Ultrastable Triazine-Based Covalent Organic Framework with an Interlayer Hydrogen Bonding for Supercapacitor Applications

Progress in the application of functionalized covalent organic framework for bioanalysis

As a new type of crystalline porous polymer materials, covalent organic frameworks (COFs) with their unique features such as large surface area, tunable pore sizes, strong π-π stacking effect and size exclusion effects, have attracted wide attention in the analytical field. Due to the lack of catalytically active metal centers in bare COFs, functionalized COFs that are hybridized or modified with nanomaterials improve reactive activation and show better analytical performance for a variety of detection scenarios with complex analytes. Herein, we focused on the functionalized COFs used in bioanalysis ranging from nucleic acids, peptides, and proteins, to microorganisms, and discussed the functionalization strategy and unique structures and properties applied in the different stages of biosensing and advantages compared to other hybrid materials. Finally, challenges and future research directions of functionalized COFs in bioanalysis are discussed.

Nitrogen-Rich Angstrom Channels within Covalent Triazine Framework Membrane Enable Efficient Acid Recovery

Membranes tailored for selective H+ transfer are highly demanded in various fields such as acid recovery and proton exchange membranes. Emerging framework materials featuring permanent micropores present more competitive selectivity than traditional polymeric membranes. However, it remains challenging to construct angstrom channels for more precise ion separations. Herein, we demonstrate the modulation of the nitrogen-rich angstrom channels within a covalent triazine framework (CTF) membrane by a mix-monomer copolymerization strategy, in which one monomer provides defect-free angstrom channels and another offers plentiful nitrogen sites. The abundant nitrogen sites with strong affinity for H+ facilitate fast H+ diffusion, and their high protonation level in acid solution imparts positive charge, enabling efficient Fe2+ retention via Donnan exclusion. The optimized CTF membrane achieves a H+ dialysis coefficient of 1.5 × 10-3 m/h and a separation factor of 11,242 for H+/Fe2+ mixtures. The ion selectivity outperforms most reported membranes benefiting from its highly confined channels. Additionally, the robust stability of the triazine groups guarantees consecutive operation in aggressive acidic solutions. This work presents an effective approach for modulating proton transport efficiency through membranes and its potential applications in acid recovery.

A critical review of COFs-based photocatalysis for environmental remediation

Covalent organic frameworks (COFs) are highly porous crystalline polymers formed through covalent bonding of molecular building blocks. Numerous fabrication strategies have been developed, including solvothermal, ionothermal, microwave, mechanochemical, and sonochemical methods, alongside ligand substitution and post-modification techniques, which allow for precise control over the structures and properties of COFs. The exceptional physicochemical stability, large specific surface area, broad visible light absorption, and extended π-conjugated systems have sparked significant interest in photocatalytic applications. Recently, COFs have shown remarkable efficacy in environmental remediation, demonstrating the ability to degrade a wide range of organic pollutants, including dyes, antibiotics, and drugs, as well as to reduce/oxidize heavy metals such as Cr(VI), U(VI), and As(III), in addition to targeting biological pollutants. This review comprehensively explores recent advancements in COFs-based photocatalysis, covering synthetic methods, COF types, modification method, theoretical calculations, environmental applications, and underlying mechanisms. Additionally, the challenges and opportunities for COFs as a robust, cost-effective technology in practical applications was discussed, and offering valuable insights for researchers in environmental remediation, materials science, and photocatalysis.

Enhanced supercapacitor performance using EG@COF: a layered porous composite

In this work, to address the issue of poor conductivity in COFs, a layered porous composite (EG@COF) was successfully synthesized. A redox-active COF (DAAQ-TFP COF) was grown on the surface of expanded graphite (EG) through a solvent-free in situ synthesis. SEM analysis displayed that the obtained composite (EG@COF) possessed a layered porous structure. Further investigations revealed that EG not only improved electrical conductivity but also regulated the pore size of the COFs. This structure was highly conducive to enhancing the specific capacitance of the electrode material. An electrochemical study demonstrated that the specific capacitance of EG@COF-3 reached 351 C g-1 at 1 A g-1, with 94.4% capacitance retention after 10 000 cycles. The excellent capacitance retention was attributed to the stable backbone of the COF. Meanwhile, an asymmetric supercapacitor (ACS) comprising activated carbon (AC) and EG@COF exhibited an energy density of 16.4 W h kg-1 at a power density of 806.0 W kg-1.

Triazine-Functionalized Nitrogen-Rich Covalent Organic Framework as an Electrode Material for Aqueous Symmetric Supercapacitor

