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

Structure Directing Acid-Amine Salt Films for Imine-Linked Covalent Organic Framework Films by Chemical Vapor Deposition

While the chemical vapor deposition (CVD) process promises high-quality films of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), strategic approaches are limited. Here we report a new strategic approach to synthesizing imine-linked COF films through acid-amine salt films by CVD. Acids are known to catalyze imine condensation between amines and aldehydes in the solution phase and have been believed to do the same in the vapor phase reaction. Upon the attempts to synthesize COF-LZU1 thin films using p-phenylenediamine, 1,3,5-triformylbenzene, by CVD, highly crystalline and smooth COF-LZU1 films are obtained only in the presence of p-toluenesulfonic acid, proving the conventional role of acid during vapor phase imine condensation. The COF-LZU1 film has a mixed orientation according to the structure analysis by grazing-incidence wide-angle X-ray scattering. In contrast, amorphous films with a face-on orientation were obtained in the absence of an acid. The role of acid in modulating structure is confirmed from the reaction using a different acid, benzenesulfonic acid, which results in the COF-LZU1 film having an edge-on orientation. The control experiments using benzoic acid and succinic acid that failed to make either acid-amine salt or COF films explain that the acid-amine-salt film formation is crucial to the formation of imine-linked COF films by CVD. Our findings not only explain the limited kinds of active acids for imine condensation in the vapor phase but also widen the field for the facile synthesis of highly crystalline COF films by CVD and the structure control of COF films through the combination of an acid-amine salt.

Shielding CO2-Philic Sites in Trimmed Covalent Organic Framework Pores by Atomic Layer Deposition

Strong adsorptive sites toward unwanted gas molecules in porous framework materials often lead to reversed sorption selectivity, creating tremendous challenges for enhancing the diffusion-driven membrane separations targeted at the weakly adsorbed species in the gas pair. While post-synthetic modification methods have been reported to downsize the pores in covalent organic frameworks (COFs), effective approaches to shield the highly adsorptive sites within the pores are rarely explored. Here, a solvent-less pore modification strategy is developed using atomic layer deposition (ALD). it is shown that controlled amounts of ZnO can be uniformly deposited into the COF pores, offering the ability to fine-tune the pore dimensions. Moreover, the Zn─O moieties grown into the COF pore are found to interact with the CO2-philic ketoenamine groups, and substantially reduce the CO2 solubility by 72.4% in the COF membrane. Accordingly, the simultaneously increased diffusion selectivity and sorption selectivity for H2/CO2 lead to a 330% improvement of the permselectivity in membrane separation, demonstrating the efficacy of the strategy for pore engineering in COFs.

Crystalline Porous Materials for Gaseous Iodine Capture: A Comprehensive Review

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

Construction of hydrophobic microenvironment on Sn0@SBA-15 for efficient and stable iodine gas capture

Tin-based materials are promising for iodine capture. However, they suffer from the instability of adsorption product SnI4 that is easily hydrolyzed even in atmospheric environment due to the presence of moisture. Herein, we report a strategy of constructing the hydrophobic microenvironment on Sn0@SBA-15 materials, which isolates moisture and subsequently stabilizes SnI4. Hydrophobic Sn0@SBA-15 materials (P-Sn0@SBA-15) were fabricated by polymethylhydrosiloxane (PHMS) modification and applied for iodine capture. The obtained P-Sn0@SBA-15 exhibited a record high iodine adsorption capacity (2599 mg/g) among inorganic adsorbents. The dominant adsorption mechanism was found that Sn0 reacted with I2 to form SnI4. Remarkably, SnI4 in P-Sn0@SBA-15 was stable up to 3 months exposure to humid atmosphere, while almost all SnI4 in Sn0@SBA-15 was hydrolyzed. The obtained P-Sn0@SBA-15 could be added to the list of iodine adsorbents due to its excellent adsorption capacity and stability. Moreover, the facile strategy could provide reference for the development of other functional materials.

