Three-dimensional Covalent Organic Frameworks Research Articles

Ultrahigh-surface area covalent organic frameworks for methane adsorption.

Developing porous materials with ultrahigh surface areas for gas storage (for example, methane) is attractive but challenging. Here, we report two isostructural three-dimensional covalent organic frameworks (COFs) with a rare self-catenated alb-3,6-Ccc2 topology and a pore size of 1.1 nanometer. Notably, these imine-linked microporous COFs show both high gravimetric Brunauer-Emmett-Teller (BET) surface areas (~4400 square meters per gram) and volumetric BET surface areas (~1900 square meters per cubic centimeter). Moreover, their volumetric methane uptake reaches up to 264 cubic centimeter (standard temperature and pressure) per cubic centimeter [cm3 (STP) cm-3] at 100 bar and 298 kelvin, and they exhibit the highest volumetric working capacity of 237 cm3 (STP) cm-3 at 5 to 100 bar and 298 kelvin among all reported porous crystalline materials.

Three-dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High-Performance Lithium Metal Battery.

Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three-dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32wt%) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6-connected cyclotriphosphazene derivative aldehyde and 4-connected porphyrin-based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron-rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por-PN-COF-Cu cells achieved a record average CE of 99.1% for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π-electron system.

Three-Dimensional Covalent Organic Framework Serving as Host and Electrocatalyst in the Cathode of Li–S Battery

Three-Dimensional Covalent Organic Framework Serving as Host and Electrocatalyst in the Cathode of Li–S Battery

Regulating the Spin-State of Cobalt in Three-Dimensional Covalent Organic Frameworks for High-Performance Sodium-Iodine Rechargeable Batteries.

Although the catalytic activity is heavily reliant on the electronic structure of the catalyst, understanding the impact of electron spin regulation on electrocatalytic performance is still rarely investigated. This work presents a novel approach involving the single-atom coordination of cobalt (Co) within metalloporphyrin-based three-dimensional covalent organic frameworks (3D-COFs) to facilitate the catalytic conversion for sodium-iodine batteries. The spin state of Co is modulated by altering the oxidation state of the porphyrin-centered Co, achieving optimal catalysis for iodine reduction. Experimental results demonstrate that CoII and CoIII are incorporated into the 3D-COFs, exhibiting spin ground states of S = 1/2 and S = 0, respectively. The low spin state of CoIII is favorable to hybridize with the sp 3d orbitals of I3-, thus facilitating the conversion of I3- to I-. Density-functional theory (DFT) calculations further reveal that the presence of CoIII enhances iodide adsorption and accelerates the formation of NaI in 3D-COFs-CoIII, thereby promoting its rapid kinetic behaviors. Notably, the I2@3D-COFs-CoIII cathode achieves a high reversible capacity of 227.7 mAh g-1 after 200 cycles at 0.5 C and demonstrates exceptional cyclic stability, exceeding 2000 cycles at 10 C with a minor capacity fading rate of less than one 0.01% per cycle.

3D Covalent Organic Framework Membranes for Molecular Separations.

Membrane separation has become an indispensable separation technology in social production, playing an important role in drug production, water purification, etc. The key core of membranes lies in achieving efficient and precise sieving between substances. As a result, a typical trade-off arises: highly permeable membranes usually sacrifice selectivity and vice versa. To address this dilemma, long-term research has focused on comprehensive understanding and modelling of synthetic membranes at various scales. A significant advancement in this arena is the advent of three-dimensional covalent organic framework (3D COF) membranes, a novel category of long-range ordered porous organic polymer materials. Characterized by an abundance of interconnected channels, diverse pore wall properties, tunable structures, and robust thermal and chemical resilience, 3D COF membranes offer a promising approach for efficient substance separation. This review undertakes a meticulous investigation of the synthesis and physicochemical properties of 3D COF membranes, accentuating the underlying design principles, fabrication methods, and application attempts. A comprehensive assessment of their research trajectory and current standing in the field of membrane processes is provided. The review culminates in a forward-looking outlook, summarizing future research directions and highlighting the substantial potential of this innovative work to shape the future of efficient membrane separation processes.

