COF-based Materials Research Articles

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery.

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Hydroxyl-functionalized ionic liquid-modified covalent organic frameworks for efficient CO2 cycloaddition conversion

Converting CO2 into high-value chemicals is an essential way to mitigate greenhouse impact and realize sustainable utilization of resources. In this work, the COF materials named X-QCOF (X = OH, OCH3) were synthesized by a three-component Povarov reaction, followed by chemical grafting of hydroxyl‑functionalized ionic liquid into the COFs neutral backbone via quaternization to obtain the hybrid materials IL-X-QCOF (X = OH, OCH3). The resultant IL-X-QCOF can efficiently catalyze the cycloaddition reaction of CO2 and epoxides in the absence of metals, additives and solvents. Among them, IL-OH-QCOF exhibits a yield of 97.2% of cyclochloroallyl carbonate with a high turnover frequency (TOF) value of 217.7. The inherent high specific surface area of the COF-based materials promotes mass transfer efficiency, and meanwhile the abundant hydroxyl groups and bromine anions occurring in the backbone create excellent catalytic effect. Attributed to the chemical grafting approach, the product yield keeps over 90% when IL-OH-QCOF is reused for 6 cycles.

Covalent Organic Framework Composites for Catalysis: Opportunities and Challenges

Covalent Organic Frameworks (COFs) on behalf of a novel category of porous substances that show interesting and promising properties in many applications due to their large surface areas, unique physicochemical properties, adjustable porosity, and flexible chemistry. The increasing demand for energy and the harm it does to the environment make the quest for a renewable clean energy source vital. Recently, photocatalysis—which converts solar energy to fuels like hydrogen and hydrocarbons or to degrade environmental contaminants—has emerged as a potential strategy for achieving this goal. In this work, synthesis, structure, and a list of design concepts and topologies are used to examine the opportunities and challenges for enhanced energy technologies employing COF-based materials. It is anticipated to drive the development of existing energy structures, inspire researchers from other fields, and increase the use of covalent organic structures in certain fields.

Advancements in the Research of COF-Based Materials for Uranyl Enrichment

As a critical fuel for nuclear power operations, uranium plays an important role in ensuring the sustainable development of nuclear energy. In China, the demand for uranium resources is expected to reach 1.0-2.0 million tons per year by 2030. Currently, the principal methods employed for the enrichment of uranyl ions include photocatalysis, electrocatalysis, and adsorption. Covalent organic frameworks (COFs) have emerged as a popular choice for uranyl ion enrichment due to their suitable pore size, substantial specific surface area, and exceptional electrical conductivity. This review primarily focuses on the evaluation and characterization methods pertaining to uranyl enrichment, as well as the utilization of COFs-based materials for uranyl enrichment.

Covalently linked MOF@COF direct Z-scheme heterojunction for visible light-driven photocatalytic degradation of flotation agents

It is necessary to find a green, highly efficient and cost-effective way to treat the water pollution caused by flotation agents that are widely used in mineral processing, coal desulfurization and water treatment. Herein, by wrapping an amino group-containing MOF core with a visible light active triazine COF through imine bonds, a covalently linked MOF@COF composite was prepared and found to work as a direct Z-scheme heterojunction photocatalyst for highly efficient visible light-driven degradation of flotation agents. As prepared MOF@COF not only inherits the merits of parent MOF and COF such as large specific surface area, porous framework, good crystallinity, and strong visible light-harvesting capability, but also shows other attractive advantages including robust stability, highly efficient photogenerated electron-hole pair separation and enhanced redox ability due to its covalently linking mode. After carefully selecting the COF content in the composite and optimizing reaction conditions, the resultant MOF@COF composite was successfully used for the photocatalytic degradation and mineralization of flotation agent pollutes in a wide concentration range, giving an apparent rate constant that was 3.2 and 3.5 times higher than those of parent MOF and COF, respectively. In view of systematical characterization and experimental analysis, the underlying reaction mechanism concerning Z-scheme heterojunction was proposed. This work provides a promising way to prepare high-performance photocatalytic materials for the degradation and removal of flotation agent pollutants using inexhaustible solar energy, and to broaden the applications of MOF and COF-based materials.

