Boosting the oxygen reduction activity of non-metallic catalysts via geometric and electronic engineering through nitrogen and chlorine dual-doping

The development of heteroatom dual-doped porous carbon frameworks with uniform doping is highly desirable for achieving highly efficient oxygen reduction reaction (ORR) activity, due to their tunable chemical and electronic structures. Herein, porous covalent triazine-based frameworks (CTFs) incorporating nitrogen/chorine dual-doped porous carbon networks were fabricated by selecting 1,3-bis(4-cyanophenyl) imidazolium chloride as a building block, in a facile and controllable way via a bottom-up strategy. The resulting nitrogen/chorine dual-doped catalyst CCTF-700 exhibits excellent ORR performance with a more positive onset and half-wave potential (0.85 V vs. RHE), higher diffusion-limited current density and significantly improved stability in comparison with the benchmark commercial 20 wt% Pt/C catalyst. It is worth mentioning that CCTF-700 shows one of the best ORR performances among all the reported metal-free electrocatalysts under alkaline conditions. This work paves the way for a controllable and reliable strategy to craft highly efficient heteroatom dual-doped carbon catalysts for energy conversion.

Liquid-Liquid Phase Separation of Aqueous Ionic Liquids in Covalent Organic Frameworks for Thermal Switchable Proton Conductivity

Covalent organic frameworks (COFs) have regular channels that can accommodate guest molecules to provide highly conductive solid electrolytes. However, designing smart, conductive COFs remains a great challenge. Herein, we report the first example of PEG-functionalized ionic liquids (ILs) anchored on the COF walls by strong hydrogen bonding to fabricate thermally responsive COFs (ILm@COF). We found that similar to the traditional IL/water mixture, the ILs undergo lower critical solution temperature (LCST)-type phase behavior within COF nanopores under high moisture levels. However, the phase separation temperature of aqueous IL decreases in COF channels due to the strong interaction between the IL and COF. Thus, the proton conductivity of ILm@COF can be reversibly switched by phase miscibility and separation in COF nanopores, and there is no obvious decrease even after 20 switching cycles. Our work provides important clues for understanding liquid-liquid phase separation in a confined nanospace and opens a new pathway to switchable proton conductivity.

Porous organic polycarbene nanotrap for efficient and selective gold stripping from electronic waste

The role of N-heterocyclic carbene, a well-known reactive site, in chemical catalysis has long been studied. However, its unique binding and electron-donating properties have barely been explored in other research areas, such as metal capture. Herein, we report the design and preparation of a poly(ionic liquid)-derived porous organic polycarbene adsorbent with superior gold-capturing capability. With carbene sites in the porous network as the "nanotrap", it exhibits an ultrahigh gold recovery capacity of 2.09 g/g. In-depth exploration of a complex metal ion environment in an electronic waste-extraction solution indicates that the polycarbene adsorbent possesses a significant gold recovery efficiency of 99.8%. X-ray photoelectron spectroscopy along with nuclear magnetic resonance spectroscopy reveals that the high performance of the polycarbene adsorbent results from the formation of robust metal-carbene bonds plus the ability to reduce nearby gold ions into nanoparticles. Density functional theory calculations indicate that energetically favourable multinuclear Au binding enhances adsorption as clusters. Life cycle assessment and cost analysis indicate that the synthesis of polycarbene adsorbents has potential for application in industrial-scale productions. These results reveal the potential to apply carbene chemistry to materials science and highlight porous organic polycarbene as a promising new material for precious metal recovery.

A CO2 -Masked Carbene Functionalized Covalent Organic Framework for Highly Efficient Carbon Dioxide Conversion

Free N-heterocyclic carbenes (NHCs) are generally prepared by treatment of imidazolium precursors with strong alkali reagents, which usually produces inactive NHC dimers. This treatment would destroy porous supports and thus make supported NHC catalysts difficult to recovery and reuse. Herein, we report the first stable CO₂ -masked N-heterocyclic carbenes (NHCs) grafted on a porous crystalline covalent organic framework (COF). The stable NHC-CO₂ moieties in the COF-NHC-CO₂ could be transformed in situ into isolated NHCs by heating, which exhibit superior catalytic performances in hydrosilylation and N-formylation reactions with CO₂ . The NHC sites can reversibly form NHC-CO₂ and thus can be easily recycled and reused while maintaining excellent catalytic activity. Density functional theory calculations revealed that NHC sites can be fully exposed after removal of CO₂ -masks and rapidly react with silanes, which endows COF-NHC with high catalytic activity.

