Efficient and simultaneous capture of iodine and methyl iodide achieved by a covalent organic framework

Zirconium metal-organic cages for iodine adsorption: Effect of substituted groups and pore structures

Zirconium metal-organic cages (MOCs) have emerged as potential adsorbents for radioactive iodine absorption, one of key fission products of concern in nuclear fuel cycles. Herein a series of substituted groups functionalized Zr-MOCs were employed to investigate the influence of substituted group on iodine adsorption, in which ZrT-1-(NH2)2 showed the highest improvement on both iodine vapor and solution-based absorption. Thereafter, five longer linkers functionalized with amino groups were chosen to construct five isoreticular MOCs for iodine absorption. Among them, ZrT-2-3,3'-(NH2)2 and ZrT-3-2,2''-(NH2)2 exhibited comparable iodine vapor absorption capacity compared with ZrT-1-(NH2)2. Impressively, iodine vapor adsorption capacities (2.62 g/g and 2.50 g/g) of ZrT-1-(NH2)2 and ZrT-3-2,2''-(NH2)2, represent the second highest among all the MOCs. These five isoreticular MOCs displayed higher iodine uptake capacities via solution-based process than ZrT-1-(NH2)2. The iodine/cyclohexane uptake capacities of ZrT-2-3-NH2 and ZrT-2-3,3'-(NH2)2 and ZrT-3-2,2''-(NH2)2 are the highest among all the MOCs. Raman and XPS demonstrate the strong charge transfer from the amino-substituted linkers to absorbed iodine. Synchrotron X-ray single-crystal diffraction provides the possible iodine species distribution in the cage, clarifying the host-guest interactions between the trapped iodine and MOCs. This work may motivate the rational design of MOCs with optimized structures to enhance the adsorption properties.

Understanding silver structural rearrangement on zeolite Y for methyl iodide capture in nuclear safety system

To enhance nuclear power safety, the adsorptive passive capture of emitted radioactive organic iodine under harsh conditions is essential. Silver states and CH3I reactive adsorption on silver zeolite Y were studied under simulated accident conditions (10 ppm CH3I at 7 bar, 0-80 % RH, and 150 °C). The roles of Ag⁺ ions, silver clusters, and external silver aggregates in silver zeolite Y during CH3I capture were analyzed. Ag⁺ ions enabled near-complete CH3I removal (<0.1 ppm), while silver clusters and external silver aggregates enhanced the overall adsorption capacity. It was also noted that the formation of AgnY+ clusters within sodalite cages could potentially block pores, leading to immediate breakthrough. Pelletized silver zeolite Y adsorbents demonstrated optimal CH3I capture capacity at sufficiently auto-reduced states. Under dry conditions, Ag⁺ ions primarily promoted light hydrocarbon by-products, whereas silver clusters contributed to the formation of heavier hydrocarbons. Humid conditions led to the weakening of adsorption affinity and rate of CH3I, along with oxygenated by-products. The findings, including silver structural rearrangement by auto-reduction, provide critical guidance for understanding the adsorption mechanism and improving the design efficiency of a nuclear containment system.

Highly Crystalline and Flexible Covalent Organic Frameworks: Advancing Efficient Iodine Adsorption

Flexible covalent organic frameworks (COFs) offer distinct advantages in elasticity and adaptability over rigid COFs, but these benefits often come at the expense of crystallinity due to challenges in polymerization, complicating both synthesis and structural characterization. Current research primarily employs single flexible monomers, which limits the tunability of these frameworks. In this study, we introduce two highly crystalline, flexible COFs, ZCST-102 and ZCST-103, constructed from dual flexible monomers. These COFs exhibit large channels, permanent porosity, high chemical stability, and exceptional crystallinity, along with enhanced structural flexibility. Notably, they achieve an iodine vapor adsorption capacity of up to 4.71 g ⋅ g-1. X-ray photoelectron spectroscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy further elucidate the interactions between iodine and the framework structures. This work emphasizes the value of incorporating flexible building blocks to maintain crystallinity while imparting functional versatility, advancing the design of dynamic porous materials.

Chiral Self-Sorting Directed Supramolecular Organic Framework of Imine Cages for Iodine Capture

Supramolecular organic frameworks (SOFs) with nanotubular pores, assembled through weak non-covalent interactions, are highly sought-after for storage, separation, and pollutant capture but are limited. Herein, a SOF assembled with a chiral imine cage is reported by leveraging kinetically driven dynamic covalent chemistry, chiral self-sorting, and dispersion interactions for efficient iodine capture. The crystallization-driven synthesis involves a triamine and a racemic mixture of axially chiral dialdehyde equipped in bimesityl (BM) skeleton that undergoes narcissistic chiral self-sorting to form racemic mixture of homochiral imine cage (BM-PIC) enantiomers, which result in the SOF (BM-PIC-SOF). Notably, excess triamine drives the chiral self-sorting into heterochiral cages in a favorable solvent. The BM-PIC-SOF is templated by solvent molecules and features nanotubular pores (1.4 nm) that are stabilized by non-covalent interactions, notably, dispersion forces between mesitylene rings. Further, the kinetic crystals of BM-PIC-SOF, upon exchange with volatile solvents, undergo single-crystal-to-single-crystal transformation at high temperature into a thermodynamic polymorph with large structural difference. BM-PIC-SOF demonstrates remarkable efficacy in adsorbing iodine not only from vapor (6.0 g.g-1) but also from organic (3.88 g.g-1) and aqueous mediums (5.01 g g-1).

