3D COFs Research Articles

Three‐Dimensional Covalent Organic Frameworks Based on Linear and Trigonal Linkers for High‐Performance H2O2 Photosynthesis

AbstractThe design of three‐dimensional covalent organic frameworks (3D COFs) using linear and trigonal linkers remains challenging due to the difficulty in achieving a specific non‐planar spatial arrangement with low‐connectivity building units. Here, we report the novel 3D COFs with linear and trigonal linkers, termed TMB‐COFs, exhibiting srs topology. The steric hindrance provides an additional force to alter the torsion angles of peripheral triangular units, guiding the linear unit to connect with the trigonal unit into 3D srs frameworks, rather than the more commonly observed two‐dimensional (2D) hcb structures. Furthermore, we comprehensively examined the hydrogen peroxide photocatalytic production capacity of the TMB‐COFs in comparison with analogous 2D COFs. The experimental results and DFT calculations demonstrate a significant enhancement in photocatalytic hydrogen peroxide production efficacy through framework regulation. This work emphasizes the steric configuration using low connectivity building units, offering a fresh perspective on the design and application of 3D COFs.

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.

Rational Design of 3D Space Connected Donor–Acceptor System in Covalent Organic Frameworks for Enhanced Photocatalytic Performance

AbstractHerein, a rational strategy is presented to reduce the energy barrier of singlet ground state to singlet excited state transitions, whilst simultaneously reducing energy losses in populating triplet excited states. The approach relies on constructing 3D space connected donor–acceptor systems in COFs. The 3D space connected D–A system in 8‐connected 3D COFs (denoted as COF‐1 and COF‐2) allows the efficient transfer of electrons, overcoming the traditional electron transport limitations of 2D COFs and significantly boosting the solar energy utilization efficiency under visible light irradiation. COF‐2, possessing an extended π‐conjugated structure relative to COF‐1, demonstrated high selectivity for the photocatalytic generation of H2O2 (6.93 mmol g−1 h−1) in natural seawater without the need for sacrificial reagents, exceeding the performance of most previously reported COF‐based photocatalysts. The 3D space connected D–A system reported in this work offers a new approach for optimizing electron and energy transfer in COF‐based photocatalysts for H2O2 production and other 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.

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

AbstractThree‐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.

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.

Fine-tuning the pore environment of ultramicroporous three-dimensional covalent organic frameworks for efficient one-step ethylene purification

The construction of functional three-dimensional covalent organic frameworks (3D COFs) for gas separation, specifically for the efficient removal of ethane (C2H6) from ethylene (C2H4), is significant but challenging due to their similar physicochemical properties. In this study, we demonstrate fine-tuning the pore environment of ultramicroporous 3D COFs to achieve efficient one-step C2H4 purification. By choosing our previously reported 3D-TPB-COF-H as a reference material, we rationally design and synthesize an isostructural 3D COF (3D-TPP-COF) containing pyridine units. Impressively, compared with 3D-TPB-COF-H, 3D-TPP-COF exhibits both high C2H6 adsorption capacity (110.4 cm3 g−1 at 293 K and 1 bar) and good C2H6/C2H4 selectivity (1.8), due to the formation of additional C-H···N interactions between pyridine groups and C2H6. To our knowledge, this performance surpasses all other reported COFs and is even comparable to some benchmark porous materials. In addition, dynamic breakthrough experiments reveal that 3D-TPP-COF can be used as a robust absorbent to produce high-purity C2H4 directly from a C2H6/C2H4 mixture. This study provides important guidance for the rational design of 3D COFs for efficient gas separation.

Three-Dimensional Tetrathiafulvalene-Based covalent organic frameworks for efficient photocatalytic nitrogen fixation

Preparing photocatalytic nitrogen-fixing catalysts that can effectively produce ammonia under mild conditions is an urgent problem to be solved. Herein, we for the first time present two three-dimensional tetrathiafulvalene-based covalent organic frameworks with high crystallinity and permanent pores, termed 3D-TTF-COFs, specifically designed for photocatalytic nitrogen fixation. The incorporation of TTF-based building blocks not only enhances light absorption capabilities but also facilitates the rapid transfer of photoexcited electrons, ensuring efficient charge carrier separation. It is worth noting that the resultant COFs exhibit remarkable NH3 generation rates of 313.8 ± 5.6 and 106.8 ± 4.2 μmol g−1h−1 under visible light irradiation, surpassing the performance of most photocatalyst materials reported so far. Furthermore, these COFs maintain structural integrity and excellent performance during cyclic testing. Additionally, we carried out density functional theory calculations to elucidate the reaction mechanism between N2 and NH3. This work provides a feasible strategy for constructing 3D COFs to achieve efficient photocatalytic nitrogen fixation.

Topological Analysis and Structural Determination of 3D Covalent Organic Frameworks.

3D covalent organic frameworks (3D COFs) constitute a new type of crystalline materials that consist of a range of porous structures with numerous applications in the fields of adsorption, separation, and catalysis. However, because of the complexity of the three-periodic net structure, it is desirable to develop a thorough structural comprehension, along with a means to precisely determine the actual structure. Indeed, such advancements would considerably contribute to the rational design and application of 3D COFs. In this review, the reported topologies of 3D COFs are introduced and categorized according to the configurations of their building blocks, and a comprehensive overview of diffraction-based structural determination methods is provided. The current challenges and future prospects for these materials will also be discussed.

Breaking Dynamic Behavior in 3D Covalent Organic Framework with Pre-Locked Linker Strategy.