Covalent triazine frameworks, with their ordered pores and crystalline structure that exhibit heteroatom impacts, demonstrate outstanding chemical stability, making them designable for charge storage applications. In this study, the triazine-based covalent organic frameworks (TPT@BDA-COF) was synthesized using 4',4''',4'''''-(1,3,5-Triazine-2,4,6-triyl) tris (([1,1'-biphenyl]-4-amine)) (TPT) and 4,4'-Oxydibenzaldehyde (BDA) following polycondensation process. Interestingly, these resulted in the fabrication of a well-connected, orderly porous crystalline structure, redox-active moiety, and significantly high doping atomic percentages of N (~13.6 %). The three-electrode electrochemical study, showed a stable electrochemical potential window of 1.8 V (-0.45 to +1.35) in 1 M NaClO4 electrolyte, it exhibited a high specific capacitance of 92.6 mF/cm2 with a high energy density 41.7 Wh/kg respectively. The symmetric supercapacitor designed using TPT@BDA-COF as both anode and cathode exhibited high specific capacitance (F/g) and gravimetric energy density (Wh/kg): 17.8, 36.9, 43.7, 47.7 and 3.5, 16.6, 13.7, 21.6 in 1 M CH3COONa, 1 M Na2SO4, 1 M NaNO3, 1 M NaClO4 electrolyte respectively. It showed excellent cyclic stability (105.2 %), and Coulombic efficiency (97.5 %) even after 10 k GCD cycles in 1 M NaClO4 at 2 A/g. Interestingly, ClO4 - anions exhibited a better chaotropic nature (water structure breaker) as compared to CH3COO-, SO4 -2, and NO3 -. Their energy storage competence is supported by the illumination of 1 white and 1 red LED upon charging a single SSC for 50 sec each. A Quantum Mechanics (QM) calculation and Molecular Dynamics (MD) simulation are performed to investigate and validate the stability of Covalent Organic Frameworks (COFs). DFT calculations were carried out using the SCF approach B3LYP-631G(d) basis set to compute the HOMO and LUMO energies and their respective location in COF.

Integrated Carbon Nanotube and Ketoenamine-Linked Covalent Organic Framework with Positive Charge Structure as High-Performance Capacitive Materials

A series of composite materials, ETB@CNT (ETB@CNT10, ETB@CNT20, ETB@CNT30, ETB@CNT40, ETB@CNT50) with different carbon nanotubes (CNTs) contents are successfully prepared by using one-pot method. Compared with the pure ET-B-COF, which is a ketoenamine-linked covalent organic framework (COF) with a positive charge structure, CNTs can effectively improve the electrochemical performance of ET-B-COF, and the specific capacitance increased with the increase of the mass of carbon nanotubes added during the preparation process. Among them, ETB@CNT40 exhibits the best electrochemical performance (37.6 F g-1) at a current density of 1 A g-1. This study indicates that the simultaneous introduction of CNTs into COFs can significantly improve the electrochemical performance of ketoenamine-linked COFs materials.

Bipolar Supercapacitive Performance of N-Containing Carbon Materials Derived from Covalent Triazine-Based Framework

The search for new electrode materials for bipolar-supercapacitor performance is the intention of numerous research in the area of functional framework materials. Among various electrode materials, covalent triazine-based frameworks (CTFs) are in the spotlight drawing much attention as potential electrode material for energy storage owing to their tunable surface area, pore size distribution, and heteroatom content. Herein, we present the synthesis of nitrogen-functionalized CTFs marked as CTF-Py-600 and CTF-Py-700 with high nitrogen content (18 % and 14 %, respectively) for supercapacitor application by applying the 2,6-dicyanopyridine monomer via the polymerization reaction under ionothermal condition. The BET surface areas of these materials are in the range of 940-1999 m2 g-1. CTF-Py-700 demonstrates outstanding electrochemical performance in both potential windows. At the negative potential window, it exhibits a higher specific capacitance of 435 F g-1 (at 1 A g-1) compared to the positive potential window, where it shows a specific capacitance of 306 F g-1 (at 1 A g-1) owing to the synergistic existence of its large surface area (1999 m2 g-1) and high nitrogen content (14 %) with inherent microporosity. Remarkable cycling stability without noticeable degradation of specific capacitance after 15000 cycles was recorded for CTF-Py-700. This suggests that the nitrogen-functionalized CTFs are going to be a highly demanded electrode material for electrochemical energy storage applications.

Triazine-Based Large-Sized Single-Crystalline Two-Dimensional Covalent Organic Framework for High-Performance Lithium-Ion Batteries

A large-sized single crystalline 2D COFs with excellent crystallinity and stability was prepared through the traditional thermal solvent method. The electrochemical performance can be significantly enhanced using a straightforward hybrid approach that involves in situ growth of the 2D COFs on multi-walled carbon nanotubes (MWCNTs). Both the advantages of COFs and CNTs are mutually enhanced. The single-crystalline feature of the obtained COFs improves the structural integrity and brings excellent chemical and electrochemical stabilities for lithium-ion battery applications. The resultant COF-CNT core-shell hybrids greatly improved the conductivity and demonstrated excellent lithium-ion storage performance with a high capacity of 228 mAh g-1 (0.2 A g-1).

Designing Heterodiatomic Carbon Hydrangea Superstructures via Machine Learning-Regulated Solvent-Precursor Interactions for Superior Zinc Storage

Carbon superstructures with exquisite morphologies and functionalities show appealing prospects in energy realms, but the systematic tailoring of their microstructures remains a perplexing topic. Here, hydrangea-shaped heterodiatomic carbon superstructures (CHS) are designed using a solution phase manufacturing route, wherein machine learning workflow is applied to screen precursor-matched solvent for optimizing solvent-precursor interaction. Based on the established solubility parameter model and molecular growth kinetics simulation, ethanol as the optimal solvent stimulates thermodynamic solubilization and growth of polymeric intermediates to evoke CHS. Featured with surface-active motifs and consecutive charge transfer paths, CHS allows high accessibility of zincophilic sites and fast ion migration with low energy barriers. A anion-cation hybrid charge storage mechanism of CHS cathode is disclosed, which entails physical alternate uptake of Zn2+/CF3SO3 - ions at electroactive sites and chemical bipedal redox of Zn2+ ions with carbonyl/pyridine motifs. Such a beneficial electrochemistry contributes to all-round improvement in Zn-ion storage, involving excellent capacities (231 mAh g-1 at 0.5 A g-1; 132 mAh g-1 at 50 A g-1), high energy density (152 Wh kg-1), and long-lasting cyclability (100 000 cycles). This work expands the design versatilities of superstructure materials and will accelerate experimental procedures during carbon manufacturing through machine learning in the future.

