Ordered Macro-Microporous Single Crystals of Covalent Organic Frameworks with Efficient Sorption of Iodine

The syntheses of the flexible TAPDA-based covalent organic frameworks utilized for capturing iodine and fluorescence sensing 2,4-dinitrophenol

The hexa(4-formyl-phenoxy)cyclotriphosphazene (NOP-6--CHO) and 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (TPT-3-CHO) are common knots of the flexible covalent organic frameworks (COFs), which may undergo Schiff base reaction with diamide and ternary amine, but with no examples of quaternary amine. Herein, we chose quaternary amine -- N,N,N',N'-tetrakis(4-aminophenyl)-1,4-phenylenediamine (TAPDA) to react with NOP-6-CHO and TPT-3-CHO to synthesize flexible TAPDA-based COFs (HTAPDA and TTAPDA) for the first time. The flexible TAPDA-based COFs have flexible units and 3D triangular or 2D hexagonal pores which make the pores nimble and self-adaptable abilities. Delightly, the flexible TAPDA-based COFs have the high BET-specific surface areas of 1103 and 1048 m2/g and show some crystallization and high thermal stability. They can adsorp I2 in both the gaseous phases (4.08 and 3.80 g g-1 at 77 K) and the solution. The flexible TAPDA-based COFs possess excellent fluorescent properties whether at dispersion or solid states and may be used for fluorescent sensing 2,4-dinitrophenol (DNP) with high selectivity and sensitivity (KSV: 2.49 × 104 and 2.36 × 104 L mol-1). Fluorescence quenching of the flexible TAPDA-based COFs is observed upon coaction of photo-induced electron transfer process and fluorescence resonance energy transfer process.

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.

Construction of hierarchically porous covalent organic frameworks with enhanced enzyme accessibility for sensitive dopamine detection

Immobilization of fragile enzymes is vital to expanding its application in the extracellular environment. Covalent organic frameworks (COFs), as a class of emerging porous materials, are promising platforms for enzyme immobilization owing to their high porosity and tunable structure. However, the interior pores of COFs often fail to play their roles because of inaccessibility, resulting in decreased performance of immobilized enzymes. Here, we introduce a facile approach to construct hierarchically macro-mesoporous COF (Hm-COF) via a template-assistant strategy. The mesoporous channels of Hm-COF were used to entrap cytochrome c (Cyt c), and the macropores of Hm-COF were adopted as diffusion channels to enhance the mass transfer of guest molecules. The resulting Hm-COF demonstrated an enhanced uptake capacity of Cyt c compared with mesoporous COF (m-COF). Furthermore, the catalytic activity of Cyt c immobilized in Hm-COF (Cyt c@Hm-COF) was remarkably higher than that of Cyt c immobilized in m-COF (Cyt c@m-COF). Taking advantage of the excellent activity, Cyt c@Hm-COF was employed as the sensor for the sensitive detection of dopamine (DA). This study opens a new avenue for the construction of COFs with hierarchical pores and high-performance immobilized enzymes.

Universal Single Atom Engineering Enhances Coulombic Efficiency of Ion Storage in Carbon Materials

Metal single atoms are widely used to optimize the microstructure of carbon materials to improve their ion storage capacity and rate performance, but the impact on another key parameter, Coulombic efficiency (CE), is not sufficiently addressed and confirmed. Herein, a universal phenomenon is reported that carbon-loaded asymmetric sulfur-modified metal-N4 moiety (MN4-S, M = Zn, Fe, Cu, and Ni) possesses higher CE than the symmetric MN4 moiety, and this phenomenon is applicable to various of carbon matrices, ions (Li+, Na+, and K+), charge and discharge rates, and electrolyte formulations. The carbon-loaded asymmetric MN4-S moiety exhibits larger CEs (0.03-0.46% higher of average CEs, 4.2-28.4% higher of the initial CEs) and smaller variance compared to the MN4 moiety, implying better reversible stability. The mechanism driving this phenomenon is revealed by the ZnN4-S sodium storage process. The asymmetric MN4-S coordination promotes the rapid ions diffusion kinetics by changing the charge density. Meanwhile, the MN4-S moiety can reduce the adsorption energy of ions and regulate the surface chemical reactivity of the material to increase the reversibility of surface ion storage, thereby achieving higher CE and better stability.

Solvent-Assisted CO2 Foaming Induced Ultralarge Pore Span Hierarchically Porous Polyimide

Inspired by natural materials, constructing hierarchically porous composite materials can better meet the increasingly demanding needs of engineering materials. Currently, lightweight polyimide components commonly used in aerospace and deep-sea applications are difficult to combine with cross-scale pores due to limitations in performance stability and porogenic strategies. Finding an efficient, environmentally friendly, convenient, and highly controllable method to prepare hierarchically porous polyimide (HPPI) to utilize structural advantages for functional suitability remains a huge challenge. Here, we propose a solvent-assisted supercritical CO2 foaming strategy to develop ultralarge pore span polyimide (ODA-ODPA). This strategy can not only realize the construction of HPPIs, but also regulate the porosities span from 15 to 75%. The HPPI mechanical parts prepared by controlling the foaming conditions can improve the oil storage and supply capacity and reduce the material quality while maintaining excellent dimensional stability thanks to the combination of micro- and nanopore. The prepared lightweight HPPI foam also shows excellent high-temperature-resistant mechanical properties. Additionally, the versatility of this strategy has been successfully demonstrated in other thermoplastic polyimide systems. This work not only provides a new method for preparing hierarchically porous materials, but also provides more possibilities for further expanding the application areas of special engineering polymers, for example, maintenance-free components for human deep space exploration and high-temperature-resistant fall buffers.

