2D Covalent Organic Frameworks Research Articles

Synergistic effect of 2D covalent organic frameworks confined 0D carbon quantum dots film: Toward molecularly imprinted cathodic photoelectrochemical platform for detection of tetracycline

The development of high photoactive cathode materials combined with the formation of a stable interface are considered important factors for the selective and sensitive photoelectrochemical (PEC) detection of tetracycline (TC). Along these lines, in this work, a novel type II heterostructure composed of two-dimensional (2D) covalent organic frameworks confined to zero-dimensional (0D) carbon quantum dots (CDs/COFs) film was successfully synthesized using the rapid in-situ polymerization method at room temperature. The PEC signal of CDs/COFs was significantly amplified by improving the light absorption and electron transfer capabilities. Furthermore, a cathodic molecularly imprinted PEC sensor (MIP-PEC) for the detection of TC was constructed through fast in-situ Ultraviolet (UV) photopolymerization on the electrode. Finally, a “turn-off” PEC cathodic signal was achieved based on the selective recognition of the imprinted cavity and the mechanism of steric hindrance increase. Under optimal conditions, the proposed sensor demonstrated a wide linear relationship with TC in the concentration range of 5.00 × 10−12–1.00 × 10−5 M, with a detection limit as low as 6.00 × 10−13 M. Meanwhile, excellent stability, selectivity, reproducibility, and applicability in real river samples was recorded. Our work provides an effective and rapid in situ construction method for fabricating highly photoactive cathode heterojunctions and uniform stable selective MIP-PEC sensing interfaces, yielding accurate antibiotics detection in the environment.

Homochiral Covalent Organic Frameworks with Superhelical Nanostructures Enable Efficient Chirality‐Induced Spin Selectivity

AbstractDespite significant advancements in fabricating covalent organic frameworks (COFs) with diverse morphologies, creating COFs with superhelical nanostructures remains challenging. We report here the controlled synthesis of homochiral superhelical COF nanofibers by manipulating pendent alkyl chain lengths in organic linkers. This approach yields homochiral 3D COFs 13‐OR with a 10‐fold interpenetrated diamondoid structure (R=H, Me, Et, nPr, nBu) from enantiopure 1,1′‐bi‐2‐naphthol (BINOL)‐based tetraaldehydes and tetraamine. COF‐13‐OEt exhibits macroscopic chirality as right‐handed and left‐handed superhelical fibers, whereas others adopt spherical or non‐helical morphologies. Time‐tracking shows a self‐assembly process from non‐helical strands to single‐stranded helical fibers and intertwined superhelices. Ethoxyl substituents, being of optimal size, balance solvophobic effects and intermolecular interactions, driving the formation of superhelical nanostructures, with handedness determined by BINOL chirality. The superhelical nature of these materials is evident in their chiral recognition and spin‐filter properties, showing significantly improved enantiodiscrimination in carbohydrate binding (up to six times higher enantioselectivity) and a remarkable chiral‐induced spin selectivity (CISS) effect with a 48–51 % spin polarization ratio, a feature absent in non‐helical analogs.

Aptamer-Conjugated Covalent-Organic Framework Nanochannels for Selective and Sensitive Detection of Aflatoxin B1.

Sensitive and selective detection of trace aflatoxin B1 (AFB1) in foods is of great importance to guarantee food safety and quality but still challenging because of its trace amount and the interference from the complex food matrix. Here, we report the integration of aptamer (Apt) and an ordered 2D covalent organic framework (COF) to solid-state anodic aluminum oxide (AAO) nanochannels (Apt/COF/AAO) for selective and sensitive detection of trace AFB1. The high specificity of Apt for AFB1 led to a selective change in the surface charge of Apt/COF/AAO and in turn the current change of the nanochannel, permitting the selective and sensitive determination of trace AFB1 in complex food samples. The developed nanofluidic sensor gave a wide linear range (1-500 pg mL-1), low detection limit (0.11 pg mL-1), and good precision (relative standard deviation of 1.5% for 11 replicate determinations of 100 pg mL-1). In addition, the developed sensor was successfully used for the detection of AFB1 in food samples with the recovery of 86.9%-102.5%. The coupling of Apt-conjugated 2D COF with an AAO nanochannel provides a promising way for sensitive and selective determination of food contaminants in complex samples.