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46 Wh kg-1 at a power density of 1 kW kg-1 and shows excellent cyclic stability of 96% for 10 000 and 90% for 30 000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

Fully Conjugated Covalent Triazine Framework Integrating Hexaazatrinaphthylene Unit as Anode Material for High-Performance Hybrid Lithium-Ion Capacitors

As a high-performance energy storage device consisting of a battery-type anode and a capacitor-type cathode, hybrid lithium-ion capacitors (HLICs) combine the advantages of high energy density of batteries and high power density of capacitors. However, the imbalance in electrochemical kinetics between the battery-type anode and the capacitor-type cathode hinders the further development of HLICs. Fully conjugated covalent organic frameworks have great potential as electrode materials for HLICs due to the designability of their structure. Herein, a fully conjugated covalent triazine framework (PT-CTF) integrating the hexaazatrinaphthylene unit was constructed, which provides abundant active sites (C═N and C═C groups) as the pseudocapacitive anode material for HLICs. And the connection of the triazine unit of PT-CTF improves the molecular conjugate degree, facilitating the transport of electrons. The fabricated PT-CTF||AC HLICs exhibit a high energy density (164.9 Wh kg-1 at 100 mA g-1), large power density (13.1 kW kg-1 at 4 A g-1), and excellent cycling capability (72% after 10 000 cycles at 2 A g-1).

The Development of Metal-Free Porous Organic Polymers for Sustainable Carbon Dioxide Photoreduction

A viable tactic to effectively address the climate crisis is the production of renewable fuels via photocatalytic reactions using solar energy and available resources like carbon dioxide (CO2) and water. Organic polymer material-based photocatalytic materials are thought to be one way to convert solar energy into valuable chemicals and other solar fuels. The use of porous organic polymers (POPs) for CO2 fixation and capture and sequestration to produce beneficial compounds to reduce global warming is still receiving a lot of interest. Visible light-responsive organic photopolymers that are functionally designed and include a large number of heteroatoms and an extended π-conjugation allow for the generation of photogenerated charge carriers, improved absorption of visible light, increased charge separation, and decreased charge recombination during photocatalysis. Due to their rigid structure, high surface area, flexible pore size, permanent porosity, and adaptability of the backbone for the intended purpose, POPs have drawn more and more attention. These qualities have been shown to be highly advantageous for numerous sustainable applications. POPs may be broadly categorized as crystalline or amorphous according to how much long-range order they possess. In terms of performance, conducting POPs outperform inorganic semiconductors and typical organic dyes. They are light-harvesting materials with remarkable optical characteristics, photostability, cheap cost, and low cytotoxicity. Through cocatalyst loading and morphological tweaking, this review presents optimization options for POPs preparation techniques. We provide an analysis of the ways in which the preparative techniques will affect the materials' physicochemical characteristics and, consequently, their catalytic activity. An inventory of experimental methods is provided for characterizing POPs' optical, morphological, electrochemical, and catalytic characteristics. The focus of this review is to thoroughly investigate the photochemistry of these polymeric organic photocatalysts with an emphasis on understanding the processes of internal charge generation and transport within POPs. The review covers several types of amorphous POP materials, including those based on conjugated microporous polymers (CMPs), inherent microporosity polymers, hyper-crosslinked polymers, and porous aromatic frameworks. Additionally, common synthetic approaches for these materials are briefly discussed.

Covalent-Organic Frameworks for Selective and Sensitive Detection of Antibiotics from Water

As the consumption of antibiotics rises, they have generated some negative impacts on organisms and the environment because they are often unable to be effectively degraded, and seeking effective detection methods is currently a challenge. Covalent-organic frameworks (COFs) are new types of crystalline porous crystals created based on the strong covalent interactions between blocked monomers, and COFs demonstrate great potential in the detection of antibiotics from aqueous solutions because of their large surface area, adjustable porosity, recyclability, and predictable structure. This review aims to present state-of-the-art insights into COFs (properties, classification, synthesis methods, and functionalization). The key mechanisms for the detection of antibiotics and the application performance of COFs in the detection of antibiotics from water are also discussed, followed by the challenges and opportunities for COFs in future research.