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.

Smart Bioorthogonal Catalytic Factory for Glaucoma Therapy

Glaucoma is characterized by high intraocular pressure (IOP), oxidative stress, and distinct optic nerve damage. Natural enzymes have unparalleled advantages in the treatment of glaucoma due to their high efficiency, specificity, and selectivity. However, their poor stability and recoverability have constrained their application. The selection of good immobilization carriers is an effective strategy to protect natural enzymes. Here, we employ a mild room-temperature aqueous-phase enzyme immobilization technique to immobilize superoxide dismutase and catalase. Then, l-arginine is added to the pores and further modified with DSPE-mPEG to construct a bioorthogonal catalytic factory (SC@COF-L-D) with excellent biocompatibility. This strategy greatly protects the natural enzyme from inactivation and improves the operational stability. SC@COF-L-D can scavenge a large amount of reactive oxygen species to reduce oxidative/nitrative damage and activate the soluble guanylate cyclase pathway, thereby lowering the IOP for effective treatment of glaucoma. This work provides a paradigm for the design of materials for glaucoma therapy.

Mesoporous Single-Crystal FeFe(CN)6 Microspheres for Superior Potassium-Ion Storage

Metal hexacyanoferrates (HCFs), also known as Prussian blue analogues, are ideal cathodes for potassium-ion batteries (PIBs) due to their nontoxicity and cost-effectiveness. Nevertheless, obtaining metal HCF cathode materials with both long-term cycling stability and high rate performance remains a daunting challenge. In this study, we present mesoporous single-crystalline iron hexacyanoferrate (MSC-FeHCF) microspheres, featuring a single-crystalline structure that contains interconnected pores spanning the entire crystal lattice. This unique architecture not only enables the electrolyte to fully penetrate into the single crystal, but also shorten the K+ diffusion distance. Additionally, the confinement effect of mesopores on interior water mitigates the excessive side reactions. The stress during battery cycling can be dispersed through multiple paths to alleviate the internal strain. The MSC-FeHCF microspheres exhibit unprecedented long-term cycling performance, achieving a specific discharge capacity of 123.5 mAh g-1 at 30 mA g-1 and 87.1 mAh g-1 after 2000 cycles at 500 mA g-1, providing 85.8 % of the initial capacity. More importantly, the MSC-FeHCF microspheres exhibit high rate capability, delivering 86.7 mAh g-1 at 3 A g-1. This study introduces an innovative strategy for engineering metal HCF cathode materials, thereby opening a novel avenue for the development of high-efficiency electrode materials for PIBs.

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.

Synthesis of high quality two dimensional covalent organic frameworks through a self-sacrificing guest strategy

The quality of covalent organic frameworks (COFs) crucially influences their mechanistic research and subsequent practical implementations. However, it has been widely observed that the structure damage induced by the activation procedure could compromise the quality of COFs. Here we develop a self-sacrificing guest method for synthesizing high-quality two-dimensional COFs (SG-COFs) by incorporating salt guests into the pores of the COF structure. These introduced salts play an indispensable role in supporting COF pores and mitigating quality loss during the activation process. Interestingly, due to the unique characteristic of salts decomposing into gases upon heating, this method can ultimately enable the synthesis of highly pure, high-quality COFs without the presence of residual guest molecules. The resulting sixteen COFs display superior crystallinity and porosity compared to those synthesized using conventional routes. Moreover, these high-quality SG-COFs have demonstrated to be highly efficient adsorbents for removal of per- and polyfluoroalkyl substances.

Construction and Band Gap-Regulation of Ordered Macro-Microporous Single Crystals of an Amine-Linked Covalent Organic Framework

