Synthesis Of Covalent Organic Frameworks Research Articles

Triptycene Based 3D Covalent Organic Frameworks (COFs)—An Emerging Class of 3D Structures

Covalent Organic Frameworks (COFs) are a newly emerged class of porous materials consisting of organic building blocks linked by strong covalent bonds. The physical and chemical properties of COFs, i.e., modularity, porosity, well-developed specific surface area, crystallinity, and chemical-thermal stability, make them a good application material, especially in the aspects of adsorption and gas separation. The organic compositions of their building blocks also render them with biocompatible properties; therefore, they also have potential in biomedical applications. Depending on the symmetry of the building blocks, COF materials form two-dimensional (2D COF) or three-dimensional (3D COF) crystal structures. 3D COF structures have a higher specific surface area, they are much lighter due to their low density, and they have a larger volume than 2D COF crystals, but, unlike the latter, 3D COF crystals are less frequently obtained and studied. Selecting and obtaining suitable building blocks to form a stable 3D COF crystal structure is challenging and therefore of interest to the chemical community. Triptycene, due to its 3D structure, is a versatile building block for the synthesis of 3D COFs. Polymeric materials containing triptycene fragments show good thermal stability parameters and have a very well-developed surface area. They often tend to be characterized by more than one type of porosity and exhibit impressive gas adsorption properties. The introduction of a triptycene backbone into the structure of 3D COFs is a relatively new procedure, the results of which only began to be published in 2020. Triptycene-based 3D COFs show interesting physicochemical properties, i.e., high physical stability and high specific surface area. In addition, they have variable porosities with different pore diameters, capable of adsorbing both gases and large biological molecules. These promising parameters, guaranteed by the addition of a triptycene backbone to the 3D structure of COFs, may create new opportunities for the application of such materials in many industrial and biomedical areas. This review aims to draw attention to the symmetry of the building blocks used for COF synthesis. In particular, we discussed triptycene as a building block for the synthesis of 3D COFs and we present the latest results in this area.

Covalent assembly synthesis of covalent organic framework and MXene based composite for the adsorption of fluoroquinolones

Widespread use of fluoroquinolones (FQs) leads to its continuous excretion and release into the environment, resulting in the accumulation in water, animal-derived food etc., and posing a threat to environment and humans. Thus, the development of highly efficient FQs removal methods is of great significance. Herein, a composite (COF@MXene) was manufactured using a covalent assembly synthesis strategy by connecting covalent organic frameworks (COF) and NH2-MXene through a Schiff-base reaction. COF@MXene had the advantages of both COF and MXene, not only had good crystallinity, thermal stability and rich functional group properties, but also had high protein exclusion ability (Exclusion efficiency>97%) and good adsorption capacities for FQs including ciprofloxacin (CIP), lomefloxacin (LOM), moxifloxacin (MOX), gatifloxacin (GAT) and levofloxacin (LEV). The maximal adsorption capacities for them ranged from 54.63 to 147.91 mg·g−1, which were higher than those of COF (15.99–64.06 mg·g−1) and MXene (27.58–33.92 mg·g−1). The adsorption experimental data of adsorption isotherm and kinetics separately followed the Langmuir and pseudo-second-order models. Through density functional theory (DFT), Forcite calculation, UV-Vis and XPS analyses, pore size selectivity, electrostatic and hydrogen bond interactions were determined as the main driving forces for FQs adsorption. Finally, COF@MXene coupled with HPLC-DAD was employed for the analysis of FQs from water, egg and drug samples, and the recoveries were satisfactory. This work reported a covalent assembly synthesis strategy for the preparation of COF@MXene composite for FQs removal. This approach may establish a viable route for gentle fabrication of COF and MXene based composites for various applications.

Synthesis of Covalent Organic Framework (COF) Films Using Vapor Deposition Polymerization

Synthesis of Covalent Organic Framework (COF) Films Using Vapor Deposition Polymerization

Cyclodextrin Incorporation into Covalent Organic Frameworks Enables Extensive Liquid and Gas Chromatographic Enantioseparations.