Characterization of a conjugate between poly(N-vinyl caprolactam) and a triazine-based covalent organic framework as a potential biomaterial

Thermoresponsive polymers (TRPs) have been explored over decades for biomedical applications, and poly(N-vinylcaprolactam) (PVCL) TRP is extensively investigated due to its low toxicity and lower critical solution temperature (LCST), close to physiological temperatures. Besides this, the utilization of covalent organic frameworks (COFs), which belong to a class of porous polymers, in bio-based applications is of great interest due to their remarkable properties. Thus, the integration of PVCL and covalent organic frameworks (COFs) as conjugate materials can lead to advanced bio-based applications; however, the need is to understand the influence of the COF on the PVCL conformation. Herein, a triazine-based COF, CC-TAPT-COF, has been synthesized and completely characterized. Later, the effect of CC-TAPT-COF on the PVCL polymer conformation was studied using various techniques. In fluorescence spectroscopy, a fluorescence quenching for PVCL in the presence of CC-TAPT-COF was observed, which indicated conformational changes. Later, results from thermal fluorescence studies and dynamic light scattering as a function of temperature showed a slight decrease in LCST value for PVCL after the addition of CC-TAPT-COF concentrations. These results showed a slight effect of CC-TAPT-COF on the PVCL conformation. Likewise, a slight decrease in the transmittance value for specific bands in infrared spectra showed a slight effect of CC-TAPT-COF on the PVCL conformation. Further, results from electron microscopy and atomic force microscopy revealed a conjugate formation between PVCL and CC-TAPT-COF due to the presence of binding interactions between them. Overall, the results from several studies showed a slight effect of CC-TAPT-COF on the PVCL during conjugate formation between PVCL and CC-TAPT-COF. This study will be beneficial for the development of COF-thermoresponsive polymer conjugates with a mixture of their unique features as advanced biomaterials.

Flexible Linker-Based Triazine-Functionalized 2D Covalent Organic Frameworks for Supercapacitor and Gas Sorption Applications

Covalent organic frameworks (COFs) having a large surface area, porosity, and substantial amounts of heteroatom content are recognized as the ideal class of materials for energy storage and gas sorption applications. In this work, we have synthesized four different porous COF materials by the polycondensation of a heteroatom-rich flexible triazine-based trialdehyde linker, namely 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (TPT-CHO), with four different triamine linkers. Triamine linkers were chosen based on differences in size, symmetry, planarity, and heteroatom content, leading to the synthesis of four different COF materials named IITR-COF-1, IITR-COF-2, IITR-COF-3, and IITR-COF-4. IITR-COF-1, synthesized within 24 h from the most planar and largest amine monomer, exhibited the largest Brunauer-Emmett-Teller (BET) surface area of 2830 m2 g-1, superior crystallinity, and remarkable reproducibility compared to the other COFs. All of the synthesized COFs were explored for energy and gas storage applications. It is shown that the surface area and redox-active triazene rings in the materials have a profound effect on energy and gas storage enhancement. In a three-electrode setup, IITR-COF-1 achieved an electrochemical stability potential window (ESPW) of 2.0 V, demonstrating a high specific capacitance of 182.6 F g-1 with energy and power densities of 101.5 Wh kg-1 and 298.3 W kg-1, respectively, at a current density of 0.3 A g-1 in 0.5 M K2SO4 (aq) with long-term durability. The symmetric supercapacitor of IITR-COF-1//IITR-COF-1 exhibited a notable specific capacitance of 30.5 F g-1 and an energy density of 17.0 Wh kg-1 at a current density of 0.12 A g-1. At the same time, it demonstrated 111.3% retention of its initial specific capacitance after 10k charge-discharge cycles. Moreover, it exhibited exceptional CO2 capture capacity of 25.90 and 10.10 wt % at 273 and 298 K, respectively, with 2.1 wt % of H2 storage capacity at 77 K and 1 bar.

Rapid Charge Transfer Enabled by Noncovalent Interaction through Guest Insertion in Supercapacitors based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) have been proposed for electrochemical energy storage, although the poor conductivity resulted from covalent bonds limits their practical performance. Here, we propose to introduce noncovalent bonds in COFs through a molecular insertion strategy for improving the conductivity of the COFs as supercapacitor. The synthesized COFs (MI-COFs) establish equilibriums between covalent bonds and noncovalent bonds, which construct a continuous charge transfer channel to enhance the conductivity. The rapid charge transfer rate enables the COFs to activate the redox sites, bringing about excellent electrochemical energy storage behavior. The results show that the MI-COFs exhibit much better performance in specific capacitance and capacity retention rate than those of most COFs-based supercapacitors. Moreover, through simply altering inserted guests, the mode and strength of noncovalent bond can be adjusted to obtain different energy storage characteristics. The introduction of noncovalent bonds is an effective and flexible way to enhance and regulate the properties of COFs, providing a valuable direction for the development of novel COFs-based energy storage materials.

The high-efficiency coupling of a Ni2+ coordinated/uncoordinated pyridine N-COF self-supporting nanofilm as an asymmetric supercapacitor

A large-area COFTAPB-BPY film with a pore size of 3.9 nm was prepared on a gas-liquid interface by the virtue of the limiting and guiding functions of sodium dodecylbenzene sulfonate, followed by modification by Ni2+ ions with the reversible redox reaction of Ni(II/III), where Ni2+ was evidently anchored on the N in BPY. The obtained COFTAPB-BPY and Ni-COFTAPB-BPY nanofilms could avoid the inevitable aggregation and stacking of bulk COFTAPB-BPY, which facilitated a high specific capacitance of 0.26 mF cm-2 for the COFTAPB-BPY nanofilm and 0.38 mF cm-2 for the Ni-COFTAPB-BPY nanofilm at 0.001 mA cm-2. Considering the pseudocapacitance and double-layer capacitance traits of Ni-COFTAPB-BPY and COFTAPB-BPY nanofilms, the asymmetric Ni-COFTAPB-BPY//COFTAPB-BPY film supercapacitor was assembled with a symmetric COFTAPB-BPY//COFTAPB-BPY film device as a control. The asymmetric Ni-COFTAPB-BPY//COFTAPB-BPY film supercapacitor could enhance the energy density of 273.9 mW h cm-3 at 14.09 W cm-3 from 85.2 mW h cm-3 at 4.38 W cm-3 for the symmetric COFTAPB-BPY//COFTAPB-BPY film device. This work provides a new perspective on the application of self-supporting COF nanofilms as film asymmetric supercapacitors.