Heterogeneity engineering provides an effective route to manipulate the chemical and physical properties of covalent organic frameworks (COFs) but is still under development for their single-crystal form. Here, we report the strategy based on a combination of the template-assisted modulated synthesis with a one-pot crystallization-reduction method to directly construct ordered macro-microporous single crystals of an amine-linked three-dimensional (3D) COF (OM-COF-300-SR). In this strategy, the colloidal crystal-templating synthesis not only assists the formation of ordered macropores but also greatly facilitates the in situ conversion of linkages (from imine to amine) in the COF-300 single crystals. The as-synthesized OM-COF-300-SR120 exhibits a reversible symmetry change from a tetragonal I41/a to monoclinic I2/c space group after activation, which was not observed previously. On the other hand, this strategy allows for a flexible control over the degree of amination (from 0 to 100%, as determined by X-ray photoelectron spectroscopy (XPS) analysis) in COF-300 crystals to regulate their band gap (from 2.57 to 2.81 eV) for the optimization of photocatalytic activity. The high degree of amination and the embedded ordered macropores render OM-COF-300-SR120 with superior photocatalytic activity (with a reaction rate constant of 0.9572 min-1) to its nonmacroporous counterpart (NM-COF-300-SR120, 0.2303 min-1) for the degradation of rhodamine B. In addition, the significant contribution of ordered macropores to confront mass transfer resistance in COF single crystals was also confirmed by the much higher catalytic activity of Au/OM-COF-300-SR120 (with an activity parameter of 7.96 × 103 s-1 mol-1) as compared with Au/NM-COF-300-SR120 (1.43 × 103 s-1 mol-1) in the model reduction reaction of 4-nitrophenol by NaBH4.

Boron-Containing Organic Two Dimensional Materials: Synthesis and Application

Organic two-dimensional materials have garnered widespread attention due to their well-defined structures, structural diversity, and rich electronic effects, demonstrating significant application potential across various fields. Atomic-level manipulation of the structures of organic two-dimensional materials has been a primary strategy for enriching and optimizing their properties. The introduction of heteroatoms often significantly affects their electronic structure, thereby endowing these materials with novel and unique properties. Boron atoms, due to their electron-deficient nature, have been extensively studied in luminescent materials, semiconductor materials, and chemical sensing materials. Consequently, boron-containing organic two-dimensional materials are also believed to be promising as a new class of materials with excellent optoelectronic and chemical activities. This article collates and summarizes the preparation and property studies of three types of boron-containing organic two-dimensional materials in recent years.

The N,N,N',N'-tetraphenylbenzidine-based conjugated hypercrosslinked polymers for adsorping iodine and fluorescence sensing 2,4-dinitrophenol, iodine

Although progress has been made in the development of hypercrosslinked polymers (HCPs) for iodine uptake, their fluorescence performance and fluorescence sensing performance are rare due to the lack of conjugated behavior in common HCPs. Herein, the N,N,N',N'-tetraphenylbenzidine-based conjugated hyper-crosslinked polymers (conjugated TPB-based HCPs) were efficiently fabricated via a one-step Friedel-Crafts arylation reaction by selecting N,N,N',N'-tetraphenylbenzidine (TPB) and N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (DPDB) as the basic building blocks and p-dimethoxybenzene (DMB) as an external crosslinker which will lead to the formation of the conjugated structures. The derived TPB-based HCPs (denoted as, TPB-DMB and DPDB-DMB) possessed excellent stability and high surface areas, Their iodine adsorption capacities are up to 4.25 and 3.56 g·g-1. The high iodine adsorption is caused by chemical adsorption. The fully conjugated structure and the 3D aryl network give the conjugated TPB-based HCPs excellent luminescence properties and fluorescence sensing properties for 2,4-dinitrophenol and iodine. The fluorescence sensing mechanisms of the conjugated  TPB-based HCPs for DNP and I2 includes photo-induced electron process and the resonance energy transfer process. This study provides a viable approach for the development of highly efficient iodine sorbents and fluorescence sensors of DNP and iodine for addressing environmental issues.

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.

Morphological Tuning of Covalent Organic Framework Single Crystals

The synthesis of high-quality single-crystal covalent organic frameworks (COFs) presents significant challenges, particularly in achieving precise control over their morphologies. Herein, we present a straightforward strategy to fine-tune the morphology of COF single crystals. Using rigid triptycene derivatives as the core building blocks and varying the amounts of aniline modulators, we successfully synthesized a series of high-quality COF single crystals with different aspect ratios and well-defined facets, JUC-663-X (X = 30 to 135, the equivalent of aniline). Their structures were characterized using PXRD, TEM, and N2 adsorption analyses to confirm the structural consistency. The study of the growth mechanism and DFT calculations elucidated the crucial role of aniline as a modulator in facilitating anisotropic competitive binding throughout the crystal growth process. Furthermore, our findings demonstrate that the aspect ratio of these single crystals significantly influences the adsorption properties of Rh B. This research not only paves new paths in the synthesis and morphological control of COF single-crystal materials but also provides profound insights into the relationship between COF morphology and functional performance.

