Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures

Local Charge Density Enhancement Strategy in Nitrogen-rich Covalent Organic Framework for Boosted Iodine Removal From Water

The leakage of nuclear pollution highlights the critical importance of effectively separating radioactive pollutants. Radioactive iodine, a high-yield fission product of nuclear reactions, poses serious environmental and health risks. However, the lack of efficient adsorbents makes the management of aqueous radioactive iodine pollution a significant challenge. N-doped materials are among the most recognized adsorbents for iodine removal, but their weak binding affinity and limited number of iodine-binding N-sites hinder their practical application. Herein, a covalent organic framework (COFs) named phen-TPA is synthesized, featuring an increased number and optimized local chemical environment of iodine-binding N-sites. This material demonstrates record-breaking iodine removal kinetics, with a kinetic constant of 14.64 g g-1 min-1 for aqueous iodine (I2), and the highest-reported iodine adsorption capacity of 11.9 g g-1 for aqueous triiodide (I3 -). Large-scale flow-through adsorption experiments show that phen-TPA can remove 99.5% aqueous I2 and I3 - from high-salinity aqueous environments, highlighting its potential for practical applications.

Cation-driven phase transition and anion-enhanced kinetics for high energy efficiency zinc-interhalide complex batteries

Aqueous Zn-halogen batteries, valued for high safety, large capacity, and low cost, suffer from the polyhalide shuttle effect and chaotic zinc electrodeposition, reducing energy efficiency and lifespan. Here we show a cation-driven positive electrode phase transition to suppress the shuttle effect and achieve uniform zinc electrodeposition, along with an anion kinetic enhancement strategy to improve energy efficiency and lifespan. Taking tetramethylammonium halide (TMAX, X = F, Cl, Br) as a subject, TMA+ promotes oriented zinc (101) deposition on the negative electrode through electrostatic shielding, significantly extending cycling life. Concurrently, it captures I3- on the positive electrode, forming a stable solid-phase interhalide complex that enhances coulombic efficiency. Compared to I3- and TMAI3, X- anions lower the Gibbs free energy differences of I- → I2X- and I2X- → TMAI2X, accelerating I-/I2X-/TMAI2X conversions and improving voltage efficiency. In TMAF-modified electrolytes, zinc interhalide complex batteries achieve a high energy efficiency of 95.2% at 0.2 A g-1 with good reversibility, showing only 0.1% capacity decay per cycle over 1000 cycles. At 1 A g-1, they show a low decay rate of 0.1‰ per cycle across 10,000 cycles. This study provides insights into enhancing energy efficiency and long-term stability for sustainable energy storage.

Crystalline Porous Materials for Gaseous Iodine Capture: A Comprehensive Review

The growing reliance on nuclear energy necessitates efficient strategies for managing spent nuclear fuel, particularly the capture of volatile radioactive iodine, which poses significant environmental and health risks. Crystalline porous materials have emerged as promising candidates for iodine adsorption due to their high surface areas, tunable porosity, and abundant active sites. This review comprehensively summarizes recent advancements in the design and application of four classes of crystalline porous materials for iodine capture: metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, and porous organic cages. The discussion focuses on key adsorption mechanisms, structural modifications, and functionalization strategies that enhance iodine adsorption capacity, retention, and recyclability. While significant progress has been made, challenges remain in scaling up synthesis, improving stability under industrial conditions, and achieving cost-effective large-scale applications. Future research should emphasize on scalable synthesis, industrial validation, and development of multifunctional adsorbents with enhanced selectivity and reusability. This review provides insights into the rational design of next-generation porous materials for efficient iodine capture, contributing to advancements in nuclear waste management and environmental sustainability.

Porous Aromatic Framework with Multifunctional Sites for Effective Recovery of Various Trace Iodine Species From Water

Recovery of environmental iodine is of great significance for both recycling iodine resources and addressing iodine pollution. However, iodine is highly sensitive to environmental factors and exists in various chemical species, which complicates the recovery of trace iodine in aqueous systems. Here a porous aromatic framework (iPAF-TEPT) is presented with multifunctional adsorption sites for efficient recovery of various iodine species, including molecular iodine (I2), iodide (I- and I3 -). The material utilizes a synergistic strategy combining charge-transfer interactions and Coulomb interactions to effectively adsorb different iodine species. Thanks to its high density of accessible ion exchange sites for I⁻ and I3⁻, and nitrogen-rich sites for I2, iPAF-TEPT demonstrates an unprecedented adsorption capacity for various iodine forms. Notably, iPAF-TEPT achieves exceptional removal efficiency for trace iodine pollutants, even at concentrations as low as 100 ppb, making it the first promising single-framework material for highly efficient treatment of aqueous iodine contamination.

Linear Polymer Cathode Materials for Highly Efficient Aqueous Zinc-Ion Batteries: Is the High Active Sites Density Necessary?

Recently, research on aqueous zinc-ion batteries (AZIBs) has always focused on improving the energy storage performance by increasing the number of active sites, particularly in designing organic/polymer materials with a high density of active sites. However, does a higher density of active sites necessarily induce enhanced energy storage performance? To verify this issue, we have designed two linear polymers, where TAPT-DHBQ contains an additional pair of active sites (carbonyl groups) compared to TABQ-DHBQ, with theoretical specific capacities of 545.26 and 379.14 mAh g-1, respectively. Interestingly, the experimental results have deviated with the specific capacities of these polymers being comparable, measuring to be 325 mAh g-1 (TABQ-DHBQ) and 280 mAh g-1 (TAPT-DHBQ). This is attributed to the competition effect between neighboring active sites, which leads to decreased utilization of active sites. As a result, the Zn//TABQ-DHBQ batteries with ZnI2 electrolyte additive have exhibited high specific capacities of 618 and 360 mAh g-1 at the current densities of 1 and 10 A g-1, along with a high energy density of 678.6 Wh kg-1 (1 A g-1). The finding underscores the importance of uniform electron cloud distribution in cathode materials for achieving efficient AZIBs.

Stable Flavone-Linked Covalent Organic Frameworks for High-Performance Lithium-ion Battery Anodes

The design and synthesis of stable and efficient anode materials for organic lithium-ion batteries (LIBs) are critical for achieving environmental sustainability. Herein, a flavone-linked covalent organic framework (FV-COF) with high crystallinity is synthesized via a cascade reaction based on the Claisen-Schmidt condensation for anodes of LIBs. The incorporation of an oxygen-rich flavonoid structure and a fully conjugated framework endows FV-COF with exceptional physicochemical stability and reversible redox capacity. Thus, FV-COF demonstrates exceptional performance as an anode material, delivering a high steady-state capacity of 1136.8 mA h g-1 after ten cycles at 0.1 A g-1 and excellent rate capability. In particular, the cyclic stability of FV-COF retained a capacity of 546.5 mAh g-1 at 5.0 A g-1 after 10 000 cycles, accompanied by a Coulombic efficiency exceeding 98%. This work demonstrates that COFs with rich redox site and stable linkages are promising candidates for developing lightweight batteries.