The separation of enantiomers using high-performance chromatography technologies represents great importance and interest. In this aspect, β-cyclodextrin (β-CD) and its derivatives have been extensively studied as chiral stationary phases (CSPs). Nevertheless, β-CD that was immobilized on a traditional matrix often exhibited low stabilities and limited operating ranges. Recently, covalent organic frameworks (COFs) with highly ordered nanopores are emerging as promising CSPs for enantioseparations, but their practical applications are still hampered by the difficulty of monomer and COF synthesis. Herein, two β-CD-driven COFs are synthesized via a fast and facile plasma-induced polymerization combined postsynthesis modification strategy. The precisely defined COF channels enhanced the accessibility of the accommodated β-CD to the analytes and acted as robust protective barriers to safeguard the β-CD from harsh environments. Therefore, the β-CD-modified COFs can be potentially general CSPs for extensive enantioseparation in both gas chromatography and high-performance liquid chromatography, and a wide range of racemates were separated. Compared to the commonly employed commercial chiral columns, these COF-based columns exhibited comparable resolution capability and superior application versatility. This work integrates the advantages and overcomes the defects of COFs and β-CD, thus advancing COFs as platforms for chiral selector modification and giving great promise for practical chromatographic enantioseparation.

Gradually Tuning the Flexibility of Two‐Dimensional Covalent Organic Frameworks via Stepwise Structural Transformation and Their Flexibility‐Dependent Properties

AbstractFlexible covalent organic frameworks (COFs) are intriguing for their dynamic properties distinctive from rigid counterparts but still suffer from limited accessibility. Especially, controlling flexibility of COFs is challenging and the impact of different flexibility on properties of COFs has rarely been unveiled. This article reports stepwise adjustment on flexibility of two‐dimensional COFs, which is realized by the designed synthesis of rigid COF (R‐COF), semi‐flexible COF (SF‐COF), and flexible COF (F‐COF) through polymerization, linker exchange, and linkage conversion with a newly developed method for reduction of hydrazone, respectively. Significant difference in breathing behavior and self‐adaptive capability of the three COFs are uncovered through vapor response and iodine capture experiments. Gas sorption experiments indicate that the porosity of F‐COF could switch from “close” state in nitrogen to “open” state in carbon dioxide, which are not observed for R‐COF and SF‐COF. This study not only develops a strategy to adjust the flexibility of COFs by tuning their linkers and linkages, but also provides a deep insight into the impact of different flexibility on properties of COFs, which lays a foundation for the development of this new class of dynamic porous materials.

Gradually Tuning the Flexibility of Two-Dimensional Covalent Organic Frameworks via Stepwise Structural Transformation and Their Flexibility-Dependent Properties.

Flexible covalent organic frameworks (COFs) are intriguing for their dynamic properties distinctive from rigid counterparts but still suffer from limited accessibility. Especially, controlling flexibility of COFs is challenging and the impact of different flexibility on properties of COFs has rarely been unveiled. This article reports stepwise adjustment on flexibility of two-dimensional COFs, which is realized by the designed synthesis of rigid COF (R-COF), semi-flexible COF (SF-COF), and flexible COF (F-COF) through polymerization, linker exchange, and linkage conversion with a newly developed method for reduction of hydrazone, respectively. Significant difference in breathing behavior and self-adaptive capability of the three COFs are uncovered through vapor response and iodine capture experiments. Gas sorption experiments indicate that the porosity of F-COF could switch from "close" state in nitrogen to "open" state in carbon dioxide, which are not observed for R-COF and SF-COF. This study not only develops a strategy to adjust the flexibility of COFs by tuning their linkers and linkages, but also provides a deep insight into the impact of different flexibility on properties of COFs, which lays a foundation for the development of this new class of dynamic porous materials.

Thermal Conductivity of Covalent-Organic Frameworks.