Regulating triazine number in covalent organic frameworks modified separator to achieve high-energy-density performance in aqueous zinc-iodine batteries

The development of separator by tunning the zincophilic and iodide ion-repulsive properties of covalent organic frameworks (COFs) that regulate cycle lifespan and capacity of aqueous zinc-iodine (Zn-I2) batteries is one of challenges. In this work, we have shown a systematic strategic-driven investigation to elucidate the role of functional triazine properties in COF modified separator towards overall performance of aqueous Zn-I2 batteries. As such, three COFs with the same topology but different triazine number in their structures, have been synthesized, among which the triazine-richest framework, TAPA-TTB-COF-based separator demonstrated to be most effective to guide uniform Zn2+ flux and simultaneously inhibit polyiodide shuttling due to the zincophilic nature and good iodide ion-repulsive capability of triazine. Consequently, the Zn||Gr@TAPA-TTB-COF@GF||Zn symmetric battery achieves a long life of more than 2100 h (5.0 mA cm-2) and the initial area capacity of the Zn||Gr@TAPA-TTB-COF@GF||I2 battery reaches up to 5.5 mAh cm-2 (20 mA cm-2). After 2000 cycles, the discharge capacity can still maintain at3.0 mAh cm-2 with a capacity decay rate of only 0.023 % per cycle. This study provides guidance for the rational design of functional COFs separators and promotes their application in high energy storage systems.

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.

Protonated amination magnetic chitosan microspheres for efficient iodide removal from nuclear wastewater: Synthesis, mechanism, and reusability

A series of novel protonated amination magnetic chitosan microspheres (P-A-MCMs) were successfully prepared for efficient iodide (I-) removal from nuclear wastewater through the amination and protonation modifications using as-synthesized core-shell-shaped magnetic chitosan microspheres (MCMs) as the matrix materials. The morphology, composition, and surface property of microspheres were fully characterized by various analytical techniques. The characterization results confirmed the successful introduction of protonated amine groups while retaining the good magnetic properties of microspheres. The I- adsorption mechanism of P-A-MCMs was primarily governed by electrostatic attraction and ion-exchange process. Among the prepared P-A-MCMs, the protonated tetraethylenepentamine magnetic chitosan microspheres (P-TEPA-MCMs) achieved over 89 % iodide removal efficiency across a wide pH range of 3 to 11. The maximum I- adsorption capacity of P-TEPA-MCMs reached 1.3482 mmol g-1 within 120 min at 298 K, which was 1.67-fold greater than unmodified MCMs. Thermodynamic and kinetic analyses revealed that the I- adsorption process of P-A-MCMs was dominated by the monolayer physisorption, following the pseudo-first-order, Langmuir and Dubinin-Radushkevish models. Notably, the P-A-MCMs maintained a high I- removal efficiency of 88.4 % after ten regeneration cycles, demonstrating excellent reusability. These findings highlight the potential of P-A-MCMs as a cost-effective, high-performance, and recyclable adsorbent for managing radioactive iodide in nuclear wastewater.

Covalent organic framework nanomaterials: Syntheses, architectures, and applications

Covalent Organic Frameworks (COFs) are characterized by high thermochemical stability, low backbone density, well-controlled physical and chemical properties, large specific surface volume and porosity, permanently open pore structure, and various synthesis strategies. These remarkable attributes confer COFs with significant potential for a myriad of applications ranging from catalysis technology, gas separation and storage, optoelectronic materials, environmental and energy sciences, and biomedical development. There are many synthetic design methods for COF materials, and dynamic covalent chemistry is the scientific basis of COF materials-oriented design, which gives the error correction ability of the covalent assembly process, and is the key to obtaining crystallization and stability at the same time. However, "crystallinity" and "stability" in the synthesis and preparation of COF materials are often like "You can't have your cake and eat it, too": on the one hand, the reversible covalent bonds used in the synthesis of highly crystalline COF framework are easy to decompose under extreme conditions, which greatly limits its application scenarios; On the other hand, although highly stable COF materials can be prepared by using irreversible covalent bonds, it is usually poor crystalline and difficult to have high performance. In addition, the strict deoxygenation operation required for synthesizing COF materials also limits its macro preparation and large-scale application. Therefore, the synthesis strategy and efficient preparation of highly stable and crystalline COF materials are a major obstacle to the practical application of this field. This paper describes the four structures of COF materials, as well as their synthesis methods, electrical energy-storing electrocatalysis, and significant environmental protection applications. The future directions, prospects, and possible barriers to the development of these materials are envisioned in.

Imine-Linked Covalent Organic Frameworks Tuned by Quaternary-Ammonium-Alkyl for Highly Effective and Selective Adsorption of Perchlorate from Water

Perchlorate (ClO4 -) contamination in surface water is an escalating issue for drinking water safety. Herein, an imine-linked covalent organic framework (COF) tuned by quaternary ammonium alkyls (R4N+) is developed for ClO4 - adsorption. The hydrophobic and cationic COF adsorbent achieves a record-breaking adsorption capacity of ClO4 - at 912.7 mg g-1, demonstrating remarkable selectivity for ClO4 - over other environmentally relevant anions and exhibiting rapid adsorption kinetics. Furthermore, the adsorbent maintains excellent recycling performance (removal efficiency ≥ 80% after 10 cycles) using tetrachloroferrate for regeneration. In dynamic flow-through experiments with real water samples, the adsorbent effectively treats ≈3200-bed volumes of feed streams (≈500 µg L-1), with an enrichment factor of 15.2. The hydrophobicity of the COF adsorbent is identified as a premise for its interaction with ClO4 -. Molecular dynamic simulations and density functional theory calculations reveal that R4N+ anchored in COF cores enriches ClO4 - via electrostatic attraction and bonds with ClO4 - via unconventional hydrogen bonds (C─H─O). These key insights pave the way for future design and optimization of adsorbents for removing oxo-anion from water, especially for ClO4 -.

