Removal of radioactive iodine from water using Ag2O grafted titanate nanolamina as efficient adsorbent

Construction of Ketoenamine-Based Covalent Organic Frameworks with Electron-Rich Sites for Efficient and Rapid Removal of Iodine from Solution

Porous covalent organic frameworks (COFs) have been widely used for the efficient removal of iodine from solution due to their abundance of electron-rich sites. In this study, two kinds of ketoenamine-based COFs, TpBD-(OMe)2 and TpBD-Me2, are successfully synthesized via Schiff base reaction under solvothermal conditions using 1, 3, 5-triformylphoroglucinol as aldehyde monomer, o-tolidine and o-dianisidine as amino monomers. The ability of TpBD-(OMe)2 and TpBD-Me2 to adsorb iodine in cyclohexane or aqueous solutions has been quantitatively analyzed and interpreted in terms of adsorption sites. TpBD-Me2 possesses two adsorption sites, -NH- and -C=O, and exhibits an adsorption capacity of 681.67 mg/g in cyclohexane, with an initial adsorption rate of 0.6 g/mol/min with respect to COF unit cell. The adsorption capacity of TpBD-(OMe)2 can be as high as 728.77 mg/g, and the initial adsorption rate of TpBD-(OMe)2 can reach 1.2 g/mol/min in the presence of oxygen atoms between the methyl group and the benzene ring. Compared with TpBD-Me2, the higher adsorption capacity and adsorption rate of TpBD-(OMe)2 towards iodine are not only reflected in organic solvents, but also in aqueous solutions. It is proven through X-ray photoelectron spectroscopy and Raman spectroscopy that iodine exists in the form of I2, I3-, and I5- within TpBD-(OMe)2 and TpBD-Me2 after adsorption. This work not only expands the application of COFs in the field of iodine adsorption, but also provides research ideas and important an experimental basis for the optimization of iodine adsorption sites.

Viologen-functionalized magnetic material for the removal of Iodine and benzanthracene in an aqueous solution

The development of magnetically active adsorbents for effective iodine removal would be highly desirable to address environmental pollution and remediation. Herein, we demonstrated the synthesis of Vio@SiO₂@Fe₃O₄ as an adsorbent via surface functionalisation of electron-deficient bipyridium (viologen) units on the surface of magnetically active silica-coated magnetite (Fe₃O₄) core. This adsorbent was characterised thoroughly using various analytical techniques, such as field emission scanning electron microscopy (FESEM), thermal gravimetric analysis, Fourier transform infrared spectroscopy (FTIR), field emission transmission electron microscopy (FETEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photon analysis (XPS). The removal of triiodide from the aqueous solution was monitored via the batch method. It revealed that the complete removal was achieved upon stirring for 70 min. The thermally stable and crystalline Vio@SiO₂@Fe₃O₄ displayed efficient removal capacity even in the presence of other competing ions and at different pHs. The adsorption kinetics data were analysed following the pseudo-first-order and pseudo-second-order models. Further, the isotherm experiment showed that the maximum uptake capacity of iodine is 1.38 g/g. It can be regenerated and reused over multiple cycles to capture iodine. Further, Vio@SiO₂@Fe₃O₄ displayed a good removal capacity toward toxic polyaromatic, Benzanthracene (BzA) pollutant with an uptake capacity of 2445 μg/g. This effective removal of toxic pollutants iodine/benzanthracene was attributed to the strong non-covalent electrostatic and π-π interaction with electron-deficient bipyridium units.

Strategy to combine two functional components: Efficient nano material development for iodine immobilization

The development of effective radioactive iodine adsorption materials from nuclear waste remains a significant challenge due to the drawbacks of the previous technologies such as complex synthesis process, high cost, and low stability. In this work, a Metal Oxidation-Carbon (MOC) composite material was designed and synthesized to solve this problem. The structure, composition, and physicochemical properties of this MOC were characterized to reveal its mesoporous material properties. Experiment results showed that this MOC material contain great physical and chemical adsorption efficiency towards iodine vapor, the adsorption capacity could up to 2647.54 mg/g. And the average desorption rate of 86.57% (in absolute ethanol) further proved its advanced recyclability. Moreover, this mesoporous material has great prospects in industrialization due to its simple one-step synthesis method, well-defined adsorption mechanism, and competitive application property.

Synthesis and applications of bismuth-impregnated biochars originated from spent coffee grounds for efficient adsorption of radioactive iodine: A mechanism study

