Eco-friendly one-pot synthesis of Prussian blue-embedded magnetic hydrogel beads for the removal of cesium from water

A simple one-step approach to fabricating Prussian blue-embedded magnetic hydrogel beads (PB-MHBs) was fabricated for the effective magnetic removal of radioactive cesium (¹³⁷Cs) from water. Through the simple dropwise addition of a mixed aqueous solution of iron salts, commercial PB and polyvinyl alcohol (PVA) to an ammonium hydroxide (NH₄OH) solution, the formation of hydrogel beads and the encapsulation of PB in beads were achieved in one pot through the gelation of PVA with in situ-formed iron oxide nanoparticles as the cross-linker. The obtained PB-MHBs, with 43.77 weight % of PB, were stable without releasing PB for up to 2 weeks and could be effectively separated from aqueous solutions by an external magnetic field, which is convenient for the large-scale treatment of Cs-contaminated water. Detailed Cs adsorption studies revealed that the adsorption isotherms and kinetics could be effectively described by the Langmuir isotherm model and the pseudo-second-order model, respectively. Most importantly, the PB-MHBs exhibited excellent selectivity for ¹³⁷Cs in ¹³⁷Cs-contaminated simulated groundwater (55 Bq/g) with a high removal efficiency (>99.5%), and the effective removal of ¹³⁷Cs from real seawater by these PB-MHBs demonstrated the excellent potential of this material for practical application in the decontamination of ¹³⁷Cs-contaminated seawater.

Versatile Poly(Diallyl Dimethyl Ammonium Chloride)-Layered Nanocomposites for Removal of Cesium in Water Purification

In this work, we elucidate polymer-layered hollow Prussian blue-coated magnetic nanocomposites as an adsorbent to remove radioactive cesium from environmentally contaminated water. To do this, Fe₃O₄ nanoparticles prepared using a coprecipitation method were thickly covered with a layer of cationic polymer to attach hollow Prussian blue through a self-assembly process. The as-synthesized adsorbent was confirmed through various analytical techniques. The adsorbent showed a high surface area (166.16 m²/g) with an excellent cesium adsorbent capacity and removal efficiency of 32.8 mg/g and 99.69%, respectively. Moreover, the superparamagnetism allows effective recovery of the adsorbent using an external magnetic field after the adsorption process. Therefore, the magnetic adsorbent with a high adsorption efficiency and convenient recovery is expected to be effectively used for rapid remediation of radioactive contamination.

Rapid removal of radioactive cesium by polyacrylonitrile nanofibers containing Prussian blue

After the Fukushima Daiichi Nuclear Power Plant disaster in Japan in 2011, the demand drastically increased for efficient technology for the removal of radioactive cesium. Prussian blue (PB) nanoparticles have shown excellent adsorption ability toward Cs. In this study, we synthesized PB nanoparticles incorporated polyacrylonitrile nanofiber (PB/PAN). PB/PAN has the porous structure of nanofibers, with diameters of several hundred nanometers. PB nanoparticles can be incorporated successfully into the PAN matrix without any change to their intrinsic crystallinity and structure. The mesoporous structure of PB/PAN and the incorporation of PB nanoparticles led to an increase in the Brunauer-Emmett-Teller surface area and pore volume. In addition, PB/PAN exhibited excellent wettability with water. With simple filtering for the removal of radioactive cesium, PB/PAN showed high removal efficiency (87 ± 3%) within 10 s for 10 mL of ¹³⁷Cs solution (1000 Bq L^-1). In addition, the ¹³⁷Cs removal by PB/PAN showed high removal efficiency (70 ± 2%, after 1 h), even in the actual seawater medium (1000 Bq L^-1 of ¹³⁷Cs). Therefore, PB-incorporated PAN nanofibers can be considered useful in the practical application of Cs removal from radioactive wastewater.