Assembly of Dye Molecules in Covalent Organic Frameworks for Enhanced Colorimetric Biosensing.

Colorimetric assays have been extensively investigated for biosensing applications due to their advantages of visual recognizability, ease of use, and low cost. However, advancing their development is a great challenge due to the inherent limitations of colorimetric dyes. Herein, we report a strategy to assemble dyes in covalent organic frameworks (COFs) to effectively reinforce the applicability of pH-responsive dyes in colorimetric bioassays. Experimental results reveal that three-dimensional COFs can promote the assembly of dyes through hydrogen bonding, resulting in the formation of a dye-supermolecule@COF assembly. Consequently, when sensitized at increased pH levels (e.g., hydroxyl ions), disruption of hydrogen bonds may trigger a rapid transition from their insoluble fixed state within the COFs into soluble, visibly detectable dye anions. This process can also be facilitated by increased hydrophilicity and elevated electrostatic repulsion between the dye anions and COFs, leading to the substantial release of chromogenic dye anions from the COF pores into the solution, thereby amplifying the colorimetric signal output. Therefore, by employing various synthesized dye-supermolecule@COFs as signal tags, we developed a colorimetric bioassay capable of accurately identifying breast cancer cell subtypes. This study not only highlights the effectiveness of dye-supermolecule@COFs in enhancing colorimetric biosensing but also underscores the potential of employing the COF-mediated dye assembly strategy for colorimetric assays.

Determination of fluoroquinolones residues in bean sprouts using covalent organic framework based solid-phase extraction coupled with UHPLC-MS/MS

A solid-phase extraction (SPE) method using three-dimensional covalent organic framework (COFs) coupled with ultra-high performance liquid chromatography-mass spectrometry was developed for the detection of 13 fluoroquinolones (FQs) in bean sprout samples. Critical extraction parameters influencing SPE efficiency were optimized and matrix-matched standard curves were used to eliminate matrix effects and validate the proposed method. The analytical method proved to have good linearity in the concentration range of 1.0–100 μg L–1 with correlation coefficients of r≥0.9995. The limits of detection were 0.10–0.45 μg kg–1, whereas the limits of quantification were 0.34–1.51 μg kg–1. The recoveries ranged from 92.7 % to 105 % with satisfactory precision (< 4.82 %). The COFs-packed SPE cartridge maintained recovery efficiency for the target FQs over five reuse cycles. The adsorption selectivity was mainly attributed to π–π interactions, hydrogen bonding, and electrostatic attraction between FQs and the adsorbent. Analysis of actual samples revealed the presence of enrofloxacin, ciprofloxacin, and norfloxacin in three batches of bean sprout samples. These results highlight the importance of monitoring antibiotics residues in bean sprouts.

A cationic three-dimensional covalent organic framework membrane for nanofiltration of molecules and rare Earth ions

Permanently microporous materials have evolved as focal point of research for tackling issues in separation science and membrane technology. Covalent organic frameworks (COFs) stand out for their distinctive synergy of crystalline nature, uniform channels, and structural diversities. Three-dimensional (3D) COFs, distinguished by angstrom-sized and interconnected channels, hold special promise for separating small targets; however, this potential remains underexplored. Here, we report feasible growth of cationic 3D COF membranes on a flexible polymer substrate for versatile nanofiltration toward both molecules and ions. Through comprehensive performance evaluations, we reveal that the resultant membrane exhibits durable and prominent molecular selectivity to separate fine species with molecular weights above 300 g mol−1 at fast methanol permeation. Lanthanide ions of industrial value also can be harvested by the membrane with rejection rates of up to 91.4%. Together with its nonselectivity to competing ions, our membrane implements efficient extraction of rare earth elements from ion mixtures. These findings illuminate the potential of 3D COFs for liquid separation and offer a solution to building versatile membranes.

Design of Three-Dimensional Mesoporous Adamantane-Based Covalent Organic Framework with Exceptionally High Surface Areas.