84-Nuclearity Lanthanide-Aluminum Cyclic Clusters: Promising Materials for Iodine Capture and Storage

Developing high-performance adsorbents for iodine uptake and storage has become an urgent priority for safe disposal and long-term storage of nuclear waste. In this work, two cyclic lanthanide-aluminum clusters with the formula [Ln12Al72(hmp)60(C2H5O2)6(μ2-OH)120(μ3-OH)18(H2O)30]Cl24·(NO3)24·(H2O)x (Ln = Tb, x ≈ 80, Tb12Al72; Ln = Gd, x ≈ 100, Gd12Al72; Hhmp = 2-(hydroxymethyl)pyridine and C2H6O2 = ethylene glycol) are reported. Single-crystal analysis reveals that its inner diameter is approximately 1.1 nm, with an outer diameter of 4.1 nm and a thickness of 3.1 nm. The packing of cyclic clusters through intermolecular interactions generates a 3D supramolecular structure with one-dimensional channels. Investigation of the iodine adsorption performance of the cluster indicates an uptake capacity of 3.14 g g-1 for Tb12Al72 and 3.1 g g-1 for Gd12Al72. The effectiveness of iodine adsorption is largely due to the accessible micropore structure along with the high density of pyridine rings and abundant hydroxyl oxygen atoms. Consistently, DFT calculations indicate that the [Al(μ-OH)n] clusters and pyridine ring regions synergistically facilitate iodine adsorption, effectively promoting the dissociation of I2 into I- anions. This unique micropore environment enhances the electrostatic stabilization of polyiodide anions through a strong Coulombic attraction, significantly boosting the capture of iodine.

Strategic Design of Novel Zinc and Cadmium Metal-Organic Frameworks for Enhanced, Reversible, and Multi-Phase Iodine Sequestration

Radioactive iodineisotopes (129I and 131I), generated duringnuclear fission, persist in gaseous and aqueous phases due to their volatilityand bioaccumulation, posing severe health risks. Multiphase iodine removalremains challenging due to the low efficiency of conventional materials, especially in aqueous media where high polarity hinders effective adsorption. Herein, a novel bidentate precursor, 4, 4'-(((2, 3, 5, 6-tetramethyl-1, 4-phenylene)bis(methylene))bis(azanediyl))dibenzoicacid (PMBADH₂), was strategically designed having two -NH linkages to enhance interactions withiodine in the phases. Using PMBADH2, Two new isostructural metal-organic frameworks(MOFs), {[Zn₂(PMBADH₂)₄(DMF)₂]·4DMF}n (SVNIT-1) and {[Cd₂(PMBADH₂)₄(DMF)₂]·4DMF}n (SVNIT-2), were synthesized. The MOFs werealso prepared on a gram scale to enhance practical applicability. Comprehensive characterization of both MOFs was performed using SCXRD, PXRD, FTIR, XPS, BET, and TGA. Both MOFs exhibited outstanding iodine uptake across vapor, organic, and aqueous phases. SVNIT-1 achieved capacities of 6.5 g g-1 (vapor), 2.8 g g-1 (organic), and 2.5 g g-1 (aqueous, including seawater), while SVNIT-2 showed comparable values of 6.1, 2.6, and 2.4 g g-1, respectively. Extensive studies on desorption, recyclability, and stability confirmed the robustness and reusability of thesematerials. Mechanistic studies using FTIR, PXRD, Raman, UV-DRS, XPS, and ESR highlighted the pivotal role of NH linkages in promoting iodine adsorption via strong hostguest interactions.

Soluble Covalent Organic Frameworks as Efficient Lithiophilic Modulator for High-Performance Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as the potential alternative of lithium-ion batteries due to their ultrahigh theoretical specific capacity (3860 mAh g-1). However, severe instability and safety problems caused by the dendrite growth and inevitable side reactions have hindered the commercialization of LMBs. To solve them, in this contribution, a design strategy of soluble lithiophilic covalent organic frameworks (COFs) is proposed. By introducing polyethylene glycol as the side chains, two COFs (CityU-28 and CityU-29) not only become soluble for the facile coating technique, but also can facilitate the lithium-ion migration in batteries. Furthermore, when coated on the lithium anode of LMB, both COFs can act as artificial solid electrolyte interphase to prevent dendrite growth thus enabling the long-term stability of the cells. Notably, the symmetric CityU-29@Li cell can work for more than 5000 h at a current density of 2 mA cm-2 and an areal capacity of 1 mAh cm-2. A remarkable capacity retention of 78.9 % after 1500 cycles and a Coulombic efficiency of about 99.9 % at 1.0 C can also be realized in CityU-29@Li||LiFePO4 full cell. This work could provide a universal design strategy for soluble COFs and enlighten their application in diverse scenarios, especially energy-related fields.

Diketopyrrolopyrrole-based Donor-Acceptor Covalent Organic Frameworks for Iodine Capture

The recovery of radioactive iodine from nuclear waste and contaminated water sources is a critical environmental concern, which poses significant technical challenges. Herein, the study has demonstrated that tuning the electronic properties of diketopyrrolopyrrole-based donor-acceptor covalent organic frameworks (COFs) enhances iodine trapping, improves charge transport, and strengthens iodine interactions - establishing a structure-property relationship. This tuning is achieved by synthesizing COFs with the diketopyrrolopyrrole-based linker 3,6-bis(4-(1,3-dioxolan-2-yl)phenyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DKP) in combination with either the electron acceptor 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline (TTT-DKP) or the electron donor N1,N1-bis(4-aminophenyl)benzene-1,4-diamine (TAPA-DKP) linkers. These COFs, with abundant sorption sites, thermal and chemical stability, and optimized pore environments, efficiently bind iodine in the vapor and solution phases. The TAPA-DKP COF, containing electron-donating moieties, showed a high iodine uptake of 3.52 g/g, exceeding the 2.81 g/g of the electron-deficient TTT-DKP in the vapor phase, both following pseudo-second-order kinetics. Density functional theory (DFT) calculations reveal adsorption sites showing that TAPA-DKP COF binds I2 more effectively via its electron-rich moieties, highlighting the role of electronic property modulation in iodine adsorption.

Crystal- and Pore-Size Dependent Iodine Adsorption Properties in MOFs

Metal-organic frameworks (MOFs) with unique pore architectures and electron-rich sites exhibit an unprecedented iodine capture property. In this contribution, the crystal-size and pore-size-dependent iodine adsorption behavior in MOFs ranging in crystal size from nanometers to micrometers with mesoporous and microporous structures is reported. Nano-sized MOFs have much higher iodine adsorption capacities and rates than Micro-sized MOFs. The pore diffusion for iodine adsorption in MOFs is the rate-controlling step and small-sized MOFs can provide larger external surface areas for iodine transport into adsorbents. Raman spectra suggest the diffusion of iodine molecules is more restricted than iodide species in micropores, and the iodine concentration gradient is more significant in microporous MOF-74 than in mesoporous PCN-222. Molecular simulation indicates iodine transports from mesopores to micropores, and aggregates in micropore cages and framework walls. The electron-rich O/N sites in MOFs attract iodine strongly and restrict iodine diffusion, while the weak interaction between iodine molecules becomes prominent at a high iodine loading amount and thus increases the iodine diffusivity in MOFs. The above result reveals a strong size dependence in iodine adsorption behaviors sensitive to MOFs' intrinsic crystal size, porosity, and guest-host interactions, and MOFs with smaller crystal sizes and mesoporous construction have better iodine capture performance.

