO₂²⁺ complex, disappears, and the distinctive absorbance spectrum of the free nonprotonated BDA ligand appears as the pH is increased, and BDA is displaced by the hydroxide ion.

Surface Functionalized MXenes for Wastewater Treatment-A Comprehensive Review

Over 80% of wastewater worldwide is released into the environment without proper treatment. Whilst environmental pollution continues to intensify due to the increase in the number of polluting industries, conventional techniques employed to clean the environment are poorly effective and are expensive. MXenes are a new class of 2D materials that have received a lot of attention for an extensive range of applications due to their tuneable interlayer spacing and tailorable surface chemistry. Several MXene-based nanomaterials with remarkable properties have been proposed, synthesized, and used in environmental remediation applications. In this work, a comprehensive review of the state-of-the-art research progress on the promising potential of surface functionalized MXenes as photocatalysts, adsorbents, and membranes for wastewater treatment is presented. The sources, composition, and effects of wastewater on human health and the environment are displayed. Furthermore, the synthesis, surface functionalization, and characterization techniques of merit used in the study of MXenes are discussed, detailing the effects of a range of factors (e.g., PH, temperature, precursor, etc.) on the synthesis, surface functionalization, and performance of the resulting MXenes. Finally, the limits of MXenes and MXene-based materials as well as their potential future research directions, especially for wastewater treatment applications are highlighted.

Fully Chelating N3O2-Pentadentate Planar Ligands Designed for the Strongest and Selective Capture of Uranium from Seawater

Based on the unique fivefold equatorial coordination of UO₂²⁺, water-compatible pentadentate planar ligands, H₂saldian and its derivatives, were designed for the strong and selective capture of UO₂²⁺ in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO₃^-/CO₃^2-, pH 8), saldian^2- shows the strongest complexation with UO₂²⁺ to form UO₂(saldian) (log β₁₁ = 28.05 ± 0.07), which is more than 10 order of magnitude greater than amidoxime-based or -inspired ligand systems most commonly employed for U capture from seawater. Good selectivity for UO₂²⁺ from other metal ions coexisting in seawater was also demonstrated.

Synergistic leaching of heavy metal-polycyclic aromatic hydrocarbon in co-contaminated soil by hydroxamate siderophore: Role of cation-π and chelation

Exploring a novel green efficient bioeluant is a golden key to unlock the ex-situ scale remediation of soil contaminated with heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs). Hydroxamate siderophore (HDS) produced by Pseudomonas fluorescens HMP01, with certain hydrophobicity and strong coordination because of its special chemical structure (e.g., hydroxamic acid and dihydroxy quinoline chromophore), was used to investigate the bioleaching efficiency of HMs and PAHs from actual contaminated soils and underlying mechanisms. Results showed that leaching efficiency for HMs and PAHs from the co-contaminated soil was higher than that of single contaminated soil due to the cation-π interaction and coordination, which was closely related to the spacial configuration changes of the complex. HDS not only increased the bioleaching efficiency of cationic HMs by chelation (the leaching amount of Cd²⁺, Pb²⁺, Hg²⁺, Cu²⁺, Zn²⁺, and Ni²⁺ achieved 27.5, 110.4, 6.9, 477.7, 10,606.9, and 137.4 mg/kg HDS, respectively) but also enhanced the bioleaching amount of PAHs by solubilization (the leaching amount of phenanthrene reached 90.2 mg/kg HDS. Also, the residual HDS in soils caused no significant ecological risk. As expected, HDS is a desirable bioeluant to promote the scale application of the ex-situ remediation of soil contaminated with HMs and PAHs.

Stable Chelation of the Uranyl Ion by Acyclic Hexadentate Ligands: Potential Applications for 230U Targeted α-Therapy

