A Novel Vanadosilicate with Hexadeca‐Coordinated Cs + Ions as a Highly Effective Cs + Remover

Boosting selective Cs+ uptake through the modulation of stacking modes in layered niobate-based perovskites

Selective separation of 137Cs is significant for the sustainable development of nuclear energy and environmental protection, due to its strong radioactivity and long half-life. However, selective capture of 137Cs+ from radioactive liquid waste is challenging due to strong coulomb interactions between the adsorbents and high-valency metal ions. Herein, we propose a strategy to resolve this issue and achieve specific Cs+ ion recognition and separation by modulating the stacking modes of layered perovskites. We demonstrate that among niobate-based perovskites, ALaNb2O7 (A = Cs, H, K, and Li), HLaNb2O7 shows an outstanding selectivity for Cs+ even in the presence of a large amount of competing Mn+ ions (Mn+ = K+, Ca2+, Mg2+, Sr2+, Eu3+, and Zr4+) owing to its suitable void fraction and space shape, brought by the stacking mode of layers. The Cs+ capture mechanism is directly elucidated at molecular level by single-crystal structural analyses and density functional theory calculations. This work not only provides key insights in the design and property optimization of perovskite-type materials for radiocesium separation, but also paves the way for the development of efficient inorganic materials for radionuclides remediation.

Magnetic hierarchical titanium ferrocyanide for the highly efficient and selective removal of radioactive cesium from water

Selective adsorption is the most suitable technique for eliminating trace amounts of 137Cs from various volumes of 137Cs-contaminated water, including seawater. Although various metal ferrocyanide (MFC)-functionalized magnetic adsorbents have been developed for the selective removal of 137Cs and magnetic recovery of adsorbents, their adsorption capacity for Cs remains low. Here, magnetic hierarchical titanium ferrocyanide (mh-TiFC) was synthesized for the first time for enhanced Cs adsorption. Hierarchical TiFC, comprising 2-dimensional TiFC flakes, was synthesized on SiO2-coated magnetic Fe3O4 particles using a sacrificial TiO2 shell as a source of Ti4+ via a reaction with ferrocyanide under acidic conditions. The resultant mh-TiFC exhibited the highest maximum adsorption capacity (434.8 mg g-1) and enhanced Cs selectivity with an excellent Kd value (6,850,000 mL g-1) compared to those of previously reported magnetic Cs adsorbents. This enhancement was attributed to the hierarchical structure, which reduced intracrystalline diffusion and increased the surface area available for direct Cs adsorption. Additionally, mh-TiFC (0.1 g L-1) demonstrated an excellent removal efficiency of 137Cs exceeding 99.85% for groundwater and seawater containing approximately 22 ppt 137Cs. Therefore, mh-TiFC offers promising applications for the treatment of 137Cs-contaminated water.

Introducing a Pyrazinoquinoxaline Derivative into a Metal-Organic Framework: Achieving Fluorescence-Enhanced Detection for Cs+ and Enhancing Photocatalytic Activity

Conventional photoresponsive materials have low photon utilization due to irregular distribution of photoactive groups, which severely limits the related real applications. Metal-organic frameworks (MOFs) can modulate the regular arrangement of functional groups to improve the electron transport paths and enhance the photon utilization, which provides strong support for the development of photoactive materials with excellent performance. In this work, one effective strategy for constructing a photoactive MOF had been developed via the utilization of Cd2+ and pyrazinoquinoxaline tetracarboxylic acid. The structural advantages of the Cd-MOF, such as a porous structure, abundant subject-object interaction sites, and a stable framework, ensure the prerequisite for various applications, while the better synergistic effect of Cd3 clusters and the pyrazinoquinoxaline derivative ensures efficient electron transfer efficiency. Therefore, by virtue of these structural advantages, the Cd-MOF can achieve fluorescence quenching detection for a variety of substrates, such as Fe3+, Cr2O72-, MnO4-, nitrofuran antibiotics, and TNP explosives, while fluorescence enhancement detection can be achieved for halogen ions, Cs+, Pb2+, and NO2-. In addition, the Cd-MOF can be used as a photocatalyst to successfully achieve the photocatalytic conversion of benzylamine to N-benzylbenzimidate under mild conditions. Thus, the Cd-MOF as a whole shows the possibility of application as a diverse fluorescence detection and photocatalyst and also illustrates the feasibility of preparing high-performance photoactive materials using the pyrazinoquinoxaline derivative.

