The latest research trends in the removal of cesium from radioactive wastewater: A review based on data-driven and visual analysis

The widespread adoption of nuclear energy has increased the amount of radioactive cesium (Cs) that is discharged into waste streams, which can have environmental risks. In this paper, we provide a comprehensive summary of current advances in aqueous Cs removal by employing a bibliometric analysis. We collected 1580 articles related to aqueous Cs treatment that were published on the Web of Science database between 2012 and 2022. By applying bibliometric analysis combined with network analysis, we revealed the research distribution, knowledge base, research hotspots, and cutting-edge technologies in the field of aqueous Cs removal. Our findings indicate that China, Japan, and South Korea are the most productive countries with respect to Cs removal research. In addition, both historic events and environmental threats might have contributed to research in Asian countries having a higher focus on Cs removal as well as strong international cooperation between Asian countries. A detailed keyword analysis reveals the main knowledge base for aqueous Cs removal and highlights the potential of the adsorption-based method for treating Cs contamination. Furthermore, the results reveal that exploration of functional materials is a popular research topic in the field of Cs removal. Since 2012, novel materials, including Prussian blue, graphene oxide, hydrogel and nanocomposites, have been widely investigated because of their high capacity for Cs removal. On the basis of the detailed information, we report the latest research trends on aqueous Cs removal, and propose future research directions and describe the challenges related to effective Cs treatment. This scientometric review provides insights into current research hotspots and cutting-edge trends in addition to contributing to the development of this crucial research field.

Tannic acid-assisted in-situ interfacial formation of Prussian blue-assembled adsorptive membranes for radioactive cesium removal

There is a growing interest in advanced materials that can effectively treat wastewater contaminated with radioactive cesium (¹³⁷Cs), which is an extremely hazardous material. Here, we report a new class of Cs-adsorptive membranes compactly assembled with Cs-adsorptive Prussian blue (PB) particles. The PB particle assembly was formed via an in-situ interfacial reaction between two PB precursors in the presence of tannic acid (TA) as a binder on a porous support. While the interfacial reaction enabled the formation of a defect-less PB network, TA enhanced the PB-PB and PB-support compatibilities, consequently producing a uniform, densely packed PB assembly near the support surface. The fabricated TA-assisted PB membrane (PB/TA-M) synergistically rejected Cs via a combination of adsorption and membrane filtration, although adsorption predominantly determined Cs rejection initially. Hence, the PB/TA-M membrane showed considerably higher Cs removal performance than commercial nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes for a sufficiently long operation time. Furthermore, the PB/TA-M membrane displayed excellent radioactive ¹³⁷Cs removal performance, significantly exceeding those of commercial NF and RO PA membranes due to its higher radiation stability, indicating its viability for application in treating actual radioactive wastewater.

A Hydrofluoric Acid-Free Green Synthesis of Magnetic M.Ti2CTx Nanostructures for the Sequestration of Cesium and Strontium Radionuclide

MAX phases are the parent materials used for the formation of MXenes, and are generally obtained by etching using the highly corrosive acid HF. To develop a more environmentally friendly approach for the synthesis of MXenes, in this work, titanium aluminum carbide MAX phase (Ti₂AlC) was fabricated and etched using NaOH. Further, magnetic properties were induced during the etching process in a single-step etching process that led to the formation of a magnetic composite. By carefully controlling etching conditions such as etching agent concentration and time, different structures could be produced (denoted as M.Ti₂CT_x). Magnetic nanostructures with unique physico-chemical characteristics, including a large number of binding sites, were utilized to adsorb radionuclide Sr²⁺ and Cs⁺ cations from different matrices, including deionized, tap, and seawater. The produced adsorbents were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The synthesized materials were found to be very stable in the aqueous phase, compared with corrosive acid-etched MXenes, acquiring a distinctive structure with oxygen-containing functional moieties. Sr²⁺ and Cs⁺ removal efficiencies of M.Ti₂CT_x were assessed via conventional batch adsorption experiments. M.Ti₂CT_x-A_III showed the highest adsorption performance among other M.Ti₂CT_x phases, with maximum adsorption capacities of 376.05 and 142.88 mg/g for Sr²⁺ and Cs⁺, respectively, which are among the highest adsorption capacities reported for comparable adsorbents such as graphene oxide and MXenes. Moreover, in seawater, the removal efficiencies for Sr²⁺ and Cs⁺ were greater than 93% and 31%, respectively. Analysis of the removal mechanism validates the electrostatic interactions between M.Ti₂C-A_III and radionuclides.