Promising CO2 Capture and Effective Iodine Adsorption of Hyper-Cross-Linked Conjugated Porous Organic Polymers Prepared from a Cyclopentannulation Reaction

Three novel conjugated porous organic polymers, denoted as C-POP1-3 and which consist of alternating pyrene cores with various contorted fluorene surrogates, were successfully synthesized from a versatile one-pot palladium-catalyzed [3+2] cyclocondensation reaction. The resulting polymers were obtained in excellent yields and displayed weight-average molecular weights (Mw) ranging from 12.2 to 20.2 kg/mol with polydispersity indices (Mw/Mn) ranging between 1.8 and 2.4, suggesting that the molecular masses are narrowly distributed and thus implying homogeneous polymer chains. Thermal stability exploration of C-POP1-3 by thermogravimetric analysis (TGA) revealed an impressive robustness with a 10% weight reduction temperature attaining 485 °C. Investigation of the inherent microporosity properties of C-POP1-3 via nitrogen adsorption experiments using Brunauer-Emmett-Teller (BET) theory discloses their surface areas which reach up to 560 m2 g-1 and pore volumes averaging 0.47 cm3 g-1. The target conjugated polymers were explored as adsorbents disclosing a maximum carbon dioxide adsorption of 83.0 mg g-1 at 273 K and low pressure for C-POP1, whereas iodine sorption tests portrayed prominent outcomes, notably for C-POP3 which proved to owe a strong affinity toward the hitherto mentioned halogen by achieving a maximum adsorption of 2220 mg g-1. Additionally, recyclability experiments confirmed the possibility to regenerate the polymers' adsorption capabilities even after seven consecutive cycles of adsorption-desorption cycles, which qualify them as auspicious iodine adsorbents.

Ionic porous materials: from synthetic strategies to applications in gas separation and catalysis

Ionic porous materials possess a unique combination of tunable pore sizes and task-specific interactions between guest molecules and the charged frameworks, which endow them with versatility across diverse domains in chemistry and materials science. Significant advancements in their applications for gas separation and catalysis have been achieved in recent years due to the incorporation of ionic functionalities and ultra-microporous structures that enable molecular-scale recognition of guest molecules. This review summarizes recent advancements in the synthetic strategies of ionic porous materials, establishing design guidelines for the incorporation of ionic moieties into the backbone to fine-tune pore sizes and chemistry. It highlights the synergistic interplay of task-specific interactions with custom-designed pore structures in key applications, including adsorption separation, membrane separation, and gas conversion. Additionally, it examines structure-property relationships, offering deeper insights into enhancing performance. The report also addresses the current challenges in the practical application of these materials. Finally, the review provides future perspectives on ionic porous materials from both scientific and industrial viewpoints. Overall, this review aims to provide insights into pore structure and chemistry, supporting the precise placement of ionic functionalities.

In situ self-cleaning removal of emerging organic contaminants with covalent organic framework armed with arylbiguanide

An in situ self-cleaning covalent organic framework featuring arylbiguanide arms (Aryl-BIG-COF) was first developed to remove emerging organic pollutants such as propranolol (PRO) from water. The main breakthroughs addressed the scarcity of functional active sites, the impracticality of ex situ regeneration, and the rapid recombination of electronhole pairs in the application of COFs. Owing to the directional capture ability and electronic structure regulation of the arylbiguanide arms, the adsorption capacity and photocatalytic degradation rate of the newly synthesized COF increased by nearly four and seven times, respectively. Its self-cleaning ability, driven by the photocatalytic regeneration of active sites, enabled in situ removal of PRO and sustained over 90 % removal efficiency after six cycles. Moreover, it demonstrated broad applicability for removing PRO and other emerging pollutants, such as bisphenol A (BPA), tetracycline (TC), and norfloxacin (NOR), across various water matrices with less residual toxicity. The coexisting organic matter and ions in natural water promoted the removal of PRO. The enhancement mechanism involved arylbiguanide arms narrowing the band gap and inducing local charge polarization, thereby increasing the separation efficiency of electronhole pairs. This work provides significant insights into the structural design and practical applications of COFs for purifying water.

General synthesis of covalent organic frameworks under ambient condition within minutes via microplasma electrochemistry approach

Covalent organic frameworks (COFs) are typically synthesized using solvothermal conditions with high temperature and long reaction time (≥120 °C, >72 h). Herein, we report a general and rapid microplasma electrochemistry strategy to synthesize COFs under ambient conditions. A series of flexible imine-bond COFs with high-crystallinity were prepared in minutes via this method, which showed 1000-fold higher space-time yield than solvothermal method. This approach also achieved the preparation of COFs with diverse linkages including rigid imine, hydrazone, β-ketoenamies and azine linkages. Moreover, four types of imine-based COFs were successfully synthesized in aqueous acetic acid, which avoided the use of harmful organic solvents, indicating that microplasma method is green and versatile for COF synthesis. The obtained COFs showed higher surface area and exhibited superior performance in volatile iodine uptake compared to those COFs prepared by solvothermal method. After screening more than ten types of COFs, the iodine adsorption capacity could be promoted from 2.81 to 6.52 g g-1. The efficiency, versatility, and simplicity of the microplasma method render it as a promising approach for the swift screening of COFs across a wide range of applications.

Virtual Database Construction and Machine-Learning-Assisted High-Throughput Evaluation of Amorphous Porous Carbon Materials as Iodine Sorbents

We present a comprehensive approach to enable the high-throughput screening and analysis of amorphous porous carbon (APC) materials as effective I2 sorbents for the nuclear industry. A diverse virtual database of 19,599 APC models was established from scratch through liquid quenching molecular dynamics simulations. Large-scale grand canonical Monte Carlo simulation at a series of I2 concentrations was carried out for sampled APCs to generate an array of I2 adsorption capacities. Machine learning and SHapley Additive exPlanations (SHAP) analysis were employed to investigate the impact of various extracted (structural and chemical) features of the APC materials on their respective I2 adsorption behavior, revealing influential factors (surface area, pore size ranges, etc.) for APC development that varied with I2 concentrations. This work attempts to provide both fundamental databases and research frameworks to accelerate the development and enhance the understanding of APC materials.

Unveiling the Potential of Thiophene-Functionalized Porous Organic Polymers for Bromine Adsorption and Selective Separation from Iodine

Bromine is a significant environmental threat due to its corrosive nature and contribution to ozone layer depletion. It often coexists with iodine and forms interhalogen complexes (IBr), which require an effective and selective bromine adsorption strategy. Leveraging the electrophilic nature of bromine, we designed an electron-rich thiophene-based porous organic polymer (POF-2). This material exhibits exceptional efficiency for bromine adsorption (2.86 g g-1) and rapid uptake kinetic from aqueous solutions, driven by noncovalent charge transfer interactions. POF-2 also demonstrates selective capture of bromine from a bromine-iodine mixture in cyclohexane. The material's electron-rich sites exhibit a stronger orbital interaction with the σ* orbital of bromine compared to iodine, leading to the observed selectivity in cyclohexane.

Construction of Guanidinium-Functionalized Covalent Organic Frameworks via Phototriggered Click Reaction as a Dual-Mode Accurate Sensor for Malondialdehyde

Malondialdehyde (MDA) serves as a pivotal indicator to estimate the lipid peroxidation status and as a biomarker for the assessment of oxidative stress and screening of disease by people excretion. However, most of the existing analytical methods for MDA suffer from complicated derivation, leading to poor accuracy and inconvenience. In this work, the guanidinium-functionalized covalent organic framework (COF) was delicacy-designed and used to tune the modular structure by the building blocks with condensation, phototriggered click reaction, and further guanidylation process. A methoxy-group-containing linker in the skeleton was adopted to form lone-pair delocalized oxygen atoms, trigger the resonance effect, attenuate the polarization of the C═N bond linkages, and weaken the interlayer repulsion, supporting the stability of the guest gating COF. The available guanidino groups grew from the ordered pore walls of the COF and served as the customized talon with an enhanced interaction site density to rapidly grab the target guest by charge-assisted strong hydrogen bonds and electrostatic attraction forces. This distinctive feature significantly bolstered sensitive signal transduction, enabling rapid MDA sensing (within 120 s) without derivation treatment, and achieved a calculated limit of detection (LOD) as low as 0.08 μM. With the accessible image-data transmission process, the portable dual-channel sensing platform achieved sensitive and accurate MDA monitoring.

