Comprehensive comparison of bismuth and silver functionalized nickel foam composites in capturing radioactive gaseous iodine

Surfactant-Mediated Crystalline Structure Evolution Enabling the Ultrafast Green Synthesis of Bismuth-MOF in Aqueous Condition

Green synthesis of stable metal-organic frameworks (MOFs) with permanent and highly ordered porosity at room temperature without needing toxic and harmful solvents and long-term high-temperature reactions is crucial for sustainable production. Herein, a rapid and environmentally friendly synthesis strategy is reported to synthesize the complex topological bismuth-based-MOFs (Bi-MOFs), [Bi9(C9H3O6)9(H2O)9] (denoted CAU-17), in water under ambient conditions by surfactant-mediated sonochemical approach, which could also be applicable to other MOFs. This strategy explores using cetyltrimethylammonium bromide (CTAB) amphiphilic molecules as structure-inducing agents to control the removal of non-coordinated water (dehydration) and enhance the degree of deprotonation of the ligands, thereby regulating the coordination and crystallization in aqueous solutions. In addition, another two new strategies for synthesizing CAU-17 by crystal reconstruction and one-step synthesis in binary solvents are provided, and the solvent-induced synthesis mechanism of CAU-17 is studied. The as-prepared CAU-17 presents a competitive iodine capture capability and effective delivery of the antiarrhythmic drug procainamide (PA) for enteropatia due to the broad pH tolerance and the unique phosphate-responsive destruction in the intestine. The findings will provide valuable ideas for the follow-up study of surfactant-assisted aqueous synthesis of MOFs and their potential applications.

Highly efficient capture of iodine vapor by [Mo3S13]2- intercalated layered double hydroxides

From the swollen LDH, bulky [Mo3S13]2- anions are facilely introduced into the LDH interlayers to assemble the Mo3S13-LDH composite, which exhibits excellent iodine capture performance and good irradiation resistance. The positive-charged LDH layers may disperse the [Mo3S13]2- uniformly within the interlayers, providing abundant adsorption sites for effectively trapping iodine. The Mo-S bond serving as a soft Lewis base has strong affinity to I2 with soft Lewis acidic characteristic, which is conducive to improvement of iodine capture via physical sorption. Besides, chemisorption has a significant contribution to the iodine adsorption. The S22-/S2- in [Mo3S13]2- can reduce the I2 to [I3]- ions, which are facilely fixed within the LDH gallery in virtue of electrostatic attraction. Meanwhile, the S22-/S2- themselves are oxidized to S8 and SO42-, while Mo4+ is oxidized (by O2 in air) to Mo6+, which combines with SO42- forming amorphous Mo(SO4)3. With the collective interactions of chemical and physical adsorption, the Mo3S13-LDH demonstrates an extremely large iodine adsorption capacity of 1580 mg/g. Under γ radiation, the structure of Mo3S13-LDH well maintains and iodine adsorption capability does not deteriorate, indicating the good irradiation resistance. This work provides an important reference to tailor cost-effective sorbents for trapping iodine from radioactive nuclear wastes.

Construction of hydroxyl-functionalized hyper-crosslinked networks from polyimide for highly efficient iodine adsorption

The rapid development of nuclear energy posed a great threat to the environment and human health. Herein, two hydroxyl-functionalized hyper-crosslinked polymers (PIHCP-1 and PIHCP-2) containing different electron active sites have been synthesized via Friedel-Crafts alkylation reaction of the polyimides. The resulting polymers showed a micro/mesoporous morphology and good thermal and chemical stability. Rely on the high porosity and multi-active sites, the PIHCPs show an ultrahigh iodine uptake capacity reached 6.73 g g-1 and the iodine removal efficiency from aqueous solution also reaches 99.7%. Kinetic analysis demonstrates that the iodine adsorption on PIHCPs was happened on the heterogeneous surfaces in the form of multilayer chemisorption. Electrostatic potential (ESP) calculation proves the great contribution of hydroxyl groups on the iodine capture performance. In addition, the iodine capture efficiency of both adsorbents can be maintained over 91% after four cyclic experiments which ensures their good recyclability for further practical applications.