The adsorption of radioactive iodine, which is capable of presenting high mobility in aquatic ecosystems and generating undesirable health effects in humans (e.g., thyroid gland dysfunction), was comprehensively examined using pristine spent coffee ground biochar (SCGB) and bismuth-impregnated spent coffee ground biochar (Bi@SCGB) to provide valuable insights into the variations in the adsorption capacity and mechanisms after pretreatment with Bi(NO₃)₃. The greater adsorption of radioactive iodine toward Bi@SCGB (adsorption capacity (Q_e) = 253.71 μg/g) compared to that for SCGB (Q_e = 23.32 μg/g) and its reduced adsorption capability at higher pH values provide evidence that the adsorption of radioactive iodine with SCGB and Bi@SCGB is strongly influenced by the presence of bismuth materials and the electrostatic repulsion between their negatively charged surfaces and negatively charged radioactive iodine (IO₃^-). The calculated R² values for the adsorption kinetics and isotherms support that chemisorption plays a crucial role in the adsorption of radioactive iodine by SCGB and Bi@SCGB in aqueous phases. The adsorption of radioactive iodine onto SCGB was linearly correlated with the contact time (h^1/2), and the diffusion of intra-particle predominantly determined the adsorption rate of radioactive iodine onto Bi@SCGB (C_{stage II} (129.20) > C_{stage I} (42.33)). Thermodynamic studies revealed that the adsorption of radioactive iodine toward SCGB (ΔG° = -8.47 to -7.83 kJ/mol; ΔH° = -13.93 kJ/mol) occurred exothermically and that for Bi@SCGB (ΔG° = -15.90 to -13.89 kJ/mol; ΔH° = 5.88 kJ/mol) proceeded endothermically and spontaneously. The X-ray photoelectron spectroscopy (XPS) analysis of SCGB and Bi@SCGB before and after the adsorption of radioactive iodine suggest the conclusion that the change in the primary adsorption mechanism from electrostatic attraction to surface precipitation upon the impregnation of bismuth materials on the surfaces of spent coffee ground biochars is beneficial for the adsorption of radioactive iodine in aqueous phases.

Water-stable porous Al24 Archimedean solids for removal of trace iodine

In this paper, we report a unique type of core-shell crystalline material that combines an inorganic zeolitic cage structure with a macrocyclic host arrangement and that can remove trace levels of iodine from water effectively. These unique assemblies are made up of an inorganic Archimedean truncatedhexahedron (tcu) polyhedron in the kernel which possesses six calixarene-like shell cavities. The cages have good adaptability to guests and can be assembled into a series of supramolecular structures in the crystalline state with different lattice pore shapes. Due to the unique core-shell porous structures, the compounds are not only stable in organic solvents but also in water. The characteristics of the cages enable rapid iodine capture from low concentration aqueous I₂/KI solutions (down to 4 ppm concentration). We have studied the detailed process and mechanism of iodine capture and aggregation at the molecular level. The facile synthesis, considerable adsorption capacity, recyclability, and β- and γ-radiation resistance of the cages should make these materials suitable for the extraction of iodine from aqueous effluent streams (most obviously, radioactive iodide produced by atomic power generation).

The removal of radioactive elements is important to human health and sustainable development. Here, the authors reveal the synthesis of water-stable Archimedean solids based on the earth-abundant element for the fast removal of trace iodine.

Facile Preparation of MCM-41/Ag2O Nanomaterials with High Iodide-Removal Efficiency

The elimination of iodide (I^-) from water is a tough subject due to its low adsorption tendency and high mobility. In this work, MCM-41/Ag₂O nanomaterials were prepared, characterized, and employed to adsorb I^- from water. The Ag₂O nanoparticles were dispersed homogeneously in the pores or at the surface of the MCM-41 support, and the Ag₂O nanoparticles in the pores had small particles sizes due to the confinement of the mesoporous channel. The prepared MCM-41/Ag₂O nanomaterials exhibited a higher specific surface area than previously reported Ag₂O-based composites. The adsorption of I^- by the nanomaterials was able to reach equilibrium at 180 min. The MCM-41/Ag₂O nanomaterials showed a better adsorption capacity per unit mass of Ag₂O than pure Ag₂O nanoparticles and previously reported Ag₂O-based composites prepared using other supports. Furthermore, the MCM-41/Ag₂O nanomaterials exhibited high selectivity for I^- in the presence of high concentrations of competitive anions, such as Cl^- or Br^-, and could function in a wide range of pH. The chemical reaction between Ag₂O and I^- and the surface adsorption were the main adsorption mechanisms. These results indicate that MCM-41/Ag₂O nanomaterials are a promising and efficient adsorbent material suitable for the removal of I^- for practical application.

Functionality screening to help design effective materials for radioiodine abatement

This paper is part of a growing body of research work looking at the synthesis of an optimal adsorbent for the capture and containment of aqueous radioiodine from nuclear fuel reprocessing waste. 32 metalated commercial ion exchange resins were subjected to a two-tier screening assessment for their capabilities in the uptake of iodide from aqueous solutions. The first stage determined that there was appreciable iodide capacity across the adsorbent range (12–220 mg·g⁻¹). Candidates with loading capacities above 40 mg·g⁻¹ were progressed to the second stage of testing, which was a fractional factorial experimental approach. The different adsorbents were treated as discrete variables and concentrations of iodide, co-contaminants and protons (pH) as continuous variables. This gave rise to a range of extreme conditions, which were representative of the industrial challenges of radioiodine abatement. Results were fitted to linear regression models, both for the whole dataset (R² = 59%) and for individual materials (R² = 18–82%). The overall model determined that iodide concentration, nitrate concentration, pH and interactions between these factors had significant influences on the uptake. From these results, the top six materials were selected for project progression, with others discounted due to either poor uptake or noticeable iodide salt precipitation behaviour. These candidates exhibited reasonable iodide uptake in most experimental conditions (average of >20 mg·g⁻¹ hydrated mass), comparing favourably with literature values for metallated adsorbents. Ag-loaded Purolite S914 (thiourea functionality) was the overall best-performing material, although some salt precipitation was observed in basic conditions. Matrix effects not withstanding it is recommended that metalated thiourea, bispicolylamine, and aminomethylphosphonic acid functionalized silicas warrant further exploration.

