Copper Ferrocyanide-Functionalized Magnetic Adsorbents Using Polyethyleneimine Coated Fe3O4 Nanoparticles for the Removal of Radioactive Cesium.

Copper ferrocyanide-functionalized magnetic nano-adsorbents were successfully synthesized by electrostatic coating of citric acid coated Fe3O4 nanoparticles with polyethyleneimine, and immobilizing copper and ferrocyanide on the surfaces of polyethyleneimine-coated nanoparticles. Radioactive cesium (Cs) adsorption tests were conducted to investigate the effectiveness of the copper ferrocyanide-functionalized magnetic nano-adsorbents toward the removal of radioactive Cs.

Copper Ferrocyanide-Functionalized Magnetic Nanoparticles for the Selective Removal of Radioactive Cesium.

Copper ferrocyanide-functionalized magnetite nanoparticles (Cu-FC-MNPs) were successfully synthesized by immobilizing copper and ferrocyanide on the surfaces of [1-(2 amino-ethyl)-3-aminopropyl] trimethoxysilane-modified magnetite nanoparticles. Radioactive cesium (Cs) adsorption tests were conducted to investigate the effectiveness of the Cu-FC-MNPS toward the removal of radioactive Cs. The Cu-FC-MNPs showed excellent separation properties using an external magnet in an aqueous solution.

Succinate Functionalization of Hyperbranched Polyglycerol-Coated Magnetic Nanoparticles as a Draw Solute During Forward Osmosis.

Hyperbranched polyglycerol-coated magnetic nanoparticles (SHPG-MNPs) were functionalized with succinate groups to form a draw solute for use in a forward osmosis (FO). After the one-step synthesis of hyperbranched polyglycerol-coated magnetic nanoparticles (HPG-MNPs), the polyglycerol groups on the surfaces of the HPG-MNPs were functionalized with succinic anhydride moieties. The resulting SHPG-MNPs showed no change of size and magnetic property compared with HPG-MNPs and displayed excellent dispersibility in water up to the concentration of 400 g/L. SHPG-MNPs solution showed higher osmotic pressure than that of HPG-MNPs solution due to the presence of surface carboxyl groups in SHPG-MNPs and could draw water from a feed solution across an FO membrane without any reverse draw solute leakage during FO process. Moreover, the water flux remained nearly constant over several SHPG-MNP darw solute regeneration cycles applied to the ultrafiltration (UF) process. The SHPG-MNPs demonstrate strong potential for use as a draw solute in FO processes.

Controlled self-assembly for high-resolution magnetic printing.

A controlled magnetic field creates patterns of superparamagnetic nanoparticles with a minimum line width of 10 µm on a flexible substrate. This magnetic printing method is also successfully used to print conductive patterns consisting of copper or carbon nanomaterials.

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.

Helical magnetic micromotors decorated with nickel ferrocyanide for the active and rapid adsorption of radiocesium in water.

Separating radioactive cesium from nuclear waste and contaminated environments is critical to mitigate radiological hazards. In response to this need, remote-controllable and Cs-selective micromotor adsorbents have been considered as a promising technology for rapid in-situ cleanup while minimizing secondary waste and radiation exposure to workers. In this study, we demonstrate the active and rapid removal of a radioactive contaminant from water by leveraging the magnetic manipulation capabilities of a helical and magnetic Ni micromotor coated with Cs-selective nickel ferrocyanide (NiFC). The use of polyvinyl alcohol fibers as a template enables the straightforward preparation of the helical wire structure, allowing for precise control over the diameter and pitch of the helix through simple twisting with Ni wires. By harnessing Ni2+ ions eluted from the Ni micromotor in an acid solution, we successfully fabricate NiFC-coated Ni (NiFC/Ni) micromotors that exhibit a selective removal efficiency greater than 98% for 137Cs, even in the presence of high concentrations of competing Na+ ions. Under the influence of an external magnetic field, the NiFC/Ni micromotor demonstrates rapid motion, achieving a pulling motion (100 body lengths per second) through a magnetic gradient and a tumbling motion (46 body lengths per second) induced by a rotating magnetic field. The tumbling motion of the NiFC/Ni micromotor substantially improves the Cs adsorption rate, resulting in a rate that surpasses that achieved under nonmoving conditions by a factor of 21. This improved adsorption rate highlights the considerable potential of magnetically manipulated micromotor self-propulsion for efficient water-pollution treatment.

Surface decontamination of radioactive cesium by a reversibly cross-linkable hydrogel using poly(vinyl alcohol) and phenylboronic acid-grafted poly(methyl vinyl ether-alt-mono-sodium maleate).