In-column immobilization of Cs-saturated crystalline silicotitanates using phenolic resins

The in situ immobilization of granulated Cs-saturated crystalline silicotitanates (Cs-CST) in fixed-bed columns has been investigated using commercially available phenol formaldehyde (PF) resin as a binding agent. Two types of PF resin were investigated as part of this study both being prepared from resol polymer having a formaldehyde:phenol ratio of 3:1. However, one of the resol polymers had water as the primary solvent and the other ethanol. Both resol polymers were observed to completely infiltrate the space between the Cs-CST beads and also the pores within the beads themselves. PF resin monoliths prepared after curing the water-based resol at 180 °C were considerably less porous than the ethanol-based counterparts cured under the same conditions. The enhanced macroporosity of the resin prepared from the ethanol-based resol was presumably the result from enhanced gas bubble generation. Little or no micro- or mesoporosity was measured using nitrogen porosimetry. For both resins cured at 180 °C, intimate contacts with the Cs-CST beads were observed that were not modified even after complete immersion in water over long time frames. Little or no migration of Cs from Cs-CST to the resin binder was observed. The compressive strength of the Cs-CST-PF resin monoliths was measured and benchmarked against cement monoliths and was found to be two to three times higher than cement in the case of the water-based resin. Leaching of the monoliths was conducted in demineralized water at 90 °C. Normalized Cs mass losses of the order of 1.0 g/m² were measured after 30 days for the ethanol-based resin monoliths. For the less porous water-based monoliths, the normalized mass loss was one order of magnitude lower. The leaching of monoliths irradiated with a 2-MGy dose of γ radiation showed no difference in Cs mass loss suggesting that the ability to retain Cs of either the CST or PF resin was not affected. PF resins are capable of acting as a mechanically robust, radiation-resistant, and impermeable active secondary barrier reducing the likelihood of Cs entry into the biosphere.

Effects of the variation of metal substitution and electrolyte on the electrochemical reaction of metal hexacyanoferrates

Metal hexacyanoferrates (MHCFs), also called Prussian blue analogs, are known as electrochemical electrodes and are ion-adsorbent. To investigate the effect of the ionic radius of the adsorbate (cations adsorbed upon reduction) and the pore size of the adsorbent (porous electrode that stores cations upon reduction), we investigated the electrochemical reactions with various alkali cations and by changing the metal sites of the MHCFs. First, we succeeded in controlling the pore sizes of the MHCFs, where the lattice constant a could be estimated as a = 0.98D_sum + 7.21, where D_sum represented the sum of the ionic diameters of the metal M and Fe. Concerning the electrochemical reaction, the redox potential increased when the hydration energy of the adsorbate decreased, implying that the hydration energy of the adsorbate affected the stability of the reduced state. With cadmium hexacyanoferrate, which has a large pore size, the variation of the redox potential was suppressed in comparison to that with copper hexacyanoferrate, which has a small pore size. With Fourier transform-infrared (FT-IR) analysis before and after the redox reactions, Na⁺ insertion accompanied by H₂O was presumed in the reduced state.

The redox potential of metal hexacyanoferrates (MHCFs), also called Prussian blue analogs, is qualitatively understood with the hydration energy of the cations in the supporting electrolyte.

Sodium-copper hexacyanoferrate-functionalized magnetic nanoclusters for the highly efficient magnetic removal of radioactive caesium from seawater

Sodium-copper hexacyanoferrate (NaCuHCF)-functionalized magnetic nanoadsorbents were fabricated for the highly efficient magnetic removal of radioactive caesium from seawater. The magnetic nanoclusters (MNCs), composed of many individual Fe₃O₄ nanoparticles, were covalently coated with polyethyleneimine (PEI) to functionalize the MNC surfaces with NaCuHCF. After simple immobilization of Cu and Na ferrocyanide on the NC surface, the resulting NaCuHCF-functionalized MNCs showed good magnetic properties and a significant adsorption capacity for Cs⁺ with a high content of NaCuHCF (36.04%). The adsorption kinetics and isotherms were well fit to a pseudo-second-order model and Langmuir isotherm, respectively. The sorption of 97.35% Cs by the NaCuHCF-PEI-MNCs completed in less than 5 min, and the maximum adsorption capacity of the adsorbent was 166.67 mg/g. The NaCuHCF-PEI-MNCs selectively adsorbed Cs even in the presence of various competing ions, such as Na, K, Mg, and Ca, and the Cs removal mechanism was revealed as ion exchange between Cs in solution and Na in the NaCuHCF-PEI-MNCs. In radioactive tests, our adsorbent displayed excellent removal performance in real seawater with a high removal efficiency exceeding 99.73%, a decontamination factor exceeding 372, and a high stability in water over a wide pH range from 4 to 10 with negligible leaching of Fe.

