Microwave-Assisted Synthesis of Covalent Organic Frameworks: A Review

Advancements in framework materials for enhanced energy harvesting

Energy harvesting, the process of capturing ambient energy from various sources and converting it into usable electrical power, has attracted a lot of attention due to its potential to provide long-term and self-sufficient energy solutions. This comprehensive review thoroughly explores the use of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for energy harvesting by piezoelectric and triboelectric nanogenerators (PENGs and TENGs). It begins by classifying and outlining the structural diversity of MOFs and COFs, which is key to understanding their importance in energy applications. Key characterization techniques are focused on emphasizing their importance in optimizing material properties for efficient energy conversion. The working mechanisms of PENGs and TENGs are discussed, focusing on their ability to transform mechanical energy into electrical energy and their advantages in operation. The use of MOFs and COFs in energy harvesting applications is then discussed, including synthesis procedures, unique characteristics relevant to electricity conversion, and various practical applications such as self-powered sensors and wearable electronics. Current challenges such as stability, scalability, and performance improvements are explored, as well as proposed future improvements to help advance current research. Finally, the study highlights the importance of framework materials for the development of energy harvesting systems, providing an invaluable resource for academics and engineers seeking to exploit the potential of these materials for renewable energy sources. The goal of this article is to stimulate further invention and implementation of efficient materials-based energy harvesting framework devices by integrating recent advances and mapping future possibilities.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers

Synthesis and assembly of two-dimensional (2D) polymeric materials present a tricky trade-off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine-based 2D covalent organic frameworks (COFs) at the interface of oil-in-water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86 %. The NCs have tunable average diameters of 114-565 nm and shell thicknesses of 12-63 nm, depending on the monomer and surfactant types/concentrations. Their BET-specific surface areas are up to 139.0 m2/g, mainly contributed by narrowly-distributed mesopores at ~5.0 nm and micropores at 1.4 nm at a volume ratio (V1.4/V5.0) of 1.68. The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water for at least six weeks with little size-distribution change, and they have been demonstrated to be highly efficient nanocatalysts in application of water-based hydrogen evolution, reaching a stable hydrogen production rate at 10.2 mmol ⋅ g-1 ⋅ h-1 for 6 hours. Such microdroplet interface-confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Rapid gram-scale microwave-assisted synthesis of organic anodes for sodium-ion batteries with environmental impact assessment

Development of sustainable synthesis methods of organic electrode materials (OEMs) for sodium (Na)-ion batteries must take hold rapidly in large scale-synthesis if subsequent commercialisation is to occur. We report a facile and rapid gram-scale synthesis method based on microwave irradiation for disodium naphthalene-2,6-dicarboxylate (Na-NDC) and mono/disodium benzene-1,4-dicarboxylate (Na-BDC) as model compounds. Phase purity and formation of materials was confirmed by various characterisation techniques. The electrochemical performance was tested in both half and full cell formats and compared to material obtained via smaller scale synthesis, revealing state-of-the art performance in terms of capacity retention and cyclability. The environmental impacts upon organic anode synthesis were quantified according to cradle-to-gate life cycle assessment (LCA). The results allow for the identification of environmental hotspots during production, indicating areas for future process optimisation. Interestingly, remarkably reduced impacts are obtained compared to conventional syntheses at milligram scale. Additionally, this work suggests potential significant improvements upon additional upscaling and solvent recycling.

Advances and Challenges in Interfacial Binding Forces for Electrocatalysts

As a practical chemical energy conversion technology, electrocatalysis could be used in fields of energy conversion and environmental protection. In recent years, significant research efforts have been devoted to the design and development of high-performance electrocatalysts because the rational design of catalysts is crucial for enhancing electrocatalytic performance. Creating electrocatalysts by forming interactions between different components at the interface is an important means of controlling and improving performance. Therefore, several common interfacial binding forces used for synthesizing electrocatalysts was systematically summarized in this review for the first time. The discussion revolves around the crucial roles these binding forces play in various electrocatalytic reaction processes. Various characterization techniques capable of proving the existence of these interfacial binding forces was also involved in the review. Finally, some prospects and challenges for designing and researching materials through the utilization of interfacial binding forces were presented.

Microwave-Assisted One-Step Synthesis of Palladium-Encapsulated Covalent Organic Frameworks for Heterogeneous Catalysis

Metal-encapsulated covalent organic frameworks (metal/COFs) represent an emerging paradigm in heterogeneous catalysis. However, the time-intensive (usually 4 or more days) and tedious multi-step synthesis of metal/COFs remains a significant stumbling block for their broad application. To address this challenge, we introduce a facile microwave-assisted in situ metal encapsulation strategy to cooperatively combine COF formation and in situ palladium(II) encapsulation in one step. With this unprecedented approach, we synthesize a diverse range of palladium(II)-encapsulated COFs (termed Mw-Pd/COF) in the air within just an hour. Notably, this strategy is scalable for large-scale production (~0.5 g). Leveraging the high crystallinity, porosity, and structural stability, one representative Mw-Pd/COF exhibits remarkable activity, functional group tolerance, and recyclability for the Suzuki-Miyaura coupling reaction at room temperature, surpassing most previously reported Pd(II)/COF catalysts with respect to catalytic performance, preparation time, and synthetic ease. This microwave-assisted in situ metal encapsulation strategy opens a facile and rapid avenue to construct metal/COF hybrids, which hold enormous potential in a multitude of applications including heterogeneous catalysis, sensing, and energy storage.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Covalent organic frameworks and related innovative materials in chiral separation and recognition