Covalent Triazine Frameworks and Porous Carbons: Perspective from an Azulene-Based Case

Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400-600 °C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) are synthesized using molten ZnCl₂ at 400-600 °C. Chemical structure analysis reveals that the CTF-Az prepared at low temperature (400 °C) exhibits polymeric features, whereas those prepared at high temperatures (600 °C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retain their rich porosity, but the polymeric features vanish. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, the study evaluates such processes in the context of CTF systems. A proof-of-concept study is performed, observing that the as-synthesized CTF-Azs exhibit promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibit excellent catalytic oxygen reduction reaction (ORR) performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment.

Graphitic Aza-Fused π-Conjugated Networks: Construction, Engineering, and Task-Specific Applications

2D π-conjugated networks linked by aza-fused units represent a pivotal category of graphitic materials with stacked nanosheet architectures. Extensive efforts have been directed at their fabrication and application since the discovery of covalent triazine frameworks (CTFs). Besides the triazine cores, tricycloquinazoline and hexaazatriphenylene linkages are further introduced to tailor the structures and properties. Diverse related materials have been developed rapidly, and a thorough outlook is necessitated to unveil the structure-property-application relationships across multiple subcategories, which is pivotal to guide the design and fabrication toward enhanced task-specific performance. Herein, the structure types and development of related materials including CTFs, covalent quinazoline networks, and hexaazatriphenylene networks, are introduced. Advanced synthetic strategies coupled with characterization techniques provide powerful tools to engineer the properties and tune the associated behaviors in corresponding applications. Case studies in the areas of gas adsorption, membrane-based separation, thermo-/electro-/photocatalysis, and energy storage are then addressed, focusing on the correlation between structure/property engineering and optimization of the corresponding performance, particularly the preferred features and strategies in each specific field. In the last section, the underlying challenges and opportunities in construction and application of this emerging and promising material category are discussed.

A Visible Light/Heat Responsive Covalent Organic Framework for Highly Efficient and Switchable Proton Conductivity

In recent years, covalent organic frameworks (COFs) have attracted enormous interest as a new generation of proton-exchange membranes, chemical sensors and electronic devices. However, to design high proton conductivity COFs,...

N-Heterocyclic carbenes and their precursors in functionalised porous materials

Though N-heterocyclic carbenes (NHCs) have emerged as diverse and powerful discrete functional molecules in pharmaceutics, nanotechnology, and catalysis over decades, the heterogenization of NHCs and their precursors for broader applications in porous materials, like metal-organic frameworks (MOFs), porous coordination polymers (PCPs), covalent-organic frameworks (COFs), porous organic polymers (POPs), and porous organometallic cages (POMCs) was not extensively studied until the last ten years. By de novo or post-synthetic modification (PSM) methods, myriads of NHCs and their precursors containing building blocks were designed and integrated into MOFs, PCPs, COFs, POPs and POMCs to form various structures and porosities. Functionalisation with NHCs and their precursors significantly expands the scope of the potential applications of porous materials by tuning the pore surface chemical/physical properties, providing active sites for binding guest molecules and substrates and realizing recyclability. In this review, we summarise and discuss the recent progress on the synthetic methods, structural features, and promising applications of NHCs and their precursors in functionalised porous materials. At the end, a brief perspective on the encouraging future prospects and challenges in this contemporary field is presented. This review will serve as a guide for researchers to design and synthesize more novel porous materials functionalised with NHCs and their precursors.