Efficient capture of radioactive iodine by ZIF-8 derived porous carbon

Due to the rapid diffusion of radioactive iodine, the demand for safe and efficient capture and storage of radioactive iodine is increasing worldwide. The use of porous carbon materials to capture iodine has aroused great interest. This work prepared porous carbon materials derived from polymetallic oxides of the zeolitic imidazolate framework (ZIF) by pyrolysis at 1000 °C. The carbon materials (CZIF-1000) have a high specific surface area of about 1110 m2/g and a total pore volume of 0.92 cm3/g. Adsorption studies have shown that the CZIF-1000 had significant adsorption performance for iodine, and the adsorption capacity can reach 790.8 mg/g at 8h. The potential mechanism of adsorption is that the carbonization causes the charge-transfer interaction and pore size distribution. Compared with the conventional adsorbents, the adsorbents showed faster kinetics and high extraction capacity for iodine. This experiment provides an effective method for designing a highly efficient adsorbent for iodine and broadens the ideas for developing new iodine extraction adsorbents.

Preparation of Halloysite/Ag2O Nanomaterials and Their Performance for Iodide Adsorption

Halloysite/Ag2O (Hal/Ag2O) nanomaterials were prepared by growing Ag2O nanoparticles on the surface of nanotubular halloysite using silver nitrate solution under alkaline conditions. The nanomaterials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption. Good dispersion of Ag2O nanoparticles with average sizes of 6.07 ± 2.5 nm and 8.04 ± 3.8 nm was achieved in the nanomaterials when using different concentrations of alkali. The nanomaterial with 6.36% Ag2O (Hal/Ag2O-2) exhibited rapid adsorption to iodide (I−); adsorption equilibrium can be reached within 100 min. The adsorption capacity of I− on Hal/Ag2O-2 is 57.5 mg/g, which is more than 143 times higher than that of halloysite. The nanomaterial also showed a better adsorption capacity per unit mass of Ag2O due to the better dispersion and less coaggregation of Ag2O in the nanomaterial than in the pure Ag2O nanoparticles. Importantly, Hal/Ag2O-2 exhibited high selectivity for I−, and its I− removal efficiency was hardly affected by the coexistence of Cl−, Br−, or SO42−, as well as the initial pH of the solution. With an excellent adsorption performance, the prepared Hal/Ag2O nanomaterial could be a new and efficient adsorbent capable of the adsorption of radioactive I− from aqueous solution.

Sintering Bi2O3–B2O3–ZnO ternary low temperature glass by hydration device to solidify iodine containing silver-coated silica gel

A new glass solidification process aims at radioactive iodine waste was explored in order to reduce the possible harm to environment. Samples with different iodine content in silver-coated silica gel were pretreated by hydration device at 300 °C and then sintered at relatively low temperatures (500, 550 and 600 °C). XRD results show that AgI is mainly chemically fixed in the glass network with some AgI particles being physically wrapped by the glass. Moreover, as the sintering temperature reached to 550 °C, B element crystallized. SEM-EDS results show that Ag and I elements are enriched, while the other elements are evenly distributed. AFM results showed that the sample surface becomes rougher as the iodine content increases in the silver coated silica gel. The FT-IR results show that the structure of the sintered sample is mainly composed of [BiO3], [BiO6] and [BO3]. This study provides a new sintering method by hydration device for the treatment of radioactive iodine waste.

Capture of aqueous radioiodine species by metallated adsorbents from wastestreams of the nuclear power industry: a review

Abstract

Iodine-129 poses a significant challenge in the drive towards lowering radionuclide emissions from used nuclear fuel recycling operations. Various techniques are employed for capture of gaseous iodine species, but it is also present, mainly as iodide anions, in problematic residual aqueous wastestreams, which have stimulated research interest in technologies for adsorption and retention of the radioiodine. This removal effort requires specialised adsorbents, which use soft metals to create selectivity in the challenging chemical conditions. A review of the literature, at laboratory scale, reveals a number of organic, inorganic and hybrid adsorbent matrices have been investigated for this purpose. They are functionalised principally by Ag metal, but also Bi, Cu and Pb, using numerous synthetic strategies. The iodide capacity of the adsorbents varies from 13 to 430 mg g−1, with ion-exchange resins and titanates displaying the highest maximum uptakes. Kinetics of adsorption are often slow, requiring several days to reach equilibrium, although some ligated metal ion and metal nanoparticle systems can equilibrate in < 1 h. Ag-loaded materials generally exhibit superior selectivity for iodide verses other common anions, but more consideration is required of how these materials would function successfully in industrial operation; specifically their performance in dynamic column experiments and stability of the bound radioiodine in the conversion to final wasteform and subsequent geological storage.

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Synthesis of Silver-Impregnated Magnetite Mesoporous Silica Composites for Removing Iodide in Aqueous Solution

Mag@silica-Ag composite has a high sorption ability for I- in aqueous solution due to its high surface area and strong affinity for the studied anion. The material adsorbed I- rapidly during the initial contact time (in 45 min, η = 80%) and reached adsorption equilibrium after 2 h. Moreover, mag@silica-Ag proved to selectively remove I- from a mixture of Cl-, NO3- and I-. The adsorption behavior fitted the Langmuir isotherm perfectly and the pseudo-second-order kinetic model. Based on the Langmuir isotherm, the maximum adsorption capacity of mag@silica-Ag was 0.82 mmol/g, which is significantly higher than previously developed adsorbents. This study introduces a practical application of a high-capacity adsorbent in removing radioactive I- from wastewaters.