Wide-area surface decontamination is essential during the sudden release of radioisotopes to the public, such as nuclear accidents or terrorist attacks. A self-generated hydrogel comprising a reversible complex between poly(vinyl alcohol) (PVA) and phenylboronic acid-grafted poly(methyl vinyl ether-alt-mono-sodium maleate) (PBA-g-PMVE-SM) was developed as a new surface decontamination coating agent to remove radioactive cesium from surfaces. The simultaneous application of PVA and PBA-g-PMVE-SM aqueous polymer solutions containing sulfur-zeolite to contaminated surfaces resulted in the spontaneous formation of a PBA-diol ester bond-based hydrogel. The sulfur-zeolite suspended in the hydrogel selectively removed 137Cs from the contaminated surface and was easily separated from the dissociable used hydrogel. This removal was performed by simple water rinsing without costly incineration to remove the organic materials for final disposal/storage of the radioactive waste, making it suitable for practical wide-area surface decontamination. In radioactive tests, the hydrogel containing sulfur-chabazite (S-CHA) showed substantial 137Cs removal efficiencies of 96.996% for painted cement and 63.404% for cement, which are 2.33 times better than the values for the commercial surface decontamination coating agent DeconGel. Due to its excellent zeolite ion-exchange ability, our hydrogel system has great potential for removing various hazardous contaminants, including radionuclides, from the surface.

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.

Sulfur-modified zeolite A as a low-cost strontium remover with improved selectivity for radioactive strontium.

Selective removal of radioactive strontium (90Sr) from the environment is important, and selective adsorption/ion exchange is appropriate for removal of trace amounts of 90Sr from large volumes of 90Sr-contaminated water. Although various inorganic ion-exchange materials, including zeolites, have been investigated intensively for removal of Sr2+ due to their excellent resistance to radiation and high ion-exchange capacity, their ion-exchange selectivity for Sr2+ is poor in the presence of competing ions such as Ca2+ and Mg2+. Here, sulfur-modified NaA zeolite (S-NaA) was prepared for low-cost, selective 90Sr removal because the elemental sulfur encapsulated in micropores provides additional Lewis acid-base interactions with Sr2+ during the Sr2+ ion-exchange. Our ion-exchange experiments revealed that S-NaA with 3 wt% sulfur (3 S-NaA) showed the highest Sr2+ selectivity among various S-NaAs containing up to 10 wt% sulfur because ion exchange involving bulky hydrated Sr2+ depends on the reduced micropore volume of S-NaA after sulfur loading. Most importantly, 3 S-NaA effectively and efficiently (>99.4%) removed 90Sr from groundwater containing 8.4 ppt 90Sr, demonstrating its excellent potential for practical application in the treatment of 90Sr-contaminated water.

Post-substitution of magnesium at CaI of nano-hydroxyapatite surface for highly efficient and selective removal of radioactive 90Sr from groundwater.

We have modified the ion-exchange affinity of nano-Hydroxyapatite (Ca5(PO4)3OH, HAP) surface for the rapid and selective adsorption of 90Sr from groundwater. The modification was achieved by the post-substitution of cations (Na+, Mg2+, Cu2+, Ba2+, Fe3+, and Al3+) for parent Ca2+ within surface structure of HAP. The diffraction patterns of modified HAP showed a slight shift of the (002) peak between 25° and 27° 2θ depending the ionic radius of the substituted cation. Magnesium substituted HAP, Mg-HAP, exhibited the highest removal efficiency (>95%) for 10 ppm of Sr2+, which is attributable to the higher ion-exchange affinity of substituted Mg2+ than parent Ca2+ toward Sr2+. The results of various analyses revealed that Mg substitution dominantly occurred at the CaI site of HAP, which enabled the Mg-HAP to adsorb Sr2+ at both of CaI and CaII sites whereas bare HAP could adsorb Sr2+ mainly at CaII site. Adsorption isotherms and the kinetics of Mg-HAP for Sr2+ were evaluated using a bi-Langmuir isotherm and a pseudo-second-order kinetic model, which demonstrated the Mg-HAP exhibited the highest adsorption capacity (64.69 mg/g) and fastest adsorption kinetics (0.161-1.714 g/(mg·min)) than previously modified HAPs. In the presence of competing cations at circumneutral pHs, the enhanced performance of the Mg-HAP led to a greater than 97% reduction of 90Sr (initial radioactivity = 9500 Bq/L) within 1 h. The distribution coefficient of Mg-HAP was 1.3-6.6 × 103 mL/g while that of bare HAP was 1.2-6.6 × 102 mL/g. The findings in the present study highlight that the ion-exchange affinity of CaI and CaII sites on HAP surface plays a key-role in 90Sr uptake. The proposed modification method can simply increase the affinity of HAP surface, therefore, this work can further improve the deployment of an in situ remediation technology for 90Sr contaminated groundwater, i.e., Mg-HAP-based permeable reactive barrier.