A Water-Stable Hydrogen-Bonded Organic Framework (HOF) for Selective Sensing of Antibiotics in Aqueous Medium

Although metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have been extensively used as fluorescent-based antibiotic sensors, newly developed hydrogen-bonded organic frameworks (HOFs) are largely unexplored toward this direction. To realize this, the luminescent HOFs must be stable in water as the analytes are mostly found in water-based effluents in environments. In addition, HOFs should be equipped with specific recognition sites in order to direct the discrimination among the antibiotics. Herein, we report a 3D porous HOF, IITKGP-HOF-6, constructed from an aromatic-rich tetratopic carboxylic acid (H4L), which exhibits excellent hydro and prolonged open-air stability (7 and 15 days, respectively). IITKGP-HOF-6 was explored for the highly selective detection of nitrofurans (NFs) family of antibiotics in aqueous medium exhibiting a remarkably low detection limit of 0.75 μM for nitrofurazone (NFZ) through luminescence quenching. Photoinduced electron transfer driven by the presence of low-lying charge-transfer excited state below to theπ π * ${\pi {\pi }^{^{\ast}}}$ and Forster energy transfer between H4L donor and NFZ acceptor are confirmed to be responsible for observed quenching using detailed quantum-chemical studies. This work demonstrates the usage of HOFs as sensory materials toward antibiotics in aqueous medium along with a clear understanding into the sensing mechanism at the molecular level.

Impact of Postsynthetic Modification on the Covalent Organic Framework (COF) Structures

Covalent organic frameworks (COFs) have emerged as a versatile class of materials owing to their well-defined crystalline structures and inherent porosity. In the realm of COFs, their appeal lies in their customizable nature, which can be further enhanced by incorporating diverse functionalities. Postsynthetic modifications (PSMs) emerge as a potent strategy, facilitating the introduction of desired functionalities postsynthesis. A significant challenge in PSM pertains to preserving the crystallinity and porosity of the COFs. In this study, we aim to investigate the intricate interplay between PSM strategies and the resulting crystalline and porous structures of the COFs. The investigation delves into the diverse methodologies employed in PSMs, to elucidate their distinct influences on the crystallinity and porosity of the COFs. Through a comprehensive analysis of recent advancements and case studies, the study highlights the intricate relationships among PSM parameters, including reaction conditions, precursor selection, and functional groups, and their impact on the structural features of COFs. By understanding how PSM strategies can fine-tune the crystalline and porous characteristics of COFs, researchers can harness this knowledge to design COFs with tailored properties for specific applications, contributing to the advancement of functional materials in diverse fields. This work not only deepens our understanding of COFs but also provides valuable insights into the broader realm of PSM strategies for other solid materials.

Ionic liquid-modified magnetic covalent organic framework for the extraction of four pyrethroids in traditional Chinese herbs

Efficient enrichment of analytes and purification of matrices are crucial for the highly sensitive detection and monitoring of pesticides in traditional Chinese herbs. This work prepared magnetic ionic liquid-controlled covalent organic framework (IL-COF@Fe3O4) as the sorbent via a simple in-situ precipitation polymerization and thiolene "click" strategy. The IL-COF@Fe3O4 exhibited remarkable adsorption performance towards pyrethroids within 5 min. The adsorption of four pyrethroids on the surface of IL-COF@Fe3O4 was according with Langmuir model and pseudo-second-order kinetic model. The adsorption energies were theoretically calculated, which were permethrin>cypermethrin>fenvalerate>bifenthrin. The modification of ILs improved extraction capacity mainly because of the interaction of imidazole and Cl or F and the pore size effect. This method was developed for the rapid extraction of four pyrethroids in Codonopsis pilosula and Angelica sinensis. The linear range was 0.05-200 μg L-1. Matrix effects were ranging from -16.14% to 9.53%, indicating the strong matrix anti-interference ability of IL-COF@Fe3O4.

2.5-dimensional covalent organic frameworks

Covalently bonded crystalline substances with micropores have broad applications. Covalent organic frameworks (COFs) are representative of such substances. They have so far been classified into two-dimensional (2D) and three-dimensional (3D) COFs. 2D-COFs have planar shapes useful for broad purposes, but obtaining good crystals of 2D-COFs with sizes larger than 10 μm is significantly challenging, whereas yielding 3D-COFs with high crystallinity and larger sizes is easier. Here, we show COFs with 2.5-dimensional (2.5D) skeletons, which are microscopically constructed with 3D bonds but have macroscopically 2D planar shapes. The 2.5D-COFs shown herein achieve large single-crystal sizes above 0.1 mm and ultrahigh-density primary amines regularly allocated on and pointing perpendicular to the covalently-bonded network plane. Owing to the latter nature, the COFs are promising as CO2 adsorbents that can simultaneously achieve high CO2/N2 selectivity and low heat of adsorption, which are usually in a mutually exclusive relationship. 2.5D-COFs are expected to broaden the frontier and application of covalently bonded microporous crystalline systems.