Selective and effective adsorption of cesium ions by metal hexacyanoferrates (MHCF, M = Cu, Co, Ni) modified chitosan fibrous biosorbent

Selective and effective adsorptive removal of radiocesium is of great importance in terms of nuclear waste management and environmental remediation, but is still challenging because of its radioactive and non-complexing nature. Herein, metal hexacyanoferrates (MHCF, M = Cu, Co, or Ni) modified fibrous chitosan was prepared by multiple sequential adsorption and self-assembly approach, and applied for the selective and effective adsorption of Cs⁺. The physically supported MHCF in chitosan fibers showed good crystallinity and stability, and the obtained fibrous composite has high specific surface area (18.2-29.4 m² g^-1). Moreover, MHCF crystals endowed the fibrous chitosan-based adsorbent with a high adsorption capacity and selectivity towards Cs⁺. Its adsorption kinetic and isotherm performance followed the pseudo second-order model and the Sips model. The q_m value of three fibrous MHCF/chitosan (M = Cu, Co, or Ni) composites was 24.9-70.3 mg g^-1. The fibrous CuHCF/chitosan composite had the highest q_m among the three composites. In summary, the modified chitosan can selectively and effectively remove Cs⁺ from complicated aqueous solutions.

Cesium ion adsorption and desorption on electrospun mesoporous silica nanofibers immobilized with Prussian blue

To fabricate an efficient Cs ion adsorbent and prevent unexpected loss of Prussian blue (PB) colloidal particles during use, PB was immobilized on the surface of electrospun mesoporous silica nanofibers (MSFs) via a newly developed method of double exposure to Fe (III) ions. To introduce PB on MSFs, the MSFs were functionalized with ethylenediamine moiety to bind to Fe (III) ions, which would firmly anchor PB. MSFs were pretreated with Fe (III) ions and exposed to K₄ [Fe(II) (CN)₆] to form PB. We found that this process did not provide a sufficient PB amount on the MSFs. To increase the PB amount, after initial PB formation, the MSFs were treated with Fe (III) ions again so that the unreacted K₄ [Fe(II) (CN)₆] remaining on the MSFs could become PB. An investigation of the adsorption isotherms and kinetics of the nanofibrous adsorbent indicated that monolayer chemisorption had occurred. The maximum Cs ion adsorption capacity using the method of double exposure to Fe (III) ions was determined to be 14.66 mg/g, which was higher by a factor of 2.24 than the case that was not prepared by this method. Cs ions were selectively adsorbed over other cations and could be removed in both acidic and basic conditions, presumably because of the robust MSFs.

Sorption methods in marine radiochemistry

The review presents the general methodology of using sorption methods to solve problems of marine radiochemistry, including sampling, preconcentration and radiochemical preparation and methods for measuring the activity of radionuclides. The possible methodological errors at various stages of sampling and sample concentration are discussed. The most widely used artificial (90Sr, 134Cs, 137Cs, 239Pu, 240Pu), natural (210Pb, 210Po; radium quartet: 223Ra, 224Ra, 226Ra, 228Ra; thorium isotopes, mainly 234Th) and cosmogenic (7Be, 32P, 33P) radiotracers are considered. The sorption of uranium from seawater is not addressed, since its concentration in seawater is usually calculated from the known dependence of uranium concentration on seawater salinity.

The bibliography includes 200 references.