Fabrication of a porous polyacrylonitrile nanofiber adsorbent for removing radioactive 60Co.

A Co2+ adsorbent was prepared using electrospun porous polyacrylonitrile (PAN) nanofibers, featuring easy recovery for reuse compared with a nanoparticle-based adsorbent. As an efficient ligand for Co2+, ethylenediaminetetraacetic acid (EDTA) was introduced on the surface of porous PAN nanofibers with the aid of a branched polyethyleneimine (PEI) linker to obtain an adsorbent with carboxylic acid groups. On the adsorbent surface, the carboxylic acid and amine groups from EDTA could adsorb Co2+ via ion exchange and chelation, and amine groups from PEI that remained after EDTA functionalization played a role in coordinating Co2+. The amine and carboxylic acid groups were simultaneously involved in the adsorption on the surface, making it possible to remove Co2+ over a wide pH range. An investigation of the adsorption isotherms and kinetics of the nanofibrous adsorbent indicated that monolayer chemisorption was achieved with a maximum Co2+ adsorption capacity of 8.32 mg/g. In addition, radioactive 60Co was efficiently removed by the adsorbent with a removal extent of more than 98%. Considering the easy separation from Co2+ solution and regeneration of the nanofibrous adsorbent and its availability in a wide pH range, the adsorbent has great advantages in practical applications.

Active and selective removal of Cs from contaminated water by self-propelled magnetic illite microspheres.

We report the fabrication of clay-mineral-based Janus microspheres that exhibit remotely steerable self-propulsion in water, facilitating their selective and active removal of radiocesium from a contaminated solution. The spray-drying of slurries of intrinsically Cs-selective illite containing iron oxide nanoparticles led to magnetic illite microspheres with superior 137Cs adsorption capability and superparamagnetic behavior. The Janus micromotor adsorbent was prepared by depositing catalytic Pt onto the half-surface of magnetic illite microspheres. The micromotor adsorbents exhibited self-propulsion at speeds as high as ~265 µm/s via asymmetric bubble generation in water containing H2O2 as a fuel. The self-propulsion of the adsorbent improved the Cs adsorption kinetics six-folds compared with the kinetics in the corresponding stationary liquid. The magnetic properties of the micromotor adsorbent enabled convenient separation and direction control of the adsorbents under an external magnetic field. In particular, the micromotor adsorbent could successfully remove more than 98.6% of 137Cs from aqueous media containing competing ions including K+, Na+, Ca2+ and Mg2+.

Characteristic and remediation of radioactive soil in nuclear facility sites: a critical review.

A huge amount of radioactive soil has been generated through decommissioning of nuclear facilities around the world. This review focuses on the difficulties and complexities associated with the remediation of radioactive soils at the site level; therefore, laboratory studies were excluded from this review. The problems faced while remediating radioactive soils using techniques based on strategies such as dry separation, soil washing, flotation separation, thermal desorption, electrokinetic remediation, and phytoremediation are discussed, along with appropriate examples. Various factors such as soil type, particle size, the fraction of fine particles, and radionuclide characteristics that strongly influence radioactive soil decontamination processes are highlighted. In this review, we also survey and compare the pool of available technologies currently being used for the remediation of radionuclide-contaminated soils, as well as the economic aspects of soil remediation using different techniques. This review demonstrates the importance of the integrated role of various factors in determining the effectiveness of the radioactive soil decontamination process.

Sorption behavior of cesium on silt and clay soil fractions.

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 µm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

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 (Kd) 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.

HER2/neu antibody conjugated poly(amino acid)-coated iron oxide nanoparticles for breast cancer MR imaging.

Superparamagnetic iron oxide nanoparticles are widely used as nanoprobes for magnetic resonance imaging (MRI). Water-soluble iron oxide nanoparticles were synthesized by coating iron oxide nanoparticles with a hydrophilic, biocompatible, biodegradable poly(amino acid) derivative, poly(2-hydroxyethyl aspartamide) graft copolymer for negative contrast enhancement on T2 weighted MRI. HER2/neu antibodies were conjugated on the surface of poly(amino acid) coated iron oxide nanoparticles for the detection of breast cancer. The antibody-grafted iron oxide nanoparticles (PAION-Ab) were about 31.1 nm in diameter. The T2 relaxivity of PAION-Ab was 246 L·mmol(-1)·sec(-1) greater than that of the commercial product such as Feridex. PAION-Ab showed low cytotoxicity even at relatively high concentrations. Furthermore, Prussian blue staining and in vitro MRI study with SKBR-3, breast cancer cells overexpressing HER2/neu receptors indicated that PAION-Ab exhibited excellent cancer cell detection ability and enhanced signal intensities in the T2-weighted image.