First successful synthesis of an Al-rich mesoporous aluminosilicate for fast radioactive strontium capture

Al-rich zeolites such as NaA (Si/Al = 1.00) have been widely applied to remove radioactive ⁹⁰Sr²⁺ because of their high surface charge density enabling efficient ion-exchange of multivalent cations. However, due to the small micropore diameters of zeolites and large molecular size of strongly hydrated Sr²⁺, Sr²⁺-exchange with zeolites suffers from very slow kinetics. In principle, mesoporous aluminosilicates with low Si/Al ratios close to unity and tetrahedrally coordinated Al sites can exhibit both high capacity and fast kinetics in Sr²⁺-exchange. Nonetheless, the synthesis of such materials has not been realized yet. In this study, we demonstrate the first successful synthesis of an Al-rich mesoporous silicate (ARMS) using a cationic organosilane surfactant as an efficient mesoporogen. The material exhibited a wormhole-like mesoporous structure with a high surface area (851 m² g^-1) and pore volume (0.77 cm³ g^-1), and an Al-rich framework (Si/Al = 1.08) with most Al sites tetrahedrally coordinated. Compared to commercially applied NaA, ARMS exhibited a dramatically improved Sr²⁺-exchange kinetics (>33-fold larger rate constant) in batch adsorption while showing similarly high Sr²⁺ capture capacity and selectivity. Due to the fast Sr²⁺-exchange kinetics, the material also exhibited 3.3-fold larger breakthrough volume than NaA in fixed-bed continuous adsorption.

Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+ -Activated Niobium Germanate by the pH Control

¹³⁷ Cs and ⁹⁰ Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs⁺ and Sr²⁺ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K⁺ -activated niobium germanate (K-NGH-1) presents efficient Cs⁺ /Sr²⁺ coadsorption and highly selective Cs⁺ /Sr²⁺ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs⁺ and Sr²⁺ (q_m ^Cs  = 182.91 mg g^-1 ; q_m ^Sr  = 41.62 mg g^-1 ). In 1 M HNO₃ solution, K-NGH-1 still possesses q_m ^Cs of 91.40 mg g^-1 for Cs⁺ but almost no adsorption for Sr²⁺ . Moreover, K-NGH-1 can effectively separate Cs⁺ from 1 M HNO₃ solutions with excess competing Sr²⁺ and M^{n +} (M^{n +}  = Na⁺ , Ca²⁺ , Mg²⁺ ) ions. Thus, efficient separation of Cs⁺ and Sr²⁺ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs⁺ /Sr²⁺ coadsorption and selective separation.

Giant Polyoxoniobate-Based Inorganic Molecular Tweezers: Metal Recognitions, Ion-Exchange Interactions and Mechanism Studies

This work reports the interesting and unique cation-exchange behaviors of the first indium-bridged purely inorganic 3D framework based on high-nuclearity polyoxoniobates as building units. Each nanoscale polyoxoniobate features a fascinating near-icosahedral core-shell structure with six pairs of unique inorganic "molecular tweezers" that have changeable openings for binding different metal cations via ion-exchanges and exhibit unusual selective metal-uptake behaviors. Further, the material has high chemical stability so that can undergo single-crystal-to-single-crystal metal-exchange processes to produce a dozen new crystals with high crystallinity. Based on these crystals and time-dependent metal-exchange experiments, we can visually reveal the detailed metal-exchange interactions and mechanisms of the material at the atomic precision level. This work demonstrates a rare systematic and atomic-level study on the ion-exchange properties of nanoclusters, which is of significance for the exploration of cluster-based ion-exchange materials that are still to be developed.

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.

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.

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.