Sulfur-encapsulated zeolite micromotors for the selective removal of cesium from high-salt water with accelerated cleanup times

Bubble-propelled sulfur-encapsulated NaX zeolite (S-NaX) micromotors were developed for the selective removal of cesium from high-salt conditions with accelerated cleanup times. NaX was first modified with sulfur to provide additional Lewis acid-base interactions with Cs⁺ for enhanced Cs⁺ selectivity, and then Pt was half-deposited on S-NaX for bubble propulsion via the catalytic decomposition of H₂O₂. The average velocity of the resulting S-NaX/Pt micromotors in 5 wt% H₂O₂ is 39.7 ± 17.1 μm/s, which is higher than that of a previously reported Cs adsorbent micromotor (35.4 μm/s). The Cs⁺ ion-exchange kinetics of the S-NaX micromotor is 1.32 times higher than that of the NaX micromotor in a 5 wt% H₂O₂ solution where the molar ratio of Na⁺ to Cs⁺ is 200, even though the sulfur in the S-NaX micromotor causes an adverse effect on the propulsion speed due to the sulfur poisoning effect. Moreover, the S-NaX micromotor in simulated groundwater also exhibited excellent Cs⁺ removal performance with distribution coefficient (K_d) values at least 3.2 times higher than those of the nonpropelled S-NaX and NaX micromotor, demonstrating the great potential for the treatment of radioactive Cs⁺-contaminated water.

Photothermal therapies to improve immune checkpoint blockade for cancer

Immune checkpoint blockade (ICB) comprising monoclonal antibodies (mAbs) against immune 'checkpoints', such as CTLA-4 and the PD1/PDL1 axis have dramatically improved clinical outcomes for patients with cancer. However, ICB by itself has failed to provide benefit in a wide range of solid tumors, where recurrence still occurs with high incidence. These poor response rates may be due to the therapeutic shortcomings of ICB; namely, a lack of cancer-specific cytotoxicity and ability to debulk tumors. To overcome these limitations, effective ICB therapy may require the combination with other complementary therapeutic platforms. Here, we propose that photothermal therapy (PTT) is an ideal therapeutic modality for combination with ICB because it can generate both tumor-specific cytotoxicity and immunogenicity. PTT elicits these specific effects because it is a localized thermal ablation technique that utilizes light-responsive nanoparticles activated by a wavelength-matched laser. While ICB immunotherapy alone improves cancer immunogenicity but does not generate robust antitumor cytotoxicity, nanoparticle-based PTT elicits targeted and controlled cytotoxicity but sub-optimal long-term immunogenicity. Thus, the two platforms offer complementary and potentially synergistic antitumor effects, which will be detailed in this review. We highlight three classes of nanoparticles used as agents of PTT (i.e., metallic inorganic nanoparticles, carbon-based nanoparticles and organic dyes), and illustrate the potential for nanoparticle-based PTT to potentiate the effects of ICB in preclinical models. Through this discussion, we aim to present PTT combined with ICB as a potent synergistic combination treatment for diverse cancer types currently refractory to ICB as well as PTT monotherapies.

Heterometallic Actinide-Containing Photoresponsive Metal-Organic Frameworks: Dynamic and Static Tuning of Electronic Properties

Acquiring fundamental knowledge of properties of actinide-based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics-electronics correlation for actinide-containing metal-organic frameworks (An-MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide-based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An-MOFs. Furthermore, the first photochromic MOF-based field-effect transistor, in which the field-effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two-LED fail-safe indicator circuit.