[Sn2S6]4- Anion-Intercalated Layered Double Hydroxides for Highly Efficient Capture of Iodine

The development of low-cost and high-efficiency iodine sorbents is of great significance for the control of nuclear pollution. In this work, we intercalate the tin sulfide cluster of [Sn2S6]4- to Mg/Al-type layered double hydroxides to obtain Sn2S6-LDH, which exhibits highly efficient capture performance of iodine vapor and iodine in solutions. The dispersion effect of the positively charged LDH layers contributes to the adequate exposure of [Sn2S6]4- anions, providing plentiful adsorption sites. For iodine vapor, Sn2S6-LDH showed an extremely large iodine capture capacity of 2954 mg/g with a large contribution from physisorption. For iodine in solutions, a significantly large sorption capacity of 1308 mg/g was achieved. During iodine capture, I2 molecules were reduced to I- ions (by S2- in [Sn2S6]4-), which then reacted with Sn4+ to form SnI4, where the molar amount of captured iodine is 4-fold that of Sn. Besides, the as-reduced I- combined with I2 again to generate [I3]-, which then entered the LDH interlayers to maintain electric neutrality. While reducing iodine, S2- itself in [Sn2S6]4- was oxidized to S8, which further combined with SnI4 to form a novel compound of SnI4(S8)2. The excellent iodine capture capability endows Sn2S6-LDH with a promising application in trapping radioactive iodine.

Three-Dimensional-Network-Structured Bismuth-Based Silica Aerogel Fiber Felt for Highly Efficient Immobilization of Iodine

The effective capture and deposition of radioactive iodine in the spent fuel reprocessing process is of great importance for nuclear safety and environmental protection. Three-dimensional (3D) fiber felt with structural diversity and tunability is applied as an efficient adsorbent with easy separation for iodine capture. Here, a bismuth-based silica aerogel fiber felt (Bi@SNF) was synthesized using a facile hydrothermal method. Abundant and homogeneous Bi nanoparticles greatly enhanced the adsorption and immobilization of iodine. Notably, Bi@SNF demonstrated a high capture capacity of 982.9 mg/g by forming stable BiI3 and Bi5O7I phases, which was about 14 times higher than that of the unloaded material. Fast uptake kinetics and excellent resistance to nitric acid and radiation were exhibited as a result of the 3D porous interconnected network and silica aerogel fiber substrate. Adjustable size and easy separation and recovery give the material potential as a radioactive iodine gas capture material.

Bi0-Reduced Graphene Oxide Composites for the Enhanced Capture and Cold Immobilization of Off-Gas Radioactive Iodine

Radioactive waste management is critical for maintaining the sustainability of nuclear fuel cycles. In this study, we propose a novel bismuth-based reduced graphene oxide (Bi0-rGO) composite for the immobilization of off-gas radioactive iodine. This material synthesized via a solvothermal route exhibited a low surface area (2.96 m2/g) combined with a maximum iodine sorption capacity of 1228 ± 25 mg/g at 200 °C. The iodine sorbent was mixed with Bi2O3 powder and distilled water to fabricate waste matrices, which were cold-sintered at 300 °C under a uniaxial pressure of 500 MPa for 20 min to achieve a relative density of ∼98% and Vickers hardness of 1.3 ± 0.1 GPa. The utilized methodology reduced the iodine leaching rate by approximately 3 orders of magnitude through the formation of a chemically durable iodine-bearing waste form (BiOI). This study demonstrates the high potential of Bi0-rGO as an innovative solution for the immobilization of radioactive waste at relatively low temperatures.

Adsorption and Detection of Iodine Species by a Thorium-Based Metal-Organic Framework

Actinide-bearing metal-organic frameworks (MOFs) encompass intriguing structures and properties, but the radioactivity of actinide cripples their applications. Herein, we have constructed a new thorium-based MOF (Th-BDAT) as a bifunctional platform for the adsorption and detection of radioiodine, a more radioactive fission product that can readily spread through the atmosphere in its molecular form or via solution as anionic species. The iodine capture within the framework of Th-BDAT from both the vapor phase and the cyclohexane solution has been verified, showing that Th-BDAT features maximum I₂ adsorption capacities (Q_max) of 959 and 1046 mg/g, respectively. Notably, the Q_max of Th-BDAT toward I₂ from cyclohexane solution ranks among the highest value for Th-MOFs reported to date. Furthermore, incorporating highly extended and π-electron-rich BDAT^4- ligands renders Th-BDAT as a luminescent chemosensor whose emission can be selectively quenched by iodate with a detection limit of 1.367 μM. Our findings thus foreshadow promising directions that might unlock the full potential of actinide-based MOFs from the point of view of practical application.

Impact of oxidation and carbonation on the release rates of iodine, selenium, technetium, and nitrogen from a cementitious waste form

Evaluation of the long-term retention mechanisms and potential release rates for the primary constituents of potential concern (COPCs) (i.e., Tc, I, Se, and nitrate) is necessary to determine if Cast Stone, a radioactive waste form, can meet performance objectives under near-surface disposal scenarios. Herein, a mineral and parameter set accounting for the solubility of I and Se in Cast Stone was developed based on pH-dependent and monolithic diffusion leaching test results, to extend a geochemical speciation model previously developed. The impact of oxidation and carbonation as environmental aging processes on the retention properties of Cast Stone for primary COPCs was systematically estimated. Physically, the effective diffusion coefficients of 4 COPCs in Cast Stone were increased after carbonation and/or oxidation, reflecting an increase in permeability to diffusion. Chemically, i) pH & pe conditions in the original Cast Stone were favorable for the stabilization of Tc, but not for I, Se, and N; ii) oxidation (with/without carbonation) of Cast Stone changed the pe & pH conditions to be detrimental for Tc stabilization; and iii) carbonation (with/without oxidation) of Cast Stone modified the pH & pe conditions to be beneficial for the stabilization of I (in system with Ag added) and Se.