Uranium-230 is an α-emitting radionuclide with favorable properties for use in targeted α-therapy (TAT), a type of nuclear medicine that harnesses α particles to eradicate cancer cells. To successfully implement this radionuclide for TAT, a bifunctional chelator that can stably bind uranium in vivo is required. To address this need, we investigated the acyclic ligands H₂dedpa, H₂CHXdedpa, H₂hox, and H₂CHXhox as uranium chelators. The stability constants of these ligands with UO₂²⁺ were measured via spectrophotometric titrations, revealing log β_ML values that are greater than 18 and 26 for the "pa" and "hox" chelators, respectively, signifying that the resulting complexes are exceedingly stable. In addition, the UO₂²⁺ complexes were structurally characterized by NMR spectroscopy and X-ray crystallography. Crystallographic studies reveal that all six donor atoms of the four ligands span the equatorial plane of the UO₂²⁺ ion, giving rise to coordinatively saturated complexes that exclude solvent molecules. To further understand the enhanced thermodynamic stabilities of the "hox" chelators over the "pa" chelators, density functional theory (DFT) calculations were employed. The use of the quantum theory of atoms in molecules revealed that the extent of covalency between all four ligands and UO₂²⁺ was similar. Analysis of the DFT-computed ligand strain energy suggested that this factor was the major driving force for the higher thermodynamic stability of the "hox" ligands. To assess the suitability of these ligands for use with ²³⁰U TAT in vivo, their kinetic stabilities were probed by challenging the UO₂²⁺ complexes with the bone model hydroxyapatite (HAP) and human plasma. All four complexes were >95% stable in human plasma for 14 days, whereas in the presence of HAP, only the complexes of H₂CHXdedpa and H₂hox remained >80% intact over the same period. As a final validation of the suitability of these ligands for radiotherapy applications, the in vivo biodistribution of their UO₂²⁺ complexes was determined in mice in comparison to unchelated [UO₂(NO₃)₂]. In contrast to [UO₂(NO₃)₂], which displays significant bone uptake, all four ligand complexes do not accumulate in the skeletal system, indicating that they remain stable in vivo. Collectively, these studies suggest that the equatorial-spanning ligands H₂dedpa, H₂CHXdedpa, H₂hox, and H₂CHXhox are highly promising candidates for use in ²³⁰U TAT.

Americium preferred: lanmodulin, a natural lanthanide-binding protein favors an actinide over lanthanides

The separation and recycling of lanthanides is an active area of research with a growing demand that calls for more environmentally friendly lanthanide sources. Likewise, the efficient and industrial separation of lanthanides from the minor actinides (Np, Am–Fm) is one of the key questions for closing the nuclear fuel cycle; reducing costs and increasing safety. With the advent of the field of lanthanide-dependent bacterial metabolism, bio-inspired applications are in reach. Here, we utilize the natural lanthanide chelator lanmodulin and the luminescent probes Eu³⁺ and Cm³⁺ to investigate the inter-metal competition behavior of all lanthanides (except Pm) and the major actinide plutonium as well as three minor actinides neptunium, americium and curium to lanmodulin. Using time-resolved laser-induced fluorescence spectroscopy we show that lanmodulin has the highest relative binding affinity to Nd³⁺ and Eu³⁺ among the lanthanide series. When equimolar mixtures of Cm³⁺ and Am³⁺ are added to lanmodulin, lanmodulin preferentially binds to Am³⁺ over Cm³⁺ whilst Nd³⁺ and Cm³⁺ bind with similar relative affinity. The results presented show that a natural lanthanide-binding protein can bind a major and various minor actinides with high relative affinity, paving the way to bio-inspired separation applications. In addition, an easy and versatile method was developed, using the fluorescence properties of only two elements, Eu and Cm, for inter-metal competition studies regarding lanthanides and selected actinides and their binding to biological molecules.

In need of environmentally friendly methods for the separation and recycling of lanthanides and actinides, the binding of the protein lanmodulin to lanthanides and actinides was studied using time resolved laser induced fluorescence spectroscopy.

Accelerated Chemical Thermodynamics of Uranium Extraction from Seawater by Plant-Mimetic Transpiration

The extraction of uranium from seawater, which is an abundant resource, has attracted considerable attention as a viable form of energy-resource acquisition. The two critical factors for boosting the chemical thermodynamics of uranium extraction from seawater are the availability of sufficient amounts of uranyl ions for supply to adsorbents and increased interaction temperatures. However, current approaches only rely on the free diffusion of uranyl ions from seawater to the functional groups within adsorbents, which largely limits the uranium extraction capacity. Herein, inspired by the mechanism of plant transpiration, a plant-mimetic directional-channel poly(amidoxime) (DC-PAO) hydrogel is designed to enhance the uranium extraction efficiency via the active pumping of uranyl ions into the adsorbent. Compared with the original PAO hydrogel without plant-mimetic transpiration, the uranium extraction capacity of the DC-PAO hydrogel increases by 79.33% in natural seawater and affords the fastest reported uranium extraction average rate of 0.917 mg g^-1 d^-1 among the most state-of-the-art amidoxime group-based adsorbents, along with a high adsorption capacity of 6.42 mg g^-1 within 7 d. The results indicate that the proposed method can enhance the efficiency of solar-transpiration-based uranium extraction from seawater, particularly in terms of reducing costs and saving processing time.