Facile post-synthesis of isomeric covalent organic frameworks via precise pore surface engineering

Isomeric covalent organic frameworks (COFs) have developed dramatically due to having the same chemical composition but distinct physicochemical characteristics. However, exploring novel synthetic strategies for the precise construction of COFs with isomeric pore microenvironments remains challenging and in its infancy. In this contribution, we have developed a controllable, simple, and efficient post-synthesis modification strategy to design isomeric COFs via precise pore surface engineering. The as-prepared isomeric COFs showed comparable crystallinity and porosity but significantly different pore microenvironments. Interestingly, the isomeric moieties endow the isomeric COFs with specific capture performances and excellent recycling ability. The specific interactions between these isomeric COFs and guests are verified by fluorescence spectra and theoretical calculation. This study will open a novel avenue for the construction of isomeric COFs and facilitate the development of isomeric COFs with specific properties.

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.

Engineered covalent organic frameworks (COFs) for adsorption-based metal separation technologies: A critical review

Porous covalent organic frameworks (COFs) are promising materials used for separation and purification during environmental remediation. This critical review focuses on two key aspects. First, it critically examines strategies to improve COF design and structure and evaluates their impact on separation performance. Second, engineering approaches for enhancing the interactions between COF-based adsorbents and metals for enhanced separation and capture are elucidated. The latest body of research on separating metals (e.g., Li, K, Sr, Hg, Cd, Pb, Cr, Au, Ag, Pd, and U) using COF-based adsorbents is discussed to understand the factors that influence their performance. However, it is to be noted that COF-based adsorbents are still in their infancy and remain largley unexplored, mainly hindered by synthetic complexities and suboptimal crystalline structures. This highlights the need for further research and development to fully unlock the excellent potential of COFs for metal separation applications, particularly in environmental and energy applications.

Strategic Nitrogen Site Alignment in Covalent Organic Frameworks for Enhanced Performance in Aqueous Zinc-Iodide Batteries

Aqueous zinc-iodine batteries (AZIBs) are gaining attention as next-generation energy storage systems due to their high theoretical capacity, enhanced safety, and cost-effectiveness. However, their practical application is hindered by challenges such as slow reaction kinetics and the persistent polyiodide shuttle effect. To address these limitations, we developed a novel class of covalent organic frameworks (COFs) featuring electron-rich nitrogen sites with varied density and distribution (N1-N4) along the pore walls. These nitrogen sites enhance iodine species confinement and mass transport. Our experimental and theoretical studies reveal that the continuous and optimized distribution of nitrogen sites within the COF structure significantly reduces internal resistance and boosts redox activity. Moreover, the N4-COF demonstrates superior performance compared to other porous materials, due to its high density and strategic alignment of active sites. The I2@N4-COF cathode achieves a remarkable specific capacity of 348 mAh g-1 at 1 C, almost 1.8 times greater than that of the I2@N1-COF, while also maintaining excellent cycling stability. This integration of a porous framework with aligned nitrogen sites in the N4-COF structure not only enhances iodine redox behavior but also offers a promising design strategy for developing high-performance AZIB electrodes.

Photoconductivity Switching in Semiconducting Two-Dimensional Crystals via Molecular Tetris

Two-dimensional organic materials are mainly constructed by using orthogonal anisotropic connectivity of covalent bonding and π-π stacking. The noncovalent connectivity between building blocks is presumed to be too delicate to stabilize the two-dimensional (2D) layers. Contrary to this assumption, we constructed graphite-like 2D layered material by utilizing pure noncovalent connectivity, i.e., weak intermolecular and π-π interaction via a molecular Tetris strategy. We produce X-ray mountable single crystals comprising polycyclic aromatic heterocycles by employing a single-crystal-to-dissolution-to-single-crystal transformation methodology. The macromechanical analysis of this layered crystal shows shearing behavior, which is quantified using nanoindentation experiments. The 2D lattice's layer space allows reversible intercalation-deintercalation of iodine, which enhances the photoconductivity by 17 folds. Combined efforts of X-ray diffraction, solid-state spectroscopy, and electrochemical studies established the mechanism of intercalation and resulting photoconductivity enhancement.

Covalent organic frameworks as superior adsorbents for the removal of toxic substances

Developing new materials capable of the safe and efficient removal of toxic substances has become a research hotspot in the field of materials science, as these toxic substances pose a serious threat to human health, both directly and indirectly. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials, have advantages such as large specific surface area, tunable pore size, designable structure, and good biocompatibility, which have been proven to be a superior adsorbent design platform for toxic substances capture. This review will summarize the synthesis methods of COFs and the properties and characteristics of typical toxicants, discuss the design strategies of COF-based adsorbents for the removal of toxic substances, and highlight the recent advancements in COF-based adsorbents as robust candidates for the efficient removal of various types of toxicants, such as animal toxins, microbial toxins, phytotoxins, environmental toxins, etc. The adsorption performance and related mechanisms of COF-based adsorbents for different types of toxic substances will be discussed. The complex host-guest interactions mainly include electrostatic, π-π interactions, hydrogen bonding, hydrophobic interactions, and molecular sieving effects. In addition, the adsorption performance of various COF-based adsorbents will be compared, and strategies such as reasonable adjustment of pore size, introduction of functionalities, and preparation of composite materials can effectively improve the adsorption efficiency of toxins. Finally, we also point out the challenges and future development directions that COFs may face in the field of toxicant removal. It is expected that this review will provide valuable insights into the application of COF-based adsorbents in the removal of toxicants and the development of new materials.