Influence of the Nanotube Morphology and Intercalated Species on the Sorption Properties of Hybrid Layered Vanadium Oxides: Application for Cesium Removal from Aqueous Streams

The present paper examines the impact that the nanotube morphology and organic or inorganic intercalated species may have on the cesium sorption by layered vanadium oxides prepared with the use of hexadecylamine as a structure-directing agent. The hybrid material represented by a chemical formula of (V₂O₅)(VO₂)_1.03(C₁₆H₃₆N)_1.46(H₂O)_x was achieved through accelerated microwave-assisted synthesis carefully optimized to ensure the best compromise between the scroll-like morphology and the hydrophobic character. To enhance its dispersibility in water, this sample was subsequently modified by progressive replacement of the C₁₆H₃₆N⁺ units by NH₄⁺ cations. The final materials represented a stacking of lamellar sheets with a worse scroll-like morphology. Both the optimization procedure and the template removal were monitored on the basis of scanning and transmission electronic microscopy, X-ray diffraction, infra-red spectroscopy, inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, and elemental analysis, supplemented by adequate simulations methods providing the reference IR spectra and XRD patterns for comparison or the textural parameters of the samples. The comparison of the cesium sorption from either a 4:1 ethanol–water mixture or aqueous solutions pointed toward the solubility of intercalated cations in the bulk solution as the main factor limiting their displacement from the interlayer space by the oncoming cesium ones. The sample obtained after 70% exchange with NH₄⁺ exhibited a maximum sorption capacity of 1.4 mmol g⁻¹ from CsNO₃ aqueous solutions and its retention efficiency remained significant from low-concentration Cs solutions in river or sea water.

Synthesis of Glue-Free NaA Zeolite Granules from Natural Kaolin for the Adsorption of Pb(II) Ions in Aqueous Solution Using a Fixed-Bed Column Study

NaA zeolite-coated metakaolin granules (MKG@NaA) were successfully synthesized from kaolin mineral by primary growth in the hydrothermal reaction without using glue or a seed crystal. The XRD and SEM analysis results revealed that a layer of NaA zeolite with a typical cubic shape and high crystallinity formed on the surface of kaolin granules. The obtained material was used as an adsorbent for lead metal ion Pb(II) adsorption studies in a fixed-bed column configuration. The operation factors such as the solution inflow rate, Pb(II) concentration, and column height were investigated. The results showed that the adsorption capacity of the material increased with increasing column height and initial concentration of the influent and decreased with increasing flow rate. With the test parameters at the Pb(II) concentration of 100 mg·L^-1, the adsorbent bed height of 8.1 cm, and the inflow rate of 2.5 mL·min^-1, the lead ion adsorption capacity was 118.5 mg·g^-1. The Thomas, Yoon-Nelson, and bed depth service time models were applied to describe the breakthrough curves for Pb(II) ion removal by a fix-bed column using the MKG@NaA absorbent and to predict the column performance under different experimental conditions with good linearity (R ² > 0.95).

Efficient Design to Monitor the Site-specific Sustained Release of a Non-Emissive Anticancer Drug

A pH-responsive smart nanocarrier with significant components was synthesized by conjugating the non-emissive anticancer drug methyl orange and polyethylene glycol derived folate moiety to the backbone of polynorbornene. Complete synthesis procedure and characterization methods of three monomers included in the work: norbornene-derived Chlorambucil (Monomer 1), norbornene grafted with polyethylene glycol, and folic acid (Monomer 2) and norbornene attached methyl orange (Monomer 3) connected to the norbornene backbone through ester linkage were clearly discussed. Finally, the random copolymer CHO PEG FOL METH was synthesized by ring-opening metathesis polymerization (ROMP) using Grubbs' second-generation catalyst. Advanced polymer chromatography (APC) was used to find the final polymer's molecular weight and polydispersity index (PDI). Dynamic light scattering, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were utilized to explore the prodrug's size and morphology. Release experiments of the anticancer drug, Chlorambucil and the coloring agent, methyl orange, were performed at different pH and time. Cell viability assay was carried out for determining the rate of survived cells, followed by the treatment of our final polymer named CHO PEG FOL METH.

Effective cesium removal from Cs-containing water using chemically activated opaline mudstone mainly composed of opal-cristobalite/tridymite (opal-CT)

Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (- 16.67 mV), compared to the effects of acid-activation (- 6.60 mV) or non-activation method (- 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method.