Tetrazine-Linked Covalent Organic Frameworks With Acid Sensing and Photocatalytic Activity.

The first synthesis and comprehensive characterization of two vinyl tetrazine-linked covalent organic frameworks (COF), TA-COF-1 and TA-COF-2, are reported. These materials exhibit high crystallinity and high specific surface areas of 1323 and 1114 m2 g-1. The COFs demonstrate favorable band positions and narrow band gaps suitable for light-driven applications. These advantages enable TA-COFs to act as reusable metal-free photocatalysts in the arylboronic acids oxidation and light-induced coupling of benzylamines. In addition, these TA-COFs show acid sensing capabilities, exhibiting visible and reversible color changes upon exposure to HClsolution, HCl vapor, and NH3 vapor. Further, the TA-COFs outperform a wide range of previously reported COF photocathodes. The tetrazine linker in the COF skeleton represents a significant advancement in the field of COF synthesis, enhancing the separation efficiency of charge carriers during the photoreaction and contributing to their photocathodic properties. TA-COFs can also degrade 5-nitro-1,2,4-triazol-3-one (NTO), an insensitive explosive present in industrial wastewater, in 20 min in a sunlight-driven photocatalytic process; thus, revealing dual functionality of the protonated TA-COFs as both photodegradation and Brønsted acid catalysts. This pioneering work opens new avenues for harnessing the potential of the tetrazine linker in COF-based materials, facilitating advances in catalysis, sensing, and other related fields.

Recent Advances and Perspectives of Covalent Organic Frameworks for Alkali-Ion Batteries

Covalent organic frameworks (COFs), a novel class of crystalline porous materials constructed by covalent bonds, possess ordered porous structures via thermodynamically controlled polymerization reactions. Because of their structurally diverse, regular pore structures, high surface area, and thermal stability can be functionally tailored through different synthetic methods to meet the needs of various applications including for secondary batteries. This review summarized recent efforts that have been devoted to designing and synthesizing COF-based materials for battery applications, including electrode materials, electrolytes, and separators. Unique characteristics of COFs allow for the rational design of targeted functions, suppression of side reactions, and promotion of ion transport for batteries. This review clarified recent research progress on COF materials for lithium-ion batteries, lithium–sulfur batteries, sodium-ion batteries, potassium-ion batteries and so on. This review pointed out the structure and chemical properties of COFs, as well as new strategies to improve battery performance. Furthermore, we concluded the major challenges and future trends of COF materials in electrochemical applications. It is hoped that this review will provide meaningful guidance for the development of COFs for alkali-ion batteries.

Heterointerface regulation of covalent organic framework-anchored graphene via a solvent-free strategy for high-performance supercapacitor and hybrid capacitive deionization electrodes.

Covalent organic frameworks (COFs) with customizable geometry and redox centers are an ideal candidate for supercapacitors and hybrid capacitive deionization (HCDI). However, their poor intrinsic conductivity and micropore-dominated pore structures severely impair their electrochemical performance, and the synthesis process using organic solvents brings serious environmental and cost issues. Herein, a 2D redox-active pyrazine-based COF (BAHC-COF) was anchored on the surface of graphene in a solvent-free strategy for heterointerface regulation. The as-prepared BAHC-COF/graphene (BAHCGO) nanohybrid materials possess high-speed charge transport offered by the graphene carrier and accelerated electrolyte ion migration within the BAHC-COF, allowing ions to effectively occupy ion storage sites inside BAHC. As a result, the BAHCGO//activated carbon asymmetric supercapacitor achieves a high energy output of 61.2 W h kg-1 and a satisfactory long-term cycling life. More importantly, BAHCGO-based HCDI possesses a high salt adsorption capacity (SAC) of 67.5 mg g-1 and excellent long-term desalination/regeneration stability. This work accelerates the application of COF-based materials in the fields of energy storage and water treatment.

Recent Progress of Covalent Organic Frameworks-Based Materials in Photocatalytic Applications: A Review.