Imidazole Encapsulation Enabled by Confinement for I2 and CH3I Coremoval

Nitrogen-rich small molecules are frequently doped into porous materials to enhance their iodine adsorption properties. To explore how imidazole confinement in metal-organic frameworks (MOFs) affects iodine adsorption, we obtained a UiO-66-based composite by embedding imidazole in UiO-66 pores via solid-phase adsorption (Im@UiO-66). Characterization confirmed that imidazole was successfully confined within the UiO-66 pores, with each unit of UiO-66 accommodating up to 27 imidazole molecules. The density functional theory (DFT) calculations suggested that the octahedral cages of UiO-66 are the primary sites for iodine capture. The adsorption studies revealed that Im@UiO-66 achieved maximum adsorption capacities for I2 and CH3I that were 12 and 7.9 times higher than those of UiO-66, respectively, reaching 6.42 g/g for I2 and 553 mg/g for CH3I. The spectroscopic analysis indicated that Im@UiO-66 absorbed iodine vapor and methyl iodide via charge-transfer interactions and N-methylation reactions. This study demonstrates that imidazole confinement can effectively enhance the adsorption performance of MOF-based materials, offering valuable insights for the design of iodine adsorbents.

Dimensionality and Molecular Packing Control of Covalent Organic Frameworks through Pendant Group Design

Tuning the dimensions and molecular packing geometry of crystalline organic frameworks and polymers represents an important challenge for reticular chemistry. Here we show that for extended structures made of 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTTA) linked with methoxy group functionalized terephthalaldehyde aldehydes, simple substituents on the aldehyde linker can have profound structure directing effects due to noncovalent interactions. Specifically, reacting 2,3-dimethoxyterephthalaldehyde with PyTTA gives a 2D covalent organic framework with unique AA-inclined-AA stacking and bilayer pyrene motifs, whereas reacting 2,5-dimethoxyterephthalaldehyde with PyTTA gives a 1D crystalline polymer with AB stacking and isolated pyrene motifs. Both materials show high crystallinity, allowing for atomic resolution structure determination using three-dimensional electron diffraction, and the similarity of their fluorescence properties shows the electronic structures of pyrene-based extended structures mostly depends on the in-plane structures, which is supported by density functional theory calculations. These two pyrene-based extended structures also show different fluorescence responses to organic vapors due to different pore environments. The current work shows the potential of noncovalent interactions in the reticular design of functional organic materials.

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.

AIEgen-functionalized metal-organic gel as a bifunctional platform for efficient adsorption and portable sensing of gaseous iodine

Herein, we proposed a novel metal-organic gel (YTU-G-1) for efficient adsorption and portable sensing of gaseous iodine. YTU-G-1 exhibits an unprecedentedly high detection sensitivity (KSV = 2.21 × 106 L mol-1) and an extremely low limit of detection (LOD) down to the pmol level (481 pmol L-1). YTU-G-1 also shows a marked iodine adsorption capacity of 1.398 g g-1. A wearable membrane was successfully fabricated via the electrospinning technique, which exhibits excellent skin-compatibility and serves as a portable tool for sensitive response to potential on-site nuclear emergencies.

Highly efficient removal of methyl iodide gas by recyclable Cu0-based mesoporous silica

Developing recyclable adsorbents for co-capture of I2 and CH3I gas is a meaningful and challenging topic. Herein, Cu0-based mesoporous silica (C-S) materials were synthesized and applied for CH3I capture for the first time. Factors (Cu0 content, temperature, contact time and CH3I concentration) affecting the adsorption behavior were investigated. The results demonstrated that the CH3I adsorption capacity of the obtained C-S materials reached up to 1060 mg/g at 200 ℃. Furthermore, the C-S material exhibited excellent reusability (91.3 %, 5 cycles). It was found that Cu0 could cleave the carbon iodine bonds, causing CH3I to dissociate into •CH3 and I-. Then the Cu+ converted from Cu0 reacted with I- to achieve the purpose of CH3I capture. The adsorption mechanism of CH3I on the C-S materials could be concluded that Cu0 reacted with CH3I form CuI (Cu + CH3I → CuI + •CH3). This work suggested that the obtained C-S materials could be promising adsorbents for CH3I capture.