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.

In situ synthesis of Prussian blue nanoparticles within a biocompatible reverse micellar system for in vivo Cs+uptake

A Prussian blue reverse micellar system forin vivoCs⁺uptake exhibiting high efficiency and a significant dose effect.

Copper hexacyanoferrate functionalized single-walled carbon nanotubes for selective cesium extraction

Single-walled carbon nanotubes (SWCNTs) are functionalized with copper hexacyanoferrate (CuHCF) nanoparticles to prepare solid substrates for sorption of cesium ions (Cs⁺) from liquid outflows.

Magnetic graphene oxide based nano-composites for removal of radionuclides and metals from contaminated solutions

Magnetic graphene oxide based composites of the nano-particle size of <10 nm were synthesized, characterized and used in sorption experiments. The adsorption of Cs(I), Co(II), Ni(II), Cu(II) and Pb(II) to nano-composites was studied in a wide range of initial concentrations and analyzed by Langmuir and Freundlich models. In addition, the effects of pH and coexisting ions on the adsorption of Cs to Prussian blue based composites were investigated. The maximum adsorption capacities of studied elements varied from 29 to 641 mg g^-1. The obtained Langmuir and Freundlich constants indicated the dominating physisorption mechanism and favorable adsorption conditions.

Highly effective K-Merlinoite adsorbent for removal of Cs+ and Sr2+ in aqueous solution

Cs⁺ and Sr²⁺ removal using K-MER adsorbent.

Tuning the Nanostructure of Highly Functionalized Silica Using Amphiphilic Organosilanes: Curvature Agent Effects

The self-assembly of amino-undecyl-triethoxysilane (AUT) as micelles in water is considered. The behavior of acid/AUT systems is governed by a complete proton transfer from the acid to the amine, leading to the formation of an ammonium headgroup. This moiety is responsible for the bending of the interface between the organic core of the micelles and the surrounding water. By playing with the size of the acid used as curvature agent, the amphiphilic behavior of the organosilane molecule may be adjusted. We follow the aggregation as the curvature agent size increases. This approach constitutes an efficient and original method in order to tune the nanostructure of highly functionalized silica at the early stage of the elaboration. Small-angle X-ray scattering, wet scanning transmission electron microscopy, dynamic light scattering, and complementary characterization techniques indicate that hybrid organic-inorganic planar objects and vesicles are obtained for smaller curvature agents. Increasing the size of the curvature agent results in a transition of the aggregation geometry from vesicles to cylindrical direct micelles, finally leading to nanofibers organized in a 2D hexagonal network resembling a "reverse MCM-41 structure". A geometrical molecular self-assembly model is finally proposed, considering the dimensions of the surfactant tail and those of the head groups.

The highly effective removal of Cs⁺ by low turbidity chitosan-grafted magnetic bentonite

Chitosan-grafted magnetic bentonite (CS-g-MB) was successfully synthesized via a plasma-induced method. The CS-g-MB composite shows good magnetic properties, low turbidity, and high stability in aqueous solution and exhibits significant adsorption capacity for Cs(+) ions. The adsorption of Cs(+) by CS-g-MB is dependent on both pH and ionic strength. In the presence of Mg(2+), K(+), Li(+), and Na(+) ions, the Cs(+) exchange is constrained in the order of Li(+)≈Mg(2+)<Na(+)<K(+), primarily as a result of the hydrated radii and hydration energies of these cations in aqueous solution. The stability of the CS-g-MB composite in simulated groundwater and in actual seawater was also investigated and this material was found to be a good candidate for the remediation of both types of water. These results demonstrate that enhanced coagulation achieved by plasma modification represents a viable yet advanced technology for wastewater management, and is capable of synthesizing new adsorbents that can be readily separated from solution and that avoid increasing the turbidity and color of the water being treated.

Switchable self-assembly of Prussian blue analogs nano-tiles triggered by salt stimulus

We showed fully reversible, ionic strength controlled self-assembly of Prussian blue analogues nano-tiles into large superlattice structures.

