Bimetallic AgCu/Cu2O hybrid for the synergetic adsorption of iodide from solution

Recent Advances in the Removal of Radioactive Iodine and Iodide from the Environment

Iodine (I2) in the form of iodide ions (I-) is an essential chemical element in the human body. Iodine is a nonmetal that belongs to the VIIA group (halogens) in the periodic table. Over the last couple of centuries, the exponential growth of human society triggered by industrialization coincided with the use of iodine in a wide variety of applications, including chemical and biological processes. However, through these processes, the excess amount of iodine eventually ends up contaminating soil, underground water, and freshwater sources, which results in adverse effects. It enters the food chain and interferes with biological processes with serious physiological consequences in all living organisms, including humans. Existing removal techniques utilize different materials such as metal-organic frameworks, layered double hydroxides, ion-exchange resins, silver, polymers, bismuth, carbon, soil, MXenes, and magnetic-based materials. From our literature survey, it was clear that absorption techniques are the most frequently experimented with. In this Review, we have summarized current advancements in the removal of iodine and iodide from human-made contaminated aqueous waste.

Synthesis and characterization of Ag@Cu-based MOFs as efficient adsorbents for iodine anions removal from aqueous solutions

Due to the critical importance of capturing radioiodine from aquatic environments for human health and ecosystems, developing highly efficient adsorbent materials with rapid kinetics for capturing iodide ions in aqueous solutions is urgently needed. Although extensive research has been conducted on iodine adsorption in gas and organic phases, limited research has been dedicated to adsorption in aqueous solutions. An effective technique for removing iodide was proposed using Ag@Cu-based MOFs synthesized by incorporating Ag into calcined HKUST-1 with varying mass ratios of Ag/Cu-C. Extensive characterization using SEM, XRD, XPS, and nitrogen adsorption-desorption analysis confirmed successful incorporation of Ag in Cu-C. Batch adsorption experiments were conducted, demonstrating that the 5% Ag@Cu-C material exhibited a high adsorption capacity of 247.1 mg g^-1 at pH 3. Mechanism investigations revealed that Cu⁰ and dissolved oxygen in water generate Cu₂O and H₂O₂, while Ag and a small amount of CuO generate Ag₂O and Cu₂O. Furthermore, iodide ions in the solution are captured by Cu⁺ and Ag⁺ adsorption sites. These findings highlighted the potential of Ag@Cu-based MOFs as highly effective adsorbents for iodine anions removal in radioactive wastewater.

Effect of different synthesis methodologies on the adsorption of iodine

Radioactive nuclides such as cesium, ruthenium, and iodine are difficult to remove in radioactive wastewater, which could be removed by coprecipitation of special chemical precipitants. In this study, dynamic Cu/Ag-mordenite (Cu/Ag-MOR) material was synthesized to be treated as the precipitant to selectively adsorb the iodine ion (I^-) through controlled chemisorption combined with physical adsorption. XRD, XPS, and FTIR characterization demonstrated the successful modification of the MOR carrier surface by Cu/Ag particles and the high selectivity of the active component Cu (I) on the dynamic Cu/Ag-MOR material. SEM, TEM, and BET methods were used to characterize the Cu/Ag-MOR material, demonstrating these results: the MOR carried a stable porous structure, which allowed the silver to be well dispersed on its surface. The silver improved the copper distribution by being well-coated by the copper species. Furthermore, the analysis of the factors influencing the chemical plating of copper showed that the pH, the concentration of EDTA-2Na and the temperature all influenced the deposition rate of Cu₂O. The activation energy for Cu₂O deposition in dynamic Cu/Ag-MOR was 20.31 kJ/mol. The highest removal of I^- in the presence of dynamic Cu/Ag-MOR could reach 99.1% in the adsorption tests. The adsorption kinetics was under a proposed second-order model, with chemisorption being the controlling step of the reaction. The adsorption/desorption experiments demonstrated the reusability of the nano-sorbent. It was also demonstrated that dynamic Cu/Ag-MOR materials showed good applicability in complex situations where multiple pollutants co-exist.