The development of three-dimensional (3D) covalent organic frameworks (COFs) with large pores and high specific surface areas is of critical for practical applications. However, it remains a tremendous challenge to reconcile the contradiction between high porosity and high specific surface areas, and increasing the length of building blocks leads to structural interpenetration in 3D COFs. Here, we report the preparation of mesoporous three-dimensional COF by a new steric hindrance engineering method. By incorporating adamantane into the monomers instead of carbon centers, we successfully achieve 2-fold interpenetrated diamondoid-structured 3D COFs, featuring permanent mesopores (up to 33 Å), exceptionally high surface areas (>3400 m2 g-1), and low crystal densities (0.123 g cm-3). These properties far surpass those of most conventional 3D COFs with similar topologies. This work not only aims to construct 3D COFs with low interpenetration but also to establish a foundation for the systematic design and structural control of 3D COFs.

External surface hydrophilic 3D-POSS-COF@GDL for the direct adsorption of bisphenols in milk samples

In case of organic frameworks (COFs) as adsorbents in the pretreatment of complex food matrices, challenges such as poor dispersion and non-specific adsorption of interfering macromolecules like proteins are often encountered. To address this issue, this work prepared a three-dimensional covalent organic framework (3D-COF) with a novel bcu topology based on polyhedral oligomeric silsesquioxane (POSS). Subsequently, gluconolactone (GDL) was modified onto the external surface of the material via the reaction with the exposed reactive residues. The resulting POSS-COF@GDL adsorbent has an enhanced hydrophilicity in the external surface, thereby significantly improves the dispersion of materials in aqueous solution and reduces the adsorption ability toward protein. Whereas, the inner of material retains hydrophobic pores that exhibit high adsorption efficiency to small hydrophobic molecules. Compared with the traditional pretreatment methods, POSS-COF@GDL can directly extract bisphenols (BPs) in milk samples without any additional treatment. The established sample pretreatment method is coupled with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), resulting in recoveries of 71.8 to 93.6%, intra- and inter-day relative standard deviations (RSDs) of <8.3%, and limits of detection (LODs) of 0.042–0.16 ng∙mL−1 for four BPs.

Piezofluorochromism in Covalent Organic Frameworks: Pressure-Induced Emission Enhancement and Blue-Shifted Emission.

Achieving enhanced or blue-shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole-based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure-induced emission enhancement (PIEE) phenomenon with a 16-fold increase in fluorescence intensity from three-dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two-dimensional COFs with flexible structures exhibited rare blue-shifted emission, whereas the variants with rigid and conjugated structures showed common red-shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure-treated engineering and provides a new perspective on the design of piezochromic materials.

Controlling the Degree of Interpenetration in Chiral Three-Dimensional Covalent Organic Frameworks via Steric Tuning.

Network interpenetration plays a crucial role in functionalizing porous framework materials. However, controlling the degree of interpenetration in covalent organic frameworks (COFs) to influence their pore sizes, shapes, and functionalities still remains a significant challenge. Here, we demonstrate a steric tuning strategy to control the degree of COF interpenetration and modulate their physicochemical properties. By imine condensations of 1,1'-bi-2-naphthol-derived tetraaldehydes bearing different alkyl substituents with the monomer tetra(p-aminophenyl)-methane, we synthesized and characterized a family of two-component and three-component chiral COFs with different interpenetrated dia networks. The alkyl groups are periodically appended on the pore walls, and their types/contents that can be synthetically tuned control the interpenetration degree of COFs by minimizing repulsive interactions between the alkyl groups. Specifically, the COF with -OH groups adopts an interpenetrated dia-c5 topology, those with -OMe/-OEt groups take an interpenetrated dia-c4 topology, whereas those with the bulky -OnPr/-OnBu groups exhibit a noninterpenetrated dia-c1 topology. The multivariate COFs with both -OH and -OnBu groups display either a noninterpenetrated or dia-c5 topology, depending on the proportion of -OnBu groups. The extent of interpenetration in COFs significantly affects their porosity, thermal stability, and chemical stability, resulting in varying selective performances in the adsorption and separation of dyes and asymmetric catalysis. This work highlights the potential of using steric hindrance to tune and control interpenetration, porosity, stability, and functionalities of COFs materials, broadening the range of their applications.