Desorption of cesium from hydrobiotite by hydrogen peroxide with divalent cations.

In this study, hydrogen peroxide (H2O2) was used to enhance the cation-exchange treatment for Cs+ desorption from clay minerals. Among various investigated clay minerals, hydrobiotite (HBT), which has interstratified layers of vermiculite and biotite, exhibited the highest Cs+ sorption capacity and the most favorable H2O2 activation because of its high Fe content. In X-ray diffraction analysis, HBT treated with H2O2 and 0.1 M Mg2+ showed substantial changes in its basal spacing, indicating expansion of the interlayer region induced by treatment of H2O2 and strongly hydrated divalent cations. In addition, more than 80% of the Cs+ was readily desorbed from HBT with 35% H2O2 solution and 0.1 M Mg2+ at room temperature. After three cycles under the same treatment conditions (35% H2O2 solution and 0.1 M Mg2+), approximately 99% removal of radioactive Cs+ was achieved. These results suggested that H2O2 treatment with solvated Mg2+ enhanced Cs+ desorption from HBT by altering the interlayer region through intercalation of hydrated divalent cations in conjunction with the H2O2 decomposition reaction.

Enhanced removal of cesium by potassium-starved microalga, Desmodesmus armatus SCK, under photoheterotrophic condition with magnetic separation.

This study investigated the feasibility of using photoheterotrophic microalga, Desmodesmus armatus SCK, for removal of cesium (Cs+) followed by recovery process using magnetic nanoparticles. The comparison of three microalgae results indicated that D. armatus SCK removed the most Cs+ at both 25 °C and 10 °C. The results also revealed that the use of microalga grown in potassium (K+)-starved condition improves the accumulation of Cs+. Heterotrophic mode with addition of volatile fatty acids (VFAs), especially acetic acids (HAc), also enhanced removal of Cs+ by K+-starved D. armatus SCK; maximum removal efficiency of Cs+ was almost 2-fold higher than that of cells grown without organic carbon source. The Cs+ taken up by this microalga was efficiently harvested using magnetic nanoparticles, polydiallyldimethylammonium (PDDA)-FeO3. Finally, this strain eliminated more than 99% of radioactive 137Cs from solutions of 10, 100, and 1000 Bq mL-1. Therefore, use of K+-starved microalga, D. armatus SCK, with VFAs could be promising means to remove the Cs from the liquid wastes.

Controlled aggregates of magnetite nanoparticles for highly sensitive MR contrast agent.

We have prepared a magnetite encapsulated polymer nanocomposite (MEPN) by an emulsification-diffusion technique and found that the encapsulation efficiency could be precisely controlled according to the portion of magnetite and the capping ligand that covers the surface of the magnetite nanoparticles. The field-dependence and temperature dependence on magnetization, measured by a superconducting quantum interference device, demonstrate that there was no size effect of the magnetite nanoparticles on the encapsulation behavior. The size distribution and T2 relaxivity of prepared MEPNs were measured using magnetic resonance imaging for analysis of the effect of aggregation and it was verified that aggregates of the magnetite nanoparticles provide enhanced relaxation ability.

Enhanced surface decontamination of radioactive Cs by self-generated, strippable hydrogels based on reversible cross-linking.

A self-generated, strippable hydrogel containing adsorbents was developed to remove the radioactive cesium from surfaces by adsorption for wide-area surface decontamination. Two aqueous polymeric solutions of polyvinyl alcohol (PVA) and phenylboronic-acid-grafted alginate (PBA-Alg) were easily applied to surfaces and subsequently self-generated a hydrogel based on the PBA-diol ester bond. Compared to the strippable coating and chemical gels, the PBA-diol ester bond-based hydrogel was easily peeled off the surfaces without a drying step due to its high elasticity, which is more practical and time saving. The resulting hydrogel displayed high 137Cs removal efficiencies of 91.61% for painted cement, 97.505% for aluminum, 94.05% for stainless steel, and 53.5% for cement, which was 2.3 times higher than that of Decongel due to the presence of the adsorbent in the hydrogel having an excellent Cs distribution coefficient (3.34 × 104 mL/g). Moreover, the volume of radioactive waste generated after the surface decontamination could be reduced by a simple magnetic separation of the adsorbent from the used hydrogel, which can reduce the waste disposal cost. Therefore, our hydrogel system has great potential as a new, cost-effective surface decontaminant in various nuclear industry fields including wide-area environmental remediation after a nuclear accident or terrorist attack.