Azobenzene-Bridged Covalent Organic Frameworks Boosting Photocatalytic Hydrogen Peroxide Production from Alkaline Water: One Atom Makes a Significant Improvement.

Covalent organic frameworks (COFs) have been demonstrated as promising photocatalysts for hydrogen peroxide (H2O2) production. However, the construction of COFs with new active sites, high photoactivity, and wide-range light absorption for efficient H2O2 production remains challenging. Herein, we present the synthesis of a novel azobenzene-bridged 2D COF (COF-TPT-Azo) with excellent performance on photocatalytic H2O2 production under alkaline conditions. Notably, although COF-TPT-Azo differs by only one atom (-N=N- vs. -C=N-) from its corresponding imine-linked counterpart (COF-TPT-TPA), COF-TPT-Azo exhibits a significantly narrower band gap, enhanced charge transport, and prompted photoactivity. Remarkably, when employed as a metal-free photocatalyst, COF-TPT-Azo achieves a high photocatalytic H2O2 production rate up to 1498 μmol g-1 h-1 at pH = 11, which is 7.9 times higher than that of COF-TPT-TPA. Further density functional theory (DFT) calculations reveal that the -N=N- linkages are the active sites for photocatalysis. This work provides new prospects for developing high-performance COF-based photocatalysts.

Dynamic Two-Dimensional Covalent Organic Frameworks with Large Solvent-Induced Lattice Expansion.

Dynamic covalent organic frameworks (COFs) can switch reversibly between crystalline phases with different unit cell parameters and porosities upon physisorption of guest molecules. While impressive changes in unit cell volumes have been realized for three-dimensional frameworks, the solvent-induced volume changes of two-dimensional (2D) COFs have remained comparably small. We have now developed a series of 2D COFs where we systematically varied the length of the interconnecting bridge units. The optimized materials achieve solvent-induced expansions of up to 85% relative to the volume of the solvent-free contracted COFs. These structural changes are fully reversible and the frameworks fully retain their high degree of crystalline order. This study introduces a versatile design strategy for dynamic 2D COFs, which could enable future applications of these materials in gas separation and sensing.

Single-Crystalline 3D Covalent Organic Frameworks with Exceptionally High Specific Surface Areas and Gas Storage Capacities.

Single-crystalline covalent organic frameworks (COFs) are highly desirable toward understanding their pore chemistry and functions. Herein, two 50-100 μm single-crystalline three-dimensional (3D) COFs, TAM-TFPB-COF and TAPB-TFS-COF, were prepared from the condensation of 4,4',4″,4‴-methanetetrayltetraaniline (TAM) with 3,3',5,5'-tetrakis(4-formylphenyl)bimesityl (TFPB) and 3,3',5,5'-tetrakis(4-aminophenyl)bimesityl (TAPB) with 4,4',4″,4‴-silanetetrayltetrabenzaldehyde (TFS), respectively, in 1,4-dioxane under the catalysis of acetic acid. Single-crystal 3D electron diffraction reveals the triply interpenetrated dia-b networks of TAM-TFPB-COF with atom resolution, while the isostructure of TAPB-TFS-COF was disclosed by synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction with Le Bail refinements. The nitrogen sorption measurements at 77 K disclose the microporosity nature of both activated COFs with their exceptionally high Brunauer-Emmett-Teller surface areas of 3533 and 4107 m2 g-1, representing the thus far record high specific surface area among imine-bonded COFs. This enables the activated COFs to exhibit also the record high methane uptake capacities up to 28.9 wt % (570 cm3 g-1) at 25 °C and 200 bar among all COFs reported thus far. This work not only presents the structures of two single-crystalline COFs with exceptional microporosity but also provides an example of atom engineering to adjust permanent microporous structures for methane storage.

Insights into the Biological Activity and Bio-Interaction Properties of Nanoscale Imine-Based 2D and 3D Covalent Organic Frameworks.