Porous Organic Polymers for Catalytic Conversion of Carbon Dioxide

To overcome the challenges of global warming and environmental pollution, it is necessary to reduce the concentration of carbon dioxide (CO₂ ) in the atmosphere, which is mainly accumulated in the air through the burning of fossil fuels. Therefore, the development of environmentally friendly strategies to capture carbon dioxide and convert it into value-added products offers a promising way forward for reducing carbon dioxide concentration in the atmosphere. In this context, POPs (porous organic polymers) have shown great potential as CO₂ selective adsorbents due to their high specific surface area, chemical stability, nanoscale porosity and structural diversity, as well as POPs based heterogeneous catalysts for CO₂ conversion. This review provides a concise account of preparation methods of various POPs, challenges and current development trends of POPs in photocatalytic CO₂ reduction, electrocatalytic CO₂ reduction and chemical CO₂ conversion.

Metal-Organic Frameworks Bonded with Metal N-Heterocyclic Carbenes for efficient catalysis

Metal N-heterocyclic carbenes (M-NHCs) on the pore walls of a porous metal-organic framework (MOF) can be used as active sites for efficient organic catalysis. Traditional approaches that need strong alkaline reagents or insoluble Ag₂O are not, however, suitable for the incorporation of NHCs on the backbones of MOFs because such reagents could destroy their frameworks or result in low reactivity. Accordingly, development of facile strategies toward functional MOFs with covalently bound M-NHCs for catalysis is needed. Herein, we describe the development of a general and facile approach to preparing MOFs with covalently linked active M-NHC (M = Pd, Ir) single-site catalysts by using a soluble Ag salt AgOC(CF₃)₃ as the source and subsequent transmetalation. The well-defined M-NHC-MOF (M = Pd, Ir) catalysts obtained in this way have shown excellent catalytic activity and stability in Suzuki reactions and hydrogen transfer reactions. This provides a general and facile strategy for anchoring functional M-NHC single-site catalysts onto functionalized MOFs for different reactions.

POSS and imidazolium-constructed ionic porous hypercrosslinked polymers with multiple active sites for synergistic catalytic CO2 transformation

In this work, we reported a facile one-pot approach to construct polyhedral oligomeric silsesquioxane (POSS) and imidazolium-based ionic porous hypercrosslinked polymers (denoted as iPHCPs) with multiple active sites towards efficient catalytic conversion of carbon dioxide (CO₂) to high value-added cyclic carbonates. The targeted iPHCPs were synthesized from a rigid molecular building block octavinylsilsesquioxane (VPOSS) and a newly-designed phenyl-based imidazolium ionic crosslinker through the AlCl₃-catalyzed Friedel-Crafts reaction. The desired multiple active sites come from the mixed anions including free Cl^- and Br^- anions, and in situ formed Lewis acidic metal-halogen complex anions [AlCl₃Br]^- within imidazolium moieties and POSS-derived Si-OH groups during the synthetic process. The typical polymer iPHCP-12 possesses a hierarchical micro-/mesoporous structure with a high surface area up to 537 m² g^-1 and shows a fluffy nano-morphology. By virtue of the co-existence of free nucleophilic Cl^- and Br^- anions, the metal complex anion [AlCl₃Br]^- with both electrophilic and nucleophilic characters and electrophilic hydrogen bond donor (HBD) Si-OH groups, iPHCP-12 is regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO₂ with various epoxides into cyclic carbonates under mild conditions. The present work provides a succinct one-pot strategy to construct task-specific ionic porous hypercrosslinked polymers from easily available modules for the targeted catalytic applications.

Recyclable and Magnetically Functionalized Metal-Organic Framework Catalyst: IL/Fe3O4@HKUST-1 for the Cycloaddition Reaction of CO2 with Epoxides

A recyclable and magnetic nanocomposite catalyst (IL/Fe₃O₄@HKUST-1) was synthesized via grafting ionic liquid (IL) [AEMIm]BF₄ into magnetically functionalized metal-organic framework Fe₃O₄@HKUST-1 in a water-ethanol media. The properties of IL/Fe₃O₄@HKUST-1 were fully characterized by powder X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, nitrogen adsorption-desorption, density-functional theory, and a magnetic property measurement system. IL/Fe₃O₄@HKUST-1 showed high activity in the solvent-free cycloaddition of CO₂ with epoxides under mild conditions. Furthermore, the catalyst can be easily separated from the reaction mixture, and the recycled catalyst maintained high performance for several cycles. The synergistic effect of the Lewis acid and base sites in IL/Fe₃O₄@HKUST-1 contributes to its greater reactivity than individual IL or HKUST-1.