Recent advances in the utilization of covalent organic frameworks (COFs) as electrode materials for supercapacitors

Due to their excellent stability, ease of modification, high specific surface area, and tunable redox potentials, covalent organic frameworks (COFs) as potential electrodes in supercapacitors (SCs) have raised much research interest because these materials can enable the achievement of high electric double-layer supercapacitance and high pseudocapacitance. Here, the design strategies and SC applications of COF-based electrode materials are summarized. The detailed principles are introduced first, followed by discussions on strategies with diverse examples. The updated advances in design and applications are also discussed. Finally, in the outlook section, we provide some guidelines on the rational design of COF-based electrode materials for high-performance SCs, which we hope will inspire novel concepts for COF-based supercapacitors.

Synthesizing Interpenetrated Triazine-based Covalent Organic Frameworks from CO2

Crystalline triazine-based covalent organic frameworks (COFs) are aromatic nitrogen-rich porous materials. COFs typically show high thermal/chemical stability, and are promising for energy applications, but often require harsh synthesis conditions and suffer from low crystallinity. In this work, we propose an environmentally friendly route for the synthesis of crystalline COFs from CO2 molecules as a precursor. The mass ratio of CO2 conversion into COFs formula unit reaches 46.3 %. The synthesis consists of two steps; preparation of 1,4-piperazinedicarboxaldehyde from CO2 and piperazine, and condensation of the dicarboxaldehyde and melamine to construct the framework. The CO2 -derived COF has a 3-fold interpenetrated structure of 2D layers determined by powder X-ray diffraction, high-resolution transmission electron microscopy, and select-area electron diffraction. The structure shows a high Brunauer-Emmett-Teller surface area of 945 m2  g-1 and high stability against strong acid (6 M HCl), base (6 M NaOH), and boiling water over 24 hours. Post-modification of the framework with oxone has been demonstrated to modulate hydrophilicity, and it exhibits proton conductivity of 2.5×10-2  S cm-1 at 85 °C, 95 % of relative humidity.

Research Progress in Donor-Acceptor Type Covalent Organic Frameworks

Covalent organic frameworks (COFs) are new organic porous materials constructed by covalent bonds, with the advantages of pre-designable topology, adjustable pore size, and abundant active sites. Many research studies have shown that COFs exhibit great potential in gas adsorption, molecular separation, catalysis, drug delivery, energy storage, etc. However, the electrons and holes of intrinsic COF are prone to compounding in transport, and the carrier lifetime is short. The donor-acceptor (D-A) type COFs, which are synthesized by introducing D and A units into the COFs backbone, combine separated electron and hole migration pathway, tunable band gap and optoelectronic properties of D-A type polymers with the unique advantages of COFs and have made great progress in related research in recent years. Here, the synthetic strategies of D-A type COFs are first outlined, including the rational design of linkages and D-A units as well as functionalization approaches. Then the applications of D-A type COFs in catalytic reactions, photothermal therapy, and electronic materials are systematically summarized. In the final section, the current challenges, and new directions for the development of D-A type COFs are presented.

2D Nano Covalent Organic Frameworks – A Porous Polymeric Promising Material Exploring New Prospects of Drug Delivery in Cancer Therapeutics

Cancer is one of the leading causes of death worldwide. Despite there are numerous treatments available for cancer therapy, early detection and efficient treatment with least side effects is still challenging. Covalent organic frameworks (COFs) are emerging crystalline porous polymeric material comprised of light weight atoms like H, B, C, N and O. The Unique characteristics of COFs is its porosity, large surface area and bio‐compatibility which makes them a suitable candidate for potential biomedical applications especially in cancer therapeutics, through targeted drug delivery. This review focused on general introduction of porous materials, history of COFs, an overview on cancer, brief discussion on the various synthetic strategies, dynamic linkages in COFs and potential biomedical application of COFs such as targeted drug delivery, photo thermal therapy (PTT) and photodynamic therapy (PDT). This review aims to provide in‐depth knowledge about COFs and its application in cancer therapeutics.

2D Covalent Organic Frameworks Based on Heteroacene Units

Covalent organic frameworks (COFs) are a unique new class of porous materials that arrange building units into periodic ordered frameworks through strong covalent bonds. Accompanied with structural rigidity and well-defined geometry, heteroacene-based COFs have natural advantages in constructing COFs with high stability and crystallinity. Heteroacene-based COFs usually have high physical and chemical properties, and their extended π-conjugation also leads to relatively low energy gap, effectively promoting π-electron delocalization between network units. Owing to excellent electron-withdrawing or -donating ability, heteroacene units have incomparable advantages in the preparation of donor-acceptor type COFs. Therefore, the physicochemical robust and fully conjugated heteroacene-based COFs solve the problem of traditional COFs lacking π-π interaction and chemical stability. In recent years, significant breakthroughs are made in this field, the choice of various linking modes and building blocks has fundamentally ensured the final applications of COFs. It is of great significance to summarize the heteroacene-based COFs for improving its complexity and controllability. This review first introduces the linkages in heteroacene-based COFs, including reversible and irreversible linkages. Subsequently, some representative building blocks are summarized, and their related applications are especially emphasized. Finally, conclusion and perspectives for future research on heteroacene-based COFs are presented.