Carbonaceous adsorbents in wastewater treatment: From mechanism to emerging application

Adsorption is of great significance in the water pollution control. Carbonaceous adsorbents, such as carbon quantum dots, carbon nanotubes, graphene, and activated carbons, have long been deployed in sustainable wastewater treatment due to their excellent physical structure and strong interaction with various pollutants; these features allow them to spark greater interest in environmental remediation. Although numerous eye-catch researches on carbon materials in wastewater treatment, there is a lack of comprehensive comparison and summary of the vivid structure-activity-application relationships of different types of carbonaceous adsorbents at the molecular and atomic level. Herein, this review aims to scrutinize and contrast the adsorption mechanisms of carbonaceous adsorbents with different dimensions, analyzing the qualitative differences in adsorption capacity from microscopic perspectives, structural diversity caused by preparation methods, and environmental external factors affecting adsorption occurrence. Then, a quantitatively in-depth critical appraisal of traditional and emerging contaminants in wastewater treatment using carbonaceous adsorbents, and innovative strategies for enhancing their adsorption capacity are discussed. Finally, in the context of growing imposed circularity and zero waste wishes, this review offers some promising insights for carbonaceous adsorbents in achieving sustainable wastewater treatment.

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.

High-Density Atomically Dispersed Metals Activate Adjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis from Nitrate

While electrocatalytic reduction of nitrate to ammonia presents a sustainable solution for addressing both the environmental and energy issues within the nitrogen cycle, it remains a great challenge to achieve high selectivity and activity due to undesired side reactions and sluggish reaction kinetics. Here, we fabricate a series of metal-N-C catalysts that feature hierarchically ordered porous structure and high-density atomically dispersed metals (HD M1/PNC). Specifically, the as-prepared HD Fe1/PNC catalyst achieves an ammonia production rate of 21.55 mol gcat-1 h-1 that is at least 1 order of magnitude enhancement compared with that of the reported metal-N-C catalysts, while maintaining a 92.5% Faradaic efficiency when run at 500 mA cm-2 for 300 h. In addition to abundant active sites, such high performance benefits from the fact that the high-density Fe can more significantly activate the adjacent N/C sites through charge redistribution for improved water adsorption/dissociation, providing sufficient active hydrogen to Fe sites for nitrate ammoniation, compared with the low-density counterpart. This finding deepens the understanding of high-density metal-N-C materials at the atomic scale and may further be used for designing other catalysts.

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.

Template-assisted synthesis of hollow anthraquinone-based covalent organic frameworks for aqueous zinc-ion hybrid supercapacitors

Anthraquinone-based hollow COFs were synthesized via a template-assisted method involving polystyrene nanospheres as the hard template, which enabled doubling the specific capacitance and energy density compared to non-templated COFs. Our approach can be extended to other COFs, offering a promising strategy for enhancing the performance of COF-based electrodes in energy storage applications.

A Solid-State Transformation of Hydrogen-Bonded Organic Frameworks for Efficient Acetylene Storage and Gas Separation

Developing robust microporous hydrogen-bonded organic frameworks (HOFs) is crucial for exploring novel physical adsorbents and revealing the structure-property relationship of hydrogen-bonding pairing behaviors. However, it is still challenging to obtain dense and stable hydrogen-bonded frameworks due to the rigidity and spatial resistance of the tectonic centers. Herein, we report a robust microporous HOF (HOF-ZSTU-4) via 4,4',4',4″-([1,1'-biphenyl]-4,4'-diylbis(azanetriyl))tetrabenzoic acid (H4BDATB) with flexible nitrogen nodes composing the tectonic center. Single-crystal X-ray diffraction (SCXRD) analysis shows that the activated framework undergoes a solid-to-solid phase transition because of the torsion of the carboxyl-carboxyl dimer, leading to the switching of the framework from the sql topology to the cds topology (HOF-ZSTU-4a). The single-component gas sorption isotherm reveals that HOF-ZSTU-4a has a C2H2 packing density of 0.54 kg L-1, marking it as the most efficient among reported HOFs. In addition, HOF-ZSTU-4a exhibits promising separation selectivity for several binary gas mixtures, and the dynamic separation performance for C2H2/CO2, CO2/N2, and CH4/N2 is verified by dynamic breakthrough experiments.

The synthesis strategies of covalent organic frameworks and advances in their application for adsorption of heavy metal and radionuclide

Covalent organic frameworks (COFs) are a novel type of porous materials, with unique properties, such as large specific surface areas, high porosity, pronounced crystallinity, tunable pore sizes, and easy functionalization, and thus have received considerable attention in recent years. COFs play an essential role in the catalytic degradation, adsorption, and separation of heavy metals, radionuclides. In recent years, considering several outstanding characteristics of COFs, including their good thermal/chemical stability, high crystallinity, and remarkable adsorption capacity, they have been widely used in the removal of various environment pollutants. This review primarily discusses the synthesis strategies of COFs along with their diverse synthesis methods, and provides a comprehensive summary and analysis of recent research advances in the use of COFs for removing heavy metal ions and radionuclides from water bodies. Additionally, the adsorption mechanism of COFs with regard to metal ions was determined by analyzing the structural characteristics of COFs. Finally, the future research directions on COFs adsorb rare earth element was discussed.