Covalent organic frameworks (COFs) are one type of porous organic materials linked by covalent bonds. COFs materials exhibit many outstanding characteristics such as high porosity, high chemical and thermal stability, large specific surface area, efficient electron transfer efficiency, and the ability for predesigned structures. These exceptional advantages enable COFs materials to exhibit remarkable performance in photocatalysis. Additionally, the activity of COFs materials as photocatalysts can be significantly upgraded by ion doping and the formation of heterojunctions. This paper summarizes the latest research progress on COF-based materials applied in photocatalytic systems. Initially, typical structures and preparation methods of COFs are analyzed and compared. Moreover, theessential principles of photocatalytic reactions over COFs-based materials and the latest research developments in photocatalytic hydrogen production, CO2 reduction, pollutants elimination, organic transformation, and overall water splitting are indicated. At last, the outlook and challenges of COF-based materials in photocatalysis are discussed. This review is intended to permit instructive guidance for the efficient use of photocatalysis based on COFs in the future.

BODIPY doping of covalent organic frameworks-based nanomaterials: A novel strategy towards biomedical applications

Covalent organic Frameworks (COFs) are a class of crystalline macromolecular materials build-up by monomers with specific symmetries or functionalities. There are important limitations in the synthesis of highly ordered COFs, such as the shape and packing of the building blocks. Thus, the presence of fluorine atoms that lie perpendicular to the bisecting plane of BODIPY derivatives together with the presence of four bulky methyl groups could hinder the crystallization process in COF synthesis. For that reason, BODIPY-based COFs are rarely incorporated to COF networks. In this work, following the mixed linker strategy, a pre-synthetic method to dope COF structures with BODIPY units was developed. The materials have been processed into fluorescent Covalent Organic Nanosheets (CONs) with defined particle-size distributions around 100 nm, suitable for cellular biomedical applications. The viability of the CONs was evaluated using Sk-Mel-103 cells, demonstrating the internalization showing 100% cell viability. We envisage that this work could accelerate the discovery of new COF-based materials for biomedical sciences.

Monolithic Covalent Organic Frameworks with Hierarchical Architecture: Attractive Platform for Contaminant Remediation

The insolubility in solvents and poor processability of powder covalent organic frameworks (COFs) considerably impede their practical application. To address these issues and bridge the gap between powder COFs and their practical application, the construction of monolithic COFs has emerged as a feasible and effective solution. Monolithic COFs (i.e., macroscopic three-dimensional architectures) with hierarchical structures have attracted tremendous interest for environmental remediation and exhibited good contaminant removal performances owing to their wide distribution of pore sizes ranging from micropores to macropores, large specific surface area, tailored chemical components, and excellent chemical stability. Monolithic COFs can be either pure COFs with self-supporting structures or composites of COFs with other materials. The resulting COF-based monoliths inherit the merits of the parent powder COFs (such as tunable pore size, tailored structure, and super chemical/thermal stability) and the intriguing features of monolithic materials, such as hierarchical structure, high porosity, and easy handling, endowing them with fast mass transfer and high adsorption capacity. This review provides a comprehensive summary of the recent advances in the synthesis of monolithic COF materials. Additionally, the recent progress of their application in environmental remediation is summarized, including metal-ion removal, organic-pollutant capture, and oil–water separation. Furthermore, this review discusses the current challenges and provides future perspectives. We sincerely hope that it will contribute to the further development of COF-based materials in other fields, especially environmental remediation.

Pyrazine-Functionalized Donor-Acceptor Covalent Organic Frameworks for Enhanced Photocatalytic H2 Evolution with High Proton Transport.

The well-defined 2D or 3D structure of covalent organic frameworks (COFs) makes it have great potential in photoelectric conversion and ions conduction fields. Herein, a new donor-accepter (D-A) COF material, named PyPz-COF, constructed from electron donor 4,4',4″,4'″-(pyrene-1,3,6,8-tetrayl)tetraaniline and electron accepter 4,4'-(pyrazine-2,5-diyl)dibenzaldehyde with an ordered and stable π-conjugated structure is reported. Interestingly, the introduction of pyrazine ring endows the PyPz-COF a distinct optical, electrochemical, charge-transfer properties, and also brings plentiful CN groups that enrich the proton by hydrogen bonds to enhance the photocatalysis performance. Thus, PyPz-COF exhibits a significantly improved photocatalytic hydrogen generation performance up to 7542µmol g-1 h-1 with Pt as cocatalyst, also in clear contrast to that of PyTp-COF without pyrazine introduction (1714µmol g-1 h-1 ). Moreover, the abundant nitrogen sites of the pyrazine ring and the well-defined 1D nanochannels enable the as-prepared COFs to immobilize H3 PO4 proton carriers in COFs through hydrogen bond confinement. The resulting material has an impressive proton conduction up to 8.10 × 10-2 S cm-1 at 353 K, 98% RH. This work will inspire the design and synthesis of COF-based materials with both efficient photocatalysis and proton conduction performance in the future.