Covalent organic frameworks for radioactive iodine capture: structure and functionality

The adsorption of radioactive iodine is a critical concern in nuclear safety and environmental protection due to its hazardous nature and long half-life. Covalent organic frameworks (COFs) have emerged as promising materials for capturing radioactive iodine owing to their tunable porosity, high surface area, and versatile functionalization capabilities. This review provides a comprehensive overview of the application of COFs in the adsorption of radioactive iodine. We begin by discussing the sources, properties, and hazards of radioactive iodine, as well as traditional capture techniques and their limitations. We then delve into the intrinsic structures of COFs, focusing on their porosity, conjugated frameworks, and hydrogen bonding, which are pivotal for effective iodine adsorption. The review further explores various functionalization strategies, including electron-rich COFs, flexible COFs, ionic COFs, COF nanosheets, and quasi-3D COFs, highlighting how these modifications enhance the adsorption performance. Finally, we conclude with an outlook on future research directions and potential applications, underscoring the significance of continued innovation in this field. This review aims to provide valuable insights for researchers and practitioners seeking to develop advanced materials for the efficient capture of radioactive iodine.

Ultrahigh Proton Selectivity by Assembled Cationic Covalent Organic Framework Nanosheets

Ionic covalent organic framework (COF) nanosheets are becoming increasingly attractive as promising two-dimensional (2D) materials for proton transport due to their ionic functionality and tailor-made pores. However, most synthetic methods for nanosheets rely on surface-assisted methods or phase transformation often yielding nanosheets with low aspect ratios. In this study, we present a bottom-up approach utilizing an oil-oil-water triphase system to achieve the large-scale synthesis of ionic COF nanosheets. The intermediate oil layer in this system modulates the diffusion rate of monomers from the top oil phase into the aqueous phase, enabling in-plane anisotropic secondary growth from the initial discrete fibrous structure into large and crystalline COF nanosheets. The ionic COF nanosheets exhibit excellent proton permeability while simultaneously excluding other cations by casting into crack-free membranes, demonstrating efficient HCl extraction from acidic water waste. This strategy for larger-scale COF nanosheet growth will offer an alternative platform for designing multifunctional COF membranes with applications in sophisticated separation technologies.

Cage-Based Metal-Organic Framework Featuring a Double-Yolk Core-Shell U6L3@U18L14 Structure for Iodine Capture

Cage-based MOFs, with their customizable chemical environments and precisely controllable nanospaces, show great potential for the selective adsorption of guest molecules with specific structures. In this work, we have constructed a novel cage-based MOF [(CH3)2NH2]2[(UO2)2(TMTTA)]·11.5DMF·2H2O (IHEP-51), utilizing a triazine derivative poly(carboxylic acid), 4,4',4″-(((1,3,5-triazine-2,4,6-triyl)tris(((4-carboxycyclohexyl)methyl)azanediyl))tris(methylene))tribenzoic acid (H6TMTTA), as an organic ligand and uranyl as a metal node. The 2-fold interpenetrated (3,6,6)-connected framework of IHEP-51 features two types of supramolecular cage structures: the Pyrgos[2]cage U6L3 and the huge cage U18L14. They are further assembled into a double-yolk core-shell U6L3@U18L14 structure, making it suitable for I2 capture. The maximum adsorption capacities of IHEP-51 for iodine in solution and gaseous iodine are 420.4 and 1561.2 mg·g-1, respectively. XPS, Raman spectra, single-crystal X-ray diffraction, and DFT calculations reveal that the adsorbed iodine is located inside the U6L3 Pyrgos[2]cage in the form of I3-, thus resulting in the formation of a (I3)2@U6L3@U18L14 ternary core-shell structure.

Catalyzing Knoevenagel Condensation and Radioiodine Sequestration with Tuned Porous Organic Polymers to Decipher the Role of Surface Area, Pore Volume, and Heteroatom

The impact of surface area, pore volume, and heteroatom type on the performance of porous organic polymers (POPs) in various applications remains unclear. To investigate this, three isoreticular POPs were employed having one common building block, resulting in varying surface areas, pore volumes, and heteroatom compositions. This study aimed to establish a correlation between the structural features of POPs (surface area, pore volume, and heteroatom type) with their adsorption capacity, and catalytic efficiency. To explore this relationship, the Knoevenagel condensation reaction was used as a model system, testing various substituted aldehydes to further validate our findings. Additionally, the capture of radioactive iodine vapor at 75 °C was simulated to examine the correlation with adsorption capacity, comparing the gravimetric iodine uptake capacity of each POP to gain insights into this relationship.

Lignin-based materials for iodine capture and storage: A review

The safety of nuclear energy, as a low-carbon energy source, has received widespread attention. One of the concerns is the appropriate handling of volatile radioactive elements (e.g., 129I and 131I) generated during the operation of nuclear reactors. These radioactive iodine isotopes are potentially hazardous to the environment and human health, so their effective removal is essential. Adsorption has become a popular method for capturing radioiodine due to its simplicity and low cost, which eliminates the need for highly corrosive solutions. Porous solid adsorbents have been widely studied and applied in practice for the efficient removal of radioactive iodine elements. However, most of these adsorbents are expensive, have limited capture capacity, and can burden the environment. Currently, researchers have now begun to experiment with the use of lignin as a substrate to develop new green and inexpensive adsorbents to enhance the capture efficiency of radioactive iodine. This review article begins by discussing the design of lignin-based iodine capture materials, detailing their application in iodine capture, and analyzing their performance, mechanisms, and practical application cases. Considering the challenges and opportunities in the field of radioactive iodine capture, it is hoped that this work can provide a reference point for future research.

Cationic covalent organic framework for the fluorescent sensing and cooperative adsorption of perfluorooctanoic acid

The contamination of water by per- and polyfluorinated substances (PFAS) is a pressing global issue due to their harmful effects on health and the environment. This study explores a cationic covalent organic framework (COF), TG-PD COF, for the efficient detection and removal of perfluorooctanoic acid (PFOA) from water. Synthesized via a simple sonochemical method, TG-PD COF shows remarkable selectivity and sensitivity to PFOA, with a detection limit as low as 1.8 µg·L⁻¹. It achieves significant PFOA adsorption exceeding 2600 mg·g⁻¹ within seconds over several cycles in batch mode and complete removal at environmentally relevant concentrations in column adsorption. Results reveal unique adsorption behavior characterized by two phases, leveraging PFOA aggregation through hydrophobic interactions. Computer simulations elucidate the mechanisms underlying TG-PD COF's sensing, adsorption, and charge transfer dynamics. Our findings position this COF design strategy as a promising solution for combating PFAS contamination in water bodies worldwide.

Zwitterionic covalent organic nanosheets for selective analysis of domoic acid in marine environment

BACKGROUND

Domoic acid (DA) is a neurotoxic compound causing amnesic shellfish poisoning, secreted by red algae and diatoms. As a glutamate analogue, DA accumulates in filter-feeding marine organisms, posing significant health risks to humans upon consumption. Detecting DA in marine environments remains challenging due to its low concentration and interference from complex matrices. Effective detection and removal require materials with high efficiency and selectivity, which traditional inorganic ionic materials lack due to their limited adsorption capacity and selectivity. Ionic covalent organic frameworks (iCOFs) expected to become highly efficient DA adsorbents due to tunable ionic sites.