3D Cationic Polymeric Network Nanotrap for Efficient Collection of Perrhenate Anion from Wastewater

Rhenium is one of the most valuable elements found in nature, and its capture and recycle are highly desirable for resource recovery. However, the effective and efficient collection of this material from industrial waste remains quite challenging. Herein, a tetraphenylmethane-based cationic polymeric network (CPN-tpm) nanotrap is designed, synthesized, and evaluated for ReO₄^- recovery. 3D building units are used to construct imidazolium salt-based polymers with positive charges, which yields a record maximum uptake capacity of 1133 mg g^-1 for ReO₄^- collection as well as fast kinetics ReO₄^- uptake. The sorption equilibrium is reached within 20 min and a k_d value of 8.5 × 10⁵ mL g^-1 is obtained. The sorption capacity of CPN-tpm remains stable over a wide range of pH values and the removal efficiency exceeds 60% for pH levels below 2. Moreover, CPN-tpm exhibits good recyclability for at least five cycles of the sorption-desorption process. This work provides a new route for constructing a kind of new high-performance polymeric material for rhenium recovery and rhenium-contained industrial wastewater treatment.

Ultratough and ultrastrong graphene oxide hybrid films via a polycationitrile approach

Graphene oxide (GO) is a classic two dimensional (2D) building block that can be used to develop high-performance materials for numerous applications, particularly in the energy and environmental fields. Currently, the precise assembly of GO nanosheets into macroscopic nanohybrids of superior strength and toughness is desirable, and faces challenges and trade-offs. Herein, we exploited the freshly established polycationitrile method as a powerful molecular crosslinking strategy to engineer ultratough and ultrastrong GO/polymer hybrid films, in which a covalent triazine-based network was constructed in a mild condition to reinforce the interface between GO nanosheets. The tensile strength and toughness reached 585 ± 25 MPa and 14.93 ± 1.09 MJ m^-3, respectively, which, to the best of our knowledge, are the current world records in all GO-based hybrid films. As an added merit of the tailor-made polymer crosslinker, the high mechanical performance can be maintained in large part at an extremely high relative humidity of 98%. This emerging interface-engineering approach paves a new avenue to produce integrated strong-and-tough 2D nanohybrid materials that are useful in aerospace, artificial muscle, energy harvesting, tissue engineering and more.

Dehydrative Formation of Isosorbide from Sorbitol over Poly(ionic liquid)-Covalent Organic Framework Hybrids

In this study, the covalent bonding of linear poly(ionic liquid)s (PILs) with covalent organic frameworks (COFs) was accessed by copolymerization of a vinyl-decorated COF with 4-vinylbenzyl chloride, followed by quaternization with tertiary amines. The resultant PIL-COF composite by anchoring a proper content of vinyl sites on the COF-based comonomer retains the crystallinity and porosity, thereby facilitating access of the reactants to the catalytic active sites. As a proof of concept, the dehydrative transformation of sorbitol into isosorbide was selected as a benchmark reaction, whose rate improved significantly in the presence of PIL-COF-0.33 compared with those of individual components and the mesoporous PIL counterpart due to uniform pore sizes and flexible linear catalytic chains. In addition, the hybrids bearing a chemical cross-linkage between PILs and COFs are robust, and PIL-COF-0.33 can be recovered and reused for 10 runs without significant reactivity loss. These findings provide the basis for a novel design concept for achieving both efficient and stable IL catalysis.

Emerging Ionic Polymers for CO2 Conversion to Cyclic Carbonates: An Overview of Recent Developments

In this mini review, we highlight some key work from the last 2 years where ionic polymers have been used as a catalyst to convert CO2 into cyclic carbonates. Emerging ionic polymers reported for this catalytic application include materials such as poly(ionic liquid)s (PILs), ionic porous organic polymers (iPOPs) or ionic covalent organic frameworks (iCOFs) among others. All these organic materials share in common the ionic moiety cations such as imidazolium, pyridinium, viologen, ammonium, phosphonium, and guanidinium, and anions such as halides, [BF4]–, [PF6]–, and [Tf2N]–. The mechanistic aspects and efficiency of the CO2 conversion reaction and the polymer design including functional groups and porosity are discussed in detail. This review should provide valuable information for researchers to design new polymers for important catalysis applications.