Environmental impact analysis of surface printing and 3D inkjet printing applications using an imine based covalent organic framework: A life cycle assessment study

Covalent organic frameworks (COFs) are emerging materials with structural modularity that allows their application in many fields. The aim of this work is to determine the environmental impact of using an imine based covalent organic framework (RT-COF-1) for both surface printing (Case A) and 3D inkjet printing (Case B) by applying Life Cycle Assessment (LCA) methodology. Experimental data on RT-COF-1 synthesis as well as results obtained by simulation of their precursors production, 1,3,5-tris-(4-aminophenyl) benzene (TAPB) and 1,3,5-benzenetricarbaldehyde (BTCA), are used. LCA results show that monomer synthesis is the most important contributor to environmental impacts in both case studies. On the other hand, the contribution of solvents used in Case A is also remarkable. The comparison between both case studies indicates that the environmental impacts of Case B is lower than that of Case A (reduction within 5%–65%). Finally, LCA results of Case B are compared to other materials used for 3D-printing, such as polymerizable ionic liquids (PILs). The results show that RT–COF–1 compares favourably with PILs in five of nine impact categories, being especially relevant the reductions achieved in the abiotic depletion and acidification potential (>90%), in the primary energy consumption (⁓35%) and carbon footprint (⁓50%), suggesting the potential of RT–COF–1 as 3D-printing material from an environmental perspective. This work is a first step for further research to highlight the main environmental burdens of using COF-based materials in this application.

Three-Dimensional Covalent Organic Frameworks with Ultra-Large Pores for Highly Efficient Photocatalysis.

Benefiting from their unique structural merits, three-dimensional (3D) large-pore COF materials demonstrate high surface areas and interconnected large channels, which makes these materials promising in practical applications. Unfortunately, functionalization strategies and application research are still absent in these structures. To this end, a series of functional 3D stp-topologized COFs are designed based on porphyrin or metalloporphyrin moieties, named JUC-640-M (M = Co, Ni, or H). Interestingly, JUC-640-H exhibits a record-breaking low crystal density (0.106 cm3 g-1) among all crystalline materials, along with the largest interconnected pore size (4.6 nm) in 3D COFs, high surface area (2204 m2 g-1), and abundant exposed porphyrin moieties (0.845 mmol g-1). Inspired by the unique structural characteristics and photoelectrical performance, JUC-640-Co is utilized for the photoreduction of CO2 to CO and demonstrates a high CO production rate (15.1 mmol g-1 h-1), selectivity (94.4%), and stability. It should be noted that the CO production rate of JUC-640-Co has exceeded those of all reported COF-based materials. This work not only produces a series of novel 3D COFs with large channels but also provides a new guidance for the functionalization and applications of COFs.

In situ utilization of photogenerated hydrogen for hydrogenation reaction over a covalent organic framework.

A fully sp2-carbon conjugated COF (Py-FTP-COF) was designed and synthesized, exhibiting excellent hydrogen evolution rate of 5.22 mmol g-1 h-1. More importantly, in situ hydrogenation of nitroarenes under visible-light irradiation without any additional hydrogen source was successfully accomplished for the first time over COF-based materials.

Acrylate-functionalized porphyrin-covalent organic framework for bacterial-targeted and reaction-enhanced synergistic phototherapy/chemotherapy toward sterilization and wound healing.