RESULTS

Thus, a zwitterionic covalent organic nanosheet (TGDB-iCONs) was synthesized to selectively capture DA. TGDB-iCONs was prepared by one-step Schiff-base reaction of the charged monomer triaminoguanidine hydrochloride. It uniformly distributed positively charged guanidinium and negatively charged chloride ions on the surface, forming zwitterionic binding sites. The self-peeling of TGDB-iCONs facilitated the exposure of active sites and improved the adsorption efficiency. Several binding forces were generated between TGDB-iCONs and DA, including complementary electrostatic hydrophilic interactions, which were verified by density functional theory (DFT) calculation. TGDB-iCONs exhibited ultra-fast adsorption kinetics (7 min) and relatively high adsorption capacity (66.48 mg/g) for DA. Furthermore, TGDB-iCONs exhibit strong salt resistance, which is attributed to the charge "shielding" effect of the zwitterionic ions present in TGDB-iCONs. TGDB-iCONs could highly selectively enrich DA and detect trace DA from marine environment including seawater, algae and marine organisms and the limit of detection as low as 0.3 ng/kg.

SIGNIFICANCE AND NOVELTY

This comprehensive study not only sheds light on the vast potential of ionic covalent organic frameworks nanosheets (iCONs) in supporting early warning, control, and traceability of DA, but also lays a solid foundation for future research endeavors aimed at designing and harnessing the unique properties of iCONs.

Post-Synthetic Modification of Porous Organic Cages for Enhanced Iodine Adsorption Performance

The capture of radioactive iodine species from nuclear waste is crucial for environmental protection and human health. Porous organic cages (POCs), an emerging porous material, have showed potential in iodine adsorption due to the advantages of tunable pores and processibility. However, integrating multiple desirable characteristics into a single POC through bottom-up assembly of pre-designed building blocks remains challenging. Post-synthetic modification (PSM) offers an alternative approach, enabling the introduction of various functions into a single POC. Herein, a viable and highly efficient three-step PSM strategy to modify a representative POC (CC3), is presented. The modified POC, OFT-RCC36+6Br-, features a charged confined space, electron-rich heteroatom, and halide ions, exhibiting significantly enhanced iodine vapor uptake compared to the parental cage. The universality of the PSM strategy has been verified by successfully modifying two other POCs. The iodine adsorption behaviors of three modified cage adsorbents in organic solvent and aqueous solution have also been investigated, all of which exhibited improved performance, especially in comparison to ionic cages modified through direct protonation. This work provides an effective PSM strategy for POCs to facilitate iodine adsorption. More importantly, the introduction of a new PSM strategy enriches the functional diversity of POCs, potentially broadening their future applications.

Task-Driven Tailored Covalent Organic Framework for Dynamic Capture of Trace Radioactive CH3 131I under High-Flow Rate Conditions

The removal of radioactive gaseous iodine is crucial for sustainable nuclear energy development, safe spent fuel management, and secure disposal of radioactive waste and radioactive medical waste. However, the efficient capture of gaseous iodine, particularly methyl iodide, under conditions of low concentration and high-flow rate that are representative of real-world scenarios remains underexplored. Herein, we adopted a "theory-first" strategy to design adsorbents with a superior affinity for methyl iodide. The rigorous theoretical calculations for both physisorption and chemisorption have guided us to rationally design a piperazine-based covalent organic framework material (Pip-COF, Pip = piperazine). The pioneering hot-testing under dynamic conditions, featuring low concentrations of 5 ppm radioactive CH3 131I and a high-flow rate of 600 mL/min, demonstrated Pip-COF's exceptional capture performance. Pip-COF exhibits saturated capacities of 39 mg/g at 75 °C and 78 mg/g at 25 °C, significantly outperforming the previously reported best COF (COF-TAPT, 6 mg/g at 25 °C) in this scenario. The gradual process of methylation and the identification of specific high-affinity sites were elucidated by time-resolved FT-IR spectroscopy and density functional theory (DFT) analysis, consistent with the design philosophy. This study exemplifies rational material design in facilitating the separation of trace pollutants in challenging environments.

Robust Imidazopyridinium Covalent Organic Framework as Efficient Iodine Capturing Materials in Gaseous and Aqueous Environment

The development of a high-performing adsorbent that can capture both iodine vapor from volatile nuclear waste and traces of iodine species from water is an important challenge, especially in industrially relevant process conditions. This study introduces novel imidazopyridinium-based covalent organic frameworks (COFs) through post-modification of a picolinaldehyde-based imine COF. These COFs demonstrate excellent iodine adsorption capacity, adsorption kinetics, and a high stability/recyclability in both vapor and water phases. Notably, one imidazopyridinium COF exhibits gaseous iodine uptake of 21 wt.% under dynamic adsorption conditions at 150 °C and a relative humidity of 50%, surpassing the performance of the currently used silver-based zeolite adsorbents (Ag@MOR (17wt.%)). Additionally, the same imidazopyridinium COFs can efficiently remove iodine species at a low concentration from aqueous solution. Seawater containing triiodide ions treated under dynamic flow-through conditions resulted in decreased concentrations down to the ppb level. The adsorption mechanisms for iodine and polyiodide species are elucidated for the imine COF and imidazopyridinium COFs; involving halogen bonding, hydrogen bonding, and charge-transfer complexes.

Synergistic Linker and Linkage of Covalent Organic Frameworks for Enhancing Gold Capture

The tunable pore walls and skeletons render covalent organic frameworks (COFs) as promising absorbents for gold (Au) ion. However, most of these COFs suffered from low surface areas hindering binding sites exposed and weak binding interaction resulting in sluggish kinetic performance. In this study, COFs have been constructed with synergistic linker and linkage for high-efficiency Au capture. The designed COFs (PYTA-PZDH-COF and PYTA-BPDH-COF) with pyrazine or bipyridine as linkers showed high surface areas of 1692 and 2076 m2 g‒1, providing high exposed surface areas for Au capture. In addition, the Lewis basic nitrogen atoms from the linkers and linkages are easily hydronium, which enabled to fast trap Au via coulomb force. The PYTA-PZDH-COF and PYTA-BPDH-COF showed maximum Au capture capacities of 2314 and 1810 mg g-1, higher than other reported COFs. More importantly, PYTA-PZDH-COF are capable of rapid adsorption kinetics with achieving 95% of maximum binding capacity in 10 min. The theoretical calculation revealed that the nitrogen atoms in linkers and linkages from both COFs are simultaneously hydronium, and then the protonated PYTA-PZDH-COF are more easily binding the AuCl4 ‒, further accelerating the binding process. This study gives the a new insight to design COFs for ion capture.

Porous Organic Cage as an Efficient Platform for Industrial Radioactive Iodine Capture

Herein, we firstly develop porous organic cage (POC) as an efficient platform for highly effective radioactive iodine capture under industrial operating conditions (typically ≥150 °C), ≤150 ppmv of I2). Due to the highly dispersed and readily accessible binding sites as well as sufficient accommodating space, the constructed NKPOC-DT-(I-) (NKPOC=Nankai porous organic cage) demonstrates a record-high I2 uptake capacity of 48.35 wt % and extraordinary adsorption capacity of unit ionic site (~1.62) at 150 °C and 150 ppmv of I2. The I2 capacity is 3.5, 1.6, and 1.3 times higher than industrial silver-based adsorbents Ag@MOR and benchmark materials of TGDM and 4F-iCOF-TpBpy-I- under the same conditions. Furthermore, NKPOC-DT-(I-)Me exhibits remarkable adsorption kinetics (k1=0.013 min-1), which is 1.2 and 1.6 times higher than TGDM and 4F-iCOF-TpBpy-I- under the identical conditions. NKPOC-DT-(I-)Me thus sets a new benchmark for industrial radioactive I2 adsorbents. This work not only provides a new insight for effectively enhancing the adsorption capacity of unit functional sites, but also advances POC as an efficient platform for radioiodine capture in industry.