Chiral recognition and enantioseparation are of paramount importance in various fields, including pharmaceuticals, agrochemicals, and material science. Covalent organic frameworks (COFs) have emerged as promising materials for chiral separation due to their unique structural features and tunable properties. This review provided a comprehensive overview of recent progress in the application of COFs and related innovative materials for chiral separation and recognition. Various strategies were analyzed for the design and synthesis of chiral COFs, including the incorporation of chiral building blocks, post-synthetic modification, and the integration of chiral selectors. The applications of chiral COFs in chromatographic techniques, membrane separations, and other emerging methods were critically evaluated with the emphasis on their advantages and limitations. Additionally, the review summarized the potential of combining COFs with other nanomaterials, such as metal-organic frameworks (MOFs) and nanoparticles, to enhance chiral recognition and separation performance. The fundamental principles and mechanisms of chiral recognition were discussed, highlighting the role of chiral selectors and their interactions with enantiomers. Finally, current challenges and future perspectives in this field were discussed, providing insights into the development of more efficient and versatile chiral separation systems based on COFs and related materials.

Flux synthesis of two-dimensional covalent organic frameworks

Covalent organic frameworks (COFs) are crystalline porous polymers constructed from organic building blocks into ordered two- or three-dimensional networks through dynamic covalent bonds. Attributed to their high porosity, well-defined structure, tailored functionality and excellent chemical stability, COFs have been considered ideal sorbents for various separation applications. The synthesis of COFs mainly employs the solvothermal method, which usually requires organic solvents in sealed Pyrex tubes, resulting in unscalable powdery products and environmental pollution that seriously limits their practical applications. Herein, our protocol focuses on an emerging synthesis method for COFs based on organic flux synthesis without adding solvents. The generality of this synthesis protocol has been applied in preparing various types of COFs, including olefin-linked, imide-linked, Schiff-based COFs on both gram and kilogram scales. Furthermore, organic flux synthesis avoids the disadvantages of solvothermal synthesis and enhances the crystallization and porosity of COFs. Typically, COF synthesis takes 3-5 d to complete, and subsequent washing procedures leading to pure COFs need 1 d. The procedure for kilogram-scale production of COFs with commercially available monomers is also provided. The resulting COFs are suitable for separation applications, particularly as adsorbent materials for industrial gas separation and water treatment applications. The protocol is suited for users with prior expertise in the synthesis of inorganic materials and porous organic materials.

Efficient Microwave Irradiation-Assisted Synthesis of Benzodioxinoquinoxaline and Its Donor-Variegated Derivatives Enabling Long-Lived Emission and Efficient Bipolar Charge Carrier Transport

To enhance the usually low-charge carrier mobilities of highly twisted donor-acceptor-type compounds that exhibit thermally activated delayed fluorescence, we designed a rodlike acceptor benzodioxinoquinoxaline. This acceptor and two donor-acceptor-donor derivatives were synthesized via microwave Buchwald-Hartwig cross-coupling reactions with yields of up to 91%. The compounds exhibit three different types of photoluminescence, which is well-explained by quantum chemical calculations. Benzodioxinoquinoxaline shows blue fluorescence, with a very short lifetime of 0.64 ns. Its derivatives exhibit either green solid-state-enhanced thermally activated delayed fluorescence (SSE-TADF) or room-temperature phosphorescence (RTP) with lifetimes approaching 7 ms. When molecularly dispersed in a polymeric host, the compounds show a photoluminescence quantum yield close to 60%. The derivatives containing acridine or phenoxazine moieties exhibit bipolar charge transport. At an electric field of 5.8 × 105 V/cm, hole and electron mobilities of the phenoxazine-containing compound reach 3.2 × 10-4 and 1.5 × 10-4 cm2 V-1 s-1, respectively. Among the studied SSE-TADF-based organic light-emitting diodes, the device containing this compound shows the highest external quantum efficiency of 12.3% due to the good charge-transporting and SSE-TADF parameters of the emitter.

Synthesis and Biomedical Applications of Covalent Organic Frameworks for Disease Diagnosis and Therapy

Covalent organic frameworks (COFs) have emerged as a distinguished class of porous materials. Owing to their ability to be constructed through covalent bonds involving light elements, such as hydrogen, boron, carbon, nitrogen, and oxygen, COFs offer greater stability and lower cytotoxicity than metal-organic frameworks do, addressing critical limitations in in vivo applications. Their unique attributes, such as high surface area, customizable pore sizes, and versatile surface functionalities, make them ideal for various biomedical applications. This review aims to provide an overview of the recent advancements in modern COFs for biomedical uses. First, a variety of methods for the synthesis of COFs are outlined, which ensures their suitability for medical use. Next, we delve into innovative biomedical applications, emphasizing their roles in disease diagnosis and therapies. Finally, challenges, such as clinical translation, biocompatibility, and controlled drug release, are critically discussed, providing comprehensive insight into the potential of COFs in revolutionizing biomedical technologies. Overall, this review offers a comprehensive overview of COFs' capabilities and future prospects in enhancing biomedical technologies.

