Room-Temperature Synthesis of Covalent Organic Framework (COF-LZU1) Nanobars in CO2 /Water Solvent

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.

Green solvent systems for material syntheses and chemical reactions

It is of great significance to develop environmentally benign, non-volatile and recyclable green solvents for different applications. This feature article overviews the properties of green solvent systems (e.g., ionic liquids, supercritical carbon dioxide, deep eutectic solvents and mixed green solvent systems) and their applications in (1) framework material syntheses, including metal-organic frameworks, covalent organic frameworks and hydrogen-bonded organic frameworks, and (2) CO2 conversion reactions, including photocatalytic and electrocatalytic reduction reactions. Finally, the future perspective for research on green solvent systems is proposed from different aspects.

Green and Facile Preparation of Covalent Organic Frameworks Based on Reaction Medium for Advanced Applications

Covalent organic frameworks (COFs), as a new class of crystalline, well-ordered, and porous materials with intermittent constructions, are formed via organic structural parts connected through covalent bonds. These materials have been employed in several fields comprising pollutant adsorption and separation, catalysis, electrical conductivity, gas storage, etc. The preparation of COFs is mainly applied in tubes with high temperatures and degassing treatment. Furthermore, the reaction medium is involved in toxic organic solvents like toluene, dioxane, mesitylene, acetonitrile, and so on. Hence, discovering clean medium and green approaches has attracted wide attention. Recently, facile, less dangerous, and greener methods have been developed for COFs synthesis in diverse applications like performing the reaction at ambient temperature or employing aqueous solvents, ionic liquids, and a mixture of organic solvents/water. This review article summarizes the eco-friendly production approaches of COFs for diverse applications.

Green and Rapid Synthesis of Acridine-Functionalized Covalent Organic Polymers for Photocatalysis by Combining Sonochemistry and Ion Induction

Covalent organic polymers (COPs) are powerful candidates for achieving the visible-light-driven degradation of organic pollutants by virtue of structural designability, but their synthesis relies on harmful reagents and high temperatures, which weakens their associated green merits. Here, we report a novel strategy for combining sonochemistry with ion induction for the rapid preparation of acridine-functionalized COPs in green and mild aqueous solutions with tunable high yields of 80 to 90%. Photochemical studies reveal the ability of these COPs to harvest visible light and their sufficient conduction potentials for generating superoxide radicals. Furthermore, the photodegradation of methylene blue confirms the good photocatalytic activity and reusability of the zinc ion-based acridine-functionalized COP, which achieves 90.8% removal in 150 min and retains 82.5% activity after 5 reuse cycles, with a rate constant of up to 3.2 times that of commercial titanium dioxide nanoparticles. This strategy paves the way for the green, rapid, and mild synthesis of acridine-functionalized COPs, enabling visible light photocatalytic degradation for water treatment and energy conversion to advance in a thoroughly environmentally friendly and cost-effective manner.

Advanced Covalent Organic Framework-Based Membranes for Recovery of Ionic Resources

Membrane technology has shown a viable potential in conversion of liquid-waste or high-salt streams to fresh waters and resources. However, the non-adjustability pore size of traditional membranes limits the application of ion capture due to their low selectivity for target ions. Recently, covalent organic frameworks (COFs) have become a promising candidate for construction of advanced ion separation membranes for ion resource recovery due to their low density, large surface area, tunable channel structure, and tailored functionality. This tutorial review aims to analyze and summarize the progress in understanding ion capture mechanisms, preparation processes, and applications of COF-based membranes. First, the design principles for target ion selectivity are illustrated in terms of theoretical simulation of ions transport in COFs, and key properties for ion selectivity of COFs and COF-based membranes. Next, the fabrication methods of diverse COF-based membranes are classified into pure COF membranes, COF continuous membranes, and COF mixed matrix membranes. Finally, current applications of COF-based membranes are highlighted: desalination, extraction, removal of toxic metal ions, radionuclides and lithium, and acid recovery. This review presents promising approaches for design, preparation, and application of COF-based membranes in ion selectivity for recovery of ionic resources.

Room temperature synthesis of flower-like hollow covalent organic framework for efficient enrichment of microcystins

The morphology of nanomaterials is one of essential factors for their unique properties. Herein, a hollow covalent organic framework with a flower-like structure (HFH-COF) was synthesized at room temperature. The synthesized HFH-COF has a very large specific surface area, mesoporous structure, excellent chemical stability, and good crystallinity. The special morphology endowed HFH-COF with high specific surface area utilization and rapid mass transfer rate, resulting in faster equilibration time and better extraction performance than spherical COF (S-COF). Subsequently, combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), an efficient and sensitive method was established for microcystins (MCs) detection. The developed method has low detection limits (0.6-0.8 pg mL^-1), wide linear ranges (1.5-1000.0 pg mL^-1, R ≥ 0.9993), and acceptable reproducibility (RSD ≤ 7.6%, n = 6). Real biological samples were analyzed by the developed method, and trace levels of MC-YR, MC-RR and MC-LR were detected. The results indicate that the synthesized HFH-COF is an ideal sorbent for efficient extraction of MCs from complex biological samples.