Relationship between zeolite structure and capture capability for radioactive cesium and strontium

Zeolites are widely used for capturing radioactive Cs⁺ and Sr²⁺, but the important structural factors determining their performance have not been clearly understood. To investigate the structure-property relationship, we prepared thirteen zeolites with various structures and Si/Al ratios. Ion-exchange experiments revealed that Cs⁺ exhibited an enhanced affinity to zeolites with high Si/Al ratios, which could be explained by the dielectric theory. Notably, zeolites containing 8-membered ring (8MR) showed extra-high Cs⁺ selectivity. Structural analysis using X-ray diffraction proved that Cs⁺ with an ionic diameter of 3.6 Å was selectively coordinated within 8MR having a cavity diameter of 3.6-4.1 Å. Such unique size-selective Cs⁺ coordination is analogous to ion complexation by macrocyclic organic ligands (e.g., crown ethers). Divalent Sr²⁺ showed decreasing affinity to zeolites as the Si/Al ratio increased, because of the increasing average Al-Al distance distribution. Sr²⁺ exchange exhibited an insignificant dependence on zeolite structures due to its strong hydration, which inhibited close interaction with zeolite frameworks. In terms of kinetics, Sr²⁺ exchange was significantly slower than Cs⁺ exchange because of the bulkiness of hydrated Sr²⁺ ions. Therefore, the micropore channels with large apertures (e.g., 12-membered ring) were beneficial for achieving fast ion-exchange kinetics, especially in the case of Sr²⁺.

Determination of cesium ions in environmental water samples with a magnetic multi-walled carbon nanotube imprinted potentiometric sensor

A potentiometric sensor, based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer composite (MMWCNTs@Cs-IIP), is introduced for the detection of cesium(i). The IIP was synthesized using cesium ions as the template ions, chitosan as the functional monomer and glutaraldehyde as the cross-linking agent. The membrane, which was coated on the surface of the GCE, was prepared using MMWCNTs@Cs(i)-IIP as the modifier, PVC as the neutral carrier, 2-nitrophenyloctyl ether as the plasticizer and sodium tetraphenylborate as the lipophilic salt. The proposed sensor exhibited a Nernstian slope of 0.05954 V dec⁻¹ in a working concentration range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M (mol L⁻¹) with a detection limit of 4 × 10⁻⁸ M. The sensor exhibited high selectivity for cesium ions and was successfully applied for the determination of Cs(i) in real samples.

A Cs(i)-selective potentiometric microsensor based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer has been developed.

Robust and Flexible Thioantimonate Materials for Cs+ Remediation with Distinctive Structural Transformation: A Clear Insight into the Ion-Exchange Mechanism

It is imperative yet challenging to efficiently sequester the ¹³⁷Cs⁺ ion from aqueous solutions because of its highly environmental mobility and extremely high radiotoxicity. The systematical clarification for underlying mechanism of Cs⁺ removal and elution at the molecular level is rare. Here, efficient Cs⁺ capture is achieved by a thioantimonate [MeNH₃]₃Sb₉S₁₅ (FJSM-SbS) with high capacity, fast kinetics, wide pH durability, excellent β and γ radiation resistances, and facile elution. The Cs⁺ removal is not significantly impacted by coexisting Na⁺, K⁺, Ca²⁺, Mg²⁺, and Sr²⁺ ions which is beneficial to the remediation of Cs⁺-contaminated real waters. Importantly, the mechanism is directly illuminated by revealing an unprecedented single-crystal to single-crystal structural transformation upon Cs⁺ uptake and elution processes. The superior Cs⁺ removal results from an unusual synergy from strong affinity of soft S^2- with Cs⁺, easily exchangeable [MeNH₃]⁺ cations, and the flexible and robust framework of FJSM-SbS with open windows as trappers.

