Applications Of Covalent Organic Frameworks Research Articles

Controllable Synthesis of Hollow Microtubular Covalent Organic Frameworks as an Enzyme-Immobilized Platform for Enhancing Catalytic Activity.

Despite great achievement that has been made in the synthesis of covalent organic frameworks (COFs), precise construction of COFs with well-defined nano/microstructures poses a rigorous challenge. Herein, we introduce a simple template-free strategy for controllable synthesis of hollow microtubular COFs. The obtained COFs show a spontaneous morphology transformation from a microfiber to a hollow microtubular structure when the concentrations of catalytic acid are regulated elaborately. Furthermore, the as-prepared COFs exhibit high crystallinity, well-defined hollow tubular morphology, and high surface areas (∼2600 m2/g). Taking the advantages of the unique morphological structure, the hollow microtubular COFs can serve as an ideal host material for enzymes. The resultant biocomposites show high catalytic performance and can be successfully applied to rapid and high-efficiency proteolysis of proteins. This work blazes a trail for controllable synthesis of the hollow microtubular COFs through a template-free process and expands the application of COFs as a promising platform for enzyme immobilization.

Rational Synthesis of Imine-Linked Fluorescent Covalent Organic Frameworks with Different pKa for pH Sensing In Vitro and In Vivo.

Precise modulation of pH in living cells plays a vital role in the study of many diseases, such as cancer and rheumatoid arthritis. Here, a series of imine-linked covalent organic frameworks (COFs) were rationally designed and developed for pH sensing in tumor cells and zebrafish. Four monomers were chosen to synthesize COFs (COF1-COF4) with different pKa by a simple orthogonal combination through condensation reaction. The as-obtained COFs exhibited a sensitive pH-dependent fluorescence response compared to their building blocks. Among them, COF2 possessed a high crystallinity, excellent fluorescence, and suitable pKa for biosensing. For bioimaging applications, COF2 was modified with poly-d-lysine (PDL) to improve its biocompatibility and endocytosis efficiency. After that, PDL-modified COF2 (PDL@COF2) was used as a novel fluorescence probe with a superior linear pH response over the range from 5.0 to 8.0 due to its fully reversible protonation and deprotonation. The fluorescent PDL@COF2 was further employed as a good candidate for pH imaging in tumor cells and zebrafish. The as-constructed environment-sensitive fluorescent COFs have greatly expanded the applications of COFs in the biological area.

Three‐Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols

AbstractWith excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal‐free heterogeneous catalysts. Here, we report two 3D radical‐based COFs (JUC‐565 and JUC‐566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom‐up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal‐free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h−1, which has exceeded other TEMPO‐modified catalytic materials tested under similar conditions. These stable COF‐based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

Controllable synthesis of uniform large-sized spherical covalent organic frameworks for facile sample pretreatment and as naked-eye indicator

The successful application of covalent organic frameworks (COFs) depends on not only their unique chemical structures but also their morphology, size, and architecture. Spherical COFs (SCOFs) are attracted special attention due to the superiority of spherical materials in many applications. However, the synthesis of uniform large-sized SCOFs remains a challenge. Herein, by carefully optimizing the synthesis of a heteropore COF, we find that solvent type and catalyst concentration play important roles in determining the morphology and size of COFs, and eventually achieve the controllable synthesis of large SCOFs with uniform sizes ranging from 200 μm to 5 mm. The obtained SCOFs keep the dual-pore feature of the heteropore COF and show good stability and high crystallinity. To exhibit the superior application potential of SCOFs, the SCOFs with a size range of 200–300 μm were demonstrated to be promising solid-phase extraction (SPE) fillers. As-prepared SCOFs-packed SPE column could effectively remove ≥99% phytochrome matrix from 6 different vegetable samples in 10 s, accompanied by 72.56–112.37% recoveries of 33 chemical hazards with different physicochemical properties, thus showing greatly promising application prospects in sample pretreatment of nontargeted food safety analysis. By utilizing acid/base-adjusted reversible color change, millimeter-sized SCOFs were developed as an easy-to-operate and reusable naked-eye indicator of acids.

Band Gap Engineering in Vinylene-Linked Covalent Organic Frameworks for Enhanced Photocatalytic Degradation of Organic Contaminants and Disinfection of Bacteria.