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.

Efficient and Rapid Extraction of Gold from E-Waste via Tailoring the Skeleton Environment of Covalent Organic Framework

The recovery and repurposing of noble metal from electronic waste has attracted significant attention due to the tremendous benefits to the economy and environment but is of great challenge. Herein, a two-dimensional oxygen-rich COF material, named TbDa-COF, was fabricated via integrating 1,3,5-tris(4-formylphenyl)benzene (TFPB) and oxygen-rich 3,3'-dihydroxybenzidine (DHB) into a π-conjugated framework. TbDa-COF permits selective gold recovery through local coordination and electrostatic interaction, which is then followed via in situ reduction to form gold nanoparticles (AuNPs) within its skeleton. The experiment results exhibited satisfactory selectivity and favorable capture capacity (247.1 mg g-1), which is attributed to the favored crystallinity, numerous active functional moieties in DHB, and the efficient reduction of gold via hydroxyl groups. Meanwhile, the characterization results demonstrated that gold nanoparticles were evenly enriched and localized on the skeleton of TbDa-COF, which exhibits excellent catalytic activity in the reduction of 4-nitrophenol (90.9%) and rhodamine B (99.3%) with NaBH4. More importantly, the strong anchoring ability between AuNPs and oxygen-rich units over the skeleton enhances the binding of AuNPs with TbDa-COF to maintain the preferred stability and easily reuse without loss of the catalytic property. The design of novel COF materials with specific functional units will open a new frontier on the recovery and reuse of noble metals; but also the composite has various potential developments in the fields of catalysis and optoelectronics.

Imidazole Cationic-Bridged Pillar[5]arene Polymer as a Recycle Adsorbent for Iodine Capture

Developing efficient and recyclable iodine adsorbents is crucial for addressing radioactive iodine pollution. An imidazole cation-bridged pillar[5]arene polymer (P5-P5I) was synthesized via a salt formation reaction. P5-P5I exhibited a high iodine vapor capture capacity of 2130.0 mg/g and a maximum adsorption capacity of 1935.3 and 942.4 mg/g for I2 and I3- in solution, respectively. The adsorption kinetics of I2 and I3- on P5-P5I in aqueous solution followed a pseudo-second-order kinetic model, reaching adsorption equilibrium within a few minutes. P5-P5I demonstrated the ability to selectively capture I2 and I3- in the presence of competing anions (10-1000-fold), removing over 97.1% of iodine from various environments. Meanwhile, under extreme conditions (strong acids, strong bases, and high temperature), P5-P5I still has a superior adsorption performance and cycling ability for I2 and I3-. Molecular modeling revealed that P5-P5I could synergistically enhance iodine capture through multiple weak interactions, including host-guest, C-H···I hydrogen bond, and electrostatic interactions. This study indicates that P5-P5I has promising applications for rapid and efficient iodine uptake from vapor and various aqueous media.

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.

Highly sensitive, responsive, and selective iodine gas sensor fabricated using AgI-functionalized graphene

Radioactive molecular iodine (I2) is a critical volatile pollutant generated in nuclear energy applications, necessitating sensors that rapidly and selectively detect low concentrations of I2 vapor to protect human health and the environment. In this study, we design and prepare a three-component sensing material comprising reduced graphene oxide (rGO) as the substrate, silver iodide (AgI) particles as active sites, and polystyrene sulfonate as an additive. The AgI particles enable reversible adsorption and conversion of I2 molecules into polyiodides, inducing substantial charge density variation in rGO. This mechanism facilitates exceptional sensitivity and selectivity, ultrafast response and recovery times, and room-temperature operation. A multifunctional sensor prototype fabricated utilizing this material achieves the fastest reported response/recovery times (22/22 seconds in dynamic mode and 4.2/11 seconds in static mode) and a detection limit of 25 ppb, surpassing standards set by the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH), while outperforming commercial I2 gas sensors. This work provides profound insights into the design of I2 sensing materials and mechanisms for real-world applications.

Ultra-Long Lifespan Aqueous Zinc-Iodine Batteries Enabled by a Defect-Rich Covalent Triazine Framework

Aqueous Zinc-iodine batteries (ZIBs) are widely viewed as promising energy storage devices due to their high energy density and intrinsic safety. However, they encounter great challenges such as grievous polyiodides shuttle and sluggish iodine (I2) redox reaction kinetics, thus undesirable cycling performance. Here a high-performance ZIB with an ultra-long lifespan is reported through the rational I2 cathode catalyst design. Specifically, a covalent triazine framework with defect-rich sites and micro-mesoporous structure (i.e., CTF500) is developed as an effective I2 cathode catalyst. Benefiting from the synergistic effect of micro-mesoporous structure and defect-rich sites for the confinement and conversion of I2 species, the resulting ZIBs with I2 loaded CTF500 (I2@CTF500) cathode show an ultra-long lifespan over 75,000 cycles at 5 A g-1, and an impressive cyclic performance over 15,000 cycles at high I2 loading of 3.59 mg cm-2, highlighting its commercial application prospect. In/ex situ spectral characterizations combined with theoretical calculations clearly reveal the reversible reaction mechanism of I2 species in I2@CTF500 cathode and the essential role of defect-rich sites in boosting the performance of ZIBs. This work not only guides the design of advanced I2 cathodes for metal-iodine batteries but also expands the range of possible applications for defect-rich CTFs.