Design strategies of covalent organic framework-based electrodes for supercapacitor application

Supercapacitors (SCs) have been recognized as a promising electrochemical energy storage (EES) device, thanks to their high-power density, long lifespan, fast charge-discharge capability, and eco-friendliness. The breakthrough of electrode materials that determine the electrochemical performance of SCs is urgently desired. Covalent organic frameworks (COFs), an emerging and burgeoning class of crystalline porous polymeric materials, have been found to have huge potential for application in EES devices by virtue of their unique properties including atomically adjustable structures, robust and tunable skeletons, well-defined and open channels, high surface areas, etc. In this feature article, we aim at summarizing the design strategies of COF-based electrode materials for SCs based on the representative advances. The current challenges and future perspectives of COFs for SC application are highlighted as well.

Covalent Organic Frameworks: Recent Progress in Biomedical Applications

Covalent organic frameworks (COFs) are a type of crystalline organic porous material with specific features and interesting structures, including porosity, large surface area, and biocompatibility. These features enable COFs to be considered as excellent candidates for applications in various fields. Recently, COFs have been widely demonstrated as promising materials for biomedical applications because of their excellent physicochemical properties and ultrathin structures. In this review, we cover the recent progress of COF materials for applications in photodynamic therapy, gene delivery, photothermal therapy, drug delivery, bioimaging, biosensing, and combined therapies. Moreover, the critical challenges and further perspectives with regards to COFs for future biology-facing applications are also discussed.

Design Hybrid Porous Organic/Inorganic Polymers Containing Polyhedral Oligomeric Silsesquioxane/Pyrene/Anthracene Moieties as a High-Performance Electrode for Supercapacitor

We synthesized two hybrid organic-inorganic porous polymers (HPP) through the Heck reaction of 9,10 dibromoanthracene (A-Br₂) or 1,3,6,8-tetrabromopyrene (P-Br₄)/A-Br₂ as co-monomers with octavinylsilsesquioxane (OVS), in order to afford OVS-A HPP and OVS-P-A HPP, respectively. The chemical structures of these two hybrid porous polymers were validated through FTIR and solid-state ¹³C and ²⁹Si NMR spectroscopy. The thermal stability and porosity of these materials were measured by TGA and N₂ adsorption/desorption analyses, demonstrating that OVS-A HPP has higher thermal stability (T_d10: 579 °C) and surface area (433 m² g^-1) than OVS-P-A HPP (T_d10: 377 °C and 98 m² g^-1) due to its higher cross-linking density. Furthermore, the electrochemical analysis showed that OVS-P-A HPP has a higher specific capacitance (177 F g ^-1 at 0.5 A F g^-1) when compared to OVS-A HPP (120 F g ^-1 at 0.5 A F g^-1). The electron-rich phenyl rings and Faradaic reaction between the π-conjugated network and anthracene moiety may be attributed to their excellent electrochemical performance of OVS-P-A HPP.

Construction of Porous Organic/Inorganic Hybrid Polymers Based on Polyhedral Oligomeric Silsesquioxane for Energy Storage and Hydrogen Production from Water

In this study, we used effective and one-pot Heck coupling reactions under moderate reaction conditions to construct two new hybrid porous polymers (named OVS-P-TPA and OVS-P-F HPPs) with high yield, based on silsesquioxane cage nanoparticles through the reaction of octavinylsilsesquioxane (OVS) with different brominated pyrene (P-Br₄), triphenylamine (TPA-Br₃), and fluorene (F-Br₂) as co-monomer units. The successful syntheses of both OVS-HPPs were tested using various instruments, such as X-ray photoelectron (XPS), solid-state ¹³C NMR, and Fourier transform infrared spectroscopy (FTIR) analyses. All spectroscopic data confirmed the successful incorporation and linkage of P, TPA, and F units into the POSS cage in order to form porous OVS-HPP materials. In addition, the thermogravimetric analysis (TGA) and N₂ adsorption analyses revealed the thermal stabilities of OVS-P-F HPP (T_d10 = 444 °C; char yield: 79 wt%), with a significant specific surface area of 375 m² g^-1 and a large pore volume of 0.69 cm³ g^-1. According to electrochemical three-electrode performance, the OVS-P-F HPP precursor displayed superior capacitances of 292 F g^-1 with a capacity retention of 99.8% compared to OVS-P-TPA HPP material. Interestingly, the OVS-P-TPA HPP showed a promising HER value of 701.9 µmol g^-1 h^-1, which is more than 12 times higher than that of OVS-P-F HPP (56.6 µmol g^-1 h^-1), based on photocatalytic experimental results.

Recent Trends in the Design, Synthesis and Biomedical Applications of Covalent Organic Frameworks

The most recent and advanced class of crystalline and permeable compounds are covalent organic frameworks (COFs). Due to their exceptional qualities, such as their porous structure, high surface area, strong chemical and thermal stabilities, low density, good water stability, luminescent nature, and so on, COFs have seen remarkable growth over the past ten years. COFs have been successfully researched for a number of applications based on these characteristics. The current state of COFs has been reported in this study, with particular attention paid to their design, topology, synthesis, and a variety of biological applications, including drug delivery systems, photodynamic and photothermal therapy, biosensing, bioimaging, etc. Moreover, several miscellaneous applications, such as catalysis, gas storage and separation, photocatalysis, sensors, solar cells, supercapacitors, and 3D printers, have also been explored. It is significant that we have examined current research on COFs with a focus on the biological applications, which are infrequently covered in the literature. Descriptions of the difficulties and prospective outcomes have also been given.