Photocatalysis is regarded as one of the most promising technologies to remove organic contaminants. At present, most of the covalent organic frameworks (COFs) used as photocatalysts are connected by imine or borate bonds, which have relatively low stability and relatively poor π-delocalization. Herein, we report, for the first time, vinylene-linked COFs constructed by various diacetylene and triazine moieties for photocatalytic degradation of organic contaminants and disinfection of bacteria. The pioneering introduction of diacetylene moieties not only enhances conjugated π-electrons delocalization but also optimizes the electronic band structures that significantly improve photocatalytic activity. Therefore, the vinylene-bridged COFs have excellent photocatalytic activity with ultrahigh stability and great π-electron delocalization, thus exhibiting ultrafast photocatalytic degradation efficiency for phenol and norfloxacin (>96%, within 15 min). Our work provides a strong basis for the rational regulation of the chemical structure of COFs to enhance their photocatalytic activity, thus broadening the application of COFs in photocatalysis.

Imparting multi-functionality to covalent organic framework nanoparticles by the dual-ligand assistant encapsulation strategy

The potential applications of covalent organic frameworks (COFs) can be further developed by encapsulating functional nanoparticles within the frameworks. However, the synthesis of monodispersed core@shell structured COF nanocomposites without agglomeration remains a significant challenge. Herein, we present a versatile dual-ligand assistant strategy for interfacial growth of COFs on the functional nanoparticles with abundant physicochemical properties. Regardless of the composition, geometry or surface properties of the core, the obtained core@shell structured nanocomposites with controllable shell-thickness are very uniform without agglomeration. The derived bowl-shape, yolk@shell, core@satellites@shell nanostructures can also be fabricated delicately. As a promising type of photosensitizer for photodynamic therapy (PDT), the porphyrin-based COFs were grown onto upconversion nanoparticles (UCNPs). With the assistance of the near-infrared (NIR) to visible optical property of UCNPs core and the intrinsic porosity of COF shell, the core@shell nanocomposites can be applied as a nanoplatform for NIR-activated PDT with deep tissue penetration and chemotherapeutic drug delivery.

Controllable Synthesis and Performance Modulation of 2D Covalent-Organic Frameworks.

Covalent-organic frameworks (COFs) are especially interesting and unique as their highly ordered topological structures entirely built from plentiful π-conjugated units through covalent bonds. Arranging tailorable organic building blocks into periodically reticular skeleton bestows predictable lattices and various properties upon COFs in respect of topology diagrams, pore size, properties of channel wall interfaces, etc. Indeed, these peculiar features in terms of crystallinity, conjugation degree, and topology diagrams fundamentally decide the applications of COFs including heterogeneous catalysis, energy conversion, proton conduction, light emission, and optoelectronic devices. Additionally, this research field has attracted widespread attention and is of importance with a major breakthrough in recent year. However, this research field is running with the lack of summaries about tailorable construction of 2D COFs for targeted functionalities. This review first covers some crucial polymeric strategies of preparing COFs, containing boron ester condensation, amine-aldehyde condensation, Knoevenagel condensation, trimerization reaction, Suzuki CC coupling reaction, and hybrid polycondensation. Subsequently, a summary is made of some representative building blocks, and then underlines how the electronic and molecular structures of building blocks can strongly influence the functional performance of COFs. Finally, conclusion and perspectives on 2D COFs for further study are proposed.

Rational Design and Application of Covalent Organic Frameworks for Solar Fuel Production.

Harnessing solar energy and converting it into renewable fuels by chemical processes, such as water splitting and carbon dioxide (CO2) reduction, is a highly promising yet challenging strategy to mitigate the effects arising from the global energy crisis and serious environmental concerns. In recent years, covalent organic framework (COF)-based materials have gained substantial research interest because of their diversified architecture, tunable composition, large surface area, and high thermal and chemical stability. Their tunable band structure and significant light absorption with higher charge separation efficiency of photoinduced carriers make them suitable candidates for photocatalytic applications in hydrogen (H2) generation, CO2 conversion, and various organic transformation reactions. In this article, we describe the recent progress in the topology design and synthesis method of COF-based nanomaterials by elucidating the structure-property correlations for photocatalytic hydrogen generation and CO2 reduction applications. The effect of using various kinds of 2D and 3D COFs and strategies to control the morphology and enhance the photocatalytic activity is also summarized. Finally, the key challenges and perspectives in the field are highlighted for the future development of highly efficient COF-based photocatalysts.

A Perspective on the Application of Covalent Organic Frameworks for Detection and Water Treatment.