Robust Covalent Organic Frameworks for Photosynthesis of H2O2: Advancements, Challenges and Strategies

Since 2020, covalent organic frameworks (COFs) are emerging as robust catalysts for the photosynthesis of hydrogen peroxide (H2O2), benefiting from their distinct advantages. However, the current efficiency of H2O2 production and solar-to-chemical energy conversion efficiency (SCC) remain suboptimal due to various constraints in the reaction mechanism. Therefore, there is an imperative to propose efficiency improvement strategies to accelerate the development of this reaction system. This comprehensive review delineates recent advances, challenges, and strategies in utilizing COFs for photocatalytic H2O2 production. It explores the fundamentals and challenges (e.g., oxygen (O2) mass transfer rate, O2 adsorption capacity, response to sunlight, electron-hole separation efficiency, charge transfer efficiency, selectivity, and H2O2 desorption) associated with this process, as well as the advantages, applications, classification, and preparation strategies of COFs for this purpose. Various strategies to enhance the performance of COFs in H2O2 production are highlighted. The review aims to stimulate further advancements in utilizing COFs for photocatalytic H2O2 production and discusses potential prospects, challenges, and application areas in this field.

ON-OFF Switching of Photocatalytic Hydrogen Evolution by Built-in Pt-Nitrogen-Carbon Reticular Heterojunctions

COF engineering with a built-in, high concentration of defined N-doped sites overcomes the "black-box" drawback of conventional trial-and-error N-doping methods (used in polymeric carbon nitride and graphene), that hamper a directed evolution of functional carbon interfaces based on structure-reactivity guidelines. The cutting-edge challenge is to dissect the many complex and interdependent functions that originate from reticular N-doping, including modification of the material optoelectronics, band alignments, interfacial contacts and co-localization of active-sites, producing a multiple-set of effectors that can all play a role to regulate photocatalysis. Herein, an ON-OFF gated photocatalytic H2 evolution (PHE) is dictated by the Pt-NPyridine-carbon active sites and probed with a dual COF platform, based on stable β-ketoenamine connectivities made of triformylphloroglucinol (Tp) as the acceptor knots and 1,4-diaminonaphtalene (Naph) or 5,8-diaminoisoquinoline (IsoQ) as donors. Our results showcase two novel COF-Naph-Tp and COF-IsoQ-Tp frameworks featuring quasi-identical slip-stacked microporous structure, and similar surface area, band gap, light harvesting envelope up to 700 nm, fluorescence emission profile/lifetime, and PEIS response at the surface/water interface (Rct=16-10±4 KΩ). A divergent behaviour is indeed observed for COF-IsoQ-Tp with record photoelectrochemical outputs (J=-16 μA cm-2, Rt=3 KΩ at 0.40 V vs RHE) and two orders of magnitude higher rate of PHE (11.3 mmol g-1 h-1, λ>400 nm, pH 5) compared to the inactive COF-Naph-Tp analogue. It turns out that PHE is regulated by the isoquinoline residues at the COF pores where emergent Pt-NPyridine-carbon functional heterojunctions are formed upon photo-deposition of Pt nanoparticles as co-catalysts, as probed by combined XPS and DFT calculations evidence. This work sets a key guideline to direct the design of carbon-based materials encoding the installation of metal-nitrogen-carbon active sites within tailored coordination environments enabling the catalytic performance.

Power Dissipation of Uniaxial Anisotropic/Interacting Polar Molecules with Linear Reaction Dynamics in an Alternating Electric Field

The influence of anisotropic potential energy and interaction between polar molecules on power absorption in chemical reactions with linear reaction dynamics in a weak alternating electric field is studied theoretically according to the reaction-diffusion equation. The expression for transient power loss is derived using two methods, electrodynamic method and equivalent circuit method, based on the electric energy conservation equation. Numerical calculations are carried out, and the results show that both the anisotropic potential energy and the interaction between polar molecules have a strong impact on energy dissipation and storage. For the anisotropic potential energy, when the applied dimensionless anisotropy is equal to 1, the power loss density increases about 32% at a low reaction rate and 27% at a high reaction rate compared to the case without anisotropic potential energy. When the dimensionless anisotropy is equal to -1, the power loss is suppressed and is reduced about 27% and 24% at low and high reaction rates, respectively. On the other hand, for the interaction between polar molecules, the power loss density decreases about 10% and 30% with low and high interaction potential energies, respectively. In addition, if the reaction rate is relatively high, the power loss will quickly decrease due to the end of the reaction process.