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.

Mn3O4@polyaniline nanocomposite with multiple active sites to capture uranium(VI) and iodide: synthesis, performance, and mechanism

A major challenge for radioactive wastewater treatment and associated environmental remediation is how to simultaneously remove cationic and anionic radionuclides. Herein, a series of Mn₃O₄@polyaniline (Mn₃O₄@PANI) nanocomposites were successfully prepared and used to remove U(VI) and I^- from aqueous solution, two highly concomitant species in nuclear pollution settings. Batch adsorption experiments reveal that the component Mn₃O₄ is predominantly responsible for U(VI) removal, but PANI for I^-. The nanocomposite with 24.2 wt% Mn₃O₄ possesses high removal percentages (> 85%) either for U(VI) or I^- over a wide pH range, fast removal kinetics, and excellent adsorption selectivity at high concentrations of competing ions. Benefiting from the contributions of the two components and the high adsorption affinities, the nanocomposite achieves the simultaneous removal to coexisting U(VI) and I^-, with a maximum adsorption capacity 102.6 mg/g for U(VI) and 126.1 mg/g for I^-. X-ray photoelectron spectroscopy (XPS) results reveal that the U(VI) adsorption occurs via coordination bonding with Mn-O, -NH- , and =N- groups in the nanocomposite, whereas I^- adsorption proceeds mainly through I anionic species exchange with Cl^- and interactions with π-bonds in PANI, as well as the electrostatic attraction onto Mn₃O₄. Considering the excellent performance and multiple active sites, the Mn₃O₄@PANI nanocomposite is promising to remove practical radioactive U(VI) and I^-.

Magnetic chitosan microspheres: An efficient and recyclable adsorbent for the removal of iodide from simulated nuclear wastewater

The efficient and recyclable magnetic chitosan microspheres (MCMs) were successfully synthesized to remove iodide from nuclear wastewater and characterized through XRD, FTIR, SEM, EDS, VSM, TGA and XPS. The characterization results indicated that the MCMs exhibited smooth spherical morphology and good magnetic properties. The removal potential of MCMs was investigated for iodide (I^-) anions at different conditions. From pH 3 to pH 9, MCMs performed the high I^- removal efficiency (>90%). The maximum I^- removal capacity of MCMs was up to 0.8087 mmol g^-1 at 298 K, well-fitting with the pseudo-second-order and Sips models. Furthermore, the I^- removal efficiency of MCMs still maintained more than 91% after five adsorption-desorption cycles, performing good regeneration and reusability. This study is expected to prompt the MCMs to become an efficient and recyclable biosorbent for iodide removal from nuclear wastewater.

Rapid synthesis of polyimidazole functionalized MXene via microwave-irradiation assisted multi-component reaction and its iodine adsorption performance

The adsorption applications of MXene-based adsorbents have intensively investigated recently. However, the performance of MXene-based adsorbents has been largely limited owing to their lack of functional groups and adsorptive sites. Therefore, surface functionalization of MXene is an important route to achieve better performance for environmental adsorption. Herein, polyionic liquid functionalized MXene (named as MXene-PIL) was prepared through a multi-component reaction and adsorptive removal of iodine by MXene-PIL was also evaluated. The successful generation of PIL on MXene was confirmed by a series of characterization measurements. Furthermore, the effects of contact time, iodine concentration, environmental temperature and other factors on the adsorption performance of MXene-PIL were investigated. Adsorption kinetic analysis including pseudo-first-order dynamic model, pseudo-second-order dynamic model and Weber-Morris model, adsorption thermodynamic analysis such as Langmuir and Freundlich models and Van't Hoff equation were used for further analysis the adsorption behavior of iodine by MXene-PIL. We demonstrated that the adsorption capacity could be as high as about 170 mg/g, which is obviously larger than the unmodified MXene and most of other reported adsorbents. Taken together, a simple strategy has been developed for in-situ generation of PIL on MXene and the resultant composites show potential application for adsorptive removal of iodine.