Removal of Radioactive Iodine Using Silver/Iron Oxide Composite Nanoadsorbents

Efficient and cost-effective removal of radioactive iodine (radioiodine) from radioactive contaminated water has become a crucial task, following nuclear power plant disasters. Several materials for removing radioiodine have been reported in the literature. However, most of these materials exhibit some limitations, such as high production cost, slow adsorption kinetics, and poor adsorption capacity. Herein, we present silver/iron oxide nanocomposites (Ag/Fe3O4) for the efficient and specific removal of iodine anions from contaminated water. The Ag/Fe3O4 were synthesized using a modified method and characterized via scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analyses. This adsorbent showed a high adsorption capacity for iodine anions (847 mg/g of the adsorbent) in pure water. Next, Ag/Fe3O4 was applied to the removal of radioiodine, and high removal efficiencies were observed in water. In addition, its desalination capacity was retained in the presence of competitive ions and varied pH. After the adsorption process, Ag/Fe3O4 was easily removed from the water by applying an external magnetic field. Moreover, the same operation can be repeated several times without a significant decrease in the performance of Ag/Fe3O4. Therefore, it is expected that the findings presented in this study will offer a new method for desalinating radioiodine in various aqueous media.

Capture of iodine in solution and vapor phases by newly synthesized and characterized encapsulated Cu2O nanoparticles into the TMU-17-NH2 MOF

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I) formed during the extensive use of nuclear energy is of paramount importance. Therefore, it is a great deal to design new adsorbents for effectively disposing of iodine from nuclear waste. In this work, a new Cu₂O/TMU-17-NH₂ composite has been prepared by a simple encapsulation of Cu₂O nanoparticles (NPs) into the metal organic framework (MOF) TMU-17-NH₂ for the first time. The as-synthesized Cu₂O/TMU-17-NH₂ was fully characterized in details and the iodine sorption/release capability of the Cu₂O/TMU-17-NH₂ composite has been investigated both in solution and in the vapor phase. According to the FE-SEM images, the Cu₂O/TMU-17-NH₂ was obtained with same morphology to that of the pristine TMU-17-NH₂. The I₂ sorption/release experiments were examined by UV-vis spectroscopy. The optimal iodine sorption was obtained by almost complete removal of iodine with a sorption capacity of about 567 mg/g. Detailed experimental evidence demonstrating that the iodine was captured by chemisorption process. Furthermore, photoluminescence (PL) properties of Cu₂O/TMU-17-NH₂ have also been investigated in which indicate that the Cu₂O/TMU-17-NH₂ composite exhibits stronger emission than the pristine TMU-17-NH₂.

Removal of heavy metals and radionuclides from water using nanomaterials: current scenario and future prospects

There is an increase in concern about the hazardous effects of radioactivity due to the presence of undesirable radioactive substances in our vicinity. Nuclear accidents such as Chernobyl (1986) and Fukushima (2011) have further raised concerns towards such incidents which have led to contamination of water bodies. Conventional methods of water purification are less efficient in decontamination of radioisotopes. They are usually neither cost-effective nor environmentally friendly. However, nanotechnology can play a vital role in providing practical solutions to this problem. Nano-engineered materials like metal oxides, metallic organic frameworks, and nanoparticle-impregnated membranes have proven to be highly efficient in treating contaminated water. Their unique characteristics such as high adsorption capacity, large specific surface area, high tensile strength, and excellent biocompatibility properties make them useful in the field of water purification. This review explores the present status and future prospects of nanomaterials as the next-generation water purification systems that can play an important role in the removal of heavy metals and radioactive contaminants from aqueous solutions.

Combined use of tannic acid-type organic composite adsorbents and ozone for simultaneous removal of various kinds of radionuclides in river water

Tannic acid-type organic composite adsorbents (PA316TAS, AR-01TAS, PYRTAS, WA10TAS, WA20TAS, and WA30TAS), combined with hydrolyzed and sulfonated tannic acid (TAS) and porous-type strongly basic anion-exchange resin (PA316), benzimidazole-type anion-exchange resin embedded in high-porous silica beads (AR-01), pyridine-type anion-exchange resin (PYR), acrylic-type weakly basic anion-exchange resin (WA10), or styrene-type weakly basic anion-exchange resins (WA20 and WA30) for simultaneous removal of various kinds of radionuclides in river water were successfully synthesized. The adsorption behavior of twelve kinds of simulated radionuclides (Mn, Co, Sr, Y, Ru, Rh, Sb, Te, Cs, Ba, Eu, and I (I^- and IO₃^-)) on these composite adsorbents has been studied in real river water at room temperature. PA316TAS adsorbents showed much higher distribution coefficients (K_d) for all metal ions. TAS structure has more selective adsorption ability for Mn, Co, Sr, Y, Cs, Ba, Eu, and IO₃^-. On the other hand, Y, Ru, Rh, Sb, Te, Eu, I (I^- and IO₃^-) were adsorbed on both PA316 and TAS structures. To evaluate the validity of these mechanistic expectations, the respective chemical adsorption behaviors of Mn, Co, Sr, etc. and PA316TAS adsorbent were examined in river water ranging in temperature from 278 to 333 K. As was expected, one adsorption mechanism for Mn, Co, Sr, Cs, and Ba systems and two types of adsorption mechanisms for Y, Ru, Rh, Sb, Te, Eu, I (I^- and IO₃^-) systems were observed. On the other hand, the precipitation of Mn, Co, Y, Ru, Rh, Te, and Eu was formed by ozonation for river water, that is, ozone can transform Mn, Co, Y, Ru, Rh, Te, and Eu ions into the insoluble precipitates. Hence, one straight line for Sr, Cs, Ba systems and two types of straight lines for Sb, I (I^- and IO₃^-) systems were obtained in river water treated with ozone. The chromatography experiments of Cs, Sr, I (I^- and IO₃^-) were carried out to calculate their maximum adsorption capacities. The obtained maximum adsorption capacities of Cs, Sr, and I^- mixed with IO₃^- were 1.7 × 10^-4 (Cs), 1.8 × 10^-3 (Cs/O₃), 7.8 × 10^-5 (Sr), 5.6 × 10^-4 (Sr/O₃), 5.4 × 10^-2 (I^- and IO₃^-), 3.1 × 10^-2 (I^- and IO₃^-/O₃) mol/g - PA316TAS. It was discovered that the maximum adsorption capacities of I^- and IO₃^- for the composite adsorbent is unprecedented high and the capacity become much greater than an order of magnitude, compared with those of previous reports. This phenomenon suggests the formation of electron-donor-acceptor (EDA) complexes or pseudo EDA complex. Based on these results, it was concluded that the combined use of tannic acid-type organic composite adsorbents and ozone made it possible to remove simultaneously and effectively various kinds of radionuclides in river water in the wide pH and temperature ranges.