Electrospun Nanofiber Supported Nano/Mesoscale Covalent Organic Frameworks Boost Iodine Sorption

Covalent Organic Frameworks (COFs) are benchmark materials for iodine sorption, but their use has largely been confined to crystalline bulk forms. In this state, COFs face diffusion limitations leading to slow sorption kinetics. To address this, a series of [2 + 3] imine-linked COFs with varying particle sizes and morphologies (mesospheres, nanoflowers, and bulk) is synthesized. Reducing particle size (from 826 ± 48 to 412 ± 22 nm) and adding surface protrusions in COF mesospheres improved iodine adsorption capacity (7.6 to 8.5 g g⁻¹), kinetics (K80%, 0.61 to 0.76 g g⁻¹ h⁻¹), and chemisorption efficiency. Notably, solvothermally synthesized (120 °C, 5 d) crystalline bulk COF with accessible porous surfaces exhibited faster kinetics (K80%, 1.13 g g⁻¹ h⁻¹) than nano/mesoCOFs.This implies nano- and mesoCOFs exhibit surface aggregation that passivates their external binding sites and hinders iodine diffusion and mass transfer. To prevent this, morphologically controlled COF particles are immobilized onto electrospun polyacrylonitrile nanofibrous membranes via in situ growth strategy, creating a hierarchical structure that improved iodine diffusion pathways. This modification increased iodine sorption kinetics by 98%-153% and strengthened the charge-transfer process compared to COF powders.

Construction of heterogeneous MOF-on-MOF for highly efficient gaseous iodine sequestration under static conditions

Considering the unexpected nuclear power waste emission and potential nuclear leakage, the exploration of robust materials for the effective capture and storage of radioactive iodine is of great importance but still remains a challenge. In this work, we report the rational synthesis of functionalized NH2-UiO-66-on-ZIF-67 architecture to enhance the static adsorption and retention of volatile iodine. Such MOF-on-MOF heterostructures was fabricated through seeding ZIF-67 core on the surface of NH2-UiO-66 satellite via a facile polyvinylpyrrolidone (PVP) regulated internal extended growth strategies. NH2-UiO-66-on-ZIF-67 exhibited unique core-satellite structure, which significantly promotes the binding interactions with iodine through synergizing of the N-rich imidazole moieties and surface functionalized amino groups within the porosity channels. As a result, the as fabricated NH2-UiO-66-on-ZIF-67 achieves enhanced mass diffusion and high capture capacity of 3600 mg/g for iodine vapor under static sorption conditions. Moreover, water vapor in humid conditions (relative humidity of 18 %) has almost no effect on the static iodine adsorption performance of the material. This study sheds light on a reliable MOF-on-MOF hybrid strategy for effective radioiodine treatment to ensure the safety nuclear waste management.

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.

Deposition of Imidazole into Mesoporous Zirconium Metal-Organic Framework for Iodine Capture

Efficient capture of radioiodine is essential for the protection of the ecological environment and the sustainable development of nuclear energy generation. Metal-organic frameworks (MOFs) and their derivatives provide alternative potential for overcoming the limitations of traditional iodine adsorbents. Herein this work, imidazole (Im) is dispersed into a robust mesoporous zirconium MOF PCN-222 by the heat deposition method, forming a high-uniformity composite Im@PCN-222. The large pore size and marked chemical resistance skeleton of PCN-222 allow the incorporation of Im to reach 43 wt % while surviving the chemical corrosion of activated Im. The nearly saturated loading of Im significantly benefits the sorption capability toward iodine and gives rise to an exceptional adsorption capacity of 10.04 g g-1 and excellent recyclability. This value is higher than that of most of the MOFs and their derivatives. Further, Im was also successfully deposited onto the PCN-222 functionalized porous Al2O3 ceramic filtration membrane, which endowed the hybrid membrane with efficient iodine sorption and separation properties. This work highlights a new strategy for the fabrication of the MOF-based radioiodine adsorption composite as well as MOF composite-based filters.

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.

Deciphering the Entropy-Driven Host-Guest Interactions within Single Covalent Organic Frameworks for Trapping of 131I. NANO LETTERS 2024;24:13861-13866. [PMID: 39422878 DOI: 10.1021/acs.nanolett.4c04883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

By combining dark-field optical microscopy with an in situ thermochemical aqueous solution system, we report a single-particle imaging strategy to investigate the host-guest interactions between covalent organic framework-300 (COF-300) as a representative COF host and a series of linear-chain fatty amines. The thermodynamic parameters, such as dissociation constant, Gibbs free energy changes, enthalpy changes, and entropy changes for the binding events within COF-300 are quantified. Correlation between the hydrophobicity of various amines and other data suggests that the mechanism of the host-guest bindings arises from the entropy-driven noncovalent interactions such as hydrogen bonds and van der Waals forces. These mechanistic insights allow for the rational design and preparation of COF-300-encapsulated n-octylamine with enhanced trapping performance of radioactive 131I-. This study not only provides thermodynamic insights into the host-guest interactions within the COF framework but also establishes a structure-property relationship between fatty amines and energetic magnitude information.