Reinforced silica monoliths functionalised with metal hexacyanoferrates for cesium decontamination: a combination of a one-pot procedure and skeleton calcination

Procedure describes the synthesis of silica monoliths functionalised with metal hexacyanoferrate (MHCF) using a high internal phase emulsion template. The materials exhibit excellent Cs ion sorption properties.

Improved adsorption properties of granulated copper hexacyanoferrate with multi-scale porous networks

Designed porous copper hexacyanoferrate micro-capsule beads (CuHCF-MCB) were prepared using freeze-drying (FD).

Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents--A Mini-Review

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.

Enhancing the adsorption capacity of Sr2+ and Cs+ onto hexagonal tungsten oxide by doped niobium

The adsorption capacity of Sr²⁺ and Cs⁺ onto hexagonal tungsten oxide was enhanced by the incorporation of Nb.

Mesoscopic structures of vermiculite and weathered biotite clays in suspension with and without cesium ions

The effect of cesium (Cs) adsorption on the mesoscopic structure of the clay minerals vermiculite and weathered biotite (WB) in suspensions was elucidated by small-angle X-ray scattering (SAXS). The clay minerals form multilayered structures, and the Cs cations (Cs(+)) are strongly adsorbed in the interlayer space of the soil clays, in particular vermiculite and WB. SAXS was used to monitor the relationship between Cs(+) adsorption at the clay interlayers and the structural changes at length scales from 1 to 1000 Å. The variation in the distance between the neighboring clay sheets and the spatial arrangement of the clay sheets with and without Cs(+) were clarified. Our quantitative analyses revealed that the number of stacked layers of pure vermiculite was decreased by Cs(+) addition, whereas that of WB increased. Moreover, the average distance between the neighboring layers of vermiculite in suspension was larger than that of WB, which reflects the different conditions of Cs(+) intercalation. These findings provide fundamental insights that are important for predicting the environmental fate of radioactive Cs in contaminated regions and for developing methods for extracting Cs from soil.

Adsorption of 137Cs on titanate nanostructures

Various types of sodium and potassium titanate nanostructures (nanotubes, nanofibers, nanoribbons, nanwires) were synthesized and characterized by X-ray diffraction, SEM and TEM, as well BET and BJH methods. Adsorption of radiotracer ¹³⁷Cs⁺ ions from aqueous solutions on synthesized titanate nanostructures was investigated in batch technique as a function of contact time, concentration of sodium ions and pH of the solutions. It was found that among the studied nanostructures nanotubes shows the highest selectivity for ¹³⁷Cs, which is related to a zeolitic character of Cs⁺ adsorption. The efficient adsorption of ¹³⁷Cs was obtained in Na⁺ solutions with concentration below 10^-2 M, at pH 7-9 and in contact time above 2 h. Moreover, nanotubes have the higher specific surface area than other nanostructures, which results in better availability of ion exchange groups and high ion exchange capacity. These properties of nanotubes indicate that they may be used for adsorption of ¹³⁷Cs from various types of nuclear wastes.

Characteristics of cesium ion sorption from aqueous solution on bentonite- and carbon nanotube-based composites

The technology development of Cs(+) capture from aqueous solution is crucial for the disposal of nuclear waste and still remains a significant challenge. Previous researches have been proven that ion exchanges with the cations and hydroxyl exchange are the main sorption mechanisms for Cs(+). Therefore, how important are the cation exchange and the hydroxyl exchange mechanisms to Cs(+) sorption? And whether can we improve the sorption capacity of the material by increasing the amount of hydroxyl groups? With these in mind, we herein designed the chitosan-grafted carbon nanotubes (CS-g-CNTs) and the chitosan-grafted bentonite (CS-g-bentonite) by plasma-induced grafting method. The interactions of Cs(+) with CNTs, bentonite, CS-g-CNTs and CS-g-bentonite composites were investigated. The sorption of Cs(+) is mainly dominated by strong cation exchange in monovalent Group I and divalent Group II. And the cation-exchange mechanism is much more effective than the hydroxyl group exchange. The effect of hydroxyl groups is dependent on the property of the matrix. We cannot improve the Cs adsorption capacity of material for Cs(+) only by increasing the amount of hydroxyl groups in any case. The spatial structure and the cation-exchange capacity of the material are important factors for choosing the sorbent for Cs(+) removal from radioactive waste water.