Covalent-organic frameworks (COFs) are a highly promising class of materials that can provide an excellent platform for thermal management applications. In this Perspective, we first review previous works on the thermal conductivities of COFs. Then we share our insights on achieving high, low, and switchable thermal conductivities of future COFs. To obtain the desired thermal conductivity, a comprehensive understanding of their thermal transport mechanisms is necessary but lacking. We discuss current limitations in atomistic simulations, synthesis, and thermal conductivity measurements of COFs and share potential pathways to overcoming these challenges. We hope to stimulate collective, interdisciplinary efforts to study the thermal conductivity of COFs and enable their wide range of thermal applications.

Catalytic oxidative desulfurization of thio-compounds by employing χ-Anderson-type polyoxometalates-porphyrin covalent organic framework (COF)

Severe environmental sulfur contents due to the consumption of fuels in automobiles and industries resulted in serious health hazards and pollution because of it, desulfurization of diesel become inevitable. Targeting the profound desulfurization of diesel, we performed experiments to deeply desulphurized the thio-compounds by catalytic-oxidative desulfurization technique. We synthesized new metalloporphyrin (C52H36N4O8Sn)4MeO-SnPor which after conversion into (C64H64N8O16Sn)4Tris-SnTP leading towards the synthesis of covalent organic framework [(N(C4H9)4]12[HNC(CH2O)3]4[(CO)4C44H24N4Sn] [NiMo6O18]4(SnTP@NiAdCOF). SnTP@NiAd COF showed the outstanding catalytic property for deep desulfurization of thio-compounds above than 96% of thiobenzoic acid (TB) and 99% of 2-aminothiophenol (2-ATP) sulfur contents were oxides after 100 min of reaction using H2O2 as an oxidant at room temperature with constant stirring. During desulfurization percentage desulfurization efficiency was checked for different time intervals by TLC and further confirmed by reverse phase high-performance liquid chromatography (RP-HPLC). Reverse-phase high-performance liquid chromatograms indicated that the peak area and peak height of thio-compounds decrease gradually with the passage of reaction time which confirmed the removal of thio-compounds from the reaction mixture. Sulfur contents removed up to 5 ppmw showed excellent catalytic characteristics of synthesized SnTP@NiAdCOF. The exceptional catalytic efficiency of prepared catalyst SnTP@NiAdCOF was because of the existence of active oxidizing centers of χ-NiAd and metalloporphyrin that are MoO and [(Por)SnII], respectively. The potential mechanism appeared to be the formation of Mo(O2) and [(Por)SnII–OOH] from MoO and [(Por)SnII], respectively that act as active oxidizing centers and efficiently converted the thio-group into oxides and sulfones. Effective removal of sulfur grants the desulfurization of fuels by using SnTP@NiAdCOF catalyst to lessen the energy expenditure and also to enhance the production of environmentally-safe fuels.

Large-Scale Synthesis of Covalent Organic Frameworks: Challenges and Opportunities.

Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the diversity of dynamic linkages and topologies, COFs have emerged as a novel field of organic materials that propose a platform for tailor-made complex structural design. Progress over the past two decades in the design, synthesis, and functional exploration of COFs in diverse applications successively established these frameworks in materials chemistry. The large-scale synthesis of COFs with uniform structures and properties is of profound importance for commercialization and industrial applications; however, this is in its infancy at present. An innovative designing and synthetic approaches have paved novel ways to address future hurdles. This review article highlights the fundamental of COFs, including designing principles, coupling reactions, topologies, structural diversity, synthetic strategies, characterization, growth mechanism, and activation aspects of COFs. Finally, the major challenges and future trends for large-scale COF fabrication are outlined.

Precision Covalent Organic Frameworks for Surface Nucleation Control.