Prussian Blue: A Safe Pigment with Zeolitic-Like Activity

Prussian blue (PB) and PB analogues (PBA) are coordination network materials that present important similarities with zeolites concretely with their ability of adsorbing cations. Depending on the conditions of preparation, which is cheap and easy, PB can be classified into soluble PB and insoluble PB. The zeolitic-like properties are mainly inherent to insoluble form. This form presents some defects in its cubic lattice resulting in an open structure. The vacancies make PB capable of taking up and trapping ions or molecules into the lattice. Important adsorption characteristics of PB are a high specific area (370 m2 g-1 determined according the BET theory), uniform pore diameter, and large pore width. PB has numerous applications in many scientific and technological fields. PB are assembled into nanoparticles that, due to their biosafety and biocompatibility, can be used for biomedical applications. PB and PBA have been shown to be excellent sorbents of radioactive cesium and radioactive and nonradioactive thallium. Other cations adsorbed by PB are K+, Na+, NH4+, and some divalent cations. PB can also capture gaseous molecules, hydrocarbons, and even luminescent molecules such as 2-aminoanthracene. As the main adsorptive application of PB is the selective removal of cations from the environment, it is important to easily separate the sorbent of the purified solution. To facilitate this, PB is encapsulated into a polymer or coats a support, sometimes magnetic particles. Finally, is remarkable to point out that PB can be recycled and the adsorbed material can be recovered.

Prediction and optimization of adsorption properties for Cs+on NiSiO@NiAlFe LDHs hollow spheres from aqueous solution: Kinetics, isotherms, and BBD model

In this work, novel NiSiO@NiAlFe layered double hydroxides (LDHs) hollow spheres were prepared by hydrothermal method. It was worth noting that LDHs' grafting towards NiSiO hollow spheres could avoid the LDHs' aggregation, and thus enhanced the material's adsorption capacity. Furthermore, adsorption kinetics, adsorption isotherms, and Box-Behnken Design (BBD) model were conducted. Results indicated that NiSiO@NiAlFe LDHs hollow spheres had sufficient adsorption capability towards Cs⁺. The adsorption kinetics satisfied the pseudo-second-order adsorption model, Temkin model and Langmuir isotherm model. The adsorption process was efficient at the alkaline condition (pH = 10). The adsorption kinetics indicated that the adsorption process could reach the equilibrium in only 20 min. The maximum adsorption capacity of Cs⁺ towards NiSiO@NiAlFe LDHs hollow spheres was estimated to be 61.5 mg g^-1. Moreover, the adsorption thermodynamics indicated that the adsorption process was exothermal, feasible and spontaneous. Thus, NiSiO@NiAlFe LDHs hollow spheres presented a broad potential for treating cesium containing wastewater.

Efficient cesium encapsulation from contaminated water by cellulosic biomass based activated wood charcoal

In this study, cost-effective cellulosic biomass based activated wood charcoal was developed from Japanese Sugi tree (Cryptomeria japonica) by concentrated nitric acid modification for adsorption of Cs from contaminated water. The physicochemical properties of specimens were investigated using N₂ adsorption-desorption isotherms (BET method), FESEM, FTIR, and XPS spectra analysis. The experimental results revealed that the surface area of the raw wood charcoal was significantly decreased after boiling nitric acid modification. However, several oxygen-containing acidic function groups (-COOH, -CO) were introduced on the surface. The adsorption study confirmed that the equilibrium contact time was 1 h, the optimum adsorption pH was neutral to alkaline and the suitable adsorbent dose was 1:100 (solid: liquid). The maximum Cs was removed when the concentration of Na and K were lower (5.0 mM) with Cs in solution. The Cs adsorption processes well approved by the Langmuir isotherm and pseudo-second-order kinetic models and the maximum adsorption capacity was 35.46 mgg^-1. The Cs adsorption mechanism was clearly described and it was assumed that the adsorption was strongly followed by chemisorptions mechanism based on the adsorbent surface properties, kinetic model and Langmuir isotherm model. Most importantly, about 98% of volume reduction was obtained by burning (500 °C) the Cs adsorbed charcoal, which ensured safe storage and disposal of radioactive waste. Therefore, this study can offer a guideline to produce a functional adsorbent for effective Cs removal and safe radioactive waste disposal.

Bioleaching and removal of radiocesium in anaerobic digestion of biomass crops: Effect of crop type on partitioning of cesium

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Anaerobic digestion (AD) of radiocesium (RCs)-contaminated crops was investigated.

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Anaerobic degradation of crops releases RCs into aqueous phase of digestate.