Due to their large surface area and pore volume, three-dimensional covalent organic frameworks (3D COFs) have emerged as competitive porous materials. However, structural dynamic behavior, often observed in imine-linked 3D COFs, could potentially unlock their potential application in gas storage. Herein, we showed how a pre-locked linker strategy introduces breaking dynamic behavior in 3D COFs. A predesigned planar linker-based 3,8-diamino-6-phenylphenanthridine (DPP) was prepared to produce non-dynamic 3D JUC-595, as the benzylideneamine moiety in DPP locked the linker flexibility and restricted the molecular bond rotation of the imine linkages. Upon solvent inclusion and release, the PXRD profile of JUC-595 remained intake, while JUC-594 with a flexible benzidine linker experienced crystal transformation due to framework contraction-expansion. As a result, the activated JUC-595 achieved higher surface areas (754 m2 g-1) than that of JUC-594 (548 m2 g-1). Furthermore, improved CO2 and CH4 storages were also seen in JUC-595 compared with JUC-594. Impressively, JUC-595 recorded a high normalized H2 storage capacity that surpassed other reported high-surface area 3D COFs. This works shows important insights on manipulating the structural properties of 3D COF to tune gas storage performance.

Three-dimensional covalent organic frameworks with nia nets for efficient separation of benzene/cyclohexane mixtures

The synthesis of three-dimensional covalent organic frameworks with highly connected building blocks presents a significant challenge. In this study, we report two 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the good performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications.

Synthesis of 12-Connected Three-Dimensional Covalent Organic Framework with lnj Topology.

The structural exploration of three-dimensional covalent organic frameworks (3D COFs) is of great significance to the development of COF materials. Different from structurally diverse MOFs, which have a variety of connectivity (3-24), now the valency of 3D COFs is limited to only 4, 6, and 8. Therefore, the exploration of organic building blocks with higher connectivity is a necessary path to broaden the scope of 3D COF structures. Herein, for the first time, we have designed and synthesized a 12-connected triptycene-based precursor (triptycene-12-CHO) with 12 symmetrical distributions of aldehyde groups, which is also the highest valency reported until now. Based on this unique 12-connected structure, we have successfully prepared a novel 3D COF with lnj topology (termed 3D-lnj-COF). The as-synthesized 3D COF exhibits honeycomb main pores and permanent porosity with a Brunauer-Emmett-Teller surface area of 1159.6 m2 g-1. This work not only provides a strategy for synthesizing precursors with a high connectivity but also provides inspiration for enriching the variety of 3D COFs.

Large-Scale and Rapid Processing of 3D COFs via 3D-Controlled Reaction–Diffusion Zones

Large-Scale and Rapid Processing of 3D COFs via 3D-Controlled Reaction–Diffusion Zones

Donor–acceptor hetero[6]radialene-based three-dimensional covalent organic frameworks for organic pollutant adsorption, photocatalytic degradation, and hydrogen production activity

By investigating the effects of electron donor topology and the hetero[6]radialene structure on the 3D COF photocatalytic activity, a twisted BF structure was found to improve organic pollutant degradation and water hydrogen production.

Metalloporphyrin-based highly conjugated three-dimensional covalent organic frameworks for the electrochemical hydrogen evolution reaction

A diagram of a metalloporphyrin-based highly conjugated 3D COF electrocatalytic hydrogen evolution process.

Integrated High Voltage, Large Capacity, and Long‐Time Cyclic Stability of Lithium Organic Battery Based on a Bipolar‐Type Cathode of Triphenylamine‐Hydrazone COF Material

AbstractCovalent organic frameworks (COFs) are a promising class of electrode materials for lithium‐ion batteries. However, the reported cathodes of COFs typically exhibit low potential and voltage plateaus, which limits their further applications. In this work, a new hydrazone three‐dimensional (3D) COF material with bipolar characteristics, PTB‐DHZ‐COF, is constructed by Schiff base condensation of monomeric PTB with DHZ. The cell with PTB‐DHZ‐COF as the cathode exhibits a wide potential range of 1.2–4.2 V and a discharge voltage plateau of over 3.6 V. PTB‐DHZ‐COFX composites are successfully prepared by compounding PTB‐DHZ‐COF with carbon nanotubes. PTB‐DHZ‐COF40 cells show high specific capacity (114.24 mAh·g−1 at 1000 mA·g−1), excellent cycling capability (86.3% capacity retention after 5000 cycles), and ultra‐high energy density (489 Wh·kg−1 at 50 mA·g−1). This work provides a new strategy for the design of new COF materials and the development of high‐performance organic energy storage electrodes.

Rapid, Mild, and Catalytic Synthesis of 2D and 3D COFs with Promising Supercapacitor Applications

Rapid, Mild, and Catalytic Synthesis of 2D and 3D COFs with Promising Supercapacitor Applications

Size–controllable synthesis of large–size spherical 3D covalent organic frameworks as efficient on–line solid-phase extraction sorbents coupled to HPLC

BackgroundCovalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on–line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 μm as sorbents might be able to address these problems, however it is still a great challenge till now. ResultsIn this work, two large-size spherical 3D COFs (COF–320 and COF–300) were size–controllably synthesized within 10–90 μm via a two–step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on–line SPE sorbents coupled to HPLC, the large–size spherical COF–320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6–8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on–line–SPE–HPLC–UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0–400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3–103.2 % (RSDs of 2.0–3.5 %) and 95.2–97.0 % (RSDs of 4.3–5.6 %) for tap water and lake water samples, respectively. SignificanceThis is the first case to synthesize the large–size spherical COFs within 10–90 μm, and this work made it possible to directly use COFs as the filling materials of on–line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.