Unwanted accumulation of ice and lime scale crystals on surfaces is a long-standing challenge with major economic and sustainability implications. Passive inhibition of icing and scaling by liquid-repellent surfaces are often inadequate, susceptible to surface failure under harsh conditions, and unsuitable for long-term/real-life usages. Such surfaces often require a multiplicity of additional features such as optical transparency, robust impact resistance, and ability to prevent contamination from low surface energy liquids. Unfortunately, most promising advances have relied on using perfluoro compounds, which are bio-persistent and/or highly toxic. Here it isshown that organic, reticular mesoporous structures, covalent organic frameworks (COFs), may offer a solution. By exploiting simple and scalable synthesis of defect-free COFs and rational post-synthetic functionalization, nanocoatings with precision nanoporosity (morphology) are prepared that can inhibit nucleation at the molecular level without compromising the related contamination prevention and robustness. The results offer a simple strategy to exploit the nanoconfinement effect, which remarkably delays the nucleation of ice and scale formation on surfaces. Ice nucleation is suppressed down to -28°C, scale formation is avoided for >2weeks in supersaturated conditions, and jets of organic solvents impacting at Weber numbers >105 are resisted with surfaces that also offer optical transparency (>92%).

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.

Interfacial synthesis of covalent organic framework composited woods for ultrafast ion conduction

Interfacial synthesis of covalent organic framework composited woods for ultrafast ion conduction

Post-synthetic modification of covalent organic frameworks for CO2 electroreduction

To achieve high-efficiency catalysts for CO2 reduction reaction, various catalytic metal centres and linker molecules have been assembled into covalent organic frameworks. The amine-linkages enhance the binding ability of CO2 molecules, and the ionic frameworks enable to improve the electronic conductivity and the charge transfer along the frameworks. However, directly synthesis of covalent organic frameworks with amine-linkages and ionic frameworks is hardly achieved due to the electrostatic repulsion and predicament for the strength of the linkage. Herein, we demonstrate covalent organic frameworks for CO2 reduction reaction by modulating the linkers and linkages of the template covalent organic framework to build the correlation between the catalytic performance and the structures of covalent organic frameworks. Through the double modifications, the CO2 binding ability and the electronic states are well tuned, resulting in controllable activity and selectivity for CO2 reduction reaction. Notably, the dual-functional covalent organic framework achieves high selectivity with a maximum CO Faradaic efficiency of 97.32% and the turnover frequencies value of 9922.68 h−1, which are higher than those of the base covalent organic framework and the single-modified covalent organic frameworks. Moreover, the theoretical calculations further reveal that the higher activity is attributed to the easier formation of immediate *CO from COOH*. This study provides insights into developing covalent organic frameworks for CO2 reduction reaction.

Efficient food safety analysis for vegetables by a heteropore covalent organic framework derived silicone tube with flow-through purification

A heteropore covalent organic framework incorporated silicone tube (S-tube@PDA@COF) was used as adsorbent to purify the matrices in vegetable extracts. The S-tube@PDA@COF was fabricated by a facile in-situ growth method and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and N2 adsorption-desorption. The as-prepared composite exhibited high removal efficiency of phytochromes and recovery (81.13–116.62%) of 15 chemical hazards from 5 representative vegetable samples. This study opens a promising avenue toward the facile synthesis of covalent organic frameworks (COFs)-derived silicone tubes for streamline operation in food sample pretreatment.

Regioselective One-Step Cyclization and Aromatization towards Directly Amino-Functionalized Covalent Organic Framework with Stable Benzodiimidazole Linkage.

The compatibility of crystallinity, stability, and functionality in covalent organic frameworks (COFs) is challenging but significant in reticular chemistry and materials science. Herein, it is presented for the first time a strategy to synthesize directly amino-functionalized COF with stable benzodiimidazole linkage by regioselective one-step cyclization and aromatization. Bandrowski's base with two types of amino groups is used as a unique monomer, providing not only construction sites for the material framework through specific region-selective reaction, but also amino active sites for functionality, which is usually difficult to achieve directly in COF synthesis because amino groups are the participants in COF bonding. In addition, the aromatic benzodiimidazole rings and the large conjugated system of the product effectively improve the crystallinity and stability, so that the as-prepared BBCOF remains unchanged in both acid and base solutions, which is obviously better than the conventional imine-linked COF. Impressively, the significantly enhanced conjugation degree by the benzodiimidazole structure also endows BBCOF with an efficient photocatalytic reduction of uranyl ion, with removal rate as high as 96.6% in single-ion system and 95% in multi-ion system. This study is of great importance to the design and synthesis of functional COFs with a commendable trade-off among crystallinity, stability, and functionality.