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RCs-solubilization efficiency rose with increase in degradability of feedstocks.

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Solid-liquid partition coefficient widely varied depending on the types of adsorbents.

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90 % of RCs removal was achieved at 30 g-zeolite/L or 1 g-Prussian blue beads/L.

Cultivation of biomass crops for energy production is a promising land-use for farmland abandoned owing to radionuclide fallout. However, radionuclides in soil are easily taken up in the crop. To understand phase partitioning of radiocesium Cs (RCs) during anaerobic digestion (AD) of crops, semi-continuous AD experiments were carried out using two types of RCs-contaminated crops. Analysis of fractionated digestate effluent revealed that AD of the crops released RCs into the water phase (up to 82 %), and the efficiency of RCs solubilization depended on crop biodegradability. Adsorption treatment for removal of RCs from the water phase of the digestate indicated a water–zeolite partition coefficient of 0.287 L/g. The efficiency of removal from the water phase was 90 % at an adsorbent dose of 30 g/L.

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.

Electroactive magnetic microparticles for the selective elimination of cesium ions in the wastewater

To improve operability as well as the removal efficiency for cesium ions in the wastewater treatment, a novel electrochemically switched ion exchange (ESIX) technique by using electroactive Prussian-blue(PB)-based magnetic microparticles (PB@Fe₃O₄ microparticle) with different uniform particle sizes in the range of 300-900 nm as the adsorption materials was developed. The obtained PB@Fe₃O₄ microparticle were characterized by Scanning electron microscopy (SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and Thermogravimetric analysis (TGA). It is found that the PB can be well coated on the surface of Fe₃O₄ microsphere, which can be easily adsorbed on the magnetic electrode substrate for the electrochemical adsorption of Cs⁺ ions. Electrochemical adsorption of 97% Cs⁺ on PB/Fe₃O₄ was achieved in less than 10 min, and the maximum adsorption capacity was 16.13 mg/g, and the distribution coefficient (K_D) of Cs⁺ ions reached as high as 3938. In addition, the electrochemical adsorption behavior of PB@Fe₃O₄ microparticle fitted well with the Freundlich adsorption isotherm and the Pseudo-second-order kinetic models. It is expected that such an ESIX technique using PB@Fe₃O₄ microparticle can be applied for the separation and recovery of dilute Cs⁺ ions from cesium-contaminated solution in a practical process.

Prussian blue nanoparticles: synthesis, surface modification, and biomedical applications

Prussian blue nanoparticles (PBNPs) are a nanomaterial that presents unique properties and an excellent biocompatibility. They can be synthesized in mild conditions and can be derivatized with polymers and/or biomolecules. PBNPs are used in biomedicine as therapy and diagnostic agents. In biomedical imaging, PBNPs constitute contrast agents in photoacoustic and magnetic resonance imaging (MRI). They are a good adsorbent to be used as antidotes for poisoning with cesium and/or thallium ions. Moreover, the ability to convert energy into heat makes them useful photothermal agents (PAs) in photothermal therapy (PTT) or as nonantibiotic substances with antibacterial properties. Finally, PBNPs can be both reduced to Prussian white and oxidized to Prussian green. A large window of redox potential exists between reduction and oxidation, which result in the enzyme-like characteristics of these NPs.

Prussian blue analogue functionalized magnetic microgels with ionized chitosan for the cleaning of cesium-contaminated clay

To deal with regeneration of nuclear-waste-contaminated soil, it is important to develop new materials and techniques for effective removal of radioactive cesium ions from clay. We report herein a synergistic remediation method for cleaning cesium-contaminated clay by Prussian blue analogue-functionalized magnetic microgel along with ionized chitosan. The magnetic microgels were prepared by surface polymerization of 4-vinyl pyridine and styrene on magnetite nanoparticles and attachment of Prussian blue analogues by ligand exchange reaction. The adsorption of cesium ions by magnetic microgels in aqueous solution follows the second-order kinetics process. And the maximum adsorption capacity was determined to be 149.70 mg/g by Langmuir adsorption model. When ionized chitosan hydrochloride was mixed with cesium-contaminated clay, we found that 200 mg/g clay of chitosan hydrochloride can realize 87.6 % of cesium release from clay within 2 h. Further use of magnetic microgel adsorbents can adsorb 95.5 % free cesium ions in solution, achieving an overall 83.7 % cleaning efficiency from cesium-contaminated clays. The microgels can be regenerated effectively and recycled magnetically while keeping the adsorption capacity constant after multiple times of use. The underlying principle demonstrated in this work can be extended to remediation of other types of radionuclides or heavy-metal ions in contaminated soil.