Global population growth and water resource scarcity are significant social problems currently being studied by many researchers focusing on finding new materials for water treatment. The aim is to obtain quality water suitable for drinking and industrial consumption. In this sense, an emergent class of crystalline porous materials known as Covalent-Organic Frameworks (COFs) offers a wide range of possibilities since their structures can be designed on demand for specific applications. Indeed, in the last decade, many efforts have been made for their use in water treatment. This perspective article aims to overview the state-of-the-art COFs collecting the most recent results in the field for water detection of pollutants and water treatment. After the introduction, where we overview the classical design strategies on COF design and synthesis for obtaining chemically stable COFs, we summarize the different experimental methodologies used for COFs processing in the form of supported and free-standing membranes and colloids. Finally, we describe the use of COFs in processes involving the detection of pollutants in water and wastewater treatment, such as the capture of organic compounds, heavy metals, and dyes, the degradation of organic pollutants, as well as in desalination processes. Finally, we provide a perspective on the field and the potential technological use of these novel materials.

Elucidating the Aromatic Properties of Covalent Organic Frameworks Surface for Enhanced Polar Solvent Adsorption.

Covalent organic frameworks (COFs) have a distinguished surface as they are mostly made by boron, carbon, nitrogen and oxygen. Many applications of COFs rely on polarity, size, charge, stability and hydrophobicity/hydrophilicity of their surface. In this study, two frequently used COFs sheets, COF-1 and covalent triazine-based frameworks (CTF-1), are studied. In addition, a theoretical porous graphene (TPG) was included for comparison purposes. The three solid sheets were investigated for aromaticity and stability using quantum mechanics calculations and their ability for water and ethanol adsorption using molecular dynamics simulations. COF-1 demonstrated the poorest aromatic character due to the highest energy delocalization interaction between B–O bonding orbital of sigma type and unfilled valence-shell nonbonding of boron. CTF-1 was identified as the least kinetically stable and the most chemically reactive. Both COF-1 and CTF-1 showed good surface properties for selective adsorption of water via hydrogen bonding and electrostatic interactions. Among the three sheets, TPG’s surface was mostly affected by aromatic currents and localized π electrons on the phenyl rings which in turn made it the best platform for selective adsorption of ethanol via van der Waals interactions. These results can serve as guidelines for future studies on solvent adsorption for COFs materials.

Covalent organic frameworks for fluorescent sensing: Recent developments and future challenges

• This review introduces the classification of COFs according to different connection units. • This review analyzes and summarizes the structure and characterization methods of COFs. • The application of COFs in fluorescent sensors is highlighted. • The major challenges and limitations of the application of COFs in fluorescent sensors are further explored. • This review is helpful to expand the wide application of COFs in fluorescent sensors. Covalent-organic frameworks (COFs) is composed of organic units connected by strong covalent bonds. COFs have diverse structure, high porosity, high thermal and mechanical stability and controllable pore, good flexible and highly conjugated crystalline structure. Two-dimensional (2D) COFs nanosheet is similar to graphene, but it has periodic pores and lots of designable functional groups. The 2D COFs nanosheet also has a large specific surface area and good electrical conductivity owing to its highly conjugated crystalline structure. At the same time, COFs have the ability to replicate multiple identical binding sites through the whole extended frameworks. This ability shows that the signal can be effectively transduced and amplified through the framework to achieve high sensitivity when a single binding event occurs at one of the binding sites. Plenty of interesting investigations on the fluorescent sensors based on COFs have been reported through fluorescence enhancement or quenching resulted from this ability. So, the flexible 2D COFs nanosheets should be an excellent candidate to construct fluorescent sensors. This review first introduces the classification of COFs according to different connection units, and then analyzes and summarizes the structure and characterization methods of COFs. The application of COFs in fluorescent sensors is highlighted and the major challenges and limitations are further explored. The review in this paper is helpful to study the wide application of COFs in fluorescent sensors.

Structural Characteristics and Environmental Applications of Covalent Organic Frameworks

Covalent organic frameworks (COFs) are emerging crystalline polymeric materials with highly ordered intrinsic and uniform pores. Their synthesis involves reticular chemistry, which offers the freedom of choosing building precursors from a large bank with distinct geometries and functionalities. The pore sizes of COFs, as well as their geometry and functionalities, can be pre-designed, giving them an immense opportunity in various fields. In this mini-review, we will focus on the use of COFs in the removal of environmentally hazardous metal ions and chemicals through adsorption and separation. The review will introduce basic aspects of COFs and their advantages over other purification materials. Various fabrication strategies of COFs will be introduced in relation to the separation field. Finally, the challenges of COFs and their future perspectives in this field will be briefly outlined.