Stepwise Protonation of Three-Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis.

Three-dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D-bcu-COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D-bcu-COFs was initially modulated by functionalizing linear linkers with benzo-thiadiazole or benzo-selenadiazole groups. Furthermore, taking advantage of the well-exposed porphyrin and imine sites in 3D-bcu-COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo-selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Highly Selective Separation of Benzene/Cyclohexane by Three-Dimensional Covalent Organic Framework with 8,8-Connected bcu Net Topology

Highly Selective Separation of Benzene/Cyclohexane by Three-Dimensional Covalent Organic Framework with 8,8-Connected bcu Net Topology

Advancements and applications of three-dimensional covalent organic frameworks

Covalent organic frameworks (COFs) represent an emerging class of crystalline porous polymers characterized by their pre-designed interconnected structures formed via dynamic covalent bonds. These materials have garnered widespread attention in recent years. While applications of two-dimensional (2D) COFs have been extensively investigated since 2005, their practicality has been impeded by their limited specific surface area and the robust π-π stacking interaction. In contrast, three-dimensional (3D) COFs boast enhanced porosity, larger specific surface area, well-exposed functional groups, and an abundance of reaction sites, positioning them at the forefront of porous material research. They find extensive applications in diverse fields, including adsorption, separation, catalysis, and so on. This featured article provides a comprehensive exploration of the latest advancements in 3D COFs across their respective application domains. Additionally, we outline the current challenges that must be addressed and shed light on the promising prospects for the utilization of 3D COFs.

Unprecedented POSS-Linked 3D Covalent Organic Frameworks with 2-Fold Interpenetrated scu or sqc Topology Regulated by Porphyrin Center for Photocatalytic CO2 Reduction.

The synthesis and characterization of porphyrin center regulated three-dimensional covalent organic frameworks (COFs) with 2-fold interpenetrated scu or sqc topology have been investigated. These COFs exhibit unique structural features and properties, making them promising candidates for photocatalytic applications in CO2 reduction and artemisinin synthesis. The porphyrin center serves as an anchor for metal ions, allowing precise control over structures and functions of the frameworks. Furthermore, the metal coordination within the framework imparts desirable catalytic properties, enabling their potential use in photocatalytic reactions. Overall, these porphyrin center regulated metal-controlled COFs offer exciting opportunities for the development of advanced materials with tailored functionalities.

Targeted synthesis of a 3D covalent organic framework with fjh topology exhibiting high photoluminescence: A robust platform for sensitive detection of furantoin

The inappropriate use of antibiotics poses significant risks to both the environment and human health, necessitating the development of accurate and sensitive detection methods. Fluorescence detection, particularly utilizing three-dimensional (3D) covalent organic frameworks (COFs), stands out as a promising avenue. Unlike two-dimensional COFs, 3D COFs can mitigate fluorescence quenching resulting from non-radiative energy loss, primarily attributed to π-π interlayer stacking. In this study, by carefully selecting and designing the building blocks, we synthesized a 3D COF named PyTTA-TTFB-COF with fjh topology and remarkable photoluminescence. This was achieved through the combination of a 4-connected square chromophore, 1,3,6,8-Tetrakis(4-aminophenyl) pyrene, with a 3-connected triangle, 1,3,5-trimethyl-2,4,6-tris(4-formylphenyl) benzene, possessing a specific stereo conformation. Significantly, PyTTA-TTFB-COF exhibits a high photoluminescence quantum yield, notably reaching 60.1% in acetonitrile. Moreover, it displays substantial fluorescence quenching when exposed to furantoin, surpassing the performance observed with other antibiotics. Competitive experiments have confirmed that PyTTA-TTFB-COF can serve as a specific fluorescent probe for the interference-free detection of furantoin.