Porphyrinic covalent organic frameworks (COFs) have emerged as prospective materials in photodynamic and photothermal sterilization. However, it is still a great challenge to construct an efficient COF-based sterilizing agent with good photothermal and photodynamic properties and bacterial targeting ability. Herein, we report a multifunctional porphyrin-COF for bacterial-targeted and reaction-enhanced synergistic phototherapy/chemotherapy for sterilization and wound healing. The ordered crystal structure of the porphyrin-COF not only effectively avoids the self-aggregation-induced quenching of the porphyrin monomer, but also facilitates the storage and transport of singlet oxygen. The acrylate substituent in the other monomer serves as a bacterial targeting moiety and the in situ reaction site with the sulfhydryl group of the bacterial surface protein via a Michael addition reaction, thus fixing the bacteria on the surface of COF and making them lose the colonization ability. Furthermore, the bonding of COF and bacteria further amplifies the therapeutic efficiency of phototherapy. Therefore, the developed multifunctional sterilization platform not only provides a new strategy for the design of novel bactericidal materials but also broadens the biological applications of COF-based materials.

Biosensor Based on Covalent Organic Framework Immobilized Acetylcholinesterase for Ratiometric Detection of Carbaryl.

A ratiometric electrochemical biosensor based on a covalent organic framework (COFThi-TFPB) loaded with acetylcholinesterase (AChE) was developed. First, an electroactive COFThi-TFPB with a two-dimensional sheet structure, positive charge and a pair of inert redox peaks was synthesized via a dehydration condensation reaction between positively charged thionine (Thi) and 1,3,5-triformylphenylbenzene (TFPB). The immobilization of AChE on the positively charged electrode surface was beneficial for maintaining its bioactivity and achieving the best catalytic effect; therefore, the positively charged COFThi-TFPB was an appropriate support material for AChE. Furthermore, the COFThi-TFPB provided a stable internal reference signal for the constructed AChE inhibition-based electrochemical biosensor to eliminate various effects which were unrelated to the detection of carbaryl. The sensor had a linear range of 2.2–60 μM with a detection limit of 0.22 μM, and exhibited satisfactory reproducibility, stability and anti-interference ability for the detection of carbaryl. This work offers a possibility for the application of COF-based materials in the detection of low-level pesticide residues.

Recent progress on covalent organic framework materials as CO2 reduction electrocatalysts.

CO2 emission caused by fuel combustion and human activity has caused severe climate change and other subsequent pollutions around the world. Carbon neutralization via various novel technologies to alleviate the CO2 level in the atmosphere has thus become one of the major topics in modern research field. These advanced technologies cover CO2 capture, storage and conversion, etc., and electrocatalytic CO2 reduction reaction (CO2RR) by heterogeneous catalysts is among the most promising methods since it could utilize renewable energy and generate valuable fuels and chemicals. Covalent organic frameworks (COFs) represent crystalline organic polymers with highly rigid, conjugated structures and tunable porosity, which exhibit significant potential as heterogeneous electrocatalysts for CO2RR. This review briefly introduces related pioneering works in COF-based materials for electrocatalytic CO2RR in recent years and provides a basis for future design and synthesis of highly active and selective COF-based electrocatalysts in this direction.

Taming of Organic Pollutants Using Cof-Based Materials: Challenges and Future Prospects

Taming of Organic Pollutants Using Cof-Based Materials: Challenges and Future Prospects

2D and 3D Covalent Organic Frameworks: Cutting-Edge Applications in Biomedical Sciences.

Covalent organic frameworks (COFs) are crystalline porous organic structures with two- or three-dimensional (2D or 3D) features and composed of building blocks being connected via covalent bonds. The manifold applications of COFs in optoelectronic devices, energy conversion and storage, adsorption, separation, sensing, organocatalysis, photocatalysis, electrocatalytic reactions, and biomedicine are increasing because of their notable intrinsic features such as large surface area, porosity, designable structure, low density, crystallinity, biocompatibility, and high chemical stability. These properties have rendered 2D and 3D COF-based materials as desirable entities for drug delivery, gene delivery, photothermal therapy, photodynamic therapy, combination therapy, biosensing, bioimaging, and anticancer activities. Herein, different reactions and methods for the synthesis of 2D and 3D COFs are reviewed with special emphasis on the construction and state-of-the-art progress pertaining to the biomedical applications of 2D and 3D COFs of varying shapes, sizes, and structures. Specifically, stimuli-responsive COFs-based systems and targeted drug delivery approaches are summarized.