Green synthesis of an ionic porous organic polymer for efficient capture of environmentally toxic MnO4- and I3- from water

The syntheses of ionic porous organic polymers (iPOPs) via an ionothermal strategy or using solvents with high boiling points are not environmentally friendly approaches. Furthermore, green synthesis of an ionic porous organic polymer has not been reported to date. The azo-coupling reaction is considered a green synthetic strategy and has been used to obtain a new ionic porous organic polymer (iPOP-6) wherein water is used as a solvent. iPOP-6 turns out to be a useful adsorbent that can scavenge toxic water pollutants (MnO4- and I3-) in an energy efficient manner via an ion exchange based adsorption process. The distribution coefficients (Kd) associated with the removal of MnO4- and I3- are greater than 105 mL g-1 - a desirable feature observed in a superior adsorbent. iPOP-6 can remove such pollutants from water samples collected from different water bodies with good capture efficiency. The removal mechanism was also ratified by theoretical studies. Overall, this work presents a new ionic POP with improved features and performance for water purification applications.

A nanotrap infused ultrathin hybrid composite material for rapid and highly selective entrapment of 99TcO4. Chem Sci 2024:d4sc04010d. [PMID: 39430929 PMCID: PMC11485004 DOI: 10.1039/d4sc04010d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

99Tc is one of the potentially toxic radioactive substances owing to its long half-life and a high degree of environmental mobility. Hence, the sequestration of 99Tc from radioactive waste has become enormously important and a contemporary research priority. However, selective extraction of this species in its stable oxoanionic form (99TcO4 -) is very challenging on account of bottlenecks such as low charge density, less hydrophilic nature, etc. Herein, an ultrathin hybrid composite material has been strategically designed and fabricated by covalent anchoring of a chemically stable amino functionalized nanosized cationic metal-organic polyhedron with a positively charged robust ionic covalent organic framework. The resulting thin-layer-based hybrid composite presented multiple exfoliated exposed interactive sites, including a Zr(iv)-secondary building unit, amine and triaminoguanidine functional groups, which can selectively interact with TcO4 - oxoanions through a synergistic combination of electrostatic, H-bonding and various other supramolecular interactions. Thus synthesized function-tailored composite, by virtue of its multiple unique characteristics, manifested an ultrafast and very selective, high distribution coefficient (∼106 mL g-1), as well as recyclable entrapment of TcO4 - oxoanions from the complex mixture of superfluous (∼5000-fold) other interfering anions in both high and ultra-trace concentrations along with simulated nuclear waste and from different water systems. Dynamic flow-through experiments were conducted with the membrane of the hybrid material in simulated wastewater, which reduced the concentration of ReO4 - (surrogate of radioactive TcO4 -) to below the WHO permissible level with rapid sequestration kinetics and excellent selectivity over excessive competing anions.

Croconic Acid Integrated Zwitterionic Conjugated Porous Polymer for Effective Iodine Adsorption

Given the rapid growth of the nuclear sector, effective treatment of radioactive iodine is critical. Herein, we report the synthesis and the iodine adsorption properties of croconic acid (CTPB) and squaric acid (STPB) containing π-conjugated novel zwitterionic conjugated porous polymers (CPPs). The CPPs have been synthesized through a condensation reaction of tris(4-aminophenyl)benzene with croconic acid or squaric acid in high yields (~95 %). The ionic nature of the polymers promoted high iodine/polyiodide vapour adsorption capacity of up to 4.6 g/g for CTPB and 3.5 g/g for STPB under ambient pressure at 80 °C. The zwitterionic framework (croconic acid or squaric acid units) coupled with the aromatic units is expected to effectively capture molecular iodine (I2) and polyiodides (I3 - and I5 -). The iodine adsorption properties of the polymers have been studied using Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Brauner-Emmett-Teller (BET) analysis, and Raman Spectroscopy. Besides this work, there are only three ionic units for effective iodine adsorption. This work demonstrates the importance of zwitterionic units in the porous network reported for iodine adsorption and separation.

Exploration of iodine adsorption performance of pyrene-based two-dimensional covalent organic frameworks

Radioiodine (mainly 129I and 131I) is known to be dangerous nuclear waste due to its high toxicity, fast mobility and long radioactive half-life. As an emerging class of novel porous organic polymers, covalent organic frameworks (COFs) have demonstrated tremendous application potential in the field of radioactive iodine capture because of their high specific surface area and tunable pore structure. Herein, three π-conjugated pyrene-based COFs, namely PyTTA-BPDA-COF, PyTTA-BPY-COF, and PyTTA-BT-COF, have been successfully prepared and used as highly efficient adsorbents for iodine capture. The experimental results show that the three COFs displayed excellent adsorption performance, with adsorption capacity of 5.03, 4.46, and 3.97 g g-1 for PyTTA-BPDA-COF, PyTTA-BPY-COF, and PyTTA-BT-COF, respectively. Additionally, the release rate of iodine-loaded COFs in methanol solution and recyclability were also impressive, demonstrating their potential for practical applications. The mechanism investigation reveals that both imine linkage and π-conjugated structure of the COFs may contribute to their high iodine adsorption capability. This work is instructive as a guide for designing and synthesizing COFs as a solid-phase adsorbent for iodine uptake.

Imaging the Iodine Sorption-Induced Synchronous Skeleton-Pore Interactions of Single Covalent Organic Framework Particles

Covalent organic frameworks (COFs) are promising iodine adsorbents. For improved performances, it is critical and essential to fundamentally understand the underlying mechanism. Here, using the operando dark-field optical microscopy (DFM) imaging technique, the observation of an extraordinary structure shrinkage of 2D triphenylbenzene (TPB)-dimethoxyterephthaldehyde (DMTP)-COF upon the adsorption of I2 vapor at the single-particle resolution is reported. Combining single-particle DFM imaging with other experimental and theoretical methods, it is revealed that the shrinkage mechanism of the TPB-DMTP-COF is attributed to the I2 sorption-induced synchronous skeleton-pore interactions. The redox reaction of I2 and TPB-DMTP-COF yields some cationic skeletons and I3 - species, which triggers the multi-directional halogen-bonding interactions of I2 and I3 - as well as strong cation-π interactions between neutral and cationic skeletons, accompanying the synchronous in-plane skeleton shrinking in the xy plane and compact out-of-plane layer packing in the z-direction. This understanding of the synchronous action between the skeleton and pore breaks the perspective on the structure robustness of 2D COFs with excellent stability during the I2 uptake, which offers pivotal guidance for the rational design and creation of advanced microporous adsorbents.

Hydrazone-Linked Covalent Organic Frameworks

Hydrazone-linked covalent organic frameworks (COFs) with structural flexibility, heteroatomic sites, post-modification ability and high hydrolytic stability have attracted great attention from scientific community. Hydrazone-linked COFs, as a subclass of Schiff-base COFs, was firstly reported in 2011 by Yaghi's group and later witnessed prosperous development in various aspects. Their adjustable structures, precise pore channels and plentiful heteroatomic sites of hydrazone-linked structures possess much potential in diverse applications, for example, adsorption/separation, chemical sensing, catalysis and energy storage, etc. Up to date, the systematic reviews about the reported hydrazone-linked COFs are still rare. Therefore, in this review, we will summarize their preparation methods, characteristics and related applications, and discuss the opportunity or challenge of hydrazone-linked COFs. We hope this review could provide new insights about hydrazone-linked COFs for exploring more appealing functions or applications.