An Overview of Metal-free Sustainable Nitrogen-based Catalytic Knoevenagel Condensation Reaction ‎

Knoevenagel condensation reaction counts as a vital condensation in organic chemistry due to the synthesis of valuable intermediates, ‎heterocycles, and fine chemicals from commercially available reactants through forming new C=C...

Microwave-Assisted Synthesis of Covalent Organic Frameworks: A Review

Covalent organic frameworks (COFs) are relatively recent materials. They have received great attention due to their interesting properties. However, the application of microwaves in their synthesis, despite its advantages such as faster and more reproducible processes, is a minority. Herein, a comprehensive compilation of the research results published in the microwave-assisted synthesis (MAS) of COFs is presented. This review includes articles of 2D and 3D COFs prepared using microwaves as source of energy. The articles have been classified depending on the functional groups including boronate ester, imines, enamines, azines, and triazines, among others. It compiles the main parameters of synthesis and characteristics of the materials together with some general issues related with COFs and microwaves. Additionally, current and future perspectives of the topic have been discussed.

Covalent organic frameworks embedded membrane via acetic-acid-catalyzed interfacial polymerization for dyes separation: Enhanced permeability and selectivity

With the increasing demand of high water-quality, membrane filtration technologies are playing further important roles in water treatment owing to their small footprints, reduced use of chemicals and stable performances. However, the inherent permeability-selectivity trade-off is still a significant obstacle restricting the broad applications of membrane separation. Hydrophilic modification via doping nanoparticles into membranes is considered an effective solution to improve the permeability while maintaining selectivity. However, agglomeration of nanoparticles often results in inhomogeneity of the modified membranes. In this study, hybrid membranes with separated covalent organic framework (COF) particles that were uniformly embedded in the membrane surface pores were firstly fabricated via acetic-acid-catalyzed in situ synthesis. Owing to the ample hydrophilic chemical groups and tunable molecular transport channels in COFs, the modified membranes yielded almost twice higher water flux (about 200 L m^-2·h^-1·bar) than the pristine membranes with simultaneously enhanced rejection of water pollutants (i.e., dyes). In addition, the pure organic structure of COF improves the polymer-filler interaction of the mixed film, thereby reducing the risk of leakage. Therefore, the hybrid membranes also exhibited relatively high stability in long-term operations and different pH conditions, which makes them promising candidates in future membrane applications.

Covalent Organic Frameworks: Design, Synthesis, and Functions

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Fluorescent COFs with a highly conjugated structure for visual drug loading and responsive release

For the first time, a facile solvothermal method to synthesize COFs with a nanosized structure and bright fluorescence was reported to monitor drug loading with the naked eye and realize responsive release.

Green synthesis of imine-based covalent organic frameworks in water

This work describes a high-yield “one-pot” green synthesis of imine-based Covalent Organic Frameworks in water, which can also be accelerated under microwave conditions.

Ultra-permeable polyamide membranes harvested by covalent organic framework nanofiber scaffolds: a two-in-one strategy

We demonstrated a two-in-one strategy for the fabrication of ultra-permeable polyamide layers featuring ultrathin thicknesses and increased water transport domains.

Polyamide-based thin-film composite nanofiltration membranes are widely used for potable water decontamination, brackish water desalination and wastewater reutilization. However, enhancing the water permeance of the polyamide layer within the thin-film composite nanofiltration membrane still remains a great challenge, because of the relatively large thickness and high transport resistance of the polyamide layer produced by intractable interfacial polymerization. Herein, we reported a two-in-one strategy to prepare ultra-permeable nanofiltration membranes via covalent organic framework (COF) nanofiber scaffold mediated interfacial polymerization. The highly porous and hydrophilic COF nanofiber scaffolds enhanced the controlled release of amine monomers, leading to ultrathin polyamide layers. Also, the relatively smooth COF nanofiber scaffolds can be spontaneously evolved into rugged and uneven architectures during interfacial polymerization, providing rough substrates for enlarging the actual areas of polyamide layers. Therefore, the increased areas of polyamide layers were employed as additional water permeable domains. Arising from the synergetic effect of the ultrathin and increased water permeation domains, the produced membranes exhibit exceptional nanofiltration performance with a water permeance of up to 31.1 L m^–2 h^–1 bar^–1 and a Na₂SO₄ rejection rate of about 95%, outperforming most other nanofiltration membranes. This highly accessible technique opens a new avenue for the design and engineering of ultra-permeable thin-film composite nanofiltration membranes, highlighting its great potential in providing clean water.