Revealing the role of interlayer spacing in radioactive-ion sieving of functionalized graphene membranes

Functionalization of graphene enables precise control over interlayer spacing during film formation, thereby enhancing the separation efficiency of radioactive ions in graphene membranes. However, the systematic impact of interlayer spacing of graphene membranes on radioactive-ion separation remains unexplored. This study aims to elucidate how interlayer spacing in functionalized graphene membranes affects the separation of radioactive ions. Utilizing polyamidoxime (PAO) to modify graphene oxide, we controlled the interlayer spacing of graphene membranes. Experimental results indicate that tuning interlayer spacing enables control of the permeation flux of radioactive ions (UO22+ 1.01 × 10-5-8.32 × 10-5 mol/m2·h, and K+ remains stable at 3.60 × 10-4 mol/m2·h), and the K+/UO22+ separation factors up to 36.2 at an interlayer spacing of 8.8 Å. Using density functional theory and molecular dynamics simulations, we discovered that the effective separation is mainly determined via interlayer spacing and the quantity of introduced functional groups, explaining the anomalous high permeation flux of target ions at low interlayer spacing (4.3 Å). This study deepens our comprehension of interlayer spacing within nanoconfined spaces for ion separation and recovery via graphene membranes, offering valuable insights for the design and synthesis of high-performance nanomembrane materials.

Ion transport mechanisms in covalent organic frameworks: implications for technology

Covalent organic frameworks (COFs) have emerged as promising materials for ion conduction due to their highly tunable structures and excellent electrochemical stability. This review paper explores the mechanisms of ion conduction in COFs, focusing on how these materials facilitate ion transport across their ordered structures, which is crucial for applications such as solid electrolytes in batteries and fuel cells. We discuss the design strategies employed to enhance ion conductivity, including pore size optimization, functionalization with ionic groups, and the incorporation of solvent molecules and salts. Additionally, we examine the various applications of ion-conductive COFs, particularly in energy storage and conversion technologies, highlighting recent advancements and future directions in this field. This review paper aims to provide a comprehensive overview of the current state of research on ion-conductive COFs, offering insights into their potential to design highly ion-conductive COFs considering not only fundamental studies but also practical perspectives for advanced electrochemical devices.

Two-Dimensional Covalent Organic Frameworks with Pentagonal Pores

The pore shapes of two-dimensional covalent organic frameworks (2D COFs) significantly limit their practical applications in separation and catalysis. Although various 2D COFs with polygonal pores have been well developed, constructing COFs with pentagonal pores remains an enormous challenge. In this work, we developed one kind of pentagonal COFs with the mcm topological structure for the first time, through the rational combination of C4 and C2 symmetric building blocks. The resulting pentagonal COFs exhibit high crystallinity, excellent porosity, and strong robustness. Moreover, the inbuilt porphyrin units render these COFs as efficient electrocatalytic catalysts toward oxygen reduction reaction with a half-wave potential of up to 0.81 V, which ranks as one of the highest values among COFs-based electrocatalysts. This work not only verified the possibility of constructing 2D COFs with pentagonal pores but also developed a strategy for the construction of functional 2D COFs for interesting applications.

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.

Dipole moment regulation for enhancing internal electric field in covalent organic frameworks photocatalysts

Covalent organic frameworks (COFs) have recently emerged as a kind of promising photocatalytic platform in addressing the growing threat of trace pollutants in aquatic environments. Along this, we propose a strategy of constructing internal electric field (IEF) in COFs through the dipole moment regulation, which intrinsically facilitates the separation and transfer of photogenerated excitons. Two COFs of BTT-TZ-COF and BTT-TB-COF are developed by linking the electron-donor of benzotrithiophene (BTT) block and the electron-acceptor of triazine (TZ) or tribenzene (TB) block, respectively. DFT calculations demonstrate TZ block with larger dipole moment can achieve more efficient IEF due to the stronger electron-attractive force and hence narrower bandgap. Moreover, featuring the highly-order crystalline structure for accelerating photo-excitons transfer and rich porosity for facilitating the adsorption, BTT-TZ-COF exhibited an excellent universal performance of photocatalytic degradations of various dyes. Specifically, a superior photodegradation efficiency of 99% Rhodamine B (RhB) is achieved within 20 min under the simulated sunlight. Therefore, this convenient construction approach of enhanced IEF in COFs through rational regulation of the dipole moment can be a promising way to realize high photocatalytic activity.