Highly selective anchoring silver nanoclusters on MOF/SOF heterostructured framework for efficient adsorption of radioactive iodine from aqueous solution

A series of Ag-modified MOF/SOF heterostructured framework adsorbents (Ag-MSHC) with strong binding of iodine were prepared by anchoring silver nanoclusters on MOF/SOF heterostructured framework (MSHC). Morphological transformation process of six novel Ag-MSHC adsorbents can be realized by tailoring the molar ratio of Fe³⁺, TMA (1,3,5-Tricarboxybenzen) and MA (melamine), finally resulting in a combination of MOFs (metal-organic frameworks) and SOFs (supramolecular organic framework). Among six adsorbents, Ag-MSHC-6 exhibited an extremely strong affinity towards I^-, whereas the maximum adsorption capacity of I^- reaches 771.6 mg/g. An increased tendency of I^- sorption occurred from Ag-MSHC-1 to Ag-MSCH-6 when the molar ratio of Fe³⁺ gradually decreased because the content of Fe³⁺ in topological structure of Ag-MSHC can hinder the incorporation of silver nanoclusters into Ag-MSHC and further influences the irreversible interactions between Ag₂O and I^-. Besides, FT-IR, XPS, TGA and SEM were used to discuss the microstructures and chemical composition of MSHC and Ag-MSHC, and we also performed batch adsorption experiments to demonstrate the iodine sorption performance and mechanism by Ag-MSHC. Taking advantage of this combination of MOFs and SOFs, high degree of doping of silver nanoclusters as well as its strong binding ability of iodine, Ag-MSHC can be considered as a superior adsorbent for radioactive iodine extraction.

Surface Interactions and Mechanisms Study on the Removal of Iodide from Water by Use of Natural Zeolite-Based Silver Nanocomposites

In this work a natural zeolite was modified with silver following two different methods to derive Ag2O and Ag0 nanocomposites. The materials were fully characterized and the results showed that both materials were decorated with nanoparticles of size of 5-25 nm. The natural and modified zeolites were used for the removal of iodide from aqueous solutions of initial concentration of 30-1400 ppm. Natural zeolite showed no affinity for iodide while silver forms were very efficient reaching a capacity of up to 132 mg/g. Post-adsorption characterizations showed that AgI was formed on the surface of the modified zeolites and the amount of iodide removed was higher than expected based on the silver content. A combination of experimental data and characterizations indicate that the excess iodide is most probably related to negatively charged AgI colloids and Ag-I complexes forming in the solution as well as on the surface of the modified zeolites.

Surface modification of polypropylene membrane for the removal of iodine using polydopamine chemistry

The development of stable and effective iodine removal systems would be highly desirable in addressing environmental issues relevant to water contamination. In the present research, a novel iodine adsorbent was synthesized by self-polymerization of dopamine (PDA) onto inert polypropylene (PP) membrane. This PP/PDA membrane was thoroughly characterized and its susrface propeties was analyzed by various analytical techniques indcluding field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), contact angle, and surface free energy measurement. The PP/PDA membranes were subsequently used for batchwise removal of iodine at different temperatures (25-70 °C), pH (2-7), and surface areas (1-10 cm²) to understand the underlying adsorption phenomena and to estimate the membrane capacity for iodine uptake. The increase in temperature and pH both led to higher adsorption of iodine. The present approach showed a removal efficiency of over 75% for iodine using 10 cm² PP/PDA membrane (18.87 m² g^-1) within 2 h at moderate temperatures (∼50 °C) and pH > 4, about 15 fold compared to the PP control membrane. The adsorption kinetics and isotherms were well fitted to the pseudo-second-order kinetic and Langmuir isotherm models (R² > 0.99). This adsorbent can be recycled and reused at least six times with stable iodine adsorption. These findings were attributed to the homogenous monolayer adsorption of the iodide on the surface due to the presence of catechol and amine groups in the PP/PDA membrane. This study proposes an efficient adsorbent for iodine removal.