Covalent Organic Frameworks (COFs) emerged as versatile materials with promising potential in biomedicine. Their customizable functionalities and tunable pore structures make them valuable for various biomedical applications such as biosensing, bioimaging, antimicrobial activity, and targeted drug delivery. Despite efforts made to create nanoscale COFs (nCOFs) to enhance their interaction with biological systems, a comprehensive understanding of their inherent biological activities remains a significant challenge. In this study, a thorough investigation is conducted into the biocompatibility and anti-neoplastic properties of two distinct imine-based nCOFs. The approach involved an in-depth analysis of these nCOFs through in vitro experiments with various cell types and in vivo assessments using murine models. These findings revealed significant cytotoxic effects on tumor cells. Moreover, the activation of multiple cellular death pathways, including apoptosis, necroptosis, and ferroptosis is determined, supported by evidence at the molecular level. In vivo evaluations exhibited marked inhibition of tumor growth, associated with the elevated spontaneous accumulation of nCOFs in tumor tissues and the modulation of cell death-related protein expression. The research contributes to developing a roadmap for the characterization of the intricate interactions between nCOFs and biological systems and opens new avenues for exploiting their therapeutic potential in advanced biomedical applications.

Modulating Pore Wall Chemistry Empowers Sonodynamic Activity of Two-Dimensional Covalent Organic Framework Heterojunctions for Pro-Oxidative Nanotherapy.

Covalent organic frameworks (COFs) have garnered growing attracted interest in the field of biomedicine; however, their application in sonodynamic therapy remains underexplored due to limited understanding of their intrinsic activity and structure-property relationships. Here, we present a pore wall chemistry modulation strategy for empowering sonodynamic activity to two-dimensional (2D) COF heterojunctions through in situ growth of COFs on bismuth oxycarbonate nanosheets (B NSs). Compared to the negligible sonodynamic effects observed in the pristine B NSs, the 2D heterojunction with vinyl-decorated COF pore walls demonstrates a 3.6-fold enhancement in sonocatalytic singlet oxygen generation. This performance also significantly outperforms that of isoreticular COFs functionalized with methoxy or non-substituted groups. Mechanistic studies reveal that the vinyl groups in the BC heterojunction facilitate the separation and transfer of charge carriers while also enhancing the adsorption of oxygen molecules. Furthermore, peroxymonosulfate (PMS) loading into the porous COFs boosts the therapeutic efficacy of antitumor nanotherapy via sonocatalytic dual oxidative species generation. These findings underscore the critical role of pore wall chemistry in modulating the sonocatalytic properties of COFs, and advance the development of COF-based sonosensitizers for pro-oxidative applications.

Non-Noble Metal Anchored 2D Covalent Organic Framework for Ambient CO2 Fixation to High-Value Compounds.

The catalytic functionalization of CO2 into high-value compounds comprises a promising approach to mitigate its atmospheric content and sustainable generation of fine chemicals. Herein, we report application of a crystalline, nano-porous 2D COF (ET-BP-COF) for utilization of CO2. The ET-BP-COF features a unique 2D kagome (kgm) topology composed of hexagonal and triangular 1D channels decorated with bipyridine sites, which were exploited for covalent anchoring of eco-friendly Cu(I) by post-synthetic method. The Cu(I) engrafted COF was applied as a recyclable catalyst for coupling CO2 with alkynes to generate two high-value compounds, α-alkylidene cyclic carbonates (α-ACCs) and 2-oxazolidinones. Notably, Cu(I)@ET-BP-COF demonstrated excellent catalytic performance for transforming propargylic amine and CO2 to 2-oxazolidinone, an essential building block for antibiotics. Besides, an efficient transformation of propargylic alcohols to generate α-ACCs, valuable commodity chemicals, has been achieved by utilizing carbon dioxide. Further, detailed theoretical simulations disclosed the insight mechanistic path of Cu(I) catalyzed coupling of CO2 with alkynes to produce 2-oxazolidinones and α-ACCs. Significantly, Cu(I)@COF was reusable for multiple cycles without losing framework rigidity and catalytic performance. This study showcases the potential application of ET-BP-COF for stable anchoring of eco-friendly metals as catalytic sites for effective utilization of CO2 to produce two high-value products.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers.