Fabrication of bimetallic MOF-74 derived materials for high-efficiency adsorption of iodine

Owing to their high porosity, open metal sites, and huge surface area, metal-organic framework (MOF) materials are commonly employed in iodine adsorption processes. Bimetallic MOFs have drawn a lot of attention since mono-metal MOFs have been unable to keep up with the demand. Bimetallic MOF materials still have drawbacks, including limited adsorption capacity, extended adsorption time, poor stability, and poor selectivity, despite their positive performance in radioactive iodine capture. It has been therefore difficult to develop adsorbents with quick iodine adsorption rates and high iodine adsorption efficiency. This study investigated the adsorption properties of a series of bimetallic MOF-74 materials (Mn-Co-MOF-74, Mn-Zn-MOF-74, and Mn-Ni-MOF-74) for radioactive iodine, as well as their design and synthesis utilizing the reflux approach. It was discovered that the adsorption performance of Mn-Ni-MOF-74 for radioiodine was superior to that of the other two bimetallic MOF-74 materials. Using the bimetallic Mn-Ni-MOF-74 as a precursor, a variety of bimetallic MOF-74 derived carbon compounds (Mn-Ni-CX) were prepared by high-temperature pyrolysis. Simultaneously, the structure of the material and the iodine adsorption characteristics have been thoroughly studied.

Hollow Bismuth-Based Nanoreactor with Ultrathin Disordered Mesoporous Silica Shell for Superior Radioactive Iodine Decontamination

The effective removal of radioactive iodine under harsh high-temperature conditions, akin to those encountered in real spent nuclear fuel reprocessing, remains a formidable challenge. Herein, a novel bismuth-based mesoporous silica nanoreactor with a distinctive hollow yolk-shell structure was successfully synthesized by using silica-coated Bi2O3 as a hard template and alkaline organic ammonia for etching (Bi@HMS-1, HMS = hollow mesoporous silica). In contrast to conventional inorganic alkali-assisted methods with organic template agents, our approach yielded a material with thinner and more disordered shell layers, along with a relatively smaller pore volume. This led to a significant reduction in the physisorption of Bi@HMS-1 onto iodine while maintaining a smooth passage of guest iodine molecules into and out of the shell channels. Consequently, the resulting sorbent exhibited an outstanding iodine sorption capacity at high temperatures, achieving a chemisorption percentage as high as 96.5%, which makes it extremely competitive among the currently reported sorbents.

Optimizing Iodine Enrichment through Induced-Fit Transformations in a Flexible Ag(I)-Organic Framework: From Accelerated Adsorption Kinetics to Record-High Storage Density

Efficient capture and storage of radioactive I2 is a prerequisite for developing nuclear power but remains a challenge. Here, two flexible Ag-MOFs (FJI-H39 and 40) with similar active sites but different pore sizes and flexibility are prepared; both of them can capture I2 with excellent removal efficiencies and high adsorption capacities. Due to the more flexible pores, FJI-H39 not only possesses the record-high I2 storage density among all the reported MOFs but also displays a very fast adsorption kinetic (124 times faster than FJI-H40), while their desorption kinetics are comparable. Mechanistic studies show that FJI-H39 can undergo induced-fit transformations continuously (first contraction then expansion), making the adsorbed iodine species enrich near the Ag(I) nodes quickly and orderly, from discrete I- anion to the dense packing of various iodine species, achieving the very fast adsorption kinetic and the record-high storage density simultaneously. However, no significant structural transformations caused by the adsorbed iodine are observed in FJI-H40. In addition, FJI-H39 has excellent stability/recyclability/obtainability, making it a practical adsorbent for radioactive I2. This work provides a useful method for synthesizing practical radioactive I2 adsorbents.

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Ionic Covalent Organic Frameworks in Adsorption and Catalysis

The ion extraction and electro/photo catalysis are promising methods to address environmental and energy issues. Covalent organic frameworks (COFs) are a class of promising template to construct absorbents and catalysts because of their stable frameworks, high surface areas, controllable pore environments, and well-defined catalytic sites. Among them, ionic COFs as unique class of crystalline porous materials, with charges in the frameworks or along the pore walls, have shown different properties and resulting performance in these applications with those from charge-neutral COFs. In this review, current research progress based on the ionic COFs for ion extraction and energy conversion, including cationic/anionic materials and electro/photo catalysis is reviewed in terms of the synthesis strategy, modification methods, mechanisms of adsorption and catalysis, as well as applications. Finally, we demonstrated the current challenges and future development of ionic COFs in design strategies and applications.

Ultrasonic-Assisted Nitrate Anion Incorporation in Triaminoguanidium Chloride Based Covalent Organic Polymer for Methylene Blue Dye Adsorption

Terephthalaldehyde-triaminoguanidium chloride covalent organic polymer, Te-TGCl COP can facilely be incorporated with NaNO3 by sonication. Te-TGCl COP incorporated with NaNO3 via ultrasonication adsorbs Methylene Blue (MB) dye. Te-TGCl COP alone shows negligible adsorption capacity for MB, however, when treated with NaNO3, its adsorption capacity emerges slightly. Moreover, ultrasonication of the NaNO3 treated COP, Te-TG-NaNO3 COP shows dramatic increase in its adsorption capacity for MB (qe for Te-TGCl COP ≈0 mg g-1; for Te-TG-NaNO3=17.65 mg g-1). Emergence of MB dye adsorption property in Te-TG-NaNO3 COP composite may be attributed primarily to the electrostatic interaction of MB dye molecules with nitrate anions and the sonochemical effect caused fibrous morphological structure of the adsorbent material. The kinetics of MB dye adsorption onto Te-TG-NaNO3 COP composite exhibits an excellent fit for the pseudo-second order model, suggesting the rate-determining step to be chemisorption. Homogeneous monolayer adsorption of MB dye onto Te-TG-NaNO3 COP composite can be suggested as the Langmuir isotherm model seemed to be fitted well.

Fabrication of Polysulfone Beads Containing Covalent Organic Polymer as a Versatile Platform for Efficient Iodine Capture

Radioactive iodine poses a significant risk to human health, particularly with regard to reproductive and metabolic functions. Designing and developing highly efficient adsorbent materials for radioactive substances remain a significant challenge. This study aimed to address this issue by the fabricating polymeric beads containing covalent organic polymer (COP) as an effective method for removing iodine vapor. To achieve this, a COP was first synthesized via the Friedel-Crafts reaction catalyzed by anhydrous aluminum chloride. Then, COP-loaded polysulfone (PSf) (COP@PSf) and PSf beads were prepared using a phase separation method. The beads produced in this research have exhibited remarkable proficiency in adsorbing iodine vapor, showing an adsorption capacity of up to 216 wt % within just 420 min, which is higher than that of most other similar beads reported in the literature.

Engineering the pore environment of antiparallel stacked covalent organic frameworks for capture of iodine pollutants

Radioiodine capture from nuclear fuel waste and contaminated water sources is of enormous environmental importance, but remains technically challenging. Herein, we demonstrate robust covalent organic frameworks (COFs) with antiparallel stacked structures, excellent radiation resistance, and high binding affinities toward I2, CH3I, and I3- under various conditions. A neutral framework (ACOF-1) achieves a high affinity through the cooperative functions of pyridine-N and hydrazine groups from antiparallel stacking layers, resulting in a high capacity of ~2.16 g/g for I2 and ~0.74 g/g for CH3I at 25 °C under dynamic adsorption conditions. Subsequently, post-synthetic methylation of ACOF-1 converted pyridine-N sites to cationic pyridinium moieties, yielding a cationic framework (namely ACOF-1R) with enhanced capacity for triiodide ion capture from contaminated water. ACOF-1R can rapidly decontaminate iodine polluted groundwater to drinking levels with a high uptake capacity of ~4.46 g/g established through column breakthrough tests. The cooperative functions of specific binding moieties make ACOF-1 and ACOF-1R promising adsorbents for radioiodine pollutants treatment under practical conditions.