Capture of I131 from medical-based wastewater using the highly effective and recyclable adsorbent of g-C3N4 assembled with Mg-Co-Al-layered double hydroxide

This paper reports a very high capacity and recyclable Mg-Co-Al-layered double hydroxide@ g-C₃N₄ nanocomposite as the new adsorbent for remediation of radioisotope-containing medical-based solutions. In this work, a convenient solvothermal method was employed to synthesize a new nano-adsorbent, whose features were determined by energy dispersive X-ray (EDS/EDX), XRD, FESEM, TEM, TGA, BET, and FT-IR spectroscopy. The as-prepared nano-adsorbent was applied to capture the radioisotope iodine-131 mainly from the medical-based wastewater under different conditions of main influential parameters, (i.e. adsorbent dose, initial I₂ concentration, sonication time, and temperature). The process was evaluated by three models of RSM, CCD-ANFIS, and CCD-GRNN. Furthermore, comprehensive kinetic, isotherm, thermodynamic, reusability cycles and optimization (by GA and DF) studies were conducted to evaluate the behavior and adsorption mechanism of I₂ on the surface of Mg-Co-Al-LDH@ g-C₃N₄ nanocomposite. High removal efficiency (95.25%) of ¹³¹I in only 30 min (i.e. during 1/384 its half-life), along with an excellent capacity that has ever been reported (2200.70 mg/g) and recyclability (seven times without breakthrough in the efficiency), turns the nanocomposite to a very promising option in remediation of ¹³¹I-containing solutions. Besides, from the models studied, ANFIS described the process with the highest accuracy and reliability with R² > 0.999.

Halide removal from water using silver doped magnetic-microparticles

This study proposes the use of new materials based on core-shell structure magnetic microparticles with Ag⁰ (Ag(0)-MPs) on their surface to remove bromides and chlorides from waters intended for human consumption. Hydrogen peroxide was used as oxidizing agent, Ag(0)-MPs is thereby oxidized to Ag (I)-MPs, which, when in contact with Cl^- and Br^- ions, form the corresponding silver halide (AgCl and AgBr) on the surface of Ag-MPs. The concentration of Cl^- and Br^- ions was followed by using ion selective electrodes (ISEs). Silver microparticles were characterized by high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy, while the presence of AgCl and AgBr on Ag-MPs was determined by microanalysis. We analyzed the influence of operational variables, including: hydrogen peroxide concentration in Ag-MP system, medium pH, influence of Cl^- ions on Br^- ion removal, and influence of tannic acid as surrogate of organic matter in the medium. Regarding the influence of pH, Br^-and Cl^- removal was constant within the pH range studied (3.5-7), being more effective for Br^- than for Cl^- ions. Accordingly, this research states that the system Ag-MPs/H₂O₂ can remove up to 67.01% of Br^- ions and 56.92% of Cl^- ions from water (pH = 7, [Ag-MPs]₀ = 100 mg L^-1, [H₂O₂]₀ = 0.2 mM); it is reusable, regenerated by radiation and can be easily removed by applying a magnetically assisted chemical separation process.

Removal of iodide from water using silver nanoparticles-impregnated synthetic zeolites

Synthetic zeolite-based Ag-nanocomposites were synthesized, characterized and used to remove iodide from aqueous solutions. The results showed high removal efficiency (up to 94.85%) and the formation silver iodide which is stable into the material. The maximum achieved adsorption capacity of the nanocomposites was between 19.54 and 20.44mg/g. The removal mechanism was meticulously studied by taking into account both water chemistry and surface interactions backed by multiple characterization techniques, such as XRD, XRF, SEM/EDX, TEM and BET. The qualitative and quantitative examination of pre- and post-adsorption of nanocomposite samples proved that the anchored silver iodide was formed via oxidation of initial silver nanoparticles followed by reaction with iodide to form a stable crystalline precipitate on the surface of the materials. A diffusion-based adsorption model indicated that the controlling mechanism is a slow intraparticle surface diffusion with diffusion coefficients in the range of 0.37-1.72×10^-13cm²/s. The investigation of competing and co-existing anions (Cl^-, Br^-, CO₃^2-, and CrO₄^2-) on the removal efficiency of iodide demonstrated a negligible effect showing a kinetically favorable precipitation reaction of iodide over other anions.

Adsorptive removal of gaseous methyl iodide by triethylenediamine (TEDA)-metal impregnated activated carbons under humid conditions

Removal of gaseous radioactive iodine (¹³¹I and ¹²⁹I) compounds from nuclear facilities is an important issue. Herein we assessed the adsorptive capacity of gaseous non-radioactive methyl iodide (CH₃¹²⁷I) as a simulant on two commercial TEDA-metal impregnated activated carbon(AC)s. The characterizations of the ACs were determined ICP-MS, XPS, and 77 K N₂ isotherms. As a result, it was found that one AC has a small amount of TEDA but a well-developed porosity, and the other one was abundant with TEDA, but the porosity was relatively less developed. The methyl iodide removal performances were evaluated under 10 ppm and 400 ppm using breakthrough experiments under various relative humidities (RH). Desorption was also carried out using nitrogen after adsorption to investigate adsorption affinity. Methyl iodide adsorption capacity of TEDA-rich AC decreased significantly as RH increased at 10 ppm. Conversely, performance degradation was clearly observed from less TEDA-impregnated AC with well-developed porosity as RH increased at 400 ppm. It is demonstrated that the amount of physisorbed methyl iodide is decreased as RH increased. Although moisture decreases the adsorption amount, it enhances the adsorption affinity. Also, additional TEDA impregnation to ACs results in improving the performance under severe condition (RH90%, 400 ppm).