Synthesis and assembly of two-dimensional (2D) polymeric materials present a tricky trade-off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine-based 2D covalent organic frameworks (COFs) at the interface of oil-in-water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET-specific surface areas are up to 139.0 m2/g, mainly contributedby narrowly-distributed mesopores at ~5.0 nm and micropores at 1.4 nm.The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalystsin application of water-based hydrogen evolution.Such microdroplet interface-confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High‐Performance Photocatalytic Carriers

Synthesis and assembly of two‐dimensional (2D) polymeric materials present a tricky trade‐off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine‐based 2D covalent organic frameworks (COFs) at the interface of oil‐in‐water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET‐specific surface areas are up to 139.0 m2/g, mainly contributed by narrowly‐distributed mesopores at ~5.0 nm and micropores at 1.4 nm. The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalysts in application of water‐based hydrogen evolution. Such microdroplet interface‐confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Tuning interlayer stacking of 2D covalent organic frameworks for high-resolution separation of C8 aromatic isomers

Covalent organic frameworks (COFs) has shown great potential as stationary phase in gas chromatography separation. However, designing COF stationary phases with high separation performance remains challenging. Here, we report a novel strategy to enhance the separation ability of COF stationary phases through tuning the interlayer stacking of COF. A rare interlayer modulation of 2D COFs from eclipsed-AA to slipped-AA was achieved through a two-step synthesis method. Simply changing the solvent used in step 1 allowed an interlayer modulation from slipped-AA to eclipsed-AA. As the proof-of-concept, 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (Tph) and 2,5-dihydroxyterephthalaldehyde (DHTA) were condensed to prepare 2D COF Tph-DHTA. The interlayer stacking of the 2D COF Tph-DHTA was tuned from eclipsed-AA model to slipped-AA by changing the solvent from o-dichlorobenzene + n-butanol (3:1, v/v) to tetrahydrofuran + n-butanol (1:7, v/v) in step 1. The as-prepared Tph-DHTA with slipped-AA stacking (s-Tph-DHTA) showed higher resolution and faster separation of C8 aromatic isomers than that with eclipsed-AA stacking (e-Tph-DHTA). The formation of slipping stacking of s-Tph-DHTA facilitated the thermodynamics, but did not affect the mass transfer resistance for the separation of C8 aromatic isomers. This work not only provides a promising way to modulate the stacking structure of COFs, but also opens a new strategy to design COF stationary phases for the separation of intractable isomers.

Highly Anion-Conductive Viologen-Based Two-Dimensional Polymer Membranes as Nanopower Generators.

Two-dimensional polymers (2DPs) and their layer-stacked 2D covalent organic frameworks (2D COFs) membranes hold great potential for harvesting sustainable osmotic energy. The nascent research has yet to simultaneously achieve high ionic flux and selectivity, primarily due to inefficient ion transport dynamics. This is directly related to ultrasmall pore size (<3 nm), much smaller than the duple Debye length in the diluted electrolyte (6-20 nm), as well as low charge density (<4.5 mC m-2). Here, we introduce a π-conjugated viologen-based 2DP (V2DP) membrane possessing a large pore size of 4.5 nm, strategically enhancing the overlapping of the electric double layer, coupled with an exceptional positive surface charge density (~6 mC m-2). These characteristics enable the membrane to facilitate high anion flux while maintaining ideal selectivity. Notably, V2DP membranes realize an impressive current density of 5.5×103 A m-2, surpassing benchmarks set by previously reported nanofluidic membranes. In the practical application scenario involving the mixing of artificial seawater and river water, the V2DP membranes exhibit a considerable ion transference number of 0.70 towards Cl-, contributing to an outstanding power density of ~55 W m-2. Theoretical calculations reveal the important role of the large quantity of anion transport sites, which act as binding sites evenly located in the positively charged N-containing pyridine rings. These binding sites enable kinematic coupling and decoupling between anions and the V2DP skeleton, establishing a continuous Cl- ion transport pathway. This work demonstrates the great promise of large-area ultrathin 2DP membranes featuring highly organized charged ion transport networks when applied for osmotic energy conversion.

Perylene-Based 2D Covalent Organic Frameworks for Selective Adsorption and Extraction of C60

Perylene-Based 2D Covalent Organic Frameworks for Selective Adsorption and Extraction of C₆₀

2D sp2 carbon-linked benzotrithiophene covalent organic frameworks for selective sulfoxidation with oxygen driven by green light