Metal-organic frameworks for biomedical applications: A review

Metal-organic frameworks (MOFs) are emergent materials in diverse prospective biomedical uses, owing to their inherent features such as adjustable pore dimension and volume, well-defined active sites, high surface area, and hybrid structures. The multifunctionality and unique chemical and biological characteristics of MOFs allow them as ideal platforms for sensing numerous emergent biomolecules with real-time monitoring towards the point-of-care applications. This review objects to deliver key insights on the topical developments of MOFs for biomedical applications. The rational design, preparation of stable MOF architectures, chemical and biological properties, biocompatibility, enzyme-mimicking materials, fabrication of biosensor platforms, and the exploration in diagnostic and therapeutic systems are compiled. The state-of-the-art, major challenges, and the imminent perspectives to improve the progressions convoluted outside the proof-of-concept, especially for biosensor platforms, imaging, and photodynamic therapy in biomedical research are also described. The present review may excite the interdisciplinary studies at the juncture of MOFs and biomedicine.

Recent advances and applications of ionic covalent organic frameworks in food analysis

Ionic covalent organic frameworks with both crystallinity and charged sites have attracted significant attention from the scientific community. The versatile textural structures, precisely defined channels, and abundant charged sites of ionic COFs offer immense potential in various areas such as separation, sample pretreatment, ion conduction mechanisms, sensing applications, catalytic reactions, and energy storage systems. This review presents a comprehensive overview of facile preparation methods for ionic covalent organic frameworks (iCOFs), along with their applications in food sample pretreatment techniques such as solid-phase extraction (SPE), magnetic solid-phase extraction (MSPE), and dispersive solid-phase extraction (DSPE). Furthermore, it highlights the extensive utilization of iCOFs in detecting various food contaminants including pesticides, contaminants from food packaging, veterinary drugs, perfluoroalkyl substances, and poly-fluoroalkyl substances. Specifically, this review critically discusses the limitations, challenges, and future prospects associated with employing iCOF materials to ensure food safety.

Microwave Assisted Fast Synthesis of a Donor-Acceptor COF Towards Photooxidative Amidation Catalysis

The synthesis of covalent organic frameworks (COFs) at bulk scale require robust, straightforward, and cost-effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2-10 days) which greatly restricts their practical application. Here, we report microwave assisted rapid and optimized synthesis of a donor-acceptor (D-A) based highly crystalline COF, TzPm-COF in second (10 sec) to minute (10 min) time scale. With increasing the reaction time from seconds to minutes crystallinity, porosity and morphological changes are observed for TzPm-COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6 meV), TzPm-COF can efficaciously produce superoxide radical anion (O2 .-) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron-withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real-time reaction progress through in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.

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.

Strategies for utilizing covalent organic frameworks as host materials for the integration and delivery of bioactives

Covalent organic frameworks (COFs), a new and developing class of porous framework materials, are considered a type of promising carrier for the integration and delivery of bioactives, which have diverse fascinating merits, such as a large specific surface area, designable and specific porosity, stable and orderly framework structure, and various active sites. However, owing to the significant differences among bioactives (including drugs, proteins, nucleic acid, and exosomes), such as size, structure, and physicochemical properties, the interaction between COFs and bioactives also varies. In this review, we firstly summarize three strategies for the construction of single or hybrid COF-based matrices for the delivery of cargos, including encapsulation, covalent binding, and coordination bonding. Besides, their smart response release behaviors are also categorized. Subsequently, the applications of cargo@COF biocomposites in biomedicine are comprehensively summarized, including tumor therapy, central nervous system (CNS) modulation, biomarker analysis, bioimaging, and anti-bacterial therapy. Finally, the challenges and opportunities in this field are briefly discussed.

Recent advances in metal-organic frameworks for stimuli-responsive drug delivery

After entering the human body, drugs for treating diseases, which are prone to delivery and release in an uncontrolled manner, are affected by various factors. Based on this, many researchers utilize various microenvironmental changes encountered during drug delivery to trigger drug release and have proposed stimuli-responsive drug delivery systems. In recent years, metal-organic frameworks (MOFs) have become promising stimuli-responsive agents to release the loaded therapeutic agents at the target site to achieve more precise drug delivery due to their high drug loading, excellent biocompatibility, and high stimuli-responsiveness. The MOF-based stimuli-responsive systems can respond to various stimuli under pathological conditions at the site of the lesion, releasing the loaded therapeutic agent in a controlled manner, and improving the accuracy and safety of drug delivery. Due to the changes in different physical and chemical factors in the pathological process of diseases, the construction of stimuli-responsive systems based on MOFs has become a new direction in drug delivery and controlled release. Based on the background of the rapidly increasing attention to MOFs applied in drug delivery, we aim to review various MOF-based stimuli-responsive drug delivery systems and their response mechanisms to various stimuli. In addition, the current challenges and future perspectives of MOF-based stimuli-responsive drug delivery systems are also discussed in this review.