Adsorption removal of cesium from drinking waters: a mini review on use of biosorbents and other adsorbents

Radiocesium (Cs) removal from waters becomes an emerging issue after the Fukushima Daiichi Nuclear Power Plant Disaster, during which a total of approximately 3.3×10(16) Bq Cs was released to contaminate the environment. This mini-review provided a summary on literature works to develop efficient adsorbent for removing Cs from waters. Adsorbent made of raw and modified minerals, composites particles, and biosorbents that are highly specific to Cs in the presence of other alkali and alkali earth metals were summarized. Development of Prussian blue (PB) nanoparticles on Cs removal and its potential use in drinking waterworks was discussed. This review is a unique report for adsorption removal of Cs from contaminated waters.

Selective removal of cesium from aqueous solutions with nickel (II) hexacyanoferrate (III) functionalized agricultural residue-walnut shell

A novel nickel (II) hexacyanoferrate (III) functionalized agricultural residue-walnut shell (Ni(II)HCF(III)-WS) was developed to selectively remove cesium ion (Cs(+)) from aqueous solutions. This paper showed the first integral study on Cs(+) removal behavior and waste reduction analysis by using biomass adsorption material. The results indicated that the removal process was rapid and reached saturation within 2h. As a special characteristic of Ni(II)HCF(III)-WS, acidic condition was preferred for Cs(+) removal, which was useful for extending the application scope of the prepared biomass material in treating acidic radioactive liquid waste. The newly developed Ni(II)HCF(III)-WS could selectively remove Cs(+) though the coexisting ions (Na(+) and K(+) in this study) exhibited negative effects. In addition, approximately 99.8% (in volume) of the liquid waste was reduced by using Ni(II)HCF(III)-WS and furthermore 91.9% (in volume) of the spent biomass material (Cs-Ni(II)HCF(III)-WS) was reduced after incineration (at 500°C for 2h). Due to its relatively high distribution coefficient and significant volume reduction, Ni(II)HCF(III)-WS is expected to be a promising material for Cs(+) removal in practice.

Highly efficient removal of 137Cs in seawater by potassium titanium ferrocyanide functionalized magnetic microspheres with multilayer core–shell structure

Transition metal ferrocyanides were deposited on silica encapsulated magnetite particles for the effective decontamination of radiocesium.

Thallium(I) sorption using Prussian blue immobilized in alginate capsules

Prussian blue (PB) was immobilized in alginate capsules. The composite sorbent was used for the recovery of Tl(I) ions from slightly acidic solutions: optimum pH being close to 4. The sorption isotherm can be described by the bi-site Langmuir sorption isotherm. This means that the metal ion can be bound through two different sorption sites: one having a strong affinity for Tl(I) (probably PB), the other having a lower affinity (probably the encapsulating material). The kinetics are described by either the pseudo-second order rate equation or the Crank's equation (resistance to intraparticle diffusion). The ionic strength (increased by addition of NaCl, KCl or CaCl₂) slightly decreased sorption capacity. The SEM-EDX analysis of PB-alginate capsules (before and after Tl(I) sorption) shows that the PB is homogeneously distributed in the capsules and that all reactive groups remain available for metal binding.

Self-assembly of condensable "bola-amphiphiles" in water/tetraethoxysilane mixtures for the elaboration of mesostructured hybrid materials

The self-assembly of condensable amphiphile molecules in water is an attractive approach for the synthesis of mesostructured hybrid materials. In this article, we focus on aminoundecyltriethoxysilane (AUT), a condensable "bola-amphiphile", i.e., an amphiphilic molecule possessing two polar heads on both sides of an aliphatic chain. In the present case, one side is a condensable triethoxysilane, and the other side is an amino group. We report on the self-assembly of AUT in mixtures of water and tetraethoxysilane (TEOS). In situ small-angle X-ray scattering (SAXS) measurements allowed us to follow the evolution of the structure from the liquid state up to the solid material formed upon catalytic polycondensation. Depending on the medium composition, hexagonal or lamellar structures can be observed in the final material. These observations allowed us to propose a model for the self-assembly of AUT in water/TEOS mixtures that we were able to validate by simulations of the SAXS profiles. By taking advantage of the modularity of such a system, it proves possible to prepare in a simple way various structured hybrid materials possessing a high number of available organic functions without using sacrificial surfactant molecules.