Electrochemical Double-Layer Capacitor based on Carbon@ Covalent Organic Framework Aerogels

High energy demand results in comprehensive research of novel materials for energy sources and storage applications. Covalent organic frameworks (COFs) possess appropriate features such as long-range order, permanent porosity, tunable pore size, and ion diffusion pathways to be competitive electrode materials. Herein, we present a deep electrochemical study of two COF-aerogels shaped into flexible COF-electrodes (ECOFs) by a simple compression method to fabricate an electrochemical double-layer capacitor (EDLC). This energy storage system has considerable interest owing to its high-power density and long cycle life compared with batteries. Our result confirmed the outstanding behavior of ECOFs as EDLC devices with a capacity retention of almost 100 % after 10 000 charge/discharge cycles and, to our knowledge, the highest areal capacitance (9.55 mF cm-2 ) in aqueous electrolytes at higher scan rates (1000 mV s-1 ) for COFs. More importantly, the hierarchical porosity observed in the ECOFs increases ion transport, which permits a fast interface polarization (low τ0 values). The complete sheds light on using ECOFs as novel electrode material to fabricate EDLC devices.

An Ultrastable Porous Polyhedral Oligomeric Silsesquioxane/Tetraphenylthiophene Hybrid as a High-Performance Electrode for Supercapacitors

In this study, we synthesized three hybrid microporous polymers through Heck couplings of octavinylsilsesquioxane (OVS) with 2,5-bis(4-bromophenyl)-1,3,4-oxadiazole (OXD-Br₂), tetrabromothiophene (Th-Br₄), and 2,5-bis(4-bromophenyl)-3,4-diphenylthiophene (TPTh-Br₂), obtaining the porous organic–inorganic polymers (POIPs) POSS-OXD, POSS-Th, and POSS-TPTh, respectively. Fourier transform infrared spectroscopy and solid state ¹³C and ²⁹Si NMR spectroscopy confirmed their chemical structures. Thermogravimetric analysis revealed that, among these three systems, the POSS-Th POIP possessed the highest thermal stability (T₅: 586 °C; T₁₀: 785 °C; char yield: 90 wt%), presumably because of a strongly crosslinked network formed between its OVS and Th moieties. Furthermore, the specific capacity of the POSS-TPTh POIP (354 F g⁻¹) at 0.5 A g⁻¹ was higher than those of the POSS-Th (213 F g⁻¹) and POSS-OXD (119 F g⁻¹) POIPs. We attribute the superior electrochemical properties of the POSS-TPTh POIP to its high surface area and the presence of electron-rich phenyl groups within its structure.

Functionalized luminescent covalent organic frameworks hybrid material as smart nose for the diagnosis of Huanglongbing

Quantitative identification of several volatile organic compounds (VOCs) associated with the same disease provides a strong guarantee of the accurate analysis of the disease. Designing a single luminescent material to interact differently with multiple analytes can generate response patterns with remarkable diversity. Here, a highly green luminescent imine-based 2D COF (TtDFP) is designed and synthesized. TtDFP has ultrasensitive detection performance for trace water in organic solvent. Constructing a ratiometric fluorescence sensor can improve sensitivity for detecting analytes. To contrast the fluorescence signals of Eu³⁺ and COFs in sensing assays, a simple postsynthetic modification (PSM) method is used to introduce Eu³⁺ into TtDFP. The obtained red luminescent hybrid material Eu³⁺@TtDFP EVA film can be a fluorescent nose capable of "sniffing out" and quantifying VOCs (GA and PhA) associated with Huanglongbing (HLB, a devastating disease of citrus) at ppb levels. This work provides a technique of developing functionalized COF hybrid material to facilitate the distinction of various VOCs, which can also be extended to monitor the levels of other VOCs relevant to human health.

Porous organic polymers for high-performance supercapacitors

With the aim of addressing the global warming issue and fossil energy shortage, eco-friendly and sustainable renewable energy technologies are urgently needed. In comparison to energy conversion, studies on energy storage fall behind and remain largely to be explored. By storing energy from electrochemical processes at the electrode surface, supercapacitors (SCs) bridge the performance gap between electrostatic double-layer capacitors and batteries. Organic electrode materials have drawn extensive attention because of their special power density, good round trip efficiency and excellent cycle stability. Porous organic polymers (POPs) have drawn extensive attention as attractive electrode materials in SCs. In this review, we present and discuss recent advancements and design principles of POPs as efficient electrode materials for SCs from the perspectives of synthetic strategies and the structure-performance relationships of POPs. Finally, we put forward the outlook and prospects of POPs for SCs.

A nanostructured covalent organic framework with readily accessible triphenylstibine moieties for high-performance supercapacitors

A pristine, redox-active triphenylstibine based COF (Sb-COF) exhibits well-uniform nanostructures which could provide sufficient electron conduction pathways and minimize the ion transport lengths, making triphenylstibine moieties readily accessible by the electrolyte. The assembled Sb-COF//rGO thus provides an excellent energy density of 69 W h Kg^-1.