Covalent Organic Frameworks: Their Composites and Derivatives for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) have attracted considerable interest in the field of rechargeable batteries owing to their three-dimensional (3D) varied pore sizes, inerratic porous structures, abundant redox-active sites, and customizable structure-adjustable frameworks. In the context of metal-ion batteries, these materials play a vital role in electrode materials, effectively addressing critical issues such as low ionic conductivity, limited specific capacity, and unstable structural integrity. However, the electrochemical characteristics of the developed COFs still fall short of practical battery requirements due to inherent issues such as low electronic conductivity, the tradeoff between capacity and redox potential, and unfavorable micromorphology. This review provides a comprehensive overview of the recent advancements in the application of COFs, COF-based composites, and their derivatives in rechargeable metal-ion batteries, including lithium-ion, lithium-sulfur, sodium-ion, sodium-sulfur, potassium-ion, zinc-ion, and other multivalent metal-ion batteries. The operational mechanisms of COFs, COF-based composites, and their derivatives in rechargeable batteries are elucidated, along with the strategies implemented to enhance the electrochemical properties and broaden the range of their applications.

Organic electrodes based on redox-active covalent organic frameworks for lithium batteries

Electroactive organic materials have received much attention as alternative electrodes for metal-ion batteries due to their high theoretical capacity, resource availability, and environmental friendliness. In particular, redox-active covalent organic frameworks (COFs) have recently emerged as promising electrodes due to their tunable electrochemical properties, insolubility in electrolytes, and structural versatility. In this Highlight, we review some recent strategies to improve the energy density and power density of COF electrodes for lithium batteries from the perspective of molecular design and electrode optimisation. Some other aspects such as stability and scalability are also discussed. Finally, the main challenges to improve their performance and future prospects for COF-based organic batteries are highlighted.

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, the essential 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.

Continuous Covalent Organic Frameworks Membranes: From Preparation Strategies to Applications

Covalent organic frameworks (COFs) are porous crystalline polymeric materials formed by the covalent bonding of organic units. The abundant organic units library gives the COFs species diversity, easily tuned pore channels, and pore sizes. In addition, the periodic arrangement of organic units endows COFs regular and highly connected pore channels, which has led to the rapid development of COFs in membrane separations. Continuous defect-free and high crystallinity of COF membranes is the key to their application in separations, which is the most important issue to be addressed in the research. This review article describes the linkage types of covalent bonds, synthesis methods, and pore size regulation strategies of COFs materials. Further, the preparation strategies of continuous COFs membranes are highlighted, including layer-by-layer (LBL) stacking, in situ growth, interfacial polymerization (IP), and solvent casting. The applications in separation fields of continuous COFs membranes are also discussed, including gas separation, water treatment, organic solvent nanofiltration, ion conduction, and energy battery membranes. Finally, the research results are summarized and the future prospect for the development of COFs membranes are outlined. More attention may be paid to the large-scale preparation of COFs membranes and the development of conductive COFs membranes in future research.

Simplifying the Synthesis of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are porous, crystalline materials constructed from organic linkers and inorganic nodes that have attracted widespread interest due to their permanent porosity and highly modular structures. However, the large volumes of organic solvents and additives, long reaction times, and specialized equipment typically required to synthesize MOFs hinder their widespread adoption in both academia and industry. Recently, our lab has developed several user-friendly methods for the gram-scale (1-100 g) preparation of MOFs. Herein, we summarize our progress in the development of high-concentration solvothermal, mechanochemical, and ionothermal syntheses of MOFs, as well as in minimizing the amount of modulators required to prepare highly crystalline Zr-MOFs. To begin, we detail our work elucidating key features of acid modulation in Zr-MOFs to improve upon current dilute solvothermal syntheses. Choosing an optimal modulator maximizes the crystallinity and porosity of Zr-MOFs while minimizing the quantity of modulator needed, reducing the waste associated with MOF synthesis. By evaluating a range of modulators, we identify the pKa, size, and structural similarity of the modulator to the linker as controlling factors in modulating ability. In the following section, we describe two high-concentration solvothermal methods for the synthesis of Zr-MOFs and demonstrate their generality among a range of frameworks. We also target the M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd; dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) family of MOFs for high-concentration synthesis and introduce a two-step preparation of several variants that proceeds through a novel kinetic phase. The high-concentration methods we discuss produce MOFs on multi-gram scale with comparable properties to those prepared under traditional dilute solvothermal conditions. Next, to further curtail solvent waste and accelerate reaction times, we discuss the mechanochemical preparation of M2(dobdc) MOFs utilizing liquid amine additives in a planetary ball mill, which we also apply to the synthesis of two related salicylate frameworks. These samples exhibit comparable porosities to traditional dilute solvothermal samples but can be synthesized in just minutes, as opposed to days, and require under 1 mL of liquid additive to prepare ~0.5 g of material. In the following section, we discuss our efforts to avoid specialized equipment and eliminate solvent use entirely by employing ionothermal conditions to prepare a variety of azolate- and salicylate-based MOFs. Simply combining metal chloride (hydrate) salts with organic linkers at temperatures above the melting points of the salts affords high-quality framework materials. Further, ionothermal conditions enable the syntheses of two new Fe(III) M2(dobdc) derivatives that cannot be synthesized under normal solvothermal conditions. Last, as a demonstrative example, we discuss our efforts to synthesize 100 g of high-quality Mg2(dobdc) in a single batch using a high-concentration (1.0 M) hydrothermal synthesis. Our Account will be of significant interest to researchers aiming to prepare gram-scale quantities of MOFs for further study.