Covalent Triazine Frameworks Obtained from Nitrile Monomers for Sustainable CO2 Catalysis

Carbon dioxide catalytic conversion (i. e., CO₂ catalysis) is considered as one of the most promising technologies to control CO₂ emissions, which is of great significance to build a sustainable society with green low-carbon cycle. In view of its thermodynamic stability and kinetic inertness, CO₂ selective activation is still desired. Nowadays, the traditional strategy is to selectively capture and efficiently convert atmospheric CO₂ into high value-added chemicals and fuels. Covalent triazine frameworks (CTFs) as a newly emerging and attractive kind of porous organic polymer (POP) have drawn worldwide attention among heterogeneous catalysis because of their nitrogen-rich porous structures and exceptional physicochemical stabilities. In this Minireview, the focus was mainly placed on the structural design and synthesis of CTFs and their applications in CO₂ catalysis including CO₂ cycloaddition, CO₂ carboxylation, CO₂ hydrogenation, CO₂ photoreduction, and CO₂ electroreduction. By discussing the structure-property relationship, valuable guidance from a sustainable perspective may be provided for developing precisely designed CTFs with high performance and excellent industrial application prospects in sustainable CO₂ catalysis.

Carbon Dioxide Conversion Upgraded by Host-guest Cooperation between Nitrogen-Rich Covalent Organic Framework and Imidazolium-Based Ionic Polymer

The chemical conversion of CO₂ into value-added chemicals is one promising approach for CO₂ utilization. It is crucial to explore highly efficient catalysts containing task-specific components for CO₂ fixation. Here, a host-guest catalytic system was developed by integrating nitrogen-rich covalent organic framework (TT-COF) and imidazolium-based ionic polymer (ImIP), which serve as hydrogen-bonding donor and nucleophilic agent, respectively, for cooperatively facilitating the activation of the epoxides and subsequent CO₂ cycloaddition. The catalytic activity of the host-guest system was remarkably superior to those of ImIP, TT-COF, and their physical mixture. Furthermore, selective adsorption for CO₂ over N₂ rendered this catalytic system effective for the cycloaddition reaction of the simulated flue gas. The protocols for the unification of two catalytically active components provide new opportunities for the development of composite systems in multiple applications.

Recent Advances on Imidazolium-Functionalized Organic Cationic Polymers for CO2 Adsorption and Simultaneous Conversion into Cyclic Carbonates

The cycloaddition reaction of CO₂ with various epoxides to generate cyclic carbonates is one of the most promising and efficient approaches for CO₂ fixation. Typical imidazolium-based ionic liquids possessing electrophilic cations and nucleophilic halogen anions have been identified as excellent and environmentally friendly candidates for synergistically activating epoxides to convert CO₂ . Therefore, the feasible construction of a series of imidazolium-functionalized organic cationic polymers can bridge the gap between homogeneous and heterogeneous catalysis, thereby obtaining highly selective CO₂ adsorption and simultaneous conversion ability. This Review describes the recent advancements made with regard to the design and synthesis of this type of polymeric networks having imidazolium functionality. They are considered as an outstanding heterogeneous catalyst for the cycloaddition of CO₂ to epoxides. Based on the perspective from the design of building blocks to the synthesis of cationic polymers, the focus mainly lies on how to introduce imidazole units into the material backbone via a covalent linking approach and how to incorporate other active sites capable of activating CO₂ and/or epoxides into such polymeric materials.

