Efficient Removal of [UO2]2+, Cs+, and Sr2+ Ions by Radiation-Resistant Gallium Thioantimonates

Cesium adsorption from an aqueous medium for environmental remediation: A comprehensive analysis of adsorbents, sources, factors, models, challenges, and opportunities

Considering the widespread and indispensable nature of nuclear energy for future power generation, there is a concurrent increase in the discharge of radioactive Cs into water streams. Recent studies have demonstrated that adsorption is crucial in removing Cs from wastewater for environmental remediation. However, the existing literature lacks comprehensive studies on various adsorption methods, the capacities or efficiencies of adsorbents, influencing factors, isotherm and kinetic models of the Cs adsorption process. A bibliometric and comprehensive analysis was conducted using 1179 publications from the Web of Science Core Collection spanning from 2014 to 2023. It reviews and summarizes current publication trends, active countries, adsorption methods, adsorption capacities or efficiencies of adsorbents, tested water sources, influencing factors, isotherm, and kinetic models of Cs adsorption. The selection of suitable adsorbents and operating parameters is identified as a crucial factor. Over the past decade, due to their notable capacity for Cs adsorption, considerable research has focused on novel adsorbents, such as Prussian blue, graphene oxide, hydrogel, and nanoadsorbents (NA). However, there remains a need for further development of application-oriented laboratory-scale experiments. Future research directions should encompass exploring adsorption mechanisms, developing new adsorbents or their combinations, practical applications of lab-scale studies, and recycling radioactive Cs from wastewater. Drawing upon this literature review, we present the most recent research patterns concerning adsorbents to remove Cs, outline potential avenues for future research, and delineate the obstacles hindering effective adsorption. This comprehensive bibliometric review provides valuable insights into prevalent research focal points and emerging trends, serving as a helpful resource for researchers and policymakers seeking to understand the dynamics of adsorbents for Cs removal from water.

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.

Open-Framework Vanadate as Efficient Ion Exchanger for Uranyl Removal

The elimination of uranium from radioactive wastewater is crucial for the safe management and operation of environmental remediation. Here, we present a layered vanadate with high acid/base stability, [Me2NH2]V3O7, as an excellent ion exchanger capturing uranyl from highly complex aqueous solutions. The material possesses an indirect band gap, ferromagnetic characteristic and a flower-like morphology comprising parallel nanosheets. The layered structure of [Me2NH2]V3O7 is predominantly upheld by the H-bond interaction between anionic framework [V3O7]nn- and intercalated [Me2NH2]+. The [Me2NH2]+ within [Me2NH2]V3O7 can be readily exchanged with UO22+. [Me2NH2]V3O7 exhibits high exchange capacity (qm = 176.19 mg/g), fast kinetics (within 15 min), high removal efficiencies (>99%), and good selectivity against an excess of interfering ions. It also displays activity for UO22+ ion exchange over a wide pH range (2.00-7.12). More importantly, [Me2NH2]V3O7 has the capability to effectively remove low-concentration uranium, yielding a residual U concentration of 13 ppb, which falls below the EPA-defined acceptable limit of 30 ppb in typical drinking water. [Me2NH2]V3O7 can also efficiently separate UO22+ from Cs+ or Sr2+ achieving the highest separation factors (SFU/Cs of 589 and SFU/Sr of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO22+ and [V3O7]nn-, whereas the ion exchange rate is influenced by the mobility of UO22+ and [Me2NH2]+. Our experimental findings indicate that [Me2NH2]V3O7 can be considered as a promising uranium scavenger for environmental remediation. Additionally, the simulation results provide valuable mechanistic interpretations for ion exchange and serve as a reference for designing novel ion exchangers.

All-in-one treatment: Capture and immobilization of 137Cs by ultra-stable inorganic solid acid materials HMMoO6·nH2O (M = Ta, Nb)

Capture and immobilization of 137Cs is urgent for radioactive contamination remediation and spent fuel treatment. Herein, an effective all-in-one treatment method to simultaneously adsorb and immobilize Cs+ without high-temperature treatment is proposed. According to the strategy of incorporating high-valency metal ions into molybdates to increase the material stability and affinity towards radionuclides, layered HMMoO6·nH2O (M = Ta (1), Nb (2)) are prepared. Both materials exhibit excellent acid resistance (even 15 mol/L HNO3). They maintain remarkable adsorption capacity for Cs+ in 1 mol/L HNO3 solutions and can selectively capture Cs+ under excessive competitive ions. Furthermore, they show successful cleanup for actual 137Cs-liquid-wastes generated during industrial production. In particular, adsorbed Cs+ can be firmly immobilized in interlayer spaces of materials due to the highly stable anionic framework. The removal mechanism is attributed to ion exchange between Cs+ and interlayer H+ by multiple characterizations. Study of the structure-function relationship shows that the occurrence of Cs+ ion exchange is closely related to plate-like layered structure. This work develops an efficient all-in-one treatment method for capturing and immobilizing radiocesium by ultra-stable inorganic solid acid materials with low energy consumption and high safety for radionuclide remediation.

First Potassium Fluoroaluminate Ionic Exchanger for Rapid and Selective Removal of Sr2+ with High Capacity

90Sr, as a typical artificial radionuclide, poses a serious threat to human health and the ecological environment. The selective removal of this radionuclide from industrial nuclear waste is crucial for our environment. Here we report a novel potassium fluoroaluminate, K2[(AlF5)H2O], which was synthesized by a simple low-temperature one-step method. It adopts a 1D AlF6-chain structure, which consists of exchangeable potassium ions in between the infinite chains of octahedral Al centers. As a remarkable inorganic ionic exchanger, K2[(AlF5)H2O] has a high chemical stability (resistance of pH=~3-12) and thermal stability (≥~300 °C). It possesses an excellent adsorption selectivity (Kd=~6.1×104 mL ⋅ g-1) and a maximum adsorption capacity of qm=~120.32 mg ⋅ g-1 for Sr2+. Importantly, it still keep a very good selectivity for Sr2+ ions even in the presence of competing Na+, Mg2+ and Ca2+ aqueous solutions. K2[(AlF5)H2O] is the first example of fluoroaluminate ionic exchange materials that can capture Sr2+. This result opens up a new way to design and synthesize inorganic ionic exchangers for the selective removal of Sr2+ ions from radioactive waste water.