Prussian blue nanocubes decorated on nitrogen-doped hierarchically porous carbon network for efficient sorption of radioactive cesium

Eliminating the radioactive ¹³⁷Cs from nuclear waste is critical to the human health and environment. Prussian blue (PB)-based materials are considered as promising adsorbents for the removal of cesium. Herein, we demonstrate a facile strategy to achieve controllable synthesis of PB nanocrystals decorated on nitrogen-doped hierarchically porous carbon (NHPC) derived from cattle bone as adsorbent to remove cesium. The PB nanocrystals with a nanocube morphology are well distributed on NHPC, which is beneficial to increase the reachable surface area during adsorption. The resulting adsorbent exhibits a remarkable adsorption performance with a capacity of 125.31 mg g^-1, a superior recyclability with 87 % of initial capacity retained after 5 cycles, and an outstanding adsorption selectivity for cesium. X-ray diffraction, X-ray photoelectron spectroscopy combined with ⁵⁷Fe Mössbauer spectroscopy results reveal that cesium ions are inserted into the crystal channels of PB to generate a new phase (CsFe₂(CN)₆·3H₂O) after adsorption. Moreover, the adsorption process is spontaneous and endothermic which can be described by the Langmuir isotherm and pseudo-second-order kinetic models. This strategy for synthesis of PB/carbon adsorbents offers efficient candidate for removal of ¹³⁷Cs from wastewater.

Prussian blue-embedded carboxymethyl cellulose nanofibril membranes for removing radioactive cesium from aqueous solution

In this study, we synthesized a Prussian blue (PB)-embedded macroporous carboxymethyl cellulose nanofibril (CMCNF) membrane for facile cesium (Cs) removal. The PB was formed in situ at Fe³⁺ sites on a CMCNF framework cross-linked using FeCl₃ as a cross-linking agent. Cubic PB particles of size 5-20 nm were observed on the macroporous CMCNF membrane surface. The PB-CMCNF membrane showed 2.5-fold greater Cs adsorption capacity (130 mg/g_PB-CMCNF) than commercial PB nanoparticles, even though the PB loading of the PB-CMCNF membrane was less than 100 mg/g_PB-CMCNF. The macroporous structure of the CMCNF membrane led to improved diffusion in the solution, thereby increasing the Cs adsorption capacity. The Cs adsorption behavior was systematically investigated in different solution chemistry. Finally, ¹³⁷Cs removal using a semicontinuous adsorption module was demonstrated in real seawater. The results showed that the PB-CMCNF membrane is a highly effective, practical material for the removal of ¹³⁷Cs from aqueous environments.

Surface modification of poly(vinyl alcohol) sponge by acrylic acid to immobilize Prussian blue for selective adsorption of aqueous cesium

Prussian blue (PB) is known to be an effective cesium adsorbent, but the direct application of PB is limited by the difficulty of its recovery from solution. In this study, PB was immobilized on a porous support media, poly(vinyl alcohol) (PVA) sponge, for use as a selective material for cesium adsorption. The commercially available PVA sponge was functionalized by the addition of poly(acrylic acid) (PAA) (i.e., PAA-PVA) to enhance the PB immobilization, which increased both PB loading and binding strength. The AA functionalization changed the major functional groups from hydroxyl to carboxylic, as confirmed by Fourier-transform infrared spectroscopy. PB was further synthesized in the PAA-PVA using layer-by-layer (LBL) assembly, which contributed to more stable PB formation, and reduced detachment of PB during washing. The prepared adsorbent, PAA-L@PVA-PB, was tested for cesium adsorption capability. Cesium adsorption was equilibrated within three hours, and the maximum cesium adsorption capacity was 4.082 mg/g, which was 5.7 times higher than Pure-L@PVA-PB. The observed decrease in solution pH during cesium adsorption inhibited overall cesium uptake, however, this was minimized by buffering. The prepared PAA-L@PVA-PB was used as a column filling material and its potential use as a countermeasure for removing radioactive cesium from a contaminated water stream was demonstrated.