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.

MIL-88A(Al)/chitosan/graphene oxide composite aerogel with hierarchical porosity for enhanced radioactive iodine adsorption

To ensure the sustainable development of the nuclear industry, the effective capture of radioiodine from nuclear wastewater has attracted much attention. Herein, a novel MIL-88A(Al)/chitosan/graphene oxide (MCG) composite aerogel was prepared by using crosslinked chitosan and graphene oxide as the 3D network skeleton, and MIL-88A(Al) nanocrystalline particles were introduced into the skeleton by freeze-drying method. MIL-88A(Al) adsorption capacities for volatile and soluble iodine were 2.02 g g-1 and 850.00 mg g-1, respectively. Owing to the synergistic effect of MIL-88A(Al), GO, CS, and the hierarchically porous structures of the MCG aerogel, the adsorption capacities for volatile and soluble iodine by the MCG aerogel were increased to 2.62 g g-1 and 1072.60 mg g-1, respectively. Furthermore, the adsorption performance of the MCG aerogel for volatile and soluble iodine could be maintained at 83 % and 82 % after 5 cycles, suggesting excellent recoverability. Meanwhile, the adsorption mechanism studies showed the interactions between iodine and NH, AlO, and CO in MCG aerogel. Furthermore, the adsorption process is consistent with the Elovich kinetic and Sips isotherm models. MCG aerogels are potential candidates for enhanced radioiodine adsorption due to their high radioiodine capture performance and excellent recyclability.

Supramolecular Assembly of Fused Macrocycle-Cage Molecules for Fast Lithium-Ion Transport

We report a new supramolecular porous crystal assembled from fused macrocycle-cage molecules. The molecule comprises a prismatic cage with three macrocycles radially attached. The molecules form a nanoporous crystal with one-dimensional (1D) nanochannels. The supramolecular porous crystal can take up lithium-ion electrolytes and achieve an ionic conductivity of up to 8.3 × 10-4 S/cm. Structural analysis and density functional theory calculations reveal that efficient Li-ion electrolyte uptake, the presence of 1D nanochannels, and weak interactions between lithium ions and the crystal enable fast lithium-ion transport. Our findings demonstrate the potential of fused macrocycle-cage molecules as a new design motif for ion-conducting molecular crystals.

N-Heteroatom Engineered Nonporous Amorphous Self-Assembled Coordination Cages for Capture and Storage of Iodine

Radioactive iodine isotopes from nuclear-related activities, present substantial risks to human health and the environment. Developing effective materials for the capture and storage of these hazardous molecules is paramount. Traditionally, nonporous solids were historically considered ineffective for adsorbing target species. In this study, we investigate the potential of four nonporous, amorphous, self-assembled coordination cages (C1, C2, C3, and C4) featuring varying numbers of nitrogen atoms within the core (pyridyl/triazine unit) and specific cavity sizes for iodine adsorption. These coordination cages demonstrate remarkable adsorption abilities for iodine in both vapor and solution phases, facilitated by enhanced electron-pair interactions. The cages exhibit high uptake capacities of up to 3.16 g g-1 at 75 °C, the highest among metal-organic cages and up to 434.29 mg g-1 in solution, highlighting the efficiency of these materials across different phases. Even at ambient temperature, they show significant iodine capture efficiency, with a maximum value of 1.5 g g-1. Furthermore, these robust materials can be recycled, enduring at least five reusable cycles without apparent fatigue. Overall, our findings present a "N-heteroatom engineering" approach for the development of recyclable amorphous containers for the capture and storage of iodine, contributing to the mitigation of nuclear-related risks.

Unveiling the Role of Cationic Pyridine Sites in Covalent Triazine Framework for Boosting Zinc-Iodine Batteries Performance

Rechargeable Zinc-iodine batteries (ZIBs) are gaining attention as energy storage devices due to their high energy density, low-cost, and inherent safety. However, the poor cycling performance of these batteries always arises from the severe leakage and shuttle effect of polyiodides (I3 - and I5 -). Herein, a novel cationic pyridine-rich covalent triazine framework (CCTF-TPMB) is developed to capture and confine iodine (I2) species via strong electrostatic interaction, making it an attractive host for I2 in ZIBs. The as-fabricated ZIBs with I2 loaded CCTF-TPMB (I2@CCTF-TPMB) cathode achieve a large specific capacity of 243 mAh g-1 at 0.2 A g-1 and an exceptionally stable cyclic performance, retaining 93.9% of its capacity over 30 000 cycles at 5 A g-1. The excellent electrochemical performance of the ZIBs can be attributed to the pyridine-rich cationic sites of CCTF-TPMB, which effectively suppress the leakage and shuttle of polyiodides, while also accelerating the conversion reaction of I2 species. Combined in situ Raman and UV-vis analysis, along with theoretical calculations, clearly reveal the critical role played by pyridine-rich cationic sites in boosting the ZIBs performances. This work opens up a promising pathway for designing advanced I2 cathode materials toward next-generation ZIBs and beyond.

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.