Vanadium pollution and health risks in marine ecosystems: Anthropogenic sources over natural contributions

Vanadium has been classified as a potentially toxic metal and has been given limited attention in comparison to similar trace metals. Similarly, worldwide and continental vanadium pollution and risks remain contested. Here, we synthesized the worldwide concentration of vanadium in marine ecosystems with the relevant ecological and human health risks. We found that vanadium in biota and seawater collected from Asia shows significant increases over the temporal analysis, with rates similar to those reported for vanadium consumption and production. Furthermore, invertebrates have a higher concentration of vanadium than fishes. Similarly, we demonstrate that sediments classified as polluted have concentrations that are not directly correlated with the highest concentrations across continents. Finally, ecological risks were higher from seawater, with potential impacts to 55% of aquatic species in Asia estimated from chronic species sensitivity distribution (SSD). The concentration endangering only 5% of seawater species (HC5) was estimated as 1.13 (0.05-21.19) μg L^-1. Estimated daily intakes revealed that overall, there are none to low health risks from aquatic product consumption, yet high risks are plausible to children with consumption patterns in the 95th percentile.

Nanospace Decoration with Uranyl-Specific "Hooks" for Selective Uranium Extraction from Seawater with Ultrahigh Enrichment Index

Mining uranium from seawater is highly desirable for sustaining the increasing demand for nuclear fuel; however, access to this unparalleled reserve has been limited by competitive adsorption of a wide variety of concentrated competitors, especially vanadium. Herein, we report the creation of a series of uranyl-specific "hooks" and the decoration of them into the nanospace of porous organic polymers to afford uranium nanotraps for seawater uranium extraction. Manipulating the relative distances and angles of amidoxime moieties in the ligands enabled the creation of uranyl-specific "hooks" that feature ultrahigh affinity and selective sequestration of uranium with a distribution coefficient threefold higher compared to that of vanadium, overcoming the long-term challenge of the competing adsorption of vanadium for uranium extraction from seawater. The optimized uranium nanotrap (2.5 mg) can extract more than one-third of the uranium in seawater (5 gallons), affording an enrichment index of 3836 and thus presenting a new benchmark for uranium adsorbent. Moreover, with improved selectivity, the uranium nanotraps could be regenerated using a mild base treatment. The synergistic combination of experimental and theoretical analyses in this study provides a mechanistic approach for optimizing the selectivity of chelators toward analytes of interest.

Bioinspired Construction of Uranium Ion Trap with Abundant Phosphate Functional Groups

Highly efficient extraction of radioactive uranium from aqueous solution remains a serious task in the nuclear energy field. To address this, we here create an effective uranium ion trap by using a novel and facile strategy that introduces bioinspired moiety phytic acid (PA) into highly robust PCN-222. The resultant metal-organic framework (MOF)-based uranium ion trap (PCN-222-PA) with a high density of accessible phosphate groups exhibits a remarkable U(VI) uptake capacity (401.6 mg·g^-1), surpassing most of the reported phosphorus-modified MOFs and various other MOF adsorbents. Kinetics study reveals that PCN-222-PA can reduce the uranium concentration from 10 mg L^-1 to 21 μg L^-1, below the acceptable limit defined by the US Environmental Protection Agency. In addition, PCN-222-PA also shows good selectivity and high stability as well as excellent recyclability toward uranium capture. Our work demonstrates a new strategy to design functional MOFs with abundant phosphate groups and provides a new perspective for extracting uranium from aqueous solution.