The paradigm for exceptional iodine capture by nonporous amorphous electron-deficient cyclophanes

Nuclear power emerges as a beacon of hope in tackling the energy crisis. However, the emission of radioactive iodine originating from nuclear waste and accidents poses a serious danger to nature and human well-being. Therefore, it becomes imperative to urgently develop suitable adsorbents capable of iodine capture and long-term storage. It's generally recognized that achieving high iodine capture efficiency necessitates the presence of electron-rich pores/cavities that facilitate charge-transfer (CT) interactions, as well as effective sorption sites capable of engaging in lone pair interactions with iodine. In this study, an unprecedented iodine capture paradigm by nonporous amorphous electron-deficient tetracationic cycloalkanes in vapor and aqueous solutions is revealed, overturning preconceived notions of iodine trapping materials. A newly reported tetracationic cyclophane, BPy-Box4+, exhibited an exceptional iodine vapor sorption capacity of 3.99 g g-1, remarkable iodine removal efficiency in aqueous media, and outstanding reusability. The iodine capture mechanism is unambiguously elucidated by theoretical calculations and the single-crystal structures of cyclophanes with a gradual increase in iodine content, underlining the vital role of host-guest (1:1 or 1:2) interactions for the enhanced iodine capture. The current study demonstrates a new paradigm for enhanced iodine capture by nonporous amorphous electron-deficient cyclophanes through host-guest complexation.

Efficient capture of iodine in steam and water media by hydrogen bond-driven charge transfer complexes

Untreated radioactive iodine (129I and 131I) released from nuclear power plants poses a significant threat to humans and the environment, so the development of materials to capture iodine from water media and steam is critical. Here, we report a charge transfer complex (TCNQ-MA CTC) with abundant nitrogen atoms and π-conjugated system for adsorption of I2 vapor and I3- from aqueous solutions. Due to the synergistic binding mechanism of benzene/triazine rings and N-containing groups with iodine, special I-π and charge transfer interaction can be formed between the guest and the host, and thus efficient removal of I2 and I3- can be realized by TCNQ-MA CTC with the adsorption capacity up to 2.42 g/g and 800 mg/g, respectively. TCNQ-MA CTC can capture 92% of I3- within 2.5 min, showing extremely fast kinetics, excellent selectivity and high affinity (Kd = 5.68 × 106 mL/g). Finally, the TCNQ-MA CTC was successfully applied in the removal of iodine from seawater with the efficiency of 93.71%. This work provides new insights in the construction of charge transfer complexes and lays the foundation for its environmental applications.

Efficient adsorption of radioactive iodine by covalent organic framework/chitosan aerogel

Radioactive iodine is considered one of the most dangerous radioactive elements in nuclear waste. Therefore, effective capture of radioactive iodine is essential for developing and using nuclear energy to solve the energy crisis. Some materials that have been developed for removing radioactive iodine still suffer from complex synthesis, low removal capacity, and non-reusability. Herein, covalent organic framework (COF)/chitosan (CS) aerogels were prepared using vacuum freeze-drying, and the COF nanoparticles were tightly attached on the green biomass material CS networks. Due to the synergistic effect of both COF and CS, the composite aerogel shows a three-dimensional porous and stable structure in the recycle usage. The COF/CS aerogel exhibits excellent iodine adsorption capacity of 2211.58 mg g-1 and 5.62 g g-1 for static iodine solution and iodine vapor, respectively, better than some common adsorbents. Furthermore, COF/CS aerogel demonstrated good recyclability performance with 87 % of the initial adsorption capacity after 5 cycles. In addition, the interaction between iodine and imine groups, amino groups, and benzene rings of aerogel are the possible adsorption mechanisms. COF/CS aerogel has excellent adsorption properties, good chemical stability, and reusable performance, which is a potential and efficient adsorbent for industrial radioactive iodine adsorption from nuclear waste.

Efficient Removal of Iodine from Water by a Calix[4]pyrrole-Based Nanofilm

The efficient removal of radioactive iodine from an aqueous solution is largely dependent on the adsorbent materials employed. In this work, we report a calix[4]pyrrole-based nanofilm and its application for the rapid removal of iodine from water. The nanofilm was synthesized through a confined dynamic condensation of tetra hydrazide calix[4]pyrrole with 1,3,5-tri-(4-formylphenyl) aldehyde at the air/dimethyl sulfoxide (DMSO) interface. The thickness of the obtained nanofilm is ∼35 nm, enabling fast mass transfer and a high ratio of accessible binding sites for iodine. The pseudo-second-order rate constant of the nanofilm for iodine is ∼0.061 g g-1 min-1, 3 orders of magnitude higher than most reported adsorbent materials. Flow-through nanofiltration tests demonstrated that the nanofilm has an adsorption capacity of 1.48 g g-1, a high removal efficiency, and good reusability. The mechanism study revealed that the moieties of Schiff base, pyrrole, and aromatic rings play a key role for binding iodine. We believe this work provides not only a new strategy for the efficient removal of radioactive iodine from water but also new ideas for designing efficient iodine adsorbents.

Ultralight crystalline hybrid composite material for highly efficient sequestration of radioiodine

Considering the importance of sustainable nuclear energy, effective management of radioactive nuclear waste, such as sequestration of radioiodine has inflicted a significant research attention in recent years. Despite the fact that materials have been reported for the adsorption of iodine, development of effective adsorbent with significantly improved segregation properties for widespread practical applications still remain exceedingly difficult due to lack of proper design strategies. Herein, utilizing unique hybridization synthetic strategy, a composite crystalline aerogel material has been fabricated by covalent stepping of an amino-functionalized stable cationic discrete metal-organic polyhedra with dual-pore containing imine-functionalized covalent organic framework. The ultralight hybrid composite exhibits large surface area with hierarchical macro-micro porosity and multifunctional binding sites, which collectively interact with iodine. The developed nano-adsorbent demonstrate ultrahigh vapor and aqueous-phase iodine adsorption capacities of 9.98 g.g-1 and 4.74 g.g-1, respectively, in static conditions with fast adsorption kinetics, high retention efficiency, reusability and recovery.

Pore Space Partition Synthetic Strategy in Imine-linked Multivariate Covalent Organic Frameworks

Partitioning the pores of covalent organic frameworks (COFs) is an attractive strategy for introducing microporosity and achieving new functionality, but it is technically challenging to achieve. Herein, we report a simple strategy for partitioning the micropores/mesopores of multivariate COFs. Our approach relies on the predesign and synthesis of multicomponent COFs through imine condensation reactions with aldehyde groups anchored in the COF pores, followed by inserting additional symmetric building blocks (with C2 or C3 symmetries) as pore partition agents. This approach allowed tetragonal or hexagonal pores to be partitioned into two or three smaller micropores, respectively. The synthesized library of pore-partitioned COFs was then applied for the capture of iodine pollutants (i.e., I2 and CH3I). This rich inventory allowed deep exploration of the relationships between the COF adsorbent composition, pore architecture, and adsorption capacity for I2 and CH3I capture under wide-ranging conditions. Notably, one of our developed pore-partitioned COFs (COF 3-2P) exhibited greatly enhanced dynamic I2 and CH3I adsorption performances compared to its parent COF (COF 3) in breakthrough tests, setting a new benchmark for COF-based adsorbents. Results present an effective design strategy toward functional COFs with tunable pore environments, functions, and properties.