Dynamic Cleavage-Remodeling of Covalent Organic Networks into Multidimensional Superstructures

Superstructures with complex hierarchical spatial configurations exhibit broader structural depth than single hierarchical structures and the associated broader application prospects. However, current preparation methods are greatly constrained by cumbersome steps and harsh conditions. Here, for the first time, a concise and efficient thermally responsive dynamic synthesis strategy for the preparation of multidimensional complex superstructures within soluble covalent organic networks (SCONs) with tunable morphology from 0D hollow supraparticles to 2D films is presented. Mechanism study reveals the thermally responsive dynamic "cleavage-remodeling" characteristics of SCONs, synthesized based on the unique bilayer structure of (2.2)paracyclophane, and the temperature control facilitates the process from reversible solubility to reorganization and construction of superstructures. Specifically, during the process, the oil-water-emulsion two-phase interface can be generated through droplet jetting, leading to the preparation of 0D hollow supraparticles and other bowl-like complex superstructures with high yield. Additionally, by modulating the volatility and solubility of exogenous solvents, defect-free 2D films are prepared relying on an air-liquid interface. Expanded experiments further confirm the generalizability and scalability of the proposed dynamic "cleavage-remodeling" strategy. Research on the enrichment mechanism of guest iodine highlights the superior kinetic mass transfer performance of superstructural products compared to single-hierarchical materials.

Ultralight and Robust Covalent Organic Framework Fiber Aerogels

Shaping covalent organic frameworks (COFs) into macroscopic objects with robust mechanical properties and hierarchically porous structure is of great significance for practical applications but remains formidable and challenging. Herein, a general and scalable protocol is reported to prepare ultralight and robust pure COF fiber aerogels (FAGs), based on the epitaxial growth synergistic assembly (EGSA) strategy. Specifically, intertwined COF nanofibers (100-200 nm) are grown in situ on electrospinning polyacrylonitrile (PAN) microfibers (≈1.7 µm) containing urea-based linkers, followed by PAN removal via solvent extraction to obtain the hollow COF microfibers. The resultant COF FAGs possess ultralow density (14.1-15.5 mg cm-3) and hierarchical porosity that features both micro-, meso-, and macropores. Significantly, the unique interconnected structure composed of nanofibers and hollow microfibers endows the COF FAGs with unprecedented mechanical properties, which can fully recover at 50% strain and be compressed for 20 cycles with less than 5% stress degradation. Moreover, the aerogels exhibit excellent capacity for organic solvent absorption (e.g., chloroform uptake of >90 g g-1). This study opens new avenues for the design and fabrication of macroscopic COFs with excellent properties.

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.

Enzyme Immobilization using Covalent Organic Frameworks: From Synthetic Strategy to COFs Functional Role

Enzymes, a class of biocatalysts, exhibit remarkable catalytic efficiency, specificity, and selectivity, governing many reactions that are essential for various cascades within living cells. The immobilization of structurally flexible enzymes on appropriate supports holds significant importance in facilitating biomimetic transformations in extracellular environments. Covalent organic frameworks (COFs) have emerged as ideal candidates for enzyme immobilization due to high surface tunability, diverse chemical/structural designs, exceptional stability, and metal-free nature. Various immobilization techniques have been proposed to fabricate COF-enzyme biocomposites, offering significant enhancements in activity and reusability for COF-immobilized enzymes as well as new insights into developing advanced enzyme-based applications. In this review, we provide a comprehensive overview of state-of-the-art strategies for immobilizing enzymes within COFs by focusing on their applicability and versatility. These strategies are systematically summarized and compared by categorizing them into postsynthesis immobilization and in situ immobilization, where their respective strengths and limitations are thoroughly discussed. Combined with an overview of critical emerging applications, we further elucidate the multifaceted roles of COFs in enzyme immobilization and subsequent applications, highlighting the advanced biofunctionality achievable through COFs.

A Naphthalenetetracarboxdiimide-Containing Covalent Organic Polymer: Preparation, Single Crystal Structure and Battery Application

Inspired by dative boron-nitrogen (B←N) bonds proven to be the promising dynamic linkage for the construction of crystalline covalent organic polymers/frameworks (COPs/COFs), we employed 1,4-bis(benzodioxaborole) benzene (BACT) and N,N'-Di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxdiimide (DPNTCDI) as the corresponding building blocks to construct a functional COP (named as CityU-25), which had been employed as an anode in rechargeable lithium ion batteries. CityU-25 displayed an excellent reversible lithium storage capability of 455 mAh/g after 170 cycles at 0.1 A/g, and an impressive one of 673 mAh/g after 720 cycles at 0.5 A/g. These findings suggest that CityU-25 is a standout candidate for advanced battery technologies, highlighting the potential application of this type of materials.

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.