Interlayer manipulation of bio-inspired Ti3C2Tx nanocontainer through intercalation of amino acid molecules to dramatically boosting uranyl hijacking capability from seawater

More than 4.5 billion tons of unconventional uranium resources [UO2(CO3)3]4- are uniformly dissolved in seawater, providing a sustainable and abundant fuel source for the development of nuclear energy. Herein, we presented a rational design and development of Ti3C2Tx nanocontainer inspired by the exceptional selectivity and affinity exhibited by superb-uranyl proteins through amino acid intercalation. The amino acid intercalation of Ti3C2Tx demonstrated exceptional UO22+ capture capacity (Arg-Ti3C2Tx, His-Ti3C2Tx, and Lys-Ti3C2Tx with qmax values of 594.46, 846.04, and 1030.17 mg/g). Furthermore, these intercalated materials exhibited remarkable sequestration efficiency and selectivity (Uinitial = ∼45.2 ∼7636 μg/L; ∼84.45% ∼98.08%; and ∼2.72 ×104 ∼1.28 ×105 KdU value), despite the presence of an overwhelming surplus of Na+, Ca2+, Mg2+, and Co2+ ions. Significantly, even in the 0.3 M NaHCO3 solution and surpassing 103-fold of the Na3VO4 system, the adsorption efficiency of Lys-Ti3C2Tx still achieved a remarkable 63.73% and 65.05%. Moreover, the Lys-Ti3C2Tx can extract ∼30.23 ∼8664.03 μg/g uranium after 24 h contact in ∼13.3 ∼5000 μg/L concentration from uranium-spiked natural seawater. The mechanism analysis revealed that the high binding capability can be attributed to the chelation of carboxyl and amino groups with uranyl ions. This innovative state-of-the-art approach in regulating uranium harvesting capability through intercalation of amino acid molecules provides novel insights for extracting uranium from seawater.

Incorporating Two Crown Ether Struts into the Backbone of Robust Zirconium-Based Metal-Organic Frameworks as Custom-Designed Efficient Collectors for Radioactive Metal Ions

The incorporation of crown ether into metal-organic frameworks (MOFs) is garnered significant attention because these macrocyclic units can fine-tune the inherent properties of the frameworks. However, the synthesis of flexible crown ethers with precise structures as the fundamental building blocks of crystalline MOFs remains a challenging endeavor, with only a limited number of transition metal examples existing to date. Herein, 18-crown-6 and 24-crown-8 struts are successfully incorporated into the skeleton of zirconium-based MOFs to obtain two new and stable crown ether-based MOFs, denoted as ZJU-X100 and ZJU-X102. These newly developed MOFs displayed high porosity and remarkable stability when exposed to various solvents, boiling water, pH values, and even concentrated HCl conditions. Thanks to their highly ordered porous structure and high-density embedding of specific binding sites within tubular channels, these two MOFs exhibited extremely fast sorption kinetics and demonstrated outstanding performance in the uptake of strontium and cesium ions, respectively. Furthermore, the structures of Sr-adsorbed ZJU-X100 and Cs-adsorbed ZJU-X102 are solved and confirmed the precise location of Sr2+/Cs+ in the cavity of 18-crown-6/24-crown-8. This makes modular mosaic of different crown ethers into the skeleton of stable zirconium-based MOFs possible and promote such materials have broad applications in sorption, sensing, and catalysis.

(C6H15N3)1.3(NH4)1.5H1.5In3SnS8: a layered metal sulfide based on supertetrahedral T2 clusters with photoelectric response and ion exchange properties

A new layered metal sulfide, namely (C6H15N3)1.3(NH4)1.5H1.5In3SnS8 (1, C6H15N3 = N-(2-aminoethyl) piperazine), has been solvothermally synthesized and characterized. Compound 1 crystallizes in the monoclinic space group C2/c. Its structure features a two-dimensional layer of {In3SnS8}n3n- with the (4,4) topology net, which is formed by interlinking supertetrahedral T2 clusters as secondary building units. Band structure calculations revealed that 1 had a band gap of 2.7 eV. The photoelectric response of 1 showed steady and reversible on/off cycles with an "on" state of 121.13 nA cm-2. Moreover, the activation of 1 by replacing the sluggish organic cations with harder K+ ions endowed the material with improved adsorption performances for Sr2+ ions from aqueous solutions.

Rapid and Selective Uptake of Radioactive Cesium from Water by a Microporous Zeolitic-like Sulfide

The fast and efficient removal of 137Cs+ ions from water is of great significance for the further treatment and disposal of highly active nuclear waste. Hitherto, although many layered metal sulfides have been proven to be very effective in capturing aqueous cesium, three-dimensional (3D) microporous examples have rarely been explored, especially compounds that are systematically used to study cesium ion exchange behaviors. In this paper, we present detailed Cs+ ion exchange properties of a 3D, microporous, zeolitic-like sulfide, namely K@GaSnS-1, in different conditions. Isotherm studies indicate that K@GaSnS-1 has a high cesium saturation capacity of 249.3 mg/g. In addition, it exhibits rapid sorption kinetics, with an equilibrium time of only 2 min. Further studies show that K@GaSnS-1 also displays a strong preference and good selectivity for cesium, with the highest distribution coefficient Kd value up to 3.53 × 104 mL/g. Also noteworthy is that the excellent cesium ion exchange properties are well-maintained despite acidic, basic, and competitive multiple-component environments. More importantly, the Cs+-exchanged products can be easily eluted and regenerated by a low-cost and eco-friendly method. These merits demonstrated by K@GaSnS-1 render it very promising in the effective and efficient separation of radioactive cesium from nuclear waste.