Cesium removal using acid- and base-activated biotite and illite

Biotite and illite have excellent cesium (Cs) adsorption capacity due to their negative charges in addition to adsorption sites of the planar, interlayer, and frayed edge sites (FES). The aim of this study is to investigate the Cs adsorption capacity using acid- and base-activated biotite and illite based on their mineralogical characteristics. The acid-activated biotite and base-activated illite exhibited high Cs removal efficiency from the low-level Cs-containing DI water (97.5 % and 97.3 %, respectively). The acid-activation of biotite increased the specific surface area (SSA, 12.08 → 43.04 m²/g), Fe(III)/Fe(II) ratio (0.56 → 0.76), and wedge zone d-spacing (1.017 → 1.065 nm), while the zeta potential (-4.06 → -4.82 mV) decreased. The base-activation of illite resulted to a decrease in the SSA (22.14 → 18.49 m²/g), zeta potential (-7.68 → -31.64 mV), and Fe(III)/Fe(II) ratio (0.92 → 0.79). However, only acid-activated biotite appeared to have a high capacity of Cs removal from Cs-containing seawater (73.9 %; base-activated illite: 26.1 %). These results indicate that the FES of biotite owing to acid-activation showed better results in regards to Cs adsorption as compared to the pH-dependent negative charges of the base-activated illite.

Towards new cesium containing manganese vanadates via a precursor method

The first two 3D cesium containing manganese vanadates were synthesized by using K2Mn(VO3)4 as the precursory reactant in concentrated Cs+ aqueous solutions.

Time-resolved in situ visualization of the structural response of zeolites during catalysis

Zeolites are three-dimensional aluminosilicates having unique properties from the size and connectivity of their sub-nanometer pores, the Si/Al ratio of the anionic framework, and the charge-balancing cations. The inhomogeneous distribution of the cations affects their catalytic performances because it influences the intra-crystalline diffusion rates of the reactants and products. However, the structural deformation regarding inhomogeneous active regions during the catalysis is not yet observed by conventional analytical tools. Here we employ in situ X-ray free electron laser-based time-resolved coherent X-ray diffraction imaging to investigate the internal deformations originating from the inhomogeneous Cu ion distributions in Cu-exchanged ZSM-5 zeolite crystals during the deoxygenation of nitrogen oxides with propene. We show that the interactions between the reactants and the active sites lead to an unusual strain distribution, confirmed by density functional theory simulations. These observations provide insights into the role of structural inhomogeneity in zeolites during catalysis and will assist the future design of zeolites for their applications.

Study of structural inhomogeneities in zeolites is important but limited by conventional techniques. Here the authors employ in situ free-electron-laser-based time-resolved coherent X-ray diffraction imaging to visualize the effect of these inhomogeneities during catalytic deoxygenation of NOx.

Macrocyclic Pyridone Pentamers for Highly Selective High-Capacity Removal of Caesium Ions from Radioactive High-Salinity Waste

We report here that macrocyclic H-bonded pyridone pentamers, containing five properly and convergently spaced electron-rich O-atoms that decorate a rigid cavity of 2.85 Å across, exhibit an extraordinarily high yet pH-independent capacity and selectivity in Cs⁺ removal. In particular, with [host]=240 μM and [Cs⁺ ]=15 μM, a single extraction efficiently removes more than 91% of Cs⁺ ions from artificial sea water, containing various competitive metal ions at a total concentration of 0.68 M ([total Mⁿ⁺ ]/[Cs⁺ ]=4.5×10⁴ ]). To our best knowledge, these pyridone pentamers represent the best small organic molecule-based extractants that target Cs⁺ ions.

Bio-Inspired Preparation of Clay-Hexacyanoferrate Composite Hydrogels as Super Adsorbents for Cs. ACS APPLIED MATERIALS & INTERFACES 2020;12:33173-33185. [PMID: 32531151 DOI: 10.1021/acsami.0c06598]

A facile and low-cost fabrication route, inspired by the adhesive proteins secreted by mussels, has been developed to prepare a clay-based composite hydrogel (DHG(Cu)) containing hexacyanoferrate (HCF) nanoparticles for the selective removal of Cs⁺ from contaminated water. Initially, montmorillonite was exfoliated prior to coating with a thin layer of polydopamine (PDOPA) via the self-polymerization of dopamine. Mixing the composite (D-clay) with the HCF precursor, followed by the addition of copper ions, led to the self-assembly of the polymer-coated exfoliated clay nanosheets into a three-dimensional network and in situ growth of KCuHCF nanoparticles embedded within the gel structure. Analytical characterization verified the fabrication route and KCuHCF immobilization by a copper-ligand complexation. Rheology testing revealed the composite hydrogel to be elastic under low strain and exhibited reversible, self-healing behavior following high strain deformation, providing a good retention of KCuHCF nanoparticles in the membrane. The adsorbent DHG(Cu) showed a superior Cs⁺ adsorption capacity (∼173 mg/g), with the performance maintained over a wide pH range, and an excellent selectivity for Cs⁺ when dispersed in seawater at low concentrations of 0.2 ppm. On the basis of its excellent mechanico-chemical properties, the fabricated hydrogel was tested as a membrane in column filtration, showing excellent removal of Cs⁺ from Milli-Q water and seawater, with the performance only limited by the fluid residence time. For comparison, the study also considered other composite hydrogels, which were fabricated as intermediates of DHG(Cu) or fabricated with Fe³⁺ as the cross-linker and reactant for HCF nanoparticle synthesis.