Constructing ordered and tunable extrinsic porosity in covalent organic frameworks via water-mediated soft-template strategy

As one of the most attractive methods for the synthesis of ordered hierarchically porous crystalline materials, the soft-template method has not appeared in covalent organic frameworks (COFs) due to the incompatibility of surfactant self-assembly and guided crystallization process of COF precursors in the organic phase. Herein, we connect the soft templates to the COF backbone through ionic bonds, avoiding their crystallization incompatibilities, thus introducing an additional ordered arrangement of soft templates into the anionic microporous COFs. The ion exchange method is used to remove the templates while maintaining the high crystallinity of COFs, resulting in the construction of COFs with ordered hierarchically micropores/mesopores, herein named OHMMCOFs (OHMMCOF-1 and OHMMCOF-2). OHMMCOFs exhibit significantly enhanced functional group accessibility and faster mass transfer rate. The extrinsic porosity can be adjusted by changing the template length, concentration, and ratio. Cationic guanidine-based COFs (OHMMCOF-3) are also constructed using the same method, which verifies the scalability of the soft-template strategy. This work provides a path for constructing ordered and tunable extrinsic porosity in COFs with greatly improved mass transfer efficiency and functional group accessibility.

High-sensitive determination of tetracycline antibiotics adsorbed on microplastics in mariculture water using pre-COF/monolith composite-based in-tube solid phase microextraction on-line coupled to HPLC-MS/MS

Microplastics (MPs) act as carriers for organic pollutants (e.g. antibiotics) and microorganisms (e.g. bacteria) in waters, leading to the proliferation of antibiotic resistance genes. Moreover, the antibiotics adsorbed on MPs may exacerbate this process. For further research, it is necessary to understand the types and amounts of antibiotics adsorbed on MPs. However, due to the heavy work of MPs collection and sample pretreatment, there is a lack of analytical methods and relevant data. In this study, an in-tube solid phase microextraction (IT-SPME) on-line coupled to HPLC-MS/MS method based on amorphous precursor polymer of three-dimensional covalent organic frameworks/monolith-based composite adsorbent was developed, which could efficiently capture, enrich and analyze tetracycline (TCs) antibiotics. Under the optimal extraction parameters, the developed method was capable of detecting TCs at levels as low as 0.48-1.76 pg. This method was applied to analyze the TCs adsorbed on MPs of different particle sizes in mariculture water for the first time, requiring a minimum amount of MPs of only 1 mg. Furthermore, it was observed that there could be an antagonistic relationship between algal biofilm and TCs loaded on MPs. This approach could open up new possibilities for analyzing pollutants on MPs and support deeper research on MPs.

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.

Light-Gating Crystalline Porous Covalent Organic Frameworks

We report light gating in synthetic one-dimensional nanochannels of stable crystalline porous covalent organic frameworks. The frameworks consist of 2D hexagonal skeletons that are extended over the x-y plane and stacked along the z-direction to create dense yet aligned 1D mesoporous channels. The pores are designed to be photoadaptable by covalently integrating tetrafluoro-substituted azobenzene units onto edges, which protrude from walls and offer light-gating machinery confined in the channels. The implanted tetrafluoroazobenzene units are thermally stable yet highly sensitive to visible light to induce photoisomerization between the E and Z forms. Remarkably, photoisomerization induces drastic changes in intrapore polarity as well as pore shape and size, which exert profound effects on the molecular adsorption of a broad spectrum of compounds, ranging from inorganic iodine to organic dyes, drugs, and enzymes. Unexpectedly, the systems respond rapidly to visible lights to gate the molecular release of drugs and enzymes. Photoadaptable covalent organic frameworks with reversibly convertible pores offer a platform for constructing light-gating porous materials and tailorable delivery systems, remotely controlled by visible lights.

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

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

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.

Single-atom platinum with asymmetric coordination environment on fully conjugated covalent organic framework for efficient electrocatalysis

Two-dimensional (2D) covalent organic frameworks (COFs) and their derivatives have been widely applied as electrocatalysts owing to their unique nanoscale pore configurations, stable periodic structures, abundant coordination sites and high surface area. This work aims to construct a non-thermodynamically stable Pt-N2 coordination active site by electrochemically modifying platinum (Pt) single atoms into a fully conjugated 2D COF as conductive agent-free and pyrolysis-free electrocatalyst for the hydrogen evolution reaction (HER). In addition to maximizing atomic utilization, single-atom catalysts with definite structures can be used to investigate catalytic mechanisms and structure-activity relationships. In this work, in-situ characterizations and theoretical calculations reveal that a nitrogen-rich graphene analogue COF not only exhibits a favorable metal-support effect for Pt, adjusting the binding energy between Pt sites to H* intermediates by forming unique Pt-N2 instead of the typical Pt-N4 coordination environment, but also enhances electron transport ability and structural stability, showing both conductivity and stability in acidic environments.