Open-framework hybrid zinc/tin selenide as an ultrafast adsorbent for Cs+, Ba2+, Co2+, and Ni2

Efficient adsorption of radioactive ¹³⁷Cs⁺ and ⁶⁰Co²⁺ and their decay products ¹³⁷Ba²⁺ and ⁶⁰Ni²⁺ bears significance for hazard elimination in case of nuclear emergency, which relies on the adsorption rate enhancement that takes advantages of compositional and structural optimization. Herein, we report a zinc-doped selenidostannate constructed from T2-supertetrahedral clusters, namely K_3.4(CH₃NH₃)_0.45(NH₄)_0.15Zn₂Sn₃Se₁₀·3.4 H₂O (ZnSnSe-1K). The soft Se and micro-porosity synergistically endow this material with a binding affinity to Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺ ions and ultrafast kinetics with R > 97.6% in 2-60 min. In particular, ZnSnSe-1K can remove 99.34% of Cs⁺ in 2 min ⁽K_d^Cs > 1.5 × 10⁵ mL g^-1), contributing to a record rate constant k₂ of 9.240 g mg^-1 min^-1 that surpasses all metal chalcogenide adsorbents. ZnSnSe-1K exhibits good acid/base tolerance (pH = 0-12), and the adsorption capacities at neutral are 253.61 ± 9.15, 108.94 ± 25.32, 45.76 ± 14.19 and 38.49 ± 2.99 mg g^-1 for Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺, respectively. The adsorption performances resist well co-existing cations and anions, and the removal rates can keep above or close to 90% even in sea water. ZnSnSe-1K is employed in continuous column and membrane filtration, both of which shows excellent elimination efficiency (R > 99%) for mixed Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺. Especially, the membrane with an ultrathin (70 µm) ZnSnSe-1K layer can remove 97-100% Cs⁺ in suction filtration with a short contact time of 0.33 s. Combined with the simple synthesis, facile elution and great irradiation resistance, ZnSnSe-1K emerges as a selenide adsorbent candidate for use in environmental remediation especially that involving nuclear waste disposal.

Dittmarite-type magnesium phosphates for highly efficient capture of Cs. JOURNAL OF HAZARDOUS MATERIALS 2023;453:131385. [PMID: 37043858 DOI: 10.1016/j.jhazmat.2023.131385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The presence of cesium ions (Cs⁺) in radioactive wastewater has attracted considerable attention owing to their extreme toxic effects. Thus, there is an urgent need to develop adsorbents for Cs⁺ with high adsorption capacities (q). While phosphate-based adsorbents have advantages for their disposal, previous adsorbents have shown limited q because of their limited capacity for ion exchange, despite showing high theoretical q values. In this study, two dittmarite-type magnesium phosphates, KMgPO₄·H₂O (KMP) and NH₄MgPO₄·H₂O (NMP), were synthesized because of their ability to contain readily exchangeable cations in their interlayers. KMP and NMP demonstrated remarkable adsorption capacities for Cs⁺ (q_e^KMP = 630 mg g^-1 and q_e^NMP = 711 mg g^-1), which were the highest among all reported adsorbents and are ∼84 % of their theoretical values. Their distribution coefficients in waters with high divalent ion concentrations were low, which limits their use for the adsorption of Cs⁺ from such environments. After adsorption, KMP and NMP were structurally transformed into struvite-type CsMgPO₄·6H₂O (CsMP), which has two different stacking structures, either cubic or hexagonal, depending on the pH of the solution. The high q values of KMP and NMP enable them to reduce the volume of radioactive waste for disposal.

Direct Separation of UO2 2+ by Coordination Sieve Effect via Spherical Coordination Traps

Molecule sieve effect (MSE) can enable direct separation of target, thus overcoming two major scientific and industrial separation problems in traditional separation, coadsorption, and desorption. Inspired by this, herein, the concept of coordination sieve effect (CSE) for direct separation of UO₂ ²⁺ , different from the previously established two-step separation method, adsorption plus desorption is reported. The used adsorbent, polyhedron-based hydrogen-bond framework (P-HOF-1), made from a metal-organic framework (MOF) precursor through a two-step postmodification approach, afforded high uptake capacity (close to theoretical value) towards monovalent Cs⁺ , divalent Sr²⁺ , trivalent Eu³⁺ , and tetravalent Th⁴⁺ ions, but completely excluded UO₂ ²⁺ ion, suggesting excellent CSE. Direct separation of UO₂ ²⁺ can be achieved from a mixed solution containing Cs⁺ , Sr²⁺ , Eu³⁺ , Th⁴⁺ , and UO₂ ²⁺ ions, giving >99.9% removal efficiency for Cs⁺ , Sr²⁺ , Eu³⁺ , and Th⁴⁺ ions, but <1.2% removal efficiency for UO₂ ²⁺ , affording benchmark reverse selectivity (S_M/U ) of >83 and direct generation of high purity UO₂ ²⁺ (>99.9%). The mechanism for such direct separation via CSE, as unveiled by both single crystal X-ray diffraction and density-functional theory (DFT) calculation, is due to the spherical coordination trap in P-HOF-1 that can exactly accommodate the spherical coordination ions of Cs⁺ , Sr²⁺ , Eu³⁺ , and Th⁴⁺ , but excludes the planar coordination UO₂ ²⁺ ion.

Ligand-Assistant Iced Photocatalytic Reduction to Synthesize Atomically Dispersed Cu Implanted Metal-Organic Frameworks for Photo-Enhanced Uranium Extraction from Seawater

Uranium extraction from natural seawater is one of the most promising routes to address the shortage of uranium resources. By combination of ligand complexation and photocatalytic reduction, porous framework-based photocatalysts have been widely applied to uranium enrichment. However, their practical applicability is limited by poor photocatalytic activity and low adsorption capacity. Herein, atomically dispersed Cu implanted UiO-66-NH₂ (Cu SA@UiO-66-NH₂ ) photocatalysts are prepared via ligand-assistant iced photocatalytic reduction route. N-Cu-N moiety acts as an effective electron acceptor to potentially facilitate charge transfer kinetics. By contrast, there exist Cu sub-nanometer clusters by the typical liquid phase photoreduction, resulting in a relatively low photocatalytic activity. Cu SA@UiO-66-NH₂ adsorbents exhibit superior antibacterial ability and improved photoreduction conversion of the adsorbed U(VI) to insoluble U(IV), leading to a high uranium sorption capacity of 9.16 mg-U/g-Ads from natural seawater. This study provides new insight for enhancing uranium uptake by designing SA-mediated MOF photocatalysts.

Low-temperature plasma induced phosphate groups onto coffee residue-derived porous carbon for efficient U(VI) extraction

For the continuous utilization of nuclear energy and efficient control of radioactive pollution, low-cost materials with high efficient U(VI) removal are of great importance. In this study, low temperature plasma method was applied for the successful modification of O-phosphorylethanolamine (O-PEA) on the porous carbon materials. The produced materials (Cafe/O-PEA) could adsorb U(VI) efficiently with the maximum sorption capacity of 648.54 mg/g at 1 hr, T=298 K, and pH=6.0, much higher than those of most carbon-based composites. U(VI) sorption was mainly controlled by strong surface complexation. From FTIR, SEM-EDS and XPS analyses, the sorption of U(VI) was related to the complexation with -NH₂, phosphate and -OH groups on Cafe/O-PEA. The low temperature plasma method was an efficient, environmentally friendly and low-cost method for surface modification of materials for the effective enrichment of U(VI) from aqueous solutions.