Prussian blue immobilized cellulosic filter for the removal of aqueous cesium

Cesium is a typical radioisotope that has a long half-life and is dangerous and can be emitted in the event of a nuclear accident. Prussian blue (PB), which is known to effectively adsorb cesium, is difficult to separate when it is dissolved in an aqueous system. In this study, PB was immobilized on a filter type support media, cellulose filter (CF), for use as a selective material for cesium adsorption. The commercially available CF was functionalized by the addition of acrylic acid (AA) (i.e., CF-AA) to enhance the PB immobilization, which increased both PB loading and binding strength. The AA functionalization changed the major functional groups from hydroxyl to carboxylic, as confirmed by Fourier-transform infrared spectroscopy. As a result of the surface modification, the PB immobilization increased 1.5 times and reduced detachment of PB during washing. The prepared adsorbent, CF-AA-PB, was tested for its cesium adsorption capability. Cesium adsorption equilibrated within 3 h, and the maximum cesium adsorption capacity was 16.66 mg/g. The observed decrease in the solution pH during cesium adsorption inhibited the overall cesium uptake; however, this was minimized by buffering. The prepared CF-AA-PB was used as a filter material and its potential use as a countermeasure for removing radioactive cesium from a contaminated water stream was demonstrated.

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.

Facile synthesis of copper ferrocyanide-embedded magnetic hydrogel beads for the enhanced removal of cesium from water

A simple one-step approach for fabricating copper ferrocyanide-embedded magnetic hydrogel beads (CuFC-MHBs) was designed, and the beads were applied to the effective removal of cesium (Cs) and then magnetically separated from water. The polyvinyl alcohol (PVA)-coated CuFC (PVA-CuFC) was first synthesized using PVA as a stabilizer and subsequently embedded in magnetic hydrogel beads made of a cross-linked network between the PVA and magnetic iron oxide nanoparticles that was prepared through the simple dropwise addition of a mixed solution of PVA-CuFC, PVA and iron salt into an ammonium hydroxide solution. The synthesis and chemical immobilization of the PVA-CuFC in the magnetic beads were simple, facile and achieved in one pot, and the process is scalable and convenient for the large-scale treatment of Cs-contaminated water. The resulting CuFC-MHBs showed effective Cs removal performance with a high K_d value of 66,780 mL/g and excellent structural stability without the release of CuFC for at least 1 month and could be effectively separated from water by an external magnet. Moreover, the CuFC-MHBs selectively adsorbed Cs with high K_d values in the presence of various competing ions, such as in simulated groundwater (24,500 mL/g) and seawater (8290 mL/g), and maintained their Cs absorption ability in a wide pH range from 3 to 11. The convenient fabrication method and effective removal of Cs from various aqueous media demonstrated that the CuFC-MHBs have great potential for practical application in the decontamination of Cs-contaminated water sources caused by nuclear accidents and radioactive liquid waste in various nuclear industry fields.