Highly efficient iodine capture and ultrafast fluorescent detection of heavy metals using PANI/LDH@CNT nanocomposite

Here, the hybrid material of polyaniline/layered double hydroxide@carbonnanotubes (PANI/LDH@CNT) is considered a multifunctional material. Instrumental methods, including FTIR, XRD, TEM, SEM, and TGA/DTA were utilized to characterize PANI/LDH@CNT. The polymerization method created PANI/LDH@CNT as an adsorbent to remove toxic iodine in hexane solution with a capture capacity of 303.20 mg g^-1 during 9 h. It is 900 mg g^-1 in the vapor phase within 24 h. After three cycles, the PANI/LDH@CNT could be regenerated while maintaining 91.90 % iodine adsorption efficiency. Due to the presence of free amine (-N) groups, OH^-, CO₂H, and π-π conjugated structures in the PANI/LDH@CNT, it is also explored for efficient iodine uptake. It was demonstrated that the pseudo-first-order (PFO) and Langmuir model had the optimum correlation with the kinetic and isotherm data, respectively. Moreover, the use of PANI/LDH@CNT is not only limited to iodine capture; it can also be utilized as a sensitive sensor that displays a fluorescence "turn-off" response for Mn⁷⁺ and Cr⁶⁺ ions and a fluorescence "turn-on" response in the case of Al³⁺ ions. The fluorescence intensity of the PANI/LDH@CNT was turned off in the presence of Mn⁷⁺ and Cr⁶⁺ because of the fluorescence inner filter effect (IFE) mechanism. In contrast, the fluorescence intensity was turned on in the case of Al³⁺, relying on the chelation-enhanced fluorescence (CHEF) effect mechanism. Under optimal conditions, the limit of detection (LOD) of 51, 59, and 81 nM for Mn⁷⁺, Cr^6+, and Al³⁺, respectively. According to the literature, this is probably the first example based on PANI/LDH@CNT as a multifunctional hybrid material employed as an adsorbent for capturing radioactive iodine and as a chemosensor for detecting heavy metal ions in aqueous solutions.

Effects of NO2 aging on bismuth nanoparticles and bismuth-loaded silica xerogels for iodine capture

The capture of long-lived radioactive iodine (¹²⁹I) from oxidizing off-gasses produced from reprocessing used nuclear fuel is paramount to human health and environmental safety. Bismuth has been investigated as a viable iodine getter but the phase stability of bismuth-based sorbents in an oxidizing environment have not yet been researched. In the current work, bismuth nanoparticle-based sorbents, as free particles (Bi-NPs) and embedded within silica xerogel monoliths made with a porogen (TEO-5), were exposed to I_2(g) before and after aging in 1 v/v% NO₂ at 150 °C. For unaged sorbents, BiI₃ was the dominant phase after iodine capture with 8-30 mass% BiOI present due to native Bi₂O₃ on the surface of the unaged nanoparticles. After 3 h of aging, 82 mass% of the Bi-NPs was converted to Bi₂O₃ with only a small amount of iodine captured as BiOI (18 mass%). After aging TEO-5 for 3 h, iodine was captured as both BiI₃ (26 %) and BiOI (74 %) and no Bi₂O₃ was detected.". Additionally, bismuth lining the micrometer-scale pores in the TEO-5 led to enhanced iodine capture. In a subsequent exposure of the sorbents to NO₂ (secondary aging), all BiI₃ converted to BiOI. Thus, direct capture of iodine as BiOI is desired (over BiI₃) to minimize loss of iodine after capture.

A robust thorium-organic framework as a bifunctional platform for iodine adsorption and Cr(VI) sensitization

Simple synthetic modulation based on thorium nitrate and tris((4-carboxyl)phenylduryl)amine (H₃TCBPA) gives rise to a new thorium-based metal-organic framework, Th-TCBPA, which features excellent hydrolytic and thermal stabilities. Incorporating electron-rich TCBPA^3- linkers not only endows Th-TCBPA with high adsorption capacity toward radioiodine vapor, but also makes it a luminescence sensor for the highly sensitive and selective detection of Cr(VI) anions.