Thermodynamic Transformation of Crystalline Organic Hybrid Iron Selenide to FexSey@CN Microrods for Sodium Ion Storage

Carbon-coated metal chalcogenide composites have been demonstrated as one type of promising anode material for sodium-ion batteries (SIBs). However, combining carbon materials with micronanoparticles of metal chalcogenide always involve complicated processes, such as polymer coating, carbonization, and sulfidation/selenization. To address this issue, herein, we reported a series of carbon-coated FexSey@CN (FexSey = FeSe2, Fe3Se4, Fe7Se8) composites prepared via the thermodynamic transformation of a crystalline organic hybrid iron selenide [Fe(phen)2](Se4) (phen = 1,10-phenanthroline). By pyrolyzing the bulk crystals of [Fe(phen)2](Se4) at different temperatures, FexSey microrods were formed in situ, where the nitrogen-doped carbon layers were coated on the surface of the microrods. Moreover, all the as-prepared FexSey@CN composites exhibited excellent sodium-ion storage capabilities as anode materials in SIBs. This work proves that crystalline organic hybrid metal chalcogenides can be used as a novel material system for the in situ formation of carbon-coated metal chalcogenide composites, which could have great potential in the application of electrochemical energy storage.

Cesium removal from wastewater: High-efficient and reusable adsorbent K1.93Ti0.22Sn3S6.43

Efficient and quick removal of radioactive Cs⁺ from wastewater is significant for the safe use of nuclear energy and human health. A novel adsorbent K_1.93Ti_0.22Sn₃S_6.43 (KTSS) was developed for Cs⁺ removal from complex natural water systems. The working mechanism of KTSS for removing Cs⁺ was the synergistic effect of ion exchange and the Cs⋯S binding, which was proved by several characterization techniques. KTSS showed ultrafast kinetics for Cs⁺ adsorption within 1 min with a removal rate of 99%. Meanwhile, KTSS exhibited a higher adsorption capacity of 450.12 mg/g than many other adsorbents to remove Cs⁺ and possessed excellent chemical stability in a wide pH range of 3-12. Thanks to the natural affinity arising from the S^2- ligands, KTSS displayed excellent selectivity for Cs⁺ even in different complex water systems. The separation factors between Cs⁺ and the coexisting ions of Na⁺, K⁺, Mg²⁺, Ca²⁺ were ranged from 408.61 to 7448.20. Fortunately, by eluting with NaNO₃ the adsorbent could realize the green regeneration and cyclic utilization. Furthermore, it was found that KTSS had tremendous advantages in the removal of Cs⁺ in comparison with the other adsorbents. Consequently, it should be considered that KTSS obtained in this study has great potential in applying ultrafast and high-efficient removal of Cs⁺ from wastewater.

Layered double hydroxide intercalated with dimethylglyoxime for highly selective and ultrafast uptake of uranium from seawater

In this study, we demonstrate the first example of a MgAl layered double hydroxide intercalated by a ketoxime compound (dimethylglyoxime, DMG), that is, MgAl-DMG-LDH (abbr. DMG-LDH), which exhibits excellent capture of uranium (U(VI)) both at high (ppm) and low (ppb) concentrations. The as-formed DMG-LDH shows an enormous maximum U(VI) sorption capacity (qUm) of 380 mg g^-1 and an exceptionally rapid sorption rate (k₂ = 2.97 g mg^-1 min^-1), reaching a high uptake of 99.14% within 5 min. For natural and contaminated seawater with high concentrations of Na⁺, Ca²⁺, Mg²⁺ and K⁺ concomitant cations, the DMG-LDH still can trap ∼85% U, displaying highly effective sorption toward U. The interaction mechanism between UO₂²⁺ and DMG^2- provides an important reference for the development of highly effective capture of U(VI) by ketoxime materials. The DMG-LDH is currently the best ketoxime material for uranium extraction from nuclear waste and seawater.

Determination, Separation and Application of 137Cs: A Review

In the context of the rapid development of the world's nuclear power industry, it is necessary to establish background data on radionuclides of different samples from different regions, and the premise of obtaining such basic data is to have a series of good sample processing and detection methods. The radiochemical analysis methods of low-level radionuclides ¹³⁷Cs (Cesium) in environmental and biological samples are introduced and reviewed in detail. The latest research progress is reviewed from the five aspects of sample pretreatment, determination, separation, calculation, application of radioactive cesium and the future is proposed.

High-capacity recovery of Cs+ ions by facilely synthesized layered vanadyl oxalatophosphates with the clear insight into remediation mechanism

Radiocesium remediation is of great significance for the sustainable development of nuclear energy and ecological protection. It is very challenging for the effective recovery of ¹³⁷Cs from aqueous solutions due to its strong radioactivity, solubility and mobility. Herein, the efficient recovery of Cs⁺ ions has been achieved by three layered vanadyl oxalatophosphates, namely (NH₄)₂[(VO)₂(HPO₄)₂C₂O₄]·5 H₂O (NVPC), Na₂[(VO)₂(HPO₄)₂C₂O₄]·2 H₂O (SVPC), and K_2.5[(VO)₂(HPO₄)_1.5(PO₄)_0.5(C₂O₄)]·4.5 H₂O (KVPC). NVPC exhibits the ultra-fast kinetics (within 5 min) and high adsorption capacity for Cs⁺ (q_m^Cs = 471.58 mg/g). It also holds broad pH durability and excellent radiation stability. Impressively, the entry of Cs⁺ can be directly visualized by the single-crystal structural analysis, and thus the underlying mechanism of Cs⁺ capture by NVPC from aqueous solutions has been illuminated at the molecular level. This is a pioneering work in the removal of radioactive ions by metal oxalatophosphate materials which highlights the great potential of metal oxalatophosphates for radionuclide remediation.