Unprecedented Application of Covalent Organic Frameworks for Polymerization Catalysis: Rh/TPB-DMTP-COF in Polymerization of Phenylacetylene and Its Functional Derivatives.

Covalent organic frameworks (COFs) are applied widely in organic catalysis; however, no precedent has been reported in polymerization catalysis. Herein, we report the new application of COFs for polymerization catalysis. Different amounts of homogeneous Rh catalyst are incorporated into the COF via post-treatment to give a series of TPB-DMTP-COF-X wt % Rh (b-e) containing varying amounts of Rh from 2.74 to 11.38 wt %. In contrast to the known Rh catalysts, TPB-DMTP-COF-X wt % Rh (b-e) display an uncommon synergistic effect and exceptional steric confinement effect of nanochannels. Therefore, they possess the advantages of both homogeneous catalysts in high activity and selectivity and heterogeneous catalysts in stability and recyclability with extremely high activity up to 1.3 × 107 g·molRh-1·h-1 and cis-selectivity up to 99% and can be readily recycled and reused five times in the polymerization of phenylacetylene and its derivatives, affording cis-transoidal polyphenylacetylene and its derivatives having helical structures, aggregation-induced emission properties, or fluorescence properties with narrow molecular weight distributions.

Edge confined covalent organic framework with efficient biocompatibility and photothermic conversion

Covalent organic frameworks (COFs) that serve as a unique type of two-dimensional materials have demonstrated promising applications in various fields. However, the issue of water insolubility seriously hinders the biological applications of COFs. In this work, we develop an edge confinement route by hydroxylating edges of a COF (CPF-Cu), generating both superior water solubility and nanoscale size, which hence largely promotes the efficient biocompatibility and cell penetrability. The CPF-Cu of which single-layer is free from aggregation demonstrates efficient fluorescence quantum yield (10.3%) by UV light and impressive photothermic conversion efficiency (39.3%) under near infrared light. Thus, this COF is the first time to achieve the integration of ultrafast cell staining and high-performance tumor treatment via photothermic therapy. The outcomes not only pave the way for the biocompatibility of two-dimensional materials by edge-functionalization routes, but also promote the multi-compatible therapeutics based on precisely designed crystalline materials.

Synthesis of Covalent Organic Framework Films at Interfaces

Abstract The diverse topological structure, designable building blocks, ordered pores and crystalline architecture of covalent organic frameworks (COFs) make them attractive in many application fields. However, COF materials obtained by solvothermal synthesis are generally poorly soluble powders and difficult to post-process, which may impede some applications of COFs. The direct preparation of COF films is effective to overcome the limitations of poor solubility of COFs. This article reviews the synthesis of COF films at interfaces and the applications of COF films. At first, the synthesis strategies for preparing monolayer COF with large crystalline domains on solid substrates are introduced. Then we discuss interface synthesis methods, including solid-liquid, liquid-liquid and liquid-gas interface, for various COF films. Subsequently, the applications of COF film in many fields such as photoelectric conversion, fluorescence, electronic devices, chemical sensing, electrocatalysis, and molecular separation are introduced briefly. Finally, prospects for the interface synthesis and application expansion of COF films are discussed.

Covalent Organic Frameworks for Biomedical Applications.

Covalent organic frameworks (COFs) are porous organic polymeric materials that are composed of organic elements and linked together by the thermodynamically stable covalent bonds. The applications of COFs in energy sector and drug delivery are afforded because of the desirable properties of COFs, such as high stability, low density, large surface area, multidimensionality, porosity, and high-ordered crystalline structure expanded. In this review COFs are reviewed, from the perspective of different types of reported COFs, different methods for their synthesis, and their potential applications in the biomedical field. The main goal of this review is to introduce COFs as a biomaterial and to identify specific advantages of different types of COFs that can be exploited for specialized biomedical applications, such as immune engineering.

Recent developments in the photocatalytic applications of covalent organic frameworks: A review