Effective removal of iodate by coprecipitation with barite: Behavior and mechanism

Radioactive iodine (¹²⁹I) is of great concern owing to its high mobility in the environment and long-term radiotoxicity. However, there is a lack of effective techniques for removing iodate (IO₃^-) from aqueous solution. This study aims to develop a new technique for removing radioactive iodate from contaminated solution by using barite (BaSO₄). We examined the coprecipitation mechanism of iodate by barite at the molecular level to determine the optimum conditions for iodate removal. Results showed that iodate was effectively removed from the aqueous solution by coprecipitation even in the presence of competitive anions. Based on comparison of our method with previous techniques, the iodate removal efficiency by barite was determined to be about two orders of magnitude greater than that by hydrotalcite-like layered double hydroxide at 10 mmol L^-1 Cl^-. Extended X-ray absorption fine structure analysis indicated that the incorporated iodate was strongly bound to the crystal lattice of barite by substituting the sulfate site in the structure when the iodine concentration was low. The charge compensation problem from the IO₃^- substitution in the SO₄^2- site was achieved by the substitution of Na⁺-IO₃^- pairs at the nearest Ba²⁺ site. Given the high removal efficiency and strong binding of iodate to barite, coprecipitation with barite is a promising tool for removing radioactive iodate from various aqueous solutions contaminated with iodate.

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.

Efficient removal of iodide anion from aqueous solution with recyclable core-shell magnetic Fe3O4@Mg/Al layered double hydroxide (LDH)

Magnetic Mg/Al layered double hydroxides (LDH) with three cationic ratios (Mg/Al = 2:1, 3:1, and 4:1) were successfully synthesized and utilized for the first time in an iodide adsorption study. The effects of the Mg/Al ratio of LDH on iodide adsorption were investigated, and physicochemical properties of synthetic LDHs depending on Mg/Al ratio were confirmed by XRD, TEM, ICP-OES, VSM, Zeta-potential, and BET analyses. The ferrimagnetic property was well preserved even after a coating of LDH on magnetite irrespective of the Mg/Al ratio. Among the three Mg/Al ratios, the calcined Fe₃O₄@4:1 Mg/Al LDH exhibited excellent performance for iodide removal with 105.04 mg/g of the maximum iodide adsorption capacity due to its wide interlayer spacing and largest BET surface area. In the presence of competing carbonate anions, the Fe₃O₄@4:1 LDH showed removal rate of >80% at a dosage of over 3 g/L solid to liquid ratio. The recyclability test of Fe₃O₄@4:1 LDH showed that the removal performance for iodide is maintained at >80% even during the first to the fourth cycles. These results demonstrated that the magnetic Mg/Al LDH adsorbent can be effectively utilized for remediation of radioactive iodide anions with high efficiency and economics.

Enhanced removal of I- on hierarchically structured layered double hydroxides by in suit growth of Cu/Cu2O

To further improve the removal ability of layered double hydroxide (LDH) for iodide (I^-) anions from wastewater, we prepared hierarchically porous Cu₅Mg₁₀Al₅-LDH and used as a matrix for in suit growth of Cu/Cu₂O on its surface, forming Cu/Cu₂O-LDH, which was characterized and applied as an adsorbent. Results displayed high I^- saturation uptake capability (137.8 mg/g) of Cu/Cu₂O-LDH compared with Cu₅Mg₁₀Al₅-LDH (26.4 mg/g) even thermal activated LDH (76.1 mg/g). Thermodynamic analysis showed that the reaction between I^- anions and Cu/Cu₂O-LDH is a spontaneous and exothermic. Uptake kinetics analysis exhibited that adsorption equilibrium can be reached after 265 min. Additionally, the adsorbent showed satisfactory selectivity in the presence of competitive anions (e.g., SO₄^2-), and could achieve good adsorption performance in a wide pH range of 3-8. A cooperative adsorption mechanism was proposed on the basis of the following two aspects: (1) ion exchange between iodide and interlayer anions; (2) the adsorption performance of Cu, Cu(II) and Cu₂O for I^-. Meanwhile, the difference between the adsorption mechanism of Cu/Cu₂O-LDH, Cu₅Mg₁₀Al₅-LDH and Cu₅Mg₁₀Al₅-CLDH adsorbents was also elaborated and verified.