Effective removal of cesium from wastewater via adsorptive filtration with potassium copper hexacyanoferrate-immobilized and polyethyleneimine-grafted graphene oxide

As an attractive alternative to radioactive cesium removal, we introduced an adsorptive filtration method using a composite membrane consisting of potassium copper hexacyanoferrate (KCuHCF) and graphene-based support. Polyethyleneimine-grafted reduced graphene oxide (PEI-rGO), used as an immobilizing matrix, was effective not only in distributing KCuHCF inside the composite with the aid of abundant amino-functionality, but also in achieving high water flux by increasing the interlayer spacing of the laminar membrane structure. Due to the rapid and selective cesium adsorption properties of KCuHCF, the fabricated membrane was found to be effective in achieving complete removal of cesium ions under a high flux (over 500 L m^-2 h^-1), which is difficult in a conventional membrane utilizing the molecular sieving effect. This approach offers strong potential in the field of elimination of radionuclides that require rapid and complete decontamination.

Anisotropic proton conduction realized by a layered vanadium selenite single crystal

A new layered vanadium selenite single crystal exhibits anisotropic proton conductivities along the [100] and [001] directions with the Grotthuss and Vehicle mechanisms, respectively.

Composite hydrogel particles encapsulated ammonium molybdophosphate for efficiently cesium selective removal and enrichment from wastewater

A novel ammonium molybdophosphate (AMP)/ polyvinyl alcohol (PVA)/ sodium alginate (SA) composite hydrogel (APS) was prepared for Cs⁺ removal and enrichment from radioactive wastewater. Batch experiments with the subject of AMP concentration, pH value, initial Cs⁺ concentration, contact time, temperature, competing ions were investigated. The results showed this APS hydrogel with high permeability and stability could effectively adsorb Cs⁺ at widely broad pH value range and low Cs⁺ concentration within a short time. Adsorption thermodynamic parameters indicated the endothermic and spontaneous nature of the adsorption process, and the Lagergren pseudo-second order model was found to exhibit the best correlation with the adsorption results. Equilibrium data was better described by the Langmuir isotherm equation, and the maximum adsorption capacity of APS hydrogel calculated was in consistent with the experimental results. Furthermore, the APS hydrogel could be easily reused at least five times without obvious decrease in absorption activity and selectivity using ammonia nitrate as the eluent, and what's more, the Cs⁺ concentration in eluent was approximately concentrated for 2 times after single cycle. All the results suggest that the environmental friendly and low-cost APS hydrogel could be used as effective and selective material for Cs⁺ removal and enrichment from wastewater.

Photocatalytic enhancement of cesium removal by Prussian blue-deposited TiO2

After the Fukushima nuclear accident, tremendous efforts were made to treat radiocesium, radiostrontium, and other radioactive materials. For the first time, we demonstrate that a TiO₂ photocatalyst can significantly enhance Cs adsorption by Prussian blue-deposited TiO₂ (PB/TiO₂) under UV irradiation. In this study, we synthesized PB/TiO₂ using the photodeposition method. After the Cs ions were adsorbed on the PB/TiO₂ in darkness, we then exposed the PB/TiO₂ to UV light irradiation. This resulted in a further increase in Cs ion adsorption of more than 10 times the amount adsorbed in darkness. This photocatalytic-enhanced adsorption of Cs ions was not observed on PB mixed with SiO₂, nor under visible light irradiation. We investigated the effects of PB concentration, PB/TiO₂ concentration, and gas purging on both dark and photocatalytic-enhanced adsorption of Cs ions by PB/TiO₂. Based on the results, we suggest that the photocatalytic-enhanced adsorption of Cs ions on PB/TiO₂ is due to photocatalytic reduction of PB, which leads to additional adsorption of Cs ions. The change in solution color before and after the reaction, and the change in solution pH in the dark and during UV irradiation strongly support this suggestion. The photocatalytic-enhanced adsorption of Cs ions was equivalent during radioactive ¹³⁷Cs removal, indicating important applications for pollutant removal from contaminated water.