Sulfide Oxidation by 2,6-Bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazinatodioxomolybdenum(VI): Mechanistic Implications with DFT Calculations for a New Class of Molybdenum(VI) Complex

Sulfide oxidation is accomplished by a new class of dioxomolybdenum(VI) catalyst (1) that uses the tridentate 2,6-bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazine ligand to form a five-coordinate molybdenum(VI) center. Resonance Raman spectra show that the dioxo groups on the Mo(VI) oxygens readily exchange with water in an acetonitrile media that allows ¹⁸O labeling of catalyst 1. The model oxidation reaction was the conversion of thioanisole (2) to the corresponding sulfoxide with 4% of 1 using an equimolar amount of H₂O₂ in MeCN-d₃. Oxygen-18 labeling experiments with either ¹⁸O-labeled 1 or ¹⁸O-labeled H₂O₂ are consistent with a sulfide oxygenation pathway that uses a η¹-Mo(OOH) hydroxoperoxyl species (3). The hypothesized intermediate 3 is initially formed in a proton transfer reaction between 1 and H₂O₂. Oxidation is hypothesized via nucleophilic attack of the sulfide on 3 that is supported from a Hammett linear free-energy relationship for para-derivatives of 2. A Hammett reactivity constant (ρ) of -1.2 ± 0.2 was obtained, which is consistent with other ρ values found in prior sulfide oxidation reactions by group 6 complexes. An Eyring plot of the 2 oxidation by 1 gives an E_a of 63.0 ± 5.2 kJ/mol, which is slightly higher than that of a similar oxidation of 2 by the molybdenum(VI) complex, oxodiperoxo (pyridine-2-carboxylato)molybdate(VI) bis(pyridine-2-carboxylic acid) monohydrate (5). Computational modeling with density functional theory (DFT) of the complete reaction profile gave enthalpy and entropy of activations (64 kJ/mol and -120 J/mol·K, respectively) within 1 standard deviation of the experimental values, further supporting the hypothesized mechanism.

Synthesis of selective biodegradable amidoxime chitosan for absorption of Th(IV) and U(VI) ions in solution

Radionuclide extraction from wastewater is a long-term process, in which the study on the reuse and decomposition of adsorbents provides the ability to complete the post-treatment after adsorption. Herein, A novel biodegradable amidoxime chitosan has been synthesized through one-step without crosslinking agent and characterized by FT-IR, SEM, XPS, TGA and element analysis. The batch adsorption experiments of U(VI) and Th(IV) on AO-CTS adsorbent were studied and maximum adsorption of U(VI) and Th(IV) were 97 and 56 mg/g, respectively. The U(VI) and Th(Ⅳ) can be effectively desorbed from the AO-CTS materials at low acidity, The AO-CTS can be reused 6 times without reducing absorbency for U(VI) and Th(Ⅳ). When finish the adsorption process, the AO-CTS can be degraded by lysozyme at room temperature, there were no toxic or harmful substances are produced.

Molecular Design of Novel Chemicals for Iron Sulfide Scale Removal

Scale deposition is a pertinent challenge in the oil and gas industry. Scales formed from iron sulfide are one of the troublous scales, particularly pyrite. Moreover, the use of biodegradable environmentally friendly chemicals reduces the cost compared to the conventional removal process. In this work, the chelating abilities of four novel chemicals, designed using the in silico technique of density functional theory (DFT), are studied as potential iron sulfide scale removers. Only one of the chemicals containing a hydroxamate functional group had a good chelating ability with Fe2+. The chelating strength and ecotoxicological properties of this chemical were compared to diethylenetriaminepentaacetic acid (DTPA), an already established iron sulfide scale remover. The new promising chemical surpassed DTPA in being a safer chemical and having a greater binding affinity to Fe2+ upon optimization, hence, a better choice. The presence of oxime (-NHOH) and carbonyl (C=O) moieties in the new chemical showed that the bidentate form of chelation is favored. Moreover, the presence of an intramolecular hydrogen bond enhanced its chelating ability.