Covalent organic frameworks (COFs) are promising photocatalysts with excellent chemical stability, broad light absorption, and tailorable molecular structures. To assemble highly crystalline 2D (two-dimensional) COFs, planar molecular units like benzotrithiophene (BTT) and 2,2′-bipyridine (Bpy) are highly desired. Herein, two COFs are assembled by the condensation of benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde with [2,2′-bipyridine]-5,5′-diacetonitrile and [2,2′-bipyridine]-5,5′-diamine, respectively. An sp2 carbon-linked COF Bpy-sp2c-BTT-COF and an imine-linked COF Bpy-IM-BTT-COF with apparent electron donor–acceptor configuration are readily furnished in which the planarity of Bpy underpins their crystallinity. The sp2-carbon linkage is more essential than the imine linkage in adjusting band structure and facilitating electron transfer over Bpy-sp2c-BTT-COF and Bpy-IM-BTT-COF. Therefore, Bpy-sp2c-BTT-COF demonstrates better performance than Bpy-IM-BTT-COF for selective sulfoxidation with oxygen driven by green light in which superoxide and single oxygen are both involved during the activation of oxygen. The linkage selection for COFs opens new doors into visible light photocatalysts for selective conversions.

Interpenetrated Donor-Acceptor Heterojunctions in 2D Conjugated Dibenzo[g,p]chrysene-Based Kagome Covalent Organic Frameworks.

Dibenzo[g,p]chrysene can be viewed as a constrained propeller-shaped tetraphenylethylene with reduced curvature and has been utilized to construct dual-pore kagome covalent organic frameworks (COFs) with tightly packed two-dimensional (2D) layers owing to its rigid and more planar structural characteristics. Here, we introduce 2D COFs based on the node 4,4',4″,4‴-(dibenzo[g,p]chrysene-2,7,10,15-tetraphenyl)tetraamine (DBCTPTA) featuring extended conjugation compared to the dibenzo[g,p]chrysene-3,6,11,14-tetraamine (DBCTA) node. We establish two exceptionally crystalline imine-linked 2D COFs with a hexagonal dual-pore kagome structure based on the DBCTPTA core. The newly synthesized thienothiophene (TT) and benzodithiophene (BDT)-based DBCTPTA COFs show a tight stacking behavior between adjacent layers. Furthermore, we obtained an unprecedented, interpenetrated electron-donor/acceptor host-guest system with an electron-donating BDT DBCTPTA COF synthesized in situ with the soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) serving as molecular acceptor. The BDT DBCTPTA COF@PCBM film shows a much shorter amplitude-averaged PL lifetime of 7 ± 2 ps compared to 30 ± 4 ps of the BDT DBCTPTA COF film, indicating the light-induced charge transfer process. The successful in situ formation of interpenetrated donor-acceptor heterojunctions within 2D COFs offers a promising strategy for establishing D-A heterojunctions in diverse framework materials with open channel systems.

Sequence-Dependent Single-Molecule DNA Sensing Using Covalent Organic Framework Nanopores.

Enzyme-free single-molecule sequencing has the potential to significantly expand the application of nanopore technology to DNA, proteins, and saccharides. Despite their advantages over biological nanopores and natural suitability for enzyme-free single-molecule sequencing, conventional solid-state nanopores have not yet achieved single-molecule DNA sequencing. The biggest challenge for the accuracy of single-molecule sequencing using solid-state nanopores lies in the precise control of the pore size and conformity. In this study, we fabricated nanopore devices by covering the tip of a quartz nanopipette with ultrathin two-dimensional (2D) covalent organic framework (COF) nanosheets (pore size ≈ 1.1 nm). The size of the periodically arranged nanopores in COF is comparable to that of protein nanopores, and the structure of each COF nanopore is consistent at the atomic scale. The COF nanopore device could roughly distinguish dAMP, dCMP, dGMP, and dTMP. Furthermore, a certain percentage of the current blockades originating from 150 nucleotides model DNA molecules (13.5% for dA50dC50dA50 and 11.1% for dC50dA50dC50) show distinct DNA sequence-specific concave and convex resistive current patterns. The finite element simulation confirmed that the current blockade pattern of a DNA molecule passing through a COF nanopore is dependent on the relative location of the nanopore with respect to the wall of the nanopipette. Our study is a significant step toward single-molecule DNA sequencing by solid-state nanopores.