Highly effective Cs+ removal by turbidity-free potassium copper hexacyanoferrate-immobilized magnetic hydrogels

Potassium copper hexacyanoferrate-immobilized magnetic hydrogel (MHPVA) has been synthesized via a facile freeze/thaw crosslinking method. The citric acid coated Fe₃O₄ is embedded into the hydrogel matrix to facilitate the dispersion of nano-sized KCuHCF particles for Cs⁺ removal, followed by the rapid recovery of the composite in a magnetic field. The Cs⁺ adsorption behavior of the MHPVA is fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The MHPVA exhibits both high Cs⁺ adsorption capacity (82.8mg/g) and distribution coefficient (K_d) of 1.18×10⁶mL/g (8.3ppm Cs⁺, V/m=1000mL/g). Sorption of above 90% Cs⁺ to the MHPVA is achieved in less than 3h of contact time. Moreover, the MHPVA reveals stable and high Cs⁺ removal efficiency across a wide pH range from 4 to 10. In terms of Cs⁺ selectivity, the MHPVA shows above 96% removal efficiency in the presence of 0.01M competing cations such as Mg²⁺, Ca²⁺, Na⁺, and K⁺ with 1ppm of Cs⁺. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.

Design of Chitosan-Grafted Carbon Nanotubes: Evaluation of How the -OH Functional Group Affects Cs+ Adsorption

In order to explore the effect of –OH functional groups in Cs⁺ adsorption, we herein used the low temperature plasma-induced grafting method to graft chitosan onto carbon nanotubes (denoted as CTS-g-CNTs), as raw-CNTs have few functional groups and chitosan has a large number of –OH functional groups. The synthesized CTS-g-CNT composites were characterized using different techniques. The effect of –OH functional groups in the Cs⁺ adsorption process was evaluated by comparison of the adsorption properties of raw-CNTs with and without grafting chitosan. The variation of environmental conditions such as pH and contact time was investigated. A comparison of contaminated seawater and simulated groundwater was also evaluated. The results indicated that: (1) the adsorption of Cs⁺ ions was strongly dependent on pH and the competitive cations; (2) for CNT-based material, the –OH functional groups have a positive effect on Cs⁺ removal; (3) simulated contaminated groundwater can be used to model contaminated seawater to evaluate the adsorption property of CNTs-based material. These results showed direct observational evidence on the effect of –OH functional groups for Cs⁺ adsorption. Our findings are important in providing future directions to design and to choose effective material to remedy the removal of radioactive cesium from contaminated groundwater and seawater, crucial for public health and the human social environment.

Selective chemical binding enhances cesium tolerance in plants through inhibition of cesium uptake

High concentrations of cesium (Cs⁺) inhibit plant growth but the detailed mechanisms of Cs⁺ uptake, transport and response in plants are not well known. In order to identify small molecules with a capacity to enhance plant tolerance to Cs⁺, chemical library screening was performed using Arabidopsis. Of 10,000 chemicals tested, five compounds were confirmed as Cs⁺ tolerance enhancers. Further investigation and quantum mechanical modelling revealed that one of these compounds reduced Cs⁺ concentrations in plants and that the imidazole moiety of this compound bound specifically to Cs⁺. Analysis of the analogous compounds indicated that the structure of the identified compound is important for the effect to be conferred. Taken together, Cs⁺ tolerance enhancer isolated here renders plants tolerant to Cs⁺ by inhibiting Cs⁺ entry into roots via specific binding to the ion thus, for instance, providing a basis for phytostabilisation of radiocesium-contaminated farmland.

Nanolayered tin phosphate: a remarkably selective Cs ion sieve for acidic waste solutions

Nanolayered tin phosphate is highly selective for Cs ions from acidic waste solutions.