Targeted synthesis of carbon-supported titanate nanofibers as host structure for nuclear waste immobilization

Inorganic ion-exchange materials show potential application for toxic radioactive ions due to their remarkable high efficiency and selectivity features. Here, two type of carbon-supported titanate (C@TNFs and C@TNFs(H)) nanofibers have been synthesized by a cost-effective in suit growth method. The resulting C@TNFs and C@TNFs(H) microspheres present uniform flower-like morphology and large surface area. The interlayer Na+ in the titanate shell provides docking sites for ion-exchange of radioactive ions (U(VI), Ba(II), and Sr(II)). Interestingly, the exceeding theoretical cation-exchange capacities (CECs) are achieved on C@TNFs for U(VI) ∼4.76 meq g−1 and Ba(II) ∼2.65 meq g−1 and C@TNFs(H) for Ba(II) ∼2.53 meq g−1 and Sr(II) ∼2.24 meq g−1, respectively. The impressive adsorption performance is mainly attributed to the synergistic effects of ion-exchange and surface complexation. More significantly, C@TNFs and C@TNFs(H) maintain high distribution coefficients (K d U) of >104 mL g−1 over a wider pH range (pH = 3.5–9.0) and high adsorption rate with short equilibrium time within 50 min. Competitive ion-exchange investigation shows a selectivity order of U(VI) > Ba(II) > Sr(II) at individual 10 ppm concentration, pH = 6.0 and T = 298 K. The related spectroscopic studies reveal the intercalative mechanism of radionuclides in the deformed titanate structure, as a result of target ions firmly trapped in the interlayer of C@TNFs and C@TNFs(H). These advantageous features allow the C@TNFs and C@TNFs(H) to be promising candidates for the remediation of toxic radioactive ions polluted water.

Efficient removal of Ba2+, Co2+ and Ni2+ by an ethylammonium-templated indium sulfide ion exchanger

Removal of radioactive ¹³³Ba, ⁶⁰Co and ⁶³Ni and their nonradioactive isotopes through ion exchange method would be highly beneficial for the safe disposal of liquid industrial waste, and it also bears importance for the emergency response to nuclear accident. Herein, we report the employment of an indium sulfide [CH₃CH₂NH₃]₆In₈S₁₅ (InS-2) with exchangeable ethylammonium cations for efficient and selective uptake of Ba²⁺, Co²⁺ and Ni²⁺. The corner-sharing linkage of P1-{In₈S₁₇} clusters in InS-2 endow the layered structure with nanoscale windows, which facilitates both transfer and accommodation of the large hydrated divalent metal ions. This results in ultrafast exchange kinetics (10-20 min) and top-level exchange capacities of 211.73 mg g^-1 for Ba²⁺, 103.57 mg g^-1 for Co²⁺, and 111.78 mg g^-1 for Ni²⁺. Particularly, InS-2 achieves ultrahigh K_d values of 2.3 × 10⁵ mL g^-1 for Ba²⁺, 2.0 × 10⁵ mL g^-1 for Co²⁺ and 1.6 × 10⁵ mL g^-1 for Ni²⁺, corresponding to remarkable removal efficiencies larger than 99.4% (C₀ ~ 6 ppm). InS-2 shows high β and γ irradiation resistance, wide pH durability (pH 3-13 for Ba²⁺, pH 3-11 for Co²⁺ and Ni²⁺), and outstanding selectivity against competitor ions (e.g. Na⁺, K⁺, Mg²⁺, Ca²⁺). The InS-2-filled ion exchange column exhibits a fantastic removal effect (R > 99%) for mixed Ba²⁺, Co²⁺, Ni²⁺, as well as Sr²⁺. The ultralong column-treatment on 20000 BVs of flow reveals an affinity order of Co²⁺ > Ni²⁺ > Ba²⁺ > Sr²⁺ for InS-2, which gives deep insights into the adsorption process and interaction between competitor ions. This excellent uptake of Ba²⁺ (Ra by analogy), Co²⁺ and Ni²⁺ ions by InS-2 highlights the great potential of metal chalcogenides as a type of promising materials for minimizing contamination in complex wastewater.

Highly Efficient Uptake of Cs+ by Robust Layered Metal-Organic Frameworks with a Distinctive Ion Exchange Mechanism

137Cs with strong radioactivity and a long half-life is highly hazardous to human health and the environment. The efficient removal of 137Cs from complex solutions is still challenging because of its high solubility and easy mobility and the influence of interfering ions. It is highly desirable to develop effective scavengers for radiocesium remediation. Here, the highly efficient uptake of Cs+ has been realized by two robust layered metal-organic frameworks (MOFs), namely [(CH3)2NH2]In(L)2·DMF·H2O (DMF = N,N'-dimethylformamide, H2L= H2aip (5-aminoisophthalic acid) for 1 and H2hip (5-hydroxyisophthalic acid) for 2). Remarkably, 1 and 2 hold excellent acid and alkali resistance and radiation stabilities. They exhibit fast kinetics, high capacities (q m Cs = 270.86 and 297.67 mg/g for 1 and 2, respectively), excellent selectivity for Cs+ uptake, and facile elution for the regeneration of materials. Particularly, 1 and 2 can achieve efficient Cs+/Sr2+ separation in a wide range of Sr/Cs molar ratios. For example, the separation factor (SF Cs/Sr) is up to ∼320 for 1. Moreover, the Cs+ uptake and elution mechanisms have been directly elucidated at the molecular level by an unprecedented single-crystal to single-crystal (SC-SC) structural transformation, which is attributed to the strong interactions between COO- functional groups and Cs+ ions, easily exchangeable [(CH3)2NH2]+, and flexible and robust anionic layer frameworks with open windows as "pockets". This work highlights layered MOFs for the highly efficient uptake of Cs+ ions in the field of radionuclide remediation.

Radioactive waste treatment technology: a review

Radioactive waste is generated from activities that utilize nuclear materials such as nuclear medicine or power plants. Depending on their half-life, they emit radiation continuously, ranging from seconds to millions of years. Exposure to ionizing radiation can cause serious harm to humans and the environment. Therefore, special attention is paid to the management of radioactive waste in order to deal with its large quantity and dangerous levels. Current treatment technologies are still being developed to improve efficiency in reducing the hazard level and waste volume, to minimize the impact on living organisms. Thus, the aim of this study was to provide an overview of the global radioactive waste treatment technologies that have been released in 2019–2021.