Recent Advances in Multifunctional Reticular Framework Nanoparticles: A Paradigm Shift in Materials Science Road to a Structured Future

Porous organic frameworks (POFs) have become a highly sought-after research domain that offers a promising avenue for developing cutting-edge nanostructured materials, both in their pristine state and when subjected to various chemical and structural modifications. Metal-organic frameworks, covalent organic frameworks, and hydrogen-bonded organic frameworks are examples of these emerging materials that have gained significant attention due to their unique properties, such as high crystallinity, intrinsic porosity, unique structural regularity, diverse functionality, design flexibility, and outstanding stability. This review provides an overview of the state-of-the-art research on base-stable POFs, emphasizing the distinct pros and cons of reticular framework nanoparticles compared to other types of nanocluster materials. Thereafter, the review highlights the unique opportunity to produce multifunctional tailoring nanoparticles to meet specific application requirements. It is recommended that this potential for creating customized nanoparticles should be the driving force behind future synthesis efforts to tap the full potential of this multifaceted material category.

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.

Photocatalytic Self-Fenton System of g-C3N4-Based for Degradation of Emerging Contaminants: A Review of Advances and Prospects

The discharge of emerging pollutants in the industrial process poses a severe threat to the ecological environment and human health. Photocatalytic self-Fenton technology combines the advantages of photocatalysis and Fenton oxidation technology through the in situ generation of hydrogen peroxide (H2O2) and interaction with iron (Fe) ions to generate a large number of strong reactive oxygen species (ROS) to effectively degrade pollutants in the environment. Graphite carbon nitride (g-C3N4) is considered as the most potential photocatalytic oxygen reduction reaction (ORR) photocatalyst for H2O2 production due to its excellent chemical/thermal stability, unique electronic structure, easy manufacturing, and moderate band gap (2.70 eV). Hence, in this review, we briefly introduce the advantages of the photocatalytic self-Fenton and its degradation mechanisms. In addition, the modification strategy of the g-C3N4-based photocatalytic self-Fenton system and related applications in environmental remediation are fully discussed and summarized in detail. Finally, the prospects and challenges of the g-C3N4-based photocatalytic self-Fenton system are discussed. We believe that this review can promote the construction of novel and efficient photocatalytic self-Fenton systems as well as further application in environmental remediation and other research fields.

NiCo-MOF Nanospheres Created by the Ultra-Fast Microwave Method for Use in High-Performance Supercapacitors

Metal-organic frameworks-through the use of creative synthetic designs-could produce MOF materials with excellent porosity, stability, particle microstructures, and conductivity, and their inherent characteristics-including their porosity and controllable structure-may result in an immense number of prospects for energy storage. In this paper, a nanosphere-like NiCo-MOF was effectively manufactured via an ultra-fast microwave technique. Additionally, the ideal synthesis conditions of the NiCo-MOF were investigated by adjusting the microwave output power and microwave reaction time. Under the reaction conditions of a 600 W microwave and a 210 s microwave reaction time, the NiCo-MOF exhibited an excellent capacitance of 1348 F/g at a current density of 1 A/g and an 86.1% capacity retention rate at 10 A/g. In addition, self-assembled NiCo-MOF/AC asymmetric capacitors showed a splendid energy density of 46.6 Wh/kg and a power density of 8000 W/kg.

Facile Microwave-Assisted Synthesis of 2D Imine-Linked Covalent Organic Frameworks for Exceptional Iodine Capture

Covalent organic frameworks (COFs) have emerged as auspicious porous adsorbents for radioiodine capture. However, their conventional solvothermal synthesis demands multiday synthetic times and anaerobic conditions, largely hampering their practical use. To tackle these challenges, we present a facile microwave-assisted synthesis of 2D imine-linked COFs, Mw-TFB-BD-X, (X = -CH₃ and -OCH₃) under air within just 1 h. The resultant COFs possessed higher crystallinity, better yields, and more uniform morphology than their solvothermal counterparts. Remarkably, Mw-TFB-BD-CH₃ and Mw-TFB-BD-OCH₃ exhibited exceptional iodine adsorption capacities of 7.83 g g^-1 and 7.05 g g^-1, respectively, placing them among the best-performing COF adsorbents for static iodine vapor capture. Moreover, Mw-TFB-BD-CH₃ and Mw-TFB-BD-OCH₃ can be reused 5 times with no apparent loss in the adsorption capacity. The exceptionally high iodine adsorption capacities and excellent reusability of COFs were mainly attributed to their uniform spherical morphology and enhanced chemical stability due to the in-built electron-donating groups, despite their low surface areas. This work establishes a benchmark for developing advanced iodine adsorbents that combine fast kinetics, high capacity, excellent reusability, and facile rapid synthesis, a set of appealing features that remain challenging to merge in COF adsorbents so far.

Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC) Prepared by Microwave and Ultrasound-Assisted Synthesis: Promising Green Strategies for the Nanoworld

Many pharmaceutically active molecules are highly lipophilic, which renders their administration and adsorption in patients extremely challenging. Among the countless strategies to overcome this problem, synthetic nanocarriers have demonstrated superb efficiency as drug delivery systems, since encapsulation can effectively prevent a molecules' degradation, thus ensuring increased biodistribution. However, metallic and polymeric nanoparticles have been frequently associated with possible cytotoxic side effects. Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC), which are prepared with physiologically inert lipids, therefore emerged as an ideal strategy to bypass toxicities issues and avoid the use of organic solvents in their formulations. Different approaches to preparation, using only moderate amounts of external energy to facilitate a homogeneous formation, have been proposed. Greener synthesis strategies have the potential to provide faster reactions, more efficient nucleation, better particle size distribution, lower polydispersities, and furnish products with higher solubility. Particularly microwave-assisted synthesis (MAS) and ultrasound-assisted synthesis (UAS) have been utilized in the manufacturing of nanocarrier systems. This narrative review addresses the chemical aspects of those synthesis strategies and their positive influence on the characteristics of SLNs and NLCs. Furthermore, we discuss the limitations and future challenges for the manufacturing processes of both types of nanoparticles.

Novel Microwave-Assisted Synthesis of COFs: 2020–2022

Covalent organic frameworks (COFs) have emerged as a new type of crystalline porous polymers of great interest. However, their preparation requires long reaction times. Microwave-assisted synthesis (MAS) offers an interesting approach to increasing the reaction rate of chemical processes. Thus, microwaves can be a key tool for the fast and scalable synthesis of COFs. Since our previous review on the topic, the preparation of COFs with microwaves has been evolving. Herein, we present a compilation of COFs studies and experiments published in the last three years on the synthesis of COFs using microwave-assisted synthesis as a source of energy. The articles include imine, triazine, and other 2D COFs synthesized using MAS. The 3D COFs have also been compiled. The chemical structure of the monomers and the COFs and their main parameters of synthesis and application are summarized for each article.

Green and Fast Strategies for Energy-Efficient Preparation of the Covalent Organic Framework TpPa-1

Three synthesis procedures for the covalent-organic framework (COF) TpPa-1 are studied with the purpose of setting up the most promising one in a fast and green way, leading to a more environmentally friendly and sustainable process. With conventional heating, good crystallinity and a high BET specific surface area (SSA) of up to 1007 m²  ⋅ g^-1 are achieved at 170 °C for 3 days using water as the quintessential green solvent. However, the application of microwave radiation in the synthesis for this crystalline porous polymer allows reaction times to be shortened to 30 min while maintaining structural and textural properties (BET SSA of 928 m²  ⋅ g^-1 ) and obtaining yields close to 98 % (vs. 90 % in the hydrothermal synthesis). The water-assisted mechanochemical synthesis is also an environmentally friendly synthetic approach; with heating at 170 °C in a two-step process (10+10 min), high crystallinity is achieved, a BET SSA of 960  m²  ⋅ g^-1 and a yield of 98 % for TpPa-1.

Fast Microwave-Assisted Synthesis, Calcination and Functionalization of a Silica Mesoporous Nanomaterial: UVM-7

We report here, for the first time, the use of a solid state microwave source for the synthesis, calcination and functionalization of a UVM-7 based hybrid mesoporous silica material. The synthesis of the UVM-7 material is obtained in 2 min at low power (50 W) by the combination of a microwave irradiation and the atrane route. Moreover, it has been successfully calcined and functionalized in just 13 and 4 min respectively with microwave assisted procedures. A total synthesis comprising each individually optimized step, can be executed in only 4 h including work-up, by contrast to a typical synthesis that comprises several days. Savings higher than one order or magnitude are obtained in time and energy. Our example is a proof of concept of the potential use of solid state microwave generators for the ultrafast on-command preparation of hybrid nanomaterials due to their accurate control and accelerating properties.

Advanced Covalent Organic Frameworks for Multi-Valent Metal Ion Batteries

Covalent organic frameworks (COFs) have received increased interest in recent years as an advanced class of materials. By virtue of the available monomers, multiple conformations and various linkages, COFs offer a wide range of opportunities for complex structural design and specific functional development of materials, which has facilitated the widespread application in many fields, including multi-valent metal ion batteries (MVMIBs), described as the attractive candidate replacing lithium-ion batteries (LIBs). With their robust skeletons, diverse pores, flexible structures and abundant functional groups, COFs are expected to help realize a high performance MVMIBs. In this review, we present an overview of COFs, describe advances in topology design and synthetic reactions, and study the application of COFs in MVMIBs, as well as discuss challenges and solutions in the preparation of COFs electrodes, in the hope of providing constructive insights into the future direction of COFs.