Beyond Solvothermal: Alternative Synthetic Methods for Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are crystalline porous organic materials that hold a wealth of potential applications across various fields. The development of COFs, however, is significantly impeded by the dearth of efficient synthetic methods. The traditional solvothermal approach, while prevalent, is fraught with challenges such as complicated processes, excessive energy consumption, long reaction times, and limited scalability, rendering it unsuitable for practical applications. The quest for simpler, quicker, more energy-efficient, and environmentally benign synthetic strategies is thus paramount for bridging the gap between academic COF chemistry and industrial application. This Review provides an overview of the recent advances in alternative COF synthetic methods, with a particular emphasis on energy input. We discuss representative examples of COF synthesis facilitated by microwave, ultrasound, mechanic force, light, plasma, electric field, and electron beam. Perspectives on the advantages and limitations of these methods against the traditional solvothermal approach are highlighted.

Secondary growth synthesis of covalent organic framework modified electrospun nanofibers for extraction of estrogens in milk samples

Secondary growth synthesis of covalent organic framework modified electrospun nanofibers for extraction of estrogens in milk samples

A BODIPY-Based 1D Covalent Organic Framework for Photocatalytic Aerobic Oxidation.

Covalent organic frameworks (COFs) as metal-free photocatalysts have attracted extensive interest. However, the organic transformations photocatalyzed by COFs under mild conditions remain a challenge. Herein, a boron-dipyrromethene (BODIPY) based 1D COF, namely JNM-12, was facilely constructed by Schiff-base condensation reaction. JNM-12 exhibited strong visible-light harvesting abilities and suitable photocatalysis energy potentials, enabling the activation of O2 to superoxide anions (O2 ⋅- ) and singlet oxygen (1 O2 ) under visible light irradiation. Benefiting from these properties, JNM-12 delivered excellent photocatalytic activity in the O2 ⋅- -mediated oxidative coupling of amines and 1 O2 -engaged aerobic oxidation of enamines. Our work paves a new way for synthesis of COFs as efficient, economical, and green photocatalysts for organic synthesis.

Photochemical Synthesis of Covalent Organic Frameworks

AbstractAs a booming class of crystalline porous materials, covalent organic frameworks (COFs) have attracted increasing attention and various methods to construct COFs have been investigated including solvothermal synthesis, ionothermal synthesis, microwave synthesis, mechanical synthesis, sonochemical synthesis, interfacial synthesis, and electrochemical synthesis. Recently, photochemical reaction has emerged as a powerful approach for COF synthesis, which utilizing the non‐toxic, abundant and renewable light as the energy source. Benefitting from its outstanding properties of low‐cost, safety, and environmental friendliness, the photochemical reaction was considered as a promising alternative to the conventional thermal reaction for COF synthesis. In this concept article, we summarized the up‐to‐date reports about the photochemical synthesis of COFs and provided a future perspective in this field. It is anticipated that this concept could be beneficial for the further development of photochemical synthesis of COFs.

Nanoarchitectonics of Hollow Covalent Organic Frameworks: Synthesis and Applications.

Hollow covalent organic frameworks (COFs) have gained significant attention because of their specific properties, including enhanced surface-to-volume ratio, large surface area, hierarchical structure, highly ordered nanostructures, and excellent chemical stability. These intrinsic characteristics endow hollow COFs with fascinating physicochemical properties and make them highly attractive for widespread applications, such as catalysis, energy storage, drug delivery, therapy, sensing, and environmental remediation. This review focuses on the recent developments in the synthesis of hollow COFs and their derivatives. In addition, their practical applications in various fields are summarized. Finally, challenges and future opportunities in terms of their synthetic methodologies and practical applications are discussed. Hollow COFs are expected to play an important role in the future of materials science.