Enhancing the Crystallinity of Keto-enamine-Linked Covalent Organic Frameworks through an in situ Protection-Deprotection Strategy

β-Keto-enamine-linked 2D covalent organic frameworks (COFs) have emerged as highly robust materials, showing significant potential for practical applications. However, the exclusive reliance on 1,3,5-triformylphloroglucinol (Tp aldehyde) in the design of such COFs often results in the production of non-porous amorphous polymers when combined with certain amine building blocks. Attempts to adjust the crystallinity and porosity by a modulator approach are inefficient because Tp aldehyde readily forms stable β-keto-enamine-linked monomers/oligomers with various aromatic amines through an irreversible keto-enol tautomerization process. Our research employed a unique protection-deprotection strategy to enhance the crystallinity and porosity of β-keto-enamine-linked squaramide-based 2D COFs. Advanced solid-state NMR studies, including 1D 13 C CPMAS, 1 H fast MAS, 15 N CPMAS, 2D 13 C-1 H correlation, 1 H-1 H DQ-SQ, and 14 N-1 H HMQC NMR were used to establish the atomic-level connectivity within the resultant COFs. The TpOMe -Sqm COFs synthesized utilizing this strategy have a surface area of 487 m2  g-1 , significantly higher than similar COFs synthesized using Tp aldehyde. Furthermore, detailed time-dependent PXRD, solid-state 13 C CPMAS NMR, and theoretical DFT studies shed more light on the crystallization and linkage conversion processes in these 2D COFs. Ultimately, we applied this protection-deprotection method to construct novel keto-enamine-linked highly porous organic polymers with a surface area of 1018 m2  g-1 .

Enhancing Iodine Capture of Porous Organic Cages through N-Heteroatom Engineering

Iodine radioisotopes, produced or released during nuclear-related activities, severely affect human health and the environment. The efficient removal of radioiodine from both aqueous and vapor phases is crucial for the sustainable development of nuclear energy. In this study, we propose an "N-heteroatom engineering" strategy to design three porous organic cages with N-containing functional groups for efficient iodine capture. Among the molecular cages investigated, FT-Cage incorporating tertiary amine groups and RT-Cage with secondary amine groups show higher adsorption capacity and much faster iodine release compared to IT-Cage with imine groups. Detailed investigations demonstrate the superiority of amine groups, along with the influence of crystal structures and porosity, for iodine capture. These findings provide valuable insights for the design of porous organic cages with enhanced capabilities for capturing iodine.

Hierarchically Porous Covalent Organic Frameworks: Synthesis Methods and Applications

Covalent organic frameworks (COFs) with high porosity have garnered considerable interest for various applications owing to their robust and customizable structure. However, conventional COFs are hindered by their narrow pore size, which poses limitations for applications such as heterogeneous catalysis and guest delivery that typically involve large molecules. The development of hierarchically porous COF (HP-COF), featuring a multi-scale aperture distribution, offers a promising solution by significantly enhancing the diffusion capacity and mass transfer for larger molecules. This review focuses on the recent advances in the synthesis strategies of HP-COF materials, including topological structure design, in-situ templating, monolithic COF synthesis, defect engineering, and crystalline self-transformation. The specific operational principles and affecting factors in the synthesis process are summarized and discussed, along with the applications of HP-COFs in heterogeneous catalysis, toxic component treatment, optoelectronics, and the biomedical field. Overall, this review builds a bridge to understand HP-COFs and provides guidance for further development of them on synthesis strategies and applications.

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 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.

Covalent Organic Network Membranes with Tunable Nanoarchitectonics from Macrocycle Building Blocks for Graded Molecular Sieving

Traditional piperazine-based polyamide membranes usually suffer from the intrinsic trade-off relationship between selectivity and permeance. The development of macrocycle membranes with customized nanoscale pores is expected to address this challenge. Herein, we introduce 1,4-diazacyclohexane (2N), 1,4,7-triazacyclononane (3N), and 1,4,8,11-tetraazacyclotetradecane (4N) as molecular building blocks to construct the nanoarchitectonics of polyamide membranes prepared from interfacial polymerization (IP). The permeance of covalent organic network membranes follows the trend of 4N-TMC > 3N-TMC > 2N-TMC, while the molecular weight cutoff (MWCO) also follows the same trend of 4N-TMC > 3N-TMC > 2N-TMC, according to their nanopore size of the membranes. The microporosity, orientation, and surface chemistry of covalent organic network membranes can be rationally designed by macrocycle building units. The ordered nanoarchitectonics allows the membranes to attain an excellent performance in graded molecular sieving. Importantly, the novel covalent organic network membranes with tunable nanoarchitectonics prepared from macrocycle building units exhibited high water permeance (32.5 LMH/bar) and retained long-term stability after 100 h of test and bovine serum albumin fouling. These results reveal the enormous potential of 3N-TMC and 4N-TMC membranes in saline textile wastewater treatments and precise molecular sieving.