Covalent Organic Frameworks (COFs) are crystalline covalent polymers with a high surface area and stable porosity. The synthesis of COFs has significantly progressed with a very high potential for functionalization . Novel and advanced COF materials have gathered significant interest among researchers in this field due to their wide range of useful applications. Using COFs or COF-linked hybrid materials as photocatalysts is a rapidly developing area of research because they provide an exciting and challenging avenue for researchers to make scientific contributions to the preparation and photochemical application of COFs. In this review, the synthetic approaches and recent advances in the photocatalytic applications of COFs are presented. Various photocatalytic applications of COFs are discussed, including heterogeneous photocatalysis covering the topics of photocatalytic degradation and photocatalysis for organic transformations, carbon dioxide reduction and conversion into valuable materials and hydrogen evolution via water splitting. The maximum calculated quantum yield and space-time yield of 5.23E-03 molecules photon −1 and 5.41E-04 molecules photon −1 mg −1 , respectively, were demonstrated by the 2D porphyrin-based Por-sp 2 c-COF for the selective oxidation of amines to imines under visible light irradiation. Altogether, COF-based materials with diverse functionalities have prospects toward a range of environmental, industrial and commercial applications. • Covalent Organic Frameworks (COFs) as photocatalysts were summarized. • Recent advances in the fabrication of COFs were reviewed. • Performance metrics of the COFs were calculated and compared. • Discussion on existing challenges and future developments was presented.

Stable Dioxin-Linked Metallophthalocyanine Covalent Organic Frameworks (COFs) as Photo-Coupled Electrocatalysts for CO2 Reduction.

In this work, we rationally designed a series of crystalline and stable dioxin-linked metallophthalocyanine covalent organic frameworks (COFs; MPc-TFPN COF, M=Ni, Co, Zn) under the guidance of reticular chemistry. As a novel single-site catalysts (SSCs), NiPc/CoPc-TFPN COF exhibited outstanding activity and selectivity for electrocatalytic CO2 reduction (ECR; Faradaic efficiency of CO (FECO )=99.8(±1.24) %/ 96.1(±1.25) % for NiPc/CoPc-TFPN COF). More importantly, when coupled with light, the FECO and current density (jCO ) were further improved across the applied potential range (-0.6 to -1.2 V vs. RHE) compared to the dark environment for NiPc-TFPN COF (jCO increased from 14.1 to 17.5 A g-1 at -0.9 V; FECO reached up to ca. 100 % at -0.8 to -0.9 V). Furthermore, an in-depth mechanism study was established by density functional theory (DFT) simulation and experimental characterization. For the first time, this work explored the application of COFs as photo-coupled electrocatalysts to improve ECR efficiency, which showed the potential of using light-sensitive COFs in the field of electrocatalysis.

Stable Dioxin‐Linked Metallophthalocyanine Covalent Organic Frameworks (COFs) as Photo‐Coupled Electrocatalysts for CO2Reduction

AbstractIn this work, we rationally designed a series of crystalline and stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs; MPc‐TFPN COF, M=Ni, Co, Zn) under the guidance of reticular chemistry. As a novel single‐site catalysts (SSCs), NiPc/CoPc‐TFPN COF exhibited outstanding activity and selectivity for electrocatalytic CO2reduction (ECR; Faradaic efficiency of CO (FECO)=99.8(±1.24) %/ 96.1(±1.25) % for NiPc/CoPc‐TFPN COF). More importantly, when coupled with light, the FECOand current density (jCO) were further improved across the applied potential range (−0.6 to −1.2 V vs. RHE) compared to the dark environment for NiPc‐TFPN COF (jCOincreased from 14.1 to 17.5 A g−1at −0.9 V; FECOreached up to ca. 100 % at −0.8 to −0.9 V). Furthermore, an in‐depth mechanism study was established by density functional theory (DFT) simulation and experimental characterization. For the first time, this work explored the application of COFs as photo‐coupled electrocatalysts to improve ECR efficiency, which showed the potential of using light‐sensitive COFs in the field of electrocatalysis.

Covalent organic frameworks as robust materials for mitigation of environmental pollutants

Today, one of the main leading global problems is the presence of different pollutants in the environment. These pollutants not only affect human health but also overshadow the life of other creatures. Thus, pollutant treatment has become a challenging issue among the researchers and the scientific community. Different adsorbents and catalysts have been applied to the removal of pollutants. However, the associated limitations like poor chemical and physical stability, low surface area and low binding capacity revived researchers’ attention to exploring alternative materials. Covalent organic frameworks (COFs) are versatile materials created based on the strong covalent interactions between blocked monomers. Unique features, including high specific surface area, high chemical-physical stability and crystallinity render COFs an intriguing sorbent and catalyst in treating pollutants. This review spotlights the applications of COFs as distinguished adsorbents to remove hazardous pollutants from the environment. At first, COFs and their properties as alternative materials were introduced. Then, different synthesis approaches of COFs and their advantages and disadvantages were discussed. Furthermore, the applications of COFs outlined to remove a wide variety of pollutants based on adsorption and degradation. Finally, the prospects of COFs for the treatment of pollutants were evaluated.