Siderophores for medical applications: Imaging, sensors, and therapeutics

Siderophores are low-molecular-weight chelators produced by microorganisms to scavenge iron from the environment and deliver it to cells via specific receptors. Tremendous researches on the molecular basis of siderophore regulation, synthesis, secretion, and uptake have inspired their diverse applications in the medical field. Replacing iron with radionuclides in siderophores, such as the most prominent Ga-68 for positron emission tomography (PET), carves out ways for targeted imaging of infectious diseases and cancers. Additionally, the high affinity of siderophores for metal ions or microorganisms makes them a potent detecting moiety in sensors that can be used for diagnosis. As for therapeutics, the notable Trojan horse-inspired siderophore-antibiotic conjugates demonstrate enhanced toxicity against multi-drug resistant (MDR) pathogens. Besides, siderophores can tackle iron overload diseases and, when combined with moieties such as hydrogels and nanoparticles, a wide spectrum of iron-induced diseases and even cancers. In this review, we briefly outline the related mechanisms, before summarizing the siderophore-based applications in imaging, sensors, and therapeutics.

Sulfonated perylene-based conjugated microporous polymer as a high-performance adsorbent for photo-enhanced uranium extraction from seawater

A sulfonated perylene-based adsorbent is prepared for photo-enhanced uranium extraction from seawater. Owing to the photo-enhanced effect, the uranium extraction capacity of PyB-SO₃H in seawater reaches 1989 mg g⁻¹, with 90% extraction efficiency.

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.

Natural and anthropogenic radionuclides in water and wastewater: Sources, treatments and recoveries

Water-energy nexus in the context of changing climate amplifies the importance of comprehending the transport, fate and recovery of radioisotope. While countries have been more interested for zero/low greenhouse gas emission technologies, energy production from nuclear power plant (NPP) can be a prominent solution. Moreover, radioisotopes are also used for other benefits such as in medical science, industrial activities and many more. These radionuclides are blended accidently or intentionally with water or wastewater because of inefficacious management of the nuclear waste; and therefore, it is an imperative task to manage nuclear waste so that the harmful consequences of the waste on environment, ecology and human health can be dispelled. Due to generation of significant amount of waste throughout its utilization, a noticeable number of physical, chemical and biological processes has been introduced as remediation processes although mechanisms of optimum removal process are still under investigation. Removal mechanisms and influencing factors for radionuclide removal are elucidated in this review so that, further, operation and process development can be promoted. Again, resource recovery, opportunities and challenges are also discussed for elevating the removal rates and minimizing the knowledge gaps existing in development and applications of novel decontamination processes.

DNA nano-pocket for ultra-selective uranyl extraction from seawater

Extraction of uranium from seawater is critical for the sustainable development of nuclear energy. However, the currently available uranium adsorbents are hampered by co-existing metal ion interference. DNAzymes exhibit high selectivity to specific metal ions, yet there is no DNA-based adsorbent for extraction of soluble minerals from seawater. Herein, the uranyl-binding DNA strand from the DNAzyme is polymerized into DNA-based uranium extraction hydrogel (DNA-UEH) that exhibits a high uranium adsorption capacity of 6.06 mg g⁻¹ with 18.95 times high selectivity for uranium against vanadium in natural seawater. The uranium is found to be bound by oxygen atoms from the phosphate groups and the carbonyl groups, which formed the specific nano-pocket that empowers DNA-UEH with high selectivity and high binding affinity. This study both provides an adsorbent for uranium extraction from seawater and broadens the application of DNA for being used in recovery of high-value soluble minerals from seawater.

The extraction of metals from seawater is an area of great potential; especially for the extraction of uranium. Here, the authors report on the synthesis of a DNA based uranium adsorbent with high selectivity and demonstrate the potential for the DNA based extraction of high-value soluble minerals from seawater.

Facile modification of graphene oxide and its application for the aqueous uranyl ion sequestration: Insights on the mechanism

Graphene oxide (GO) has been proved with favorable affinity to U(VI), while some drawbacks such as poor dispersity and low adsorption performance limit its application. Herein, cetyltrimethylammonium bromide (CTAB) modified graphene oxide (MGO) composites were successfully fabricated, characterized and compared with graphene oxide (GO) in the sequestration of U(VI) in aqueous solutions. The results showed that maximum adsorption rate of MGO (99.21%) was obviously higher than that of GO (66.51%) under the same initial condition. Simultaneous introduction of C-H and NO coupled with the enhanced dispersity of GO after modification were mainly responsible for the updated performance verified with multiple characterization techniques. Based on the results of kinetics and isotherms investigations, the experimental data were best described by Pseudo-first-order kinetic model and Redlich-Peterson isotherm model. The results of ΔH, ΔS and ΔG show that adsorptive behaviors of uranyl ion on MGO are endothermic and spontaneous. The study provides a feasible alternative to the chemical modification of GO and enhancing the performance towards uranyl ion removal from solution.