Highly selective cesium(I) capture under acidic conditions by a layered sulfide

Radiocesium remediation is desirable for ecological protection, human health and sustainable development of nuclear energy. Effective capture of Cs+ from acidic solutions is still challenging, mainly due to the low stability of the adsorbing materials and the competitive adsorption of protons. Herein, the rapid and highly selective capture of Cs+ from strongly acidic solutions is achieved by a robust K+-directed layered metal sulfide KInSnS4 (InSnS-1) that exhibits excellent acid and radiation resistance. InSnS-1 possesses high adsorption capacity for Cs+ and can serve as the stationary phase in ion exchange columns to effectively remove Cs+ from neutral and acidic solutions. The adsorption of Cs+ and H3O+ is monitored by single-crystal structure analysis, and thus the underlying mechanism of selective Cs+ capture from acidic solutions is elucidated at the molecular level.

Rapid Cs+ Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In³⁺ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs⁺ adsorption kinetics, as well as high Cs⁺ affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs⁺-incorporated DGIST-3. In Cs⁺-containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs⁺, which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.

Phosphate group functionalized magnetic metal-organic framework nanocomposite for highly efficient removal of U(VI) from aqueous solution

The phosphate group functionalized metal-organic frameworks (MOFs) as the adsorbent for removal of U(VI) from aqueous solution still suffer from low adsorption efficiency, due to the low grafting rate of groups into the skeleton structure. Herein, a novel phosphate group functionalized metal-organic framework nanoparticles (denoted as Fe₃O₄@SiO₂@UiO-66-TPP NPs) designed and prepared by the chelation between Zr and phytic acid, showing fast adsorption rate and outstanding selectivity in aqueous media including 10 coexisting ions. The Fe₃O₄@SiO₂@UiO-66-TPP was properly characterized by TEM, FT-IR, BET, VSM and Zeta potential measurement. The removal performance of Fe₃O₄@SiO₂@UiO-66-TPP for U(VI) was investigated systematically using batch experiments under different conditions, including solution pH, incubation time, temperature and initial U(VI) concentration. The adsorption kinetics, isotherm, selectivity studies revealed that Fe₃O₄@SiO₂@UiO-66-TPP NPs possess fast adsorption rates (approximately 15 min to reach equilibrium), high adsorption capacities (307.8 mg/g) and outstanding selectivity (S_u = 94.4%) towards U(VI), which in terms of performance are much better than most of the other magnetic adsorbents. Furthermore, the adsorbent could be reused for U(VI) removal without obvious loss of adsorption capacity after five consecutive cycles. The research work provides a novel strategy to assemble phosphate group-functionalized MOFs.

Stable 3D neutral gallium thioantimonate frameworks decorated with transition metal complexes for a tunable photocatalytic hydrogen evolution

Incorporating transition metal (TM) complexes into cluster-based chalcogenide frameworks is an effective synthetic strategy to induce structural diversity and control the optoelectronic properties, which may further improve their photocatalytic performance. However, limited studies have been conducted on frameworks constructed by TM complexes covalently bonded with supertetrahedral Tn clusters, let alone on their properties, especially photocatalytic H₂ activity. Herein, three new isostructural three-dimensional (3D) neutral inorganic-organic open frameworks of gallium thioantimonate comprised of thiogallate-based supertetrahedral T3 clusters that are covalently bonded with TM complexes ([TM(TEPA)]²⁺, TM = Mn/Ni/Fe, TEPA = tetraethylenepentamine) at the edges and are linked by single Sb³⁺ ions at the corner, namely, NCF-3-Mn/Ni/Fe have been solvothermally synthesized and structurally characterized, and display good thermal and chemical stability. Benefiting from an adjustable TM centre, the title compounds possess tunable photocatalytic H₂ evolution activity, among which NCF-3-Mn exhibits the highest photocatalytic activity probably due to its favourable band structure and enhanced carrier separation efficiency.

Effective Enrichment of Low-Concentration Rare-Earth Ions by Three-Dimensional Thiostannate K2Sn2S5

Rare-earth elements (REEs) in industrial wastewaters have great value for recycling and reuse, but their characteristic of low concentration poses a challenge to an efficient enrichment from wastewaters. In recent years, thiometallates featuring two-dimensional layers have shown great potential in the enrichment of REEs via the ion-exchange process. However, investigations on thiometallates featuring three-dimensional anionic frameworks for the recovery of REEs have not been reported. Herein, K₂Sn₂S₅ (KTS-2), a thiostannate possessing a three-dimensional porous framework, was chosen as an ion-exchange material for capturing REEs from an aqueous solution. Indeed, KTS-2 exhibited excellent ion-exchange performance for all 16 REEs (except Pm). Specifically, KTS-2 displayed a high capture capacity (232.7 ± 7.8 mg/g) and a short equilibrium time (within 10 min) for Yb³⁺ ions. In addition, KTS-2 had a high distribution coefficient for Yb³⁺ ions (K_d > 10⁵ mL/g) in the presence of excessive interfering ions. Impressively, KTS-2 could reach removal rates of above 95% for all 16 REEs in a large quantity of wastewater with low initial concentration (∼7 mg/L). Moreover, KTS-2 could be used as an eco-friendly material for ion exchange of REEs, since the released K⁺ cations would not cause secondary pollution to the water solution.

Development of porous material via chitosan-based Pickering medium internal phase emulsion for efficient adsorption of Rb+, Cs+ and Sr2

The radioactive Rb⁺, Cs⁺ and Sr²⁺ have serious threat for the aquatic life and human health, its removal has been granted increasing concern. Hence the adsorbent with excellent adsorption performance and favourable reusability is strongly demanded. This work prepared a novel porous polymer of chitosan-g-polyacrylamide (CTS-g-PAM) by grafting the acrylamide (AM) onto the chitosan (CTS) with sufficient pore structure via an eco-friendly surfactant-free (corn oil)-in-water Pickering medium internal phase emulsion (O/W Pickering MIPE), solely stabilized by CTS. Interestingly, its pore structure could be tuned by varying the emulsion character via changing the molecular weight and concentration of CTS, as well as the pH values. Due to the abundant -COO^- and -NH₂ functional groups in the porous material of CTS-g-PAM, the high adsorption capacities of 195.43, 237.44 and 185.63 mg/g for Rb⁺, Cs⁺ and Sr²⁺ could be reached within 40, 30 and 20 min, respectively. Moreover, the CTS-g-PAM had excellent regeneration ability and reusability. Herein, we provided a feasible and low-cost pathway for preparation of the porous adsorbent with tunable porous structure for adsorption and separation application.