Recent advances in the removal of radioactive iodine by bismuth-based materials

Nowadays, the demand for nuclear power is continue increasing due to its safety, cleanliness, and high economic benefits. Radioactive iodine from nuclear accidents and nuclear waste treatment processes poses a threat to humans and the environment. Therefore, the capture and storage of radioactive iodine are vital. Bismuth-based (Bi-based) materials have drawn much attention as low-toxicity and economical materials for removing and immobilizing iodine. Recent advances in adsorption and immobilization of vapor iodine by the Bi-based materials are discussed in this review, in addition with the removal of iodine from solution. It points out the neglected areas in this research topic and provides suggestions for further development and application of Bi-based materials in the removal of radioactive iodine.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I₂ molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g^-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NO_X treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

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.

Radioiodine sorbent selection criteria

Methods for preventing radioiodine from entering the environment are needed in processes related to nuclear energy and medical isotope production. The development and performance of many different types of sorbents to capture iodine have been reported on for decades; however, there is yet to be a concise overview on the important parameters that should be considered when selecting a material for chemically capturing radioiodine. This paper summarizes several criteria that should be considered when selecting candidate sorbents for implementation into real-world systems. The list of selection criteria discussed are 1) optimal capture performance, 2) kinetics of adsorption, 3) performance under relevant process conditions, 4) properties of the substrate that supports the getter, and 5) environmental stability and disposition pathways for iodine-loaded materials.

Recent advances in the applications of thorium-based metal-organic frameworks and molecular clusters

This perspective highlights the recent advances in the structural and practical aspects of thorium-based metal-organic frameworks (Th-MOFs) and molecular clusters. Thorium, as an underexplored actinide, features surprisingly rich coordination geometries and accessibility of the 5f orbital. These features lead to a myriad of topologies and electronic structures, many of which are undocumented for other tetravalent metal-containing MOFs or clusters. Moreover, Th-MOFs inherit the modularity, structural tunability, porosity, and versatile functionality of the state-of-the-art MOFs. Recognizing the radioactive nature of these thorium-bearing materials that may limit their practical uses, Th-MOFs and Th-clusters still have great potential for various applications, including radionuclide sequestration, hydrocarbon storage/separation, radiation detection, photoswitch, CO₂ conversion, photocatalysis, and electrocatalysis. The objective of this updated perspective is to propose pathways for the renaissance of interest in thorium-based materials.

Role of Zeolite Structural Properties toward Iodine Capture: A Head-to-head Evaluation of Framework Type and Chemical Composition

This study evaluated zeolite-based sorbents for iodine gas [I_2(g)] capture. Based on the framework structures and porosities, five zeolites, including two faujasite (FAU), one ZSM-5 (MFI), one mesoMFI, one ZSM-22 (TON), as well as two mesoporous materials, were evaluated for I_2(g) capture at room temperature and 150 °C in an iodine-saturated environment. From these preliminary studies, the three best-performing zeolites were ion-exchanged with Ag⁺ and evaluated for I_2(g) capture under similar conditions. Energy-dispersive X-ray spectroscopy data suggest that Ag-FAU frameworks were the materials with the highest capacity for I_2(g) in this study, showing ∼3× higher adsorption compared to Ag-mordenite (Ag-MOR) at room temperature, but X-ray diffraction measurements show that the faujasite structure collapsed during the adsorption studies because of dealumination. The Ag-MFI zeolites are decent sorbents in real-life applications, showing both good sorption capacities and higher stability. In-depth analyses and characterizations, including synchrotron X-ray absorption spectroscopy, revealed the influence of structural and chemical properties of zeolites on the performance for iodine adsorption from the gas phase.

Facile synthesis of novel Bi0-SBA-15 adsorbents by an improved impregnation reduction method for highly efficient capture of iodine gas

Development of high efficient adsorbents to capture iodine is of great significance for the active development of nuclear power. Herein, Bi⁰-SBA-15 was firstly synthesized and applied for capture of iodine gas. Bi⁰-SBA-15 materials were prepared by an improved impregnation reduction method. The benefit of this method was that the Bi⁰ nanoparticles with flocculent and spherical morphologies were loaded on the surface of SBA-15, which provide abundant active sites for iodine and improve the utilization rate of active sites, so as to attain a record high capture capacity (up to 925 mg/g within 60 min) and high stablitiy (91.2%) at 200 °C. The results demonstrated that the loading of Bi⁰ on the surface showed a significant impact on the structure of Bi⁰-SBA-15 and did greatly enhance the iodine capture. Furthermore, the high iodine capture capacity mainly derived from the chemical adsorption in the stable form of BiI₃. The obtained Bi⁰-SBA-15 materials exhibited excellent aqueous and irradiation stability. Thus, the results indicated that the new and highly efficient Bi⁰-SBA-15 was a potential radioactive iodine gas capture material.