Construction of hydrophobic interface on natural biomaterials for higher efficient and reversible radioactive iodine adsorption in water

For the pollution of radioactive materials, it is of great importance to develop efficient adsorbents for radioactive iodine adsorption in aqueous solution. In this work, a simple and green strategy was developed to construct hydrophobic surface on natural cotton fibers (n-CF) based on organic-soluble carbon dots (OCDs) for the first time. The results demonstrated the successful constructed hydrophobic n-CF@OCDs expressed excellent stability and selectivity for iodine (I₂) adsorption in water. The maximum adsorption capacity for I₂ on n-CF@OCDs is calculated to be 190.1 mg g^-1, which is about 6.8 times higher than that of n-CF (28.1 mg g^-1), this highly I₂ adsorption efficiency should be attributed to the hydrophobic properties of adsorbent. The adsorption mechanism was also discussed in this work. In addition, the adsorbed I₂ could be desorbed easily with a simple reductive process at ambient conditions, which can lead to not only the restore of I₂ but also the recycling of adsorbent, illustrating their good practicability. Furthermore, this universal strategy can also be used for construction of hydrophobic surface on various natural biomaterials, demonstrating its potential application in constructing of hydrophobic surface and used for the adsorption and removal of nonpolar pollutions or radioactive waste in aqueous solutions.

Decontamination of radioactive wastewater: State of the art and challenges forward

Radioactive substances have been widely used in many industrial sectors, e.g. nuclear power station, biomedical engineering, etc. With increasing applications of nuclear technology, more and more radioactive wastewater is being generated via different channels, which indeed is posing an emerging challenge and threat to the environment and human health. Given such a situation, this review attempts to offer a holistic view with regard to the state of the art of technology for decontamination of radioactive wastewater as well as shed lights on the challenges forward. Different from reclamation of other types of wastewaters, the most challenging issue in decontamination of radioactive wastewater is the effective stabilization and solidification of soluble radioactive nuclides present in wastewater, which are critical for final disposal. Moreover, the potential risk of human exposure to wastewater radiation needs to be carefully assessed, and this issue should also be taken into consideration in the selection, design and operation of the radioactive wastewater treatment process. These clearly differentiate the treatment principle of radioactive wastewater from those of traditional industrial and municipal wastewaters. Lastly, the challenges from the perspectives of technology development, environmental and human health impacts and possible solutions forward are also elucidated.

Nanometer mixed-valence silver oxide enhancing adsorption of ZIF-8 for removal of iodide in solution

Nano mixed-valence silver oxide (Ag₂O-Ag₂O₃) modified the zeolitic imidazolate framework-8 (ZIF-8) composite (Ag₂O-Ag₂O₃@ZIF-8) was firstly prepared via a simple and efficient method, characterized and applied for iodide ion (I^-) uptake from simulated radioactive wastewater. The results showed that Ag₂O-Ag₂O₃ nanoparticles doped and uniformly dispersed on the surface of ZIF-8 matrix. The adsorption capacity of the as-synthesized adsorbents increased with the increasing Ag doped amount, and the maximum adsorption capacity for 20%-Ag₂O-Ag₂O₃@ZIF-8 was 232.12 mg/g. The calculated thermodynamic parameters indicating that the adsorption was a spontaneous and exothermic. It was worth mentioning that each Ag-based adsorbent exhibited high uptake rate of I^-, and all the adsorption tests were equilibrated for a few minutes. This could be ascribed to its large specific surface area and the absolutely dominant position of chemical adsorption for as-prepared samples. Furthermore, the adsorption was barely affected by pH and competitive anions (e.g. Cl^-, SO₄^2-, CO₃^2-), even in simulated salt lake water. Additionally, a mechanism explaining the excellent properties for adsorbents could be epitomized into three aspects, namely, the uptake performance of Ag₂O for I^-, the strong oxidization of Ag₂O₃ for I^-, and the adsorption of AgI for I₂.

Silver Nanomaterial-Immobilized Desalination Systems for Efficient Removal of Radioactive Iodine Species in Water

Increasing concerns regarding the adverse effects of radioactive iodine waste have inspired the development of a highly efficient and sustainable desalination process for the treatment of radioactive iodine-contaminated water. Because of the high affinity of silver towards iodine species, silver nanoparticles immobilized on a cellulose acetate membrane (Ag-CAM) and biogenic silver nanoparticles containing the radiation-resistant bacterium Deinococcus radiodurans (Ag-DR) were developed and investigated for desalination performance in removing radioactive iodines from water. A simple filtration of radioactive iodine using Ag-CAM under continuous in-flow conditions (approximately 1.5 mL/s) provided an excellent removal efficiency (>99%) as well as iodide anion-selectivity. In the bioremediation study, the radioactive iodine was rapidly captured by Ag-DR in the presence of high concentration of competing anions in a short time. The results from both procedures can be visualized by using single-photon emission computed tomography (SPECT) scanning. This work presents a promising desalination method for the removal of radioactive iodine and a practical application model for remediating radioelement-contaminated waters.

Magnetite nanoparticles supported on organically modified montmorillonite for adsorptive removal of iodide from aqueous solution: Optimization using response surface methodology

Magnetite nanoparticles supported on organically modified montmorillonite (MNP-OMMTs) were successfully synthesized by a facile coprecipitation method. The surface of natural clay was modified using a cationic surfactant, hexadecyltrimethylammonium. The synthesized MNP-OMMTs were used as an adsorbent to remove iodide from aqueous solutions. The maximum adsorption capacity of the adsorbent was 322.42mg/g, which is much higher than other previously reported adsorbents for removing iodide in aqueous solution. The experimental data were well fitted to a pseudo-second-order kinetic model, and the adsorption behavior followed the Langmuir isotherm. A thermodynamic study indicated that iodide adsorption was spontaneous and endothermic. The individual and combined effects of key process parameters (pH, temperature, and initial iodide concentration) were studied using a response surface methodology. The maximum iodide removal efficiency of 93.81% was obtained under the optimal conditions of pH3.9, a temperature of 41.3°C, and an initial iodide concentration of 113.8mg/L.