Novel One-Pot Solvothermal Synthesis of High-Performance Copper Hexacyanoferrate for Cs+ Removal from Wastewater

Efficient removal of radioactive cesium from complex wastewater is a challenge. Unlike traditional precipitation and hydrothermal synthesis, a novel vast specific surface area adsorbent of copper hexacyanoferrates named EA-CuHCF was synthesized using a one-pot solvothermal method under the moderate ethanol media characterized by XRD, SEM, EDS, BET, and FTIR. It was found that the maximum adsorption capacity towards Cs+ was 452.5 mg/g, which is far higher than most of the reported Prussian blue analogues so far. Moreover, EA-CuHCF could effectively adsorb Cs+ at a wide pH range and low concentration of Cs+ in geothermal water within 30 minutes, and the removal rate of Cs+ was 92.1%. Finally, the separation factors between Cs+ and other competitive ions were higher than 553, and the distribution coefficient of Cs+ reached up to 2.343 × 104 mL/g. These properties suggest that EA-CuHCF synthesized by the solvothermal method has high capacity and selectivity and can be used as a candidate for Cs+ removal from wastewater.

Selective Capture Mechanism of Radioactive Thorium from Highly Acidic Solution by a Layered Metal Sulfide

Thorium as a potential nuclear fuel for the next-generation thorium-based molten salt reactors holds significant environmental and economic promise over the current uranium-based nuclear reactors. However, because thorium (Th⁴⁺) usually coexists with other rare earth elements, alkali or alkaline earth metals in minerals, or highly acidic radioactive waste, seeking acid-resistant sorbents with excellent selectivity, high capacity, and fast removal rate for Th⁴⁺ is still a challenging task. In this work, we investigated a robust layered metal sulfide (KInSn₂S₆, KMS-5) for Th⁴⁺ removal from strong acidic solutions. We report that KMS-5 could capture Th⁴⁺ from a 0.1 M HNO₃ solution with extremely high efficiency (∼99.9%), fast sorption kinetics (equilibrium time < 10 min), and large distribution coefficient (up to 1.5 × 10⁶ mL/g). Furthermore, KMS-5 exhibited excellent sorption selectivity towards Th⁴⁺ in the presence of large amounts of competitive metal ions like Eu³⁺, Na⁺, and Ca²⁺. This extraordinary capture property for Th⁴⁺ is attributed to the facile ion exchange of Th⁴⁺ with K⁺ in the interlayers and subsequent formation of a stable coordination complex via Th-S bonds. These results indicate that KMS-5 is a promising functional sorbent for the effective capture of Th⁴⁺ from highly acidic solutions.

Efficient Sr-90 removal from highly alkaline solution by an ultrastable crystalline zirconium phosphonate

We report here a distinct case of strontium removal under 1 M NaOH solution by an ultrastable crystalline zirconium phosphonate framework (SZ-7) with high adsorption capacity (183 mg g^-1) and in-depth removal performance (K_d = 3.9 × 10⁵ mL g^-1), demonstrating the potential application of SZ-7 for ⁹⁰Sr removal in highly alkaline nuclear waste.

Difunctional covalent organic framework hybrid material for synergistic adsorption and selective removal of fluoroquinolone antibiotics

Due to the low efficiency of traditional sewage treatment methods, the effective removal of zwitterionic fluoroquinolone (FQs) antibiotics is of vital significant for environment protection. In this work, a SO₃H-anchored covalent organic framework (TpPa-SO₃H) was deliberately designed by linking phenolic trialdehyde with triamine through Schiff reaction, then low-content Tb³⁺ ions were loaded onto covalent organic framework according to wet-chemistry immersion dispersion method which benefitting for efficient FQs antibiotics uptaking. Tb@TpPa-SO₃H functionalized with regularly distributed sulfonic acid groups and terbium ions which could provide difunctional binding sites. Tb³⁺ sites could capture carboxylic acid group of FQs molecules according to the complexes coordination effect and sulfonic acid sites play a significant role in the adsorption of FQs molecules through electrostatic interaction with amine group. Tb@TpPa-SO₃H with dual complementary function sites exhibited ultra-fast adsorption kinetics (< 2 min, average over 99% removing rate) and high adsorption capacities of 989, 956, and 998 mg g^-1 for Norfloxacin (NOR), ciprofloxacin (CIP), enrofloxacin (ENR), respectively. Furthermore, Tb@TpPa-SO₃H showed excellent selectivity for the adsorption of FQs in tanglesome system. This work not only explored synergistic adsorption in ion-functionalized 2D covalent organic framework with dual binding sites, but also delineated a promising strategy for the elimination of organic pollutants in environmental remediation.

An anionic potassium-organic framework for selective removal of uranyl ions

Effective and selective removal of radioactive metal ions from aqueous solutions is of great importance due to their harmful effects on humans and other living species. However, it is a big challenge for researchers to develop effective adsorbents with high selectivity and a wide pH application range even if some progress has been achieved. Herein, we report an anionic potassium organic framework (UPC-K1) with protonated dimethylamine (Me2NH2+) residing inside the rhomboid channels. The unique 3D firm structure of UPC-K1 is constructed by the cross-linking of the 2D arrangement using weak K-O bonds (2.9270 Å) and strong hydrogen bonds (1.6498 Å), which endows it with excellent chemical stability in organic solvents, boiling water, and aqueous solution in the pH range 3-10. Based on the cation exchange, depending on pore size selectivity, UPC-K1 shows excellent adsorption performance towards UO22+ in aqueous solutions at 298 K with the following characteristics: (1) effective removal in the pH range 3-10; (2) high selectivity over other metal cations; (3) a high adsorption capacity of 551.4 mg g-1; (4) a rapid adsorption equilibrium within 3 hours under stirring; and (5) effective adsorption at low concentrations, with a residual concentration of 0.69 ppm even at an initial concentration of 10.3 ppm after stirring for 24 hours. These results indicate the great potential of UPC-K1 in the treatment of uranium-containing nuclear wastewater.