Chemically‐Modified 2D Covalent Organic Framework as an HTL Dopant for High‐Performance, Stable, and Sustainable Perovskite Solar Cells and Modules

AbstractDespite significant advances in perovskite solar cells (PeSCs), the operational instability and susceptibility to Pb leakage of PeSCs severely limit their widespread application. To address these issues, this study investigates the effect of doping the Spiro‐OMeTAD hole‐transporting layer (HTL) with a chemically‐modified 2D conjugated covalent organic framework (Tp‐Azo‐COF) on the photovoltaic performance and stability of PeSCs. Enriched with abundant carbonyl (C═O) groups and azo (N═N) nodes, Tp‐Azo‐COF has excellent chelation and adsorption capabilities, and experimental results confirm that Tp‐Azo‐COF effectively decreases Pb leakage and Li‐ion migration, improving the environmental safety and operational stability of PeSCs. The optimized PeSCs (0.12 cm2) exhibit an efficiency of 24.25%, a new benchmark for COF‐modified devices, and maintain robust performance in large‐area modules (18 cm2) with an efficiency of 21.96%. Under accelerated aging tests, including continuous light irradiation at maximum power point tracking for 980 h, the module demonstrated exceptional durability, with near‐100% efficiency retention. The COF doping strategy developed in this study significantly enhances operational stability and minimizes Pb leakage in PeSCs, paving the way for the sustainable, large‐scale deployment of perovskite photovoltaics.

2D Covalent Organic Framework Covalently Anchored with Carbon Nanotube as High-Performance Cathodes for Lithium and Sodium-Ion Batteries.

Covalent organic frameworks (COFs), featuring structural diversity, permanent porosity, and functional versatility, have emerged as promising electrode materials for rechargeable batteries. To date, amorphous polymer, COF, or their composites are mostly explored in lithium-ion batteries (LIBs), while their research in other alkali metal ion batteries is still in infancy. This can be due to the challenges that arise from large volume changes, slow diffusion kinetics, and inefficient active site utilization by the large Na+ or K+ ion. Herein, microwave-assisted imide-based 2D COF, TAPB-NDA covalently connected with amine-functionalized carbon nanotubes (TAPB-NDA@CNT) targeting the application in both Li-/Na-ion batteries, is synthesized. As-synthesized, TAPB-NDA@CNT50 displays the good performance as LIB cathode with a specific capacity of ≈138mAhg-1 at 25mAg-1, long cycling stability (81.2% retention after 2000 cycles at 300mAg-1), with excellent reversible capacity retention of ≈79.6%. Similarly, TAPB-NDA@CNT50, when employed in sodium-ion battery (SIB), exhibited 136.7mAhg-1 specific capacity at 25mAg-1, retained ≈80% of the reversible capacity after 1000 cycles at 300mAg-1 and showing excellent rate performance. The structural advantage of TAPB-NDA@CNT will encourage researchers to design COF-based cathodes for the alkali ion batteries.

Harnessing the clean energy: Phosphorus-alkynyl covalent organic frameworks for photocatalytic hydrogen production

Given the diminishing reserves of fossil fuels, the development of renewable alternative energy sources is of global importance. Photocatalytic hydrogen (H2) evolution stands out as a promising and cost-effective method to harness sunlight for producing carbon-free H2 fuel. Recently, two-dimensional (2D) covalent organic frameworks (COFs) have garnered considerable research interest in photocatalysis on account of their exceptional surface area and predictable assembly of diverse molecules with adjustable electronic properties. Herein, six 2D COFs are constructed by topologically assembling phosphorus-alkynyl functional moieties and benzene-based building units, including benzene (COF-1), triazine (COF-2), heptazine (COF-3), triphenyl-benzene (COF-4), triphenyl-triazine (COF-5), and triphenyl-heptazine (COF-6), employing first-principles calculations. Our computational results illustrate that the variation of benzene-based building units significantly regulates the electronic structures of COFs, all of which possess semiconductor properties with tunable bandgaps spanning from 1.56 to 2.56 eV. Of particular importance, COF-1, COF-2, COF-4, COF-5, and COF-6 can spontaneously stimulate the hydrogen evolution reaction (HER) under their own light-induced bias without the need for sacrificial agents and co-catalysts. Among them, COF-4 and COF-5 show the best HER activity without light-induced bias, with ΔG values of 0.02 and −0.01 eV, respectively, whose excellent photocatalytic performance can be ascribed to their appropriate electronic band structures, pronounced optical absorption, and low work functions. This finding offers profound insights for exploring other highly efficient HER photocatalysts.