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

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

Three-dimensional fluorinated covalent organic frameworks coated capillary for the separation of fluoroquinolones by capillary electrochromatography

In this work, a three-dimensional fluorinated covalent organic frameworks (3D FCOFs) JUC-515 was synthesized from tetra(4-aminophenyl)methane (TAM) and 2,3,5,6-tetrafluoroterephthalol (TFA) by an ionic liquid method. JUC-515 was introduced into the capillary column and bonded to the inner wall of the capillary column by chemical bonding. Through a variety of characterization results, JUC-515 was successfully synthesized and introduced into the capillary column. The effects of buffer solution concentration, organic additive content and pH of the buffer solution on the separation of fluoroquinolones (FQs) were investigated in detail. The JUC-515-coated capillary column showed good resolution (>1.5) and reproducibility. The relative standard deviations (RSDs) of the retention time for intraday, interday, column-to-column and interbatch precision were less than 0.88%, 2.45%, 2.74% and 3.32%, respectively. The RSDs of the peak area for intraday, interday, column-to-column and interbatch precision were less than 3.79%, 4.31%, 3.33% and 5.62%, respectively. The JUC-515-coated capillary column could be used no less than 150 times. The results showed that the JUC-515-coated capillary column had good separation performance. In addition, by separating fluorinated β-phenylalanine analogs, β-phenylalanine and trifluoromethyl β-phenylalanine analogs, the separation mechanism based on fluorine interactions was discussed. In conclusion, JUC-515 had good potential as a stationary phase for capillary electrochromatography.

Synthesis of Tröger's base-based [3]arenes for efficient iodine adsorption

Enantiomers of Tröger's base-based [3]arenes R6N-E[3] and S6N-E[3] were synthesized successfully as two optically pure Tröger's base-based macrocycles in which three Tröger's base subunits were incorporated. Among these Tröger's base-based[3]arenes, M[3] showed high absorption of iodine up to 4.02 g g-1 in vapor.

Polyphosphonate-segmented macroporous organosilicon frameworks for efficient dynamic enrichment of uranium with in-situ regeneration

Efficient separation and enrichment of uranium from radioactive effluents is of strategic significance for sustainable development of nuclear energy and environmental protection. Macropore structure of adsorbent is conducive to accessibility of the pore and transport of the adsorbate during dynamic adsorption. However, the low specific surface area results in fewer ligand sites and subsequently reduces the adsorption capacity. Herein, we present a novel strategy for efficient dynamic uranium enrichment using polyphosphonate-segmented macroporous organosilicon frameworks (PMOFs). PMOFs are constructed through the copolymerization of diethyl vinylphosphonate and triethoxyvinylsilane, followed by hydrolysis and condensation of the oligomers. The introduction of polyphosphonate segments into the frameworks endows PMOFs with a macroporous structure (31 µm) and a high ligand content (up to 72 wt%). Consequently, the optimized PMOF-3 demonstrated an ultrahigh dynamic adsorption capacity of 114.8 mg/g among covalently conjugated silicon-based materials. Additionally, PMOF-3 achieves a high enrichment factor (120) in the dynamic enrichment of uranium on a fixed bed column, which can be in-situ regenerated with 1 M NaHCO₃ as the eluent. This work presents a new strategy for efficient dynamic enrichment of nuclides, which can be extended to the separation of other specific pollutants, shedding new light on adsorbent design and technical innovation.

Particle Size Regulation of Single-Crystalline Covalent Organic Frameworks for High Performance of Gas Chromatography

Although polycrystalline covalent organic frameworks (PCOFs) have already shown great potential as stationary phases for chromatography, irregular shape and size distribution of PCOFs make regulation of particle size of PCOFs for high separation performance impossible, which is accessible by the application of single-crystalline COFs (SCOFs). Herein, we showed preparation of three-dimensional SCOF (SCOF-303) bonded capillaries (SCOF-303-capillary) with different particle sizes (about 0.4-1.6 μm) and further investigated gas chromatographic separation ability of these SCOF-303-capillaries for isomers of xylene, dichlorobenzene, and pinene. It was found resolution and column efficiency of SCOF-303-capillaries for isomers decreased with the increase in particle size, mainly resulting from the weaker size-exclusion effect and higher mass transfer resistance of the larger particle size of flexible SCOF-303. The obtained SCOF-303-capillary (particle size of ∼0.4 μm) offered baseline separation of xylene isomers with the high resolution of 2.26-3.52, great efficiency of 7879 plates m^-1 for p-xylene, better than PCOF-303-capillary, and commercial DB-5 and HP-FFAP capillary columns as well as many reported capillaries. This work not only shows the great potential of SCOFs for gas chromatography but also provides the theoretical direction for the design of the efficient COF based stationary phase by adjusting the particle sizes.

An iodide-containing covalent organic framework for enhanced radiotherapy

Metal-free radiosensitizers, particularly iodine, have shown promise in enhancing radiotherapy due to their suitable X-ray absorption capacities and negligible biotoxicities. However, conventional iodine compounds have very short circulating half-lives and are not retained in tumors very well, which significantly limits their applications. Covalent organic frameworks (COFs) are highly biocompatible crystalline organic porous materials that are flourishing in nanomedicine but have not been developed for radiosensitization applications. Herein, we report the room-temperature synthesis of an iodide-containing cationic COF by the three-component one-pot reaction. The obtained TDI-COF can be a tumor radiosensitizer for enhanced radiotherapy by radiation-induced DNA double-strand breakage and lipid peroxidation and inhibits colorectal tumor growth by inducing ferroptosis. Our results highlight the excellent potential of metal-free COFs as radiotherapy sensitizers.