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

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

Synthesis of Covalent Organic Frameworks (COFs)-Nanocellulose Composite and Its Thermal Degradation Studied by TGA/FTIR

At present, the synthesis methods of crystalline porous materials often involve powder products, which not only affects the practical application but also has complex synthesis operations and limited scale. Based on the mechanochemical method, we choose COF-TpPa-1, preparing TpPa-1-DANC composites. Covalent organic frameworks (COFs) are a kind of crystalline material formed by covalent bonds of light elements. COFs possess well pore structure and high thermal stability. However, the state of synthesized powders limits their application. Cellulose nanocrystals (CNCs) are promising renewable micron materials with abundant hydroxyl groups on their surface. It is possible to prepare high-strength materials such as film, water, and aerogel. Firstly, the nanocellulose was oxidized by the sodium periodate method to obtain aldehyde cellulose nanocrystals (DANC). TpPa-1-DANC not only had the crystal characteristic peak of COFs at 2θ ≈ 5° but also had a BET surface area of 247 m²/g. The chemical bonds between COFs and DANC formed by Schiff base reaction appeared in FTIR and XPS. The pyrolysis behavior of the composite was characterized by TG-IR, which showed that the composite had good thermal stability. With the advantages of nanocellulose as a material in every dimension, we believe that this method can be conducive to the large-scale synthesis of COFs composites, and has the possibility of multi-form synthesis of COFs.

Recent progress in microwave-assisted preparations of 2D materials and catalysis applications

On the urgency of metal-free catalysts, two-dimensional materials (2DMs) have caused extensive researches because of distinctive optical and electronic properties. In the last decade, microwave methods have emerged in rapid and effective preparations of 2DMs for catalysis. Microwave heating offers several advantages namely direct, fast, selective heating and uniform reaction temperature compared to conventional heating methods, thus bringing about high-yield and high-purity products in minutes or even seconds. This review summarizes recent advances in microwave-assisted preparations of 2DMs-based catalysts and their state-of-the-art catalytic performances. Microwave heating mechanisms are briefly introduced mainly focusing on microwave-matter interactions, which can guide the choice of precursors, liquid media, substrates, auxiliaries and experiment parameters during microwave radiation. We especially provide a detailed insight into various microwave-assisted procedures, classified as exfoliation, synthesis, doping, modification and construction towards different 2DMs nanomaterials. We also discuss how microwave affects the synthetic composition and microstructure of 2DMs-based catalysts, thereby deeply influencing their optical and electronic properties and the catalytic performances. Finally, advantages, challenges and prospects of microwave-assisted approaches for 2DMs nanomaterials are summarized to inspire the effective and large-scale fabrication of novel 2DMs-based catalysts.

Batch and Flow Synthesis of CeO2 Nanomaterials Using Solid-state Microwave Generators

Microwave-assisted synthesis in combination with flow synthesis offers an interesting approach to develop faster and more sustainable procedures for the preparation of homogeneous nanomaterials. Recently, solid-state generators of microwaves appeared as a tool with improved control over power and frequency. Cerium oxide, despite its excellent catalytic activity, has not been prepared before using solid-state generators or microwave-assisted flow chemistry. We report a procedure for the preparation of nanoparticulated CeO₂ (around 4 nm) under 2.45 GHz microwaves in only 30 s. The materials are further calcined at 800 °C to increase particle size, with a better defined particle size and crystallinity. The procedure was tested in batch at pH 11 and 12 and diverse potencies, and the products were characterized by TEM, XRD, DLS, and N₂ adsorption–desorption isotherms. The materials were similar at the diverse pH values and potencies. XRD confirms the crystallinity of the CeO₂ material with a fluorite-like structure. They are composed of particles around 40 nm that aggregate as structures of around 100 nm. The procedure was successfully adapted to flow synthesis, obtaining materials with structure and properties equivalent to batch synthesis. The batch and flow materials offer peroxidase properties, opening the door for their use as ROS scavengers.

Porous organic polymers for light-driven organic transformations

As a new generation of porous materials, porous organic polymers (POPs), have recently emerged as a powerful platform of heterogeneous photocatalysis. POPs are constructed using extensive organic synthesis methodologies, with various functional organic units being connected via high-energy covalent bonds. This review systematically presents the recent advances in POPs for visible-light driven organic transformations. Herein, we firstly summarize the common construction strategies for POP-based photocatalysts based on two major approaches: pre-design and post-modification; secondly, we categorize and summarize the synthesis methods and organic reaction types for constructing various types of POPs. We then classify and introduce the specific reactions of current light-driven POP-mediated organic transformations. Finally, we outline the current state of development and the problems faced in light-driven organic transformations by POPs, and we present some perspectives to motivate the reader to explore solutions to these problems and confront the present challenges in the development process.

Dicarbonyl compounds in the synthesis of heterocycles under green conditions

Carbon–carbon and carbon-heteroatom bond forming reactions are strategically employed for the generation of a variety of heterocyclic systems. This class of compounds represents the most general structural unit, present in many natural compounds. They are recognized for their valuable biologically properties and wide range of applications in medicinal, pharmaceutical, and other related fields of chemistry. This is an updated review on the use of dicarbonyl compounds under environmentally friendly conditions to access a series of heterocyclic structures, e.g., quinoxaline, quinazolinones, benzochalcogenazoles, indoles, among others. Synthetic protocols involving copper-catalyzed, multicomponent and cascade reactions, decarboxylative cyclization, recycling of CO2, and electrochemical approaches are presented and discussed.