Study of pre-treatment of quinoline in aqueous solution using activated carbon made from low-cost agricultural waste (walnut shells) modified with ammonium persulfate

Activated carbon made from agricultural waste (walnut shells) was investigated as a suitable adsorbent for effectively removing quinoline from industrial wastewater. The activated carbon was treated with phosphoric acid and oxidized by ammonium persulfate and its ability to adsorb pyridine and quinoline in aqueous solution was investigated. Kinetic parameters for the adsorption process were determined through pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion models. Equilibrium experiments and adsorption isotherms were analyzed using Langmuir and Freundlich adsorption isotherms. After reaching equilibrium, the activated carbon adsorbed quinoline in preference to pyridine: the equilibrium adsorptions from individual aqueous solutions (200 μL L^-1) of quinoline and pyridine were 166.907 mg g^-1 and 72.165 mg g^-1, respectively. Thermodynamic studies of quinoline adsorption were conducted at different temperatures and indicated that quinoline adsorption was an endothermic and spontaneous process. The column-adsorption of quinoline and pyridine was consistent with the Thomas model and the Yoon-Nelson model. The removal efficiency of quinoline reached more than 97% for a velocity of 6 mL min^-1 at the initial adsorption stage.

Fabrication of a novel polyvinylidene fluoride membrane via binding SiO2 nanoparticles and a copper ferrocyanide layer onto a membrane surface for selective removal of cesium

A novel polyvinylidene fluoride (PVDF) membrane was fabricated through chemical binding SiO₂ nanoparticles (NPs) and copper ferrocyanide (CuFC) layers onto a membrane surface simultaneously to improve the removal efficiency of Cs. The results indicated that the SiO₂ NPs were strongly deposited onto the membrane surface, and the CuFC layer was firmly attached on the surface of SiO₂ NPs and the membrane. CuFC/SiO₂/PVDF membrane remained stable after the acidic solution and sonication stress treatments. CuFC/SiO₂/PVDF membrane showed good permeate flux and high selectivity on removal of Cs, and adsorbing capacity reached 1440.4 mg m^-2 for Cs. The membrane remained high rejections of Cs in a wide pH, and could be regenerated well by H₂O₂ and N₂H₄. Selective adsorption and electrostatic interaction govern the rejection of Cs. The coexisting cations decreased the rejection of Cs mainly in accordance to the order of cations' hydration radii as K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. In addition, the rejection of Cs could still reach 99.4% in 8 h in the filtration of humic acid solution and natural surface water. The membrane could removal of Cs from water effectively by directly rapid filtration, suggesting it can be applied as promising technology for radioactive wastewater treatment.

Effective removal of cesium from wastewater solutions using an innovative low-cost adsorbent developed from sewage sludge molten slag

This study investigates the effective removal of cesium (Cs) from aqueous solution using sewage sludge molten (SSM) slag that has undergone the surface modification with alkali (NaOH) hydrothermal treatment. The raw and modified slags were characterised systematically using the BET method, the FESEM, the XRF, the XRD spectroscopy and the CEC analysis to understand the physicochemical changes of the materials, and its sensitivity to Cs ions adsorption. Batch adsorption experiments were carried out to investigate the effects of adsorbent dose, contact time, solution pH, different initial Cs concentrations, temperature and the effect of competitive ions on Cs adsorption. The adsorption isotherm, kinetic and thermodynamic studies were also evaluated based on the experimental results. A higher Cs removal efficiency of almost 100% (for 20-100 mg/L of initial concentration) was achieved by the modified SSM slag, and the maximum adsorption capacity was found to be 52.36 mg/g. Several types of synthetic zeolites such as zeolite X, zeolite Y, zeolite A, and sodalite were formed on surface of the modified slag through the modification process which might be enhanced the Cs adsorption capacity. Kinetic parameters were fitted by the pseudo-second order model. The adsorption isotherms data of modified slag were well-fitted to the Langmuir (R² = 0.989) and Freundlich isotherms (R² = 0.988). The thermodynamic studies indicated that the adsorption process by the modified slag was spontaneous and exothermic. In the competitive ions effect, the modified slag effectively captured the Cs ion in the presence of Na⁺ and K⁺, especially at their lower concentrations. Moreover, the modified slag was reused for several cycles after the successful elution process with an appropriate eluting agent (0.5 M H₂SO₄), without deterioration of its original performance. Therefore, the SSM modified slag could be effectively used as a low-cost potential adsorbent for high Cs adsorption 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.