An Alkyne-Bridged Covalent Organic Framework Featuring Interactive Pockets for Bromine Capture

The high degree of corrosivity and reactivity of bromine, which is released from various sources, poses a serious threat to the environment. Moreover, its coexistence with iodine forming an equilibrium compound, iodine monobromide (IBr) necessitates the selective capture of bromine from halogen mixtures. The electrophilicity of halogens to π-electron rich structures enabled us to strategically design a covalent organic framework for halogen capture, featuring a defined pore environment with localized sorption sites. The higher capture capacity of bromine (4.6 g g-1) over iodine by ~41 % shows its potential in selective capture. Spectroscopic results uncovering the preferential interaction sites are supported by theoretical investigations. The alkyne bridge is a core functionality promoting the selectivity in capture by synergistic physisorption, rationalized by the higher orbital overlap of bromine due to its smaller atomic size as well as reversible chemical interactions. The slip stacking in the structure has further promoted this phenomenon by creating clusters of molecular interaction sites with bromine intercalated between the layers. The inclusion of unsaturated moieties, i.e. triple bonds and the complementary pore geometry offer a promising design strategy for the construction of porous materials for halogen capture.

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.

Hydrophobic nanosheet silicalite-1 zeolite for iodine and methyl iodide capture

Effective capture of radioactive iodine from nuclear fuel reprocessing is of great importance for public safety as well as the secure utility of nuclear energy. In this work, a hydrophobic nanosheet silicalite-1 (NSL-1) zeolite with an adjustable size was developed for efficient iodine (I2) and methyl iodide (CH3I) adsorption. The optimized all-silica zeolite NSL-1 exhibits an excellent I2 uptake capacity of 553 mg/g within 45 min and a CH3I uptake capacity of 262 mg/g within 1 h. Benefiting from the reduced thickness and enhanced porosity, microporous NSL-1 possesses enhanced iodine adsorption capacity and fast adsorption kinetics, which is a considerable high value among inorganic materials. Unexpectedly, the remarkable characters of high hydrophobicity, acid-resistance and anti-oxidation endow it a higher iodine uptake capacity than traditional aluminosilicate zeolites. More importantly, the high uptake selectivity toward I2 possessed by NSL-1 owing to its hydrophobic skeleton under simulated dynamic conditions. The low cost, facile and scalable synthesis of NSL-1 further highlights great prospects for applications in the nuclear industry. This work provides useful insights for designing efficient adsorbents for iodine capture.

Synthesis of Calix[4]arene-Based Porous Organic Cages and Their Gas Adsorption

Two crystalline large-sized porous organic cages (POCs) based on conical calix[4]arene (C4A) were designed and synthesized. The four-jaw C4A unit tends to follow the face-directed self-assembly law with the planar triangular building blocks such as tris(4-aminophenyl)amine (TAPA) or 1,3,5-tris(4-aminophenyl)benzene (TAPB) to generate a predictable cage with a stoichiometry of [6+8]. The formation of the large cages is confirmed through their relative molecular mass measured using MALDI-TOF/TOF spectra. The protonated molecular ion peaks of C4A-TAPA and C4A-TAPB were observed at m/z 5109.0 (calculated for C336H240O24N32: m/z 5109.7) and m/z 5594.2 (calculated for C384H264O24N24: m/z 5598.4). C4A-POCs exhibit I-type N2 adsorption-desorption isotherms with the BET surface areas of 1444.9 m2 ⋅ g-1 and 1014.6 m2 ⋅ g-1. The CO2 uptakes at 273 K are 62.1 cm3 ⋅ g-1 and 52.4 cm3 ⋅ g-1 at a pressure of 100 KPa. The saturated iodine vapor static uptakes at 348 K are 3.9 g ⋅ g-1 and 3.5 g ⋅ g-1. The adsorption capacity of C4A-TAPA for SO2 reaches to 124.4 cm3 ⋅ g-1 at 298 K and 1.3 bar. Additionally, the adsorption capacities of C4A-TAPA for C2H2, C2H4, and C2H6 were evaluated.

β-Ketoenamine-linked covalent organic framework for efficient iodine capture

Exploring the materials that effectively capture radioactive iodine is crucial in managing nuclear waste produced from nuclear power plants. In this study, a β-ketoenamine-linked covalent organic framework (bCOF) is reported as an effective adsorbent to capture iodine from both vapor and solution. The bCOF's high porosity and heteroatom-rich skeleton offer notable iodine vapor uptake capacity of up to 2.51 g g-1 at 75 °C under ambient pressure. Furthermore, after five consecutive adsorption-desorption cycles, the bCOF demonstrates high reusability performance with significant iodine vapor capacity retention. The adsorption mechanism was also investigated using various ex situ structural characterization techniques, and these mechanistic studies revealed the existence of a strong chemical interaction between the bCOF and iodine. The bCOF also showed good iodine uptake performance of up to 512 mg g-1 in cyclohexane with high removal efficiencies. The bCOF's performance in adsorbing iodine from both vapor and solution makes it a promising material to be used as an effective adsorbent in capturing radioactive iodine emissions from nuclear power plants.

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.

Starch-mediated colloidal chemistry for highly reversible zinc-based polyiodide redox flow batteries

Aqueous Zn-I flow batteries utilizing low-cost porous membranes are promising candidates for high-power-density large-scale energy storage. However, capacity loss and low Coulombic efficiency resulting from polyiodide cross-over hinder the grid-level battery performance. Here, we develop colloidal chemistry for iodine-starch catholytes, endowing enlarged-sized active materials by strong chemisorption-induced colloidal aggregation. The size-sieving effect effectively suppresses polyiodide cross-over, enabling the utilization of porous membranes with high ionic conductivity. The developed flow battery achieves a high-power density of 42 mW cm-2 at 37.5 mA cm-2 with a Coulombic efficiency of over 98% and prolonged cycling for 200 cycles at 32.4 Ah L-1posolyte (50% state of charge), even at 50 °C. Furthermore, the scaled-up flow battery module integrating with photovoltaic packs demonstrates practical renewable energy storage capabilities. Cost analysis reveals a 14.3 times reduction in the installed cost due to the applicability of cheap porous membranes, indicating its potential competitiveness for grid energy storage.