Cross-linked chitosan microspheres entrapping silver chloride via the improved emulsion technology for iodide ion adsorption

Radioactive iodine waste from nuclear plant became the severe environmental problem and led to the public health concern. The cross-linked chitosan adsorbed iodide anions through the electrical attraction, yet performing limited-efficiently. Targeting as the better adsorption, the modified chitosan sorbent as AgCl@CM (silver chloride entrapped in the cross-linked chitosan microspheres) for iodine adsorption was proposed and implemented by chemisorption from AgCl and physisorption from chitosan via the improved emulsion method (emulsions mixing-collision and polymerization). With the broad application from pH 2 to pH 10, the spherical AgCl@CM (from 0.20 g silver nitrate) performed the I¹²⁷ anions (instead of radioactive iodine) adsorption efficiency of higher than 90 % in 20 min, with the maximum adsorption capacity of 1.5267 mmol/g, well-fitting with the pseudo-first-order model and Sips isothermal model. AgCl@CM also performed I¹²⁷ adsorption with the significant selectivity relative to Cl^-. The micro-spherical AgCl@CM sorbents were therefore prospective-effectively for iodine waste water treatment.

Cesium retention and release from sulfur polymer concrete matrix under normal and accidental conditions

This paper proposes an efficient two-stage process for stabilization and solidification of the Cs-137 isotope in a sulfur polymer concrete (SPC) matrix. Lignite slag (SL) and fly ash (FA) were applied as active fillers for cesium immobilization. To study the release of Cs-137 isotope and determine the tracer activity in the leachates, we applied a slightly modified ANSI/ANS 16.1 protocol and the gamma spectrometry technique. The measured effective diffusion coefficients for the Cs-137 isotope were between 0.84·10^-9 and 3.10·10^-9 cm²·s^-1. Normalized leaching rates were within the range of 1.74·10^-5 - 3.85·10^-5 g·cm^-2·d^-1, fulfilling acceptance criteria for radioactive wasteforms. As well as standard leaching under static conditions, we also studied dynamic leaching of SPC samples at increased temperatures and leaching in an aggressive environment. The Cs-137 effective diffusion coefficients were found to increase by 3 - 4 orders of magnitude (10^-6 - 10^-5 cm²·s^-1), while the normalized leaching rate reached values of up to 2.36·10^-3 g·cm^-2·d^-1 after 28 days of leaching. The proposed cesium immobilization mechanism is based on the formation of cesium silicate and aluminosilicate phases, together with effective matrix sealing during the SPC manufacturing process.

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.

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.

Enhanced Uptake of Iodide from Solutions by Hollow Cu-Based Adsorbents

Cu₂O exhibits excellent adsorption performance for the removal of I⁻ anions from solutions by doping of metallic Ag or Cu. However, the adsorption process only appears on the surface of adsorbents. To further improve the utilization efficiencies of Cu content of adsorbents in the uptake process of I⁻ anions, hollow spheres of metallic Cu, Cu/Cu₂O composite and pure Cu₂O were prepared by a facile solvothermal method. Samples were characterized and employed for the uptake of I⁻ anions under various experimental conditions. The results show that Cu content can be tuned by adjusting reaction time. After the core was hollowed out, the uptake capacity of the samples increased sharply, and was proportional to the Cu content. Moreover, the optimal uptake was reached within only few hours. Furthermore, the uptake mechanism is proposed by characterization and analysis of the composites after uptake. Cu-based adsorbents have higher uptake performance when solutions are exposed to air, which further verified the proposed uptake mechanism. Finally, hollow Cu-based adsorbents exhibit excellent selectivity for I⁻ anions in the presence of large concentrations of competitive anions, such as Cl⁻, SO₄²⁻ and NO₃⁻, and function well in an acidic or neutral environment. Therefore, this study is expected to promote the development of Cu-based adsorbents into a highly efficient adsorbent for the removal of iodide from solutions.