Remarkable damage in talc caused by electron beam irradiation with a dose of up to 1000 kGy: lattice shrinkage in the Z- and Y-axis and corresponding intrinsic microstructural transformation process speculation

To reduce the polluted areas caused by the migration of radioactive or toxic matter, a clear understanding of soil matrix stability, especially the lattice, is essential under irradiation conditions like those of β-ray irradiation. In reality, the matrix of soil or clay is silicate, with talc being one of the most simple species with a similar structure to that matter, exhibiting "2 : 1" stacking and a complete crystal. Therefore, in this work, it was irradiated by an electron beam in air with dose up to 1000 kGy. Then, variations in lattice and the intrinsic microstructural transformation process, especially in terms of defect formation and transformation, were explored. The main results show that irradiation led to talc lattice plane shrinkage and amorphization. Shrinkage and amorphization levels in the Z-axis were more serious than those in the Y-axis. For a 1000 kGy-irradiated sample, the shrinkage level of the (002) lattice plane was close to 2% near 0.2 Å and that of (020) was close to 1.3% near 0.06 Å. Variation in the (002) lattice plane was more obvious than that of (020). The main mechanisms involve the cleavage of tetrahedral Si-O and linkage of tetrahedra and octahedra. Tetrahedral Si-O cleavage was visible, leading to serious amorphization. Nevertheless, lattice plane shrinkage, especially in the Z-axis, was mainly caused by linkage cleavage in this direction. In addition to linkage cleavage, dehydroxylation and H2O volatilization occurred, coupled with H2O radiolysis. Nevertheless, those factors are secondary to lattice variation.

Prussian blue analogs-based layered double hydroxides for highly efficient Cs+ removal from wastewater

In this work, novel Prussian blue analogs-based layered double hydroxide (PBA@ZnTi-LDH) was in situ synthesized and used for radioactive Cs⁺ removal from wastewater. The results suggested that this PBA@ZnTi-LDH prepared using LDH as skeleton and transition metal source showed higher adsorption capacity (243.9 mg/g) and water stability than conventional PBAs, and promising application in scale-up Cs⁺ removal. Thus, it was granulated by calcium alginate and the PBA@ZnTi-LDH/CaALG exhibited favorable post-separation and fixed-bed adsorption ability at different Cs⁺ concentrations and flow rates, highlighting its application perspective on Cs⁺ removal from various kinds of wastewater. Moreover, the real-world Cs⁺ removal was preliminarily explored using natural complex Cs⁺-containing water. As a result, this stable and easily separated PBA@ZnTi-LDH/CaALG showed high removal efficiency, selectivity and good reusability, which was promising in scale-up Cs⁺ removal from the real-world wastewater.

Efficient Removal of Cs+ and Sr2+ Ions by Granulous (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O/Polyacrylonitrile Composite

The need to effectively and selectively remove radioactive ¹³⁷Cs and ⁹⁰Sr from nuclear waste solutions persists to mitigate their environmental mobility and high radiotoxicity. Because it is difficult to effectively remove them from acidic environments that degrade most sorbents, new sorbent materials are highly desirable. Here, efficient removal of Cs⁺ and Sr²⁺ is achieved by the composite of layered tin sulfide (Me₂NH₂)_4/3(Me₃NH)_2/3Sn₃S₇·1.25H₂O (FJSM-SnS) and polyacrylonitrile (PAN) (FJSM-SnS/PAN). The granulous composite possesses regular particle morphology and good mechanical strength as an engineered form. It shows excellent acid-base and γ-irradiation resistance, high maximum adsorption capacities (q_m) of 296.12 and 62.88 mg/g for Cs⁺ and Sr²⁺ ions, respectively, and high selectivity even in the presence of excess Na⁺ ions or using lake water. Impressively, q_m^Cs of FJSM-SnS/PAN reaches 89.29 mg/g under even acidic conditions (pH = 2.5). The column loaded with FJSM-SnS/PAN granules exhibits high removal rates (R) toward low-concentration Cs⁺ and Sr²⁺ ions under both neutral and acidic conditions. Moreover, the composite can be recycled and reused with high R^Cs and R^Sr. This work highlights the great potential of metal sulfide ion-exchangers in engineered form for the efficient removal of Cs⁺ or Sr²⁺ ions, especially under acidic conditions, for radionuclide remediation.

Efficient Photocatalytic Extraction of Uranium over Ethylenediamine Capped Cadmium Sulfide Telluride Nanobelts

The photocatalysts for hexavalent uranium (U(VI)) reduction suffered from the low uranium uptake capacity and weak long-wavelength light absorption. Herein, we synthesized the CdS_xTe_1-x nanobelts capped by ethylenediamine (EDA), which provided amino groups as the adsorption sites. With the increase of the Te content, the amino groups on the CdS_xTe_1-x nanobelts decreased because of the variation of the electron density of Cd²⁺, whereas the light adsorption was enhanced due to the narrowed bandgap. In photocatalytic reduction of U(VI), the CdS_0.95Te_0.05-EDA nanobelts exhibited a considerable U(VI) removal ratio of 97.4% with a remarkable equilibrium U(VI) extraction amount on per weight unit of the adsorbent (q_e) of 836 mg/g. The bandgap structure and Fourier transform infrared spectroscopy (FT-IR) spectra analysis revealed that the optimum photocatalytic activity of CdS_xTe_1-x nanobelts was achieved at a 5% of Te^2- doping, which balanced the factors of amino groups and bandgap. This adsorption-photoreduction process offers an ultrahigh uranium extraction capacity over wide uranium concentrations.

Facile syntheses of silver thioantimonates exhibiting second-harmonic generation responses and large birefringence

Two chalcogenide crystalline compounds, [enH2][Ag4Sb2S6] (en = ethylenediamine) and [enH][Ag2SbS3], have been successfully synthesized by mild ionothermal and solvothermal means. [enH][Ag2SbS3] crystallizes in the noncentrosymmetric (NCS) and polar space group Pc, and its linear and nonlinear optical (NLO) properties have been investigated for the first time. Second harmonic generation (SHG) measurements revealed that [enH][Ag2SbS3] affords powder SHG performance values of 2.5 × KDP @1064 nm and 0.2 × AgGaS2 @2100 nm. Additional particle size vs. SHG efficiency measurements indicate that [enH][Ag2SbS3] is phase-matchable. The calculated birefringence Δn is 0.177 at 1064 nm, which is sufficiently large (the largest value among NCS thioantimonates) to achieve phase matching. [enH2][Ag4Sb2S6] crystallizes in the centrosymmetric space group P21/c and its structure features a double-layered variant honeycomb-like anionic network parallel to the ac plane separated by [enH2]2+ cations. The optical band gaps of [enH2][Ag4Sb2S6] and [enH][Ag2SbS3] are found to be 2.37 and 2.53 eV, respectively. Theoretical studies using density functional theory have been implemented to further elucidate the relationship between the band structure and NLO properties in [enH][Ag2SbS3].