Supramolecular Reinforcement of a Large-Pore 2D Covalent Organic Framework

Two-dimensional covalent organic frameworks (2D-COFs) are a class of crystalline porous organic polymers that consist of covalently linked, two-dimensional sheets that can stack together through noncovalent interactions. Here we report the synthesis of a novel COF, called PyCOFamide, which has an experimentally observed pore size that is greater than 6 nm in diameter. This is among the largest pore size reported to date for a 2D-COF. PyCOFamide exhibits permanent porosity and high crystallinity as evidenced by the nitrogen adsorption, powder X-ray diffraction, and high-resolution transmission electron microscopy. We show that the pore size of PyCOFamide is large enough to accommodate fluorescent proteins such as Superfolder green fluorescent protein and mNeonGreen. This work demonstrates the utility of noncovalent structural reinforcement in 2D-COFs to produce larger and persistent pore sizes than previously possible.

Double signal ratiometric electrochemical riboflavin sensor based on macroporous carbon/electroactive thionine-contained covalent organic framework

Riboflavin (RF) is one of the necessary vitamins. If human body lacks RF, it will lead to inflammation and dysfunction of mouth, lips and skin. Thus sensitive and accurate determination of RF is necessary. Here, an electroactive covalent-organic framework nanobelt (COF_TFPB-Thi) with thickness of 1.4 nm was prepared by amine-aldehyde condensation reaction between thionine and 1, 3, 5-tris (p-formylphenyl) benzene, which was then grown vertically on three-dimensional porous carbon derived from kenaf stem (3D-KSC) for double signal ratiometric electrochemical detection of RF. The resulted 3D-KSC/COF_TFPB-Thi showed two reduction peaks at -0.08 V and -0.23 V, which came from the reduction of COF_TFPB-Thi and the conjugated structure of COF_TFPB-Thi, respectively_. In the presence of RF, those RF molecules near the electrode surface were oxidized at 0.6 V. Then some oxidized RF (RF_ox) adsorbed on COF_TFPB-Thi would oxidize COF_TFPB-Thi into COF_TFPB-Thi(ox) while other RF_ox adsorbed on 3D-KSC kept unchanged. When the potential was scanned from 0.6 V to -0.6 V, both COF_TFPB-Thi(ox) and RF_ox adsorbed on 3D-KSC were reduced at -0.08 V and -0.45 V accordingly, while the reduction peak of -0.23 V of the conjugated structure of COF_TFPB-Thi kept constant. When j_-0.45/j_-0.23 was used as the response signal, the detection limit was 44 nM and the linear range was 0.13 μM -0.23 mM. By using j_-0.08/j_-0.23 as the response signal, a detection limit of 90 nM and a linear range of 0.30 μM-0.23 mM (S/N = 3) were obtained. By using double signals, the measurement results can be corrected to make the results more accurate and reliable. The sensor also showed good selectivity, reproducibility and stability, which provided a good application prospects.

Rational design of covalent triazine frameworks based on pore size and heteroatomic toward high performance supercapacitors

A series of covalent triazine frameworks (CTFs) are prepared via ionothermal synthesis for supercapacitors. Due to the feature of adjustable pore structure and rich nitrogen, CTFs with regular structure can be used as a group of model compounds to further investigate the influence of pore size and heteroatom on supercapacitors. By comparing the performance of CTFs with different pore structures and nitrogen contents, the experimental results show that BPY-CTF with high specific surface area of 2278 m² g^-1, mesopores structure, and suitable nitrogen content displays a specific capacitance of 393.6 F g^-1 at 0.5 A g^-1. According to the results and analysis, the existence of mesopores largely enhance the contact area between the electrode material and electrolyte, and then boost the charge transfer. On the other hand, N-doping has a prominent effect on improving the Faradaic pseudo-capacitance and conductivity for CTF electrode materials. This work will inspire further research on the development of highly efficient electrode materials for energy storage devices.

Sono-Cavitation and Nebulization-Based Synthesis of Conjugated Microporous Polymers for Energy Storage Applications

Conjugated microporous polymers (CMPs) are promising energy storage materials owing to their rigid and cross-linked microporous structures. However, the fabrication of nano- and microstructured CMP films for practical applications is currently limited by processing challenges. Herein, we report that combined sono-cavitation and nebulization synthesis (SNS) is an effective method for the synthesis of CMP films from a monomer precursor solution. Using the SNS, the scalable fabrication of microporous and redox-active CMP films can be achieved via the oxidative C-C coupling polymerization of the monomer precursor. Intriguingly, the ultrasonic frequency used during SNS strongly affects the synthesis of the CMP films, resulting in an approximately 30% improvement in reaction yields and ca. 1.3-1.7-times enhanced surface areas (336-542 m²/g) at a high ultrasonic frequency of 180 kHz compared to those at 120 kHz. Furthermore, we prepare highly conductive, three-dimensional porous electrodes [CMP/carbon nanotube (CNT)] by a layer-by-layer sequential deposition of CMP films and CNTs via SNS. Finally, an asymmetric supercapacitor comprising the CMP/CNT cathode and carbon anode shows a high specific capacitance of 477 F/g at 1 A/g with a wide working potential window (0-1.4 V) and robust cycling stability, exhibiting 94.4% retention after 10,000 cycles.