Engineering of molecularly imprinted cavity within 3D covalent organic frameworks: An innovation for enhanced extraction and removal of microcystins

The scarcity of selective adsorbents for efficient extraction and removal of microcystins (MCs) from complex samples greatly limits the precise detection and effective control of MCs. Three-dimensional covalent organic frameworks (3D COFs), characterized by their large specific surface areas and highly ordered rigid structure, are promising candidates, but suffer from lack of specific recognition. Herein, we design to engineer molecularly imprinted cavities within 3D COFs via molecularly imprinted technology, creating a novel adsorbent with exceptional selectivity, kinetics and capacity for the efficient extraction and removal of MCs. As proof-of-concept, a new CC bond-containing 3D COF, designated JNU-7, is designed and prepared for copolymerization with methacrylic acid, the pseudo template L-arginine and ethylene dimethacrylate to yield the JNU-7 based molecularly imprinted polymer (JNU-7-MIP). The JNU-7-MIP exhibits a great adsorption capacity (156 mg g−1) for L-arginine. Subsequently, the JNU-7-MIP based solid-phase extraction coupled with high performance liquid chromatography-mass spectrometry achieves low detection limit of 0.008 ng mL−1, wide linear range of 0.025–100 ng mL−1, high enrichment factor of 186, rapid extraction of 10 min, and good recoveries of 92.4%−106.5% for MC-LR. Moreover, the JNU-7-MIP can rapidly remove the MC-LR from 1 mg L−1 to levels (0.26–0.35 μg L−1) lower than the WHO recommended limit for drinking water (1 μg L−1). This work reveals the considerable potential of 3D COF based MIPs as promising adsorbents for the extraction and removal of contaminants in complex real samples.

Gas-Triggered Gate-Opening in a Flexible Three-Dimensional Covalent Organic Framework.

The development of novel soft porous crystals (SPCs) that can be transformed from nonporous to porous crystals is significant because of their promising applications in gas storage and separation. Herein, we systematically investigated for the first time the gas-triggered gate-opening behavior of three-dimensional covalent organic frameworks (3D COFs) with flexible building blocks. FCOF-5, a 3D COF containing C-O single bonds in the backbone, exhibits a unique "S-shaped" isotherm for various gases, such as CO2, C2, and C3 hydrocarbons. According to in situ characterization, FCOF-5 undergoes a pressure-induced closed-to-open structural transition due to the rotation of flexible C-O single bonds in the framework. Furthermore, the gated hysteretic sorption property of FCOF-5 can enable its use as an absorbent for the efficient removal of C3H4 from C3H4/C3H6 mixtures. Therefore, 3D COFs synthesized from flexible building blocks represent a new type of SPC with gate-opening characteristics. This study will strongly inspire us to design other 3D COF-based SPCs for interesting applications in the future.

Preparation of self-standing ultra-thin three-dimensional covalent organic frameworks by interfacial polymerization for dye separation

Three-dimensional covalent organic frameworks (3D COFs) have garnered considerable attention in the adsorption of small molecules owing to their unique 3D pore structure and easily modifiable functional group sites. However, most 3D COFs exhibit lattice interpenetration, making the membrane fabrication process difficult. Most 3D COFs are prepared as powders using solvothermal methods, which severely limits their application in material separation. Therefore, self-supporting 3D COFs membranes were fabricated using room-temperature interfacial polymerization, a low-energy method. Traditional alkane/water interfacial polymerization methods have disadvantages such as poor water solubility of the monomer, volatile solvents, and low crystallinity. Herein, an imine-linked, self-standing, 3D COFs membrane with an ultrathin layer was engineered at the alkane/ionic liquid interface. Owing to the improved crystalline structure, which exposed a large number of imine-linked sites within a 3D pore channel, the constructed 3D COFs membrane exhibited a high Brunauer–Emmett–Teller surface area of 1061.4 m2·g−1 and high water flux of approximately 76 L·m−2 h−1 bar−1 and demonstrated excellent rejection rates of 97.76% and 95.36% for two cationic dyes, rhodamine B and methylene blue, respectively. The membrane exhibited high rejection rates after seven testing cycles. This study reveals the great potential of self-standing 3D COFs membranes as dye separation.