Effective separation of dyes/salts by sulfonated covalent organic framework membranes based on phenolamine network conditioning

This study developed a modified polyacrylonitrile (PAN) membrane controlled by a phenol-amine network and enhanced with a sulfonated covalent organic framework (SCOF), aimed at improving the efficiency of textile wastewater treatment. Utilizing a phenol-amine network control strategy allows for precise manipulation of interfacial reactions in the synthesis of SCOF, achieving highly uniform modification on the surface of the PAN membrane. This modified membrane demonstrated high rejection of over 98% for various water-soluble dyes, including Alcian blue 8GX, Coomassie Brilliant Blue G250, methyl blue, congo red, and rose bengal, and also exhibited specific selectivity in processing salt-containing wastewater. By adjusting the deposition time of the phenol-amine and the concentration of SCOF monomers, optimal retention performance and permeate flux were achieved, effectively separating dyes and salts. This research provides a new and effective solution for treating textile wastewater, especially in separating and recovering dyes and salts, offering broad application prospects in environmental management and water resource management, and highlighting its significant practical implications.

Hollow Core-Shell Bismuth Based Al-Doped Silica Materials for Powerful Co-Sequestration of Radioactive I2 and CH3I

Developing pure inorganic materials capable of efficiently co-removing radioactive I2 and CH3I has always been a major challenge. Bismuth-based materials (BBMs) have garnered considerable attention due to their impressive I2 sorption capacity at high-temperature and cost-effectiveness. However, solely relying on bismuth components falls short in effectively removing CH3I and has not been systematically studied. Herein, a series of hollow mesoporous core-shell bifunctional materials with adjustable shell thickness and Si/Al ratio by using silica-coated Bi2O3 as a hard template and through simple alkaline-etching and CTAB-assisted surface coassembly methods (Bi@Al/SiO2) is successfully synthesized. By meticulously controlling the thickness of the shell layer and precisely tuning of the Si/Al ratio composition, the synthesis of BBMs capable of co-removing radioactive I2 and CH3I for the first time, demonstrating remarkable sorption capacities of 533.1 and 421.5 mg g-1, respectively is achieved. Both experimental and theoretical calculations indicate that the incorporation of acid sites within the shell layer is a key factor in achieving effective CH3I sorption. This innovative structural design of sorbent enables exceptional co-removal capabilities for both I2 and CH3I. Furthermore, the core-shell structure enhances the retention of captured iodine within the sorbents, which may further prevent potential leakage.

A Cucurbit[8]uril-Based Supramolecular Framework Material for Reversible Iodine Capture in the Vapor Phase and Solution

The safe and efficient management of hazardous radioactive iodine is significant for nuclear waste reprocessing and environmental industries. A novel supramolecular framework compound based on cucurbit[8]uril (Q[8]) and 4-aminopyridine (4-AP) is reported in this paper. In the single crystal structure of Q[8]-(4-AP), two 4-AP molecules interact with the outer surface of Q[8] and the two other 4-AP molecules are encapsulated into the Q[8] cavity to form the self-assembly Q[8]-(4-AP). Iodine adsorption experiments show that the as-prepared Q[8]-(4-AP) not only has a high adsorption capacity (1.74 g· g-1) for iodine vapor but also can remove the iodine in the organic solvent and the aqueous solution with the removal efficiencies of 95% and 91%, respectively. The presence of a large number of hydrogen bonds between the iodine molecule and the absorbent, as seen in the single crystal structure of iodine-loaded Q[8]-(4-AP) (I2@Q[8]-(4-AP)), is thought to be responsible for the exceptional iodine adsorption capacity of the material. In addition, the adsorption-desorption tests reveal that the self-assembly material has no significant loss of iodine capture capacity after five cycles, indicating that it has sufficient reusability.

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.

Strategies for high-temperature methyl iodide capture in azolate-based metal-organic frameworks

Efficiently capturing radioactive methyl iodide (CH3I), present at low concentrations in the high-temperature off-gas of nuclear facilities, poses a significant challenge. Here we present two strategies for CH3I adsorption at elevated temperatures using a unified azolate-based metal-organic framework, MFU-4l. The primary strategy leverages counter anions in MFU-4l as nucleophiles, engaging in metathesis reactions with CH3I. The results uncover a direct positive correlation between CH3I breakthrough uptakes and the nucleophilicity of the counter anions. Notably, the optimal variant featuring SCN- as the counter anion achieves a CH3I capacity of 0.41 g g-1 at 150 °C under 0.01 bar, surpassing all previously reported adsorbents evaluated under identical conditions. Moreover, this capacity can be easily restored through ion exchange. The secondary strategy incorporates coordinatively unsaturated Cu(I) sites into MFU-4l, enabling non-dissociative chemisorption for CH3I at 150 °C. This modified adsorbent outperforms traditional materials and can be regenerated with polar organic solvents. Beyond achieving a high CH3I adsorption capacity, our study offers profound insights into CH3I capture strategies viable for practically relevant high-temperature scenarios.