One-step synthesis of Ag2O@Mg(OH)2 nanocomposite as an efficient scavenger for iodine and uranium

Ag₂O nanoparticles anchored on the Mg(OH)₂ nanoplates (Ag₂O@Mg(OH)₂) were successfully prepared by a facile one-step method, which combined the Mg(OH)₂ formation with Ag₂O deposition. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption analysis. It was found that Ag₂O nanoparticles anchored on the Mg(OH)₂ nanoplates show good dispersion and less aggregation relative to the single Ag₂O nanoaggregates. In addition, iodide (I^-) removal by the Ag₂O@Mg(OH)₂ nanocomposite was studied systematically. Batch experiments reveal that the nanocomposite exhibits extremely high I^- removal rate (<10min), and I^- removal capacity is barely affected by the concurrent anions, such as Cl^-, SO₄^2-, CO₃^2- and NO₃^-. Furthermore, I^- and UO₂²⁺ could be simultaneously removed by the nanocomposite with high efficiency. Due to the simple synthetic procedure, the excellent removal performances for iodine and uranium, and the easy separation from water, the Ag₂O@Mg(OH)₂ nanocomposite has real potential for application in radioactive wastewater treatment, especially during episodic environmental crisis.

Facile Fabrication of Nanofibrillated Chitin/Ag2O Heterostructured Aerogels with High Iodine Capture Efficiency

Nanofibrillated chitin/Ag₂O aerogels were fabricated for radioiodine removal. Chitin was first fabricated into nanofibers with abundant acetyl amino groups (–NHCOCH₃) on the surface. Then, highly porous chitin nanofiber (ChNF) aerogels were obtained via freeze-drying. The ChNF aerogels exhibited a low bulk density of 2.19 mg/cm³ and a high specific surface area of 179.71 m²/g. Ag₂O nanoparticles were evenly anchored on the surfaces of ChNF scaffolds via strong interactions with –NHCOCH₃ groups, subsequently yielding Ag₂O@ChNF heterostructured aerogels. The composites were used as efficient absorbents to remove radioiodine anions from water and capture a high amount of I₂ vapor in the forms of AgI and iodine molecules. The adsorption capacity of the composite monoliths can reach up to 2.81 mmol/g of I⁻ anions. The high adsorbability of the composite monolithic aerogel signifies its potential applications in radioactive waste disposal.

Radio-iodide uptake by modified poly (glycidyl methacrylate) as anion exchange resin

Poly(glycidyl methacrylate) (PGMA) microspheres were prepared by radiation induced polymerization of glycidyl methacrylate (GMA) monomer. The factors affecting the degree of polymerization and yield (%) of PGMA such as type of solvent, monomer concentration, and irradiation dose were investigated. It was found that the PGMA yield (%) increases with increasing monomer concentration up to 50% and absorbed dose of 5 kGy. The resulting PGMA containing the epoxy group waschemically modified by hydroxyl amine to act as anion-exchange resin for uptake of 131I− ions. The modified PGMA (MPGMA) was characterized by Fourier transform infra-red (FT-IR) spectrophotometer, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). I-131 is produced from the fission of U-235 with low-enrichment uranium (LEU) targets in the Egyptian Second Research Reactor (ETRR-2). Separation of iodide from the radioactive solution by batchwise and column techniques was employed to determine the adsorption capacity of the MPGMA. Quality control of 131I product solution and radiochemical purity was examined by using the ascending paper chromatography method. The uptake behavior of MPGMA towards 131I− ions were studied at different experimental conditions and achieved by X-ray fluorescence (XRF). The synthesized MPGMA showed good results as anion-exchange and an effective adsorbent for uptaking 131I− ions.

Safe disposal of radioactive iodide ions from solutions by Ag2O grafted sodium niobate nanofibers

Radioactive iodine isotopes are released into the environment by the nuclear industry and medical research institutions using radioactive materials, and have negative effects on organisms living within the ecosystem. Thus, safe disposal of radioactive iodine is necessary and crucial. For this reason, the uptake of iodide ions was investigated in Ag2O nanocrystal grafted sodium niobate nanofibers, which were prepared by forming a well-matched phase coherent interface between them. The resulting composite was applied as an efficient adsorbent for I(-) anions by forming an AgI precipitate, which also remained firmly attached to the substrates. Due to their one-dimensional morphology, the new adsorbents can be easily dispersed in liquids and readily separated after purification. This significantly enhances the adsorption efficiency and reduces the separation costs. The change in structure from the pristine sodium niobate to Ag2O anchored sodium niobate and to the used adsorbent was examined by using various characterization techniques. The effects of Ag(+) concentration, pH, equilibration time, ionic strength and competing ions on the iodide ion removal ability of the composite were studied. The Ag2O nanocrystal grafted sodium niobate adsorbent showed a high adsorption capacity and excellent selectivity for I(-) anions in basic solutions. Our results are useful for the further development of improved adsorbents for removing I(-) anions from basic wastewater.