Polymer Nanorings with Uranium Specific Clefts for Selective Recovery of Uranium from Acidic Effluents via Reductive Adsorption

Nanostructured polymeric materials, functionalized with an appropriate receptor, have opened up newer possibilities for designing a reagent that shows analyte-specific recognition and efficient scavenging of an analyte that has either a detrimental influence on human physiology and environment or on its recovery for further value addition. Higher active surface area, morphological diversity, synthetic tunability for desired surface functionalization, and the ease of regeneration of a nanostructured material for further use have provided such materials with a distinct edge over conventional reagents. The use of a biodegradable polymeric backbone has an added significance owing to the recent concern over the impact of polymers on the environment. Functionalization of biodegradable sodium alginate with AENA (6.85% grafting) as the receptor functionality led to a unique open framework nanoring (NNRG) morphology with a favorable spatial orientation for specific recognition and efficient binding to uranyl ions (U) in an aqueous medium over a varied pH range. Nanoring morphology was confirmed by transmission electron microscopy and atomic force microscopy images. The nanoscale design maximizes the surface area for the molecular scavenger. A combination of all these features along with the reversible binding phenomenon has made NNRG a superior reagent for specific, efficient uptake of UO₂²⁺ species from an acidic (pH 3-4) solution and compares better than all existing UO₂²⁺-scavengers reported till date. This could be utilized for the recovery of uranyl species from a synthetic acidic effluent of the nuclear power. The results of the U uptake experiments reveal a maximum adsorption capacity of 268 mg of U per g of NNRG in a synthetic nuclear effluent. X-ray photoelectron spectroscopy studies revealed a reductive complexation process and stabilization of U(IV)-species in adsorbed uranium species (U@NNRG).

Biological, biomolecular, and bio-inspired strategies for detection, extraction, and separations of lanthanides and actinides

Lanthanides and actinides are elements of ever-increasing technological importance in the modern world. However, the similar chemical and physical properties within these groups make purification of individual elements a challenge. Current industrial standards for the extraction, separation, and purification of these metals from natural sources, recycled materials, and industrial waste are inefficient, relying upon harsh conditions, repetitive steps, and ligands with only modest selectivity. Biological, biomolecular, and bio-inspired strategies towards improving these separations and making them more environmentally sustainable have been researched for many years; however, these methods often have insufficient selectivity for practical application. Recent developments in the understanding of how lanthanides are selectively acquired and used by certain bacteria offer the opportunity for a newer, more efficient take on these designs, as well as the possibility for fundamentally new designs and strategies. Herein, we review current cell-based and biomolecular (primarily small-molecule and protein-based) methods for detection, extraction, and separations of f-block elements. We discuss how the increasing knowledge regarding the selective recognition, uptake, trafficking, and storage of these elements in biological systems has informed and will continue to promote development of novel approaches to achieve these ends.

Aryl Diazonium-Assisted Amidoximation of MXene for Boosting Water Stability and Uranyl Sequestration via Electrochemical Sorption

Despite that two-dimensional transition metal carbides and carbonitrides (MXenes) are burgeoning candidates for remediation of environmental pollutants, the construction of robust functionalized MXene nanosheets with a high affinity for target heavy metal ions and radionuclides remains a challenge. Here we report the successful placement of amidoxime chelating groups on Ti₃C₂T_x MXene surface by diazonium salt grafting. The introduction of amidoxime functional groups significantly enhances the selectivity of Ti₃C₂T_x nanosheets for uranyl ions and also greatly improves their stability in aqueous solution, enabling efficient, rapid, and recyclable uranium extraction from aqueous solutions containing competitive metal ions. Benefiting from the excellent conductivity of MXenes, the amidoxime functionalized Ti₃C₂T_x nanosheets show outstanding electrochemical performance such that when loaded on carbon cloth the application of an electric field increases the uranium adsorption capacity from 294 to 626 mg/g, outperforming all organic electrochemical sorption materials reported previously. The present work provides an effective strategy to functionalize MXene nanosheets with fundamental implications for the design of MXene-based selective electrosorption electrode materials.