Aqueous Electrochemical Partial Oxidation of Gaseous Ethylbenzene by a Ru-Modified Covalent Triazine Framework

Aqueous electrochemical oxidation of hydrocarbons into valuable compounds, such as alcohols and carbonyl compounds, has attracted much attention because these systems can operate under mild conditions without toxic oxidants or flammable solvents. The key requirements to achieve such oxidation reactions are (1) highly reactive species on an electrocatalyst for the activation of C-H bonds and (2) efficient transportation pathway for water-insoluble hydrocarbons to an electrode surface. We have determined that a gas diffusion electrode (GDE) supporting Ru atom-modified covalent triazine frameworks (Ru-CTF) has an activity for the electrooxidation of gaseous ethylbenzene to acetophenone using an aqueous electrolyte. A high-valency Ru═O species was formed in Ru-CTF as an effective active site for O-atom insertion into stable C-H bonds. Furthermore, Ru-CTF showed excellent stability during four consecutive cycles with the replacement of the electrolyte every 12 h, although the reactive Ru═O species is generated. As for the transportation pathway for substrates, the amount of acetophenone generated from gaseous ethylbenzene was much larger than that from ethylbenzene dissolved in an electrolyte. This result indicates that the three-dimensional microstructures in the GDE maximize the transportation of gaseous hydrocarbons and the oxidation reaction occurs at the triple-phase boundary, which enables the use of aqueous electrolytes.

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.

Integration of metalloporphyrin into cationic covalent triazine frameworks for the synergistically enhanced chemical fixation of CO2

Cobalt porphyrin as a Lewis acidic site was integrated into imidazolium-functionalized porous cationic covalent triazine frameworks for the cooperatively enhanced catalysis CO₂ cycloaddition to produce cyclic carbonates.

Effect of Building Block Transformation in Covalent Triazine-Based Frameworks for Enhanced CO2 Uptake and Metal-Free Heterogeneous Catalysis

Covalent triazine frameworks (CTFs) have provided a unique platform in functional material design for a wide range of applications. This work reports a series of new CTFs with two new heteroaromatic building blocks (pyrazole and isoxazole groups) through a building-block transformation approach aiming for carbon capture and storage (CCS) and metal-free catalysis. The CTFs were synthesized from their respective building blocks [(4,4'-(1H-pyrazole-3,5-diyl)dibenzonitrile (pyz) and 4,4'-(isoxazole-3,5-diyl)dibenzonitrile (isox))] under ionothermal conditions using ZnCl₂ . Both of the building blocks were designed by an organic transformation of an acetylacetone containing dinitrile linker to pyrazole and isoxazole groups, respectively. Due to this organic transformation, (i) linker aromatization, (ii) higher surface areas and nitrogen contents, (iii) higher aromaticity, and (iv) higher surface basicity was achieved. Due to these enhanced properties, CTFs were explored for CO₂ uptake and metal-free heterogeneous catalysis. Among all, the isox-CTF, synthesized at 400 °C, showed the highest CO₂ uptake (4.92 mmol g^-1 at 273 K and 2.98 mmol g^-1 at 298 K at 1 bar). Remarkably, these CTFs showed excellent metal-free catalytic activity for the aerobic oxidation of benzylamine at mild reaction conditions. On studying the properties of the CTFs, it was observed that organic transformations and ligand aromatization of the materials are crucial factor to tune the important parameters that influence the CO₂ uptake and the catalytic activity. Overall, this work highlights the substantial effect of designing new CTF materials by building-block organic transformations resulting in better properties for CCS applications and heterogeneous catalysis.

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built-In Functions

A new approach has been developed to design organic polymers using topology diagrams. This strategy enables covalent integration of organic units into ordered topologies and creates a new polymer form, that is, covalent organic frameworks. This is a breakthrough in chemistry because it sets a molecular platform for synthesizing polymers with predesignable primary and high-order structures, which has been a central aim for over a century but unattainable with traditional design principles. This new field has its own features that are distinct from conventional polymers. This Review summarizes the fundamentals as well as major progress by focusing on the chemistry used to design structures, including the principles, synthetic strategies, and control methods. We scrutinize built-in functions that are specific to the structures by revealing various interplays and mechanisms involved in the expression of function. We propose major fundamental issues to be addressed in chemistry as well as future directions from physics, materials, and application perspectives.

An unsymmetrical covalent organic polymer for catalytic amide synthesis

Herein, we present the first report on the Covalent Organic Polymer (COP) directed non-classical synthesis of an amide bond. An economical route has been chosen for the synthesis of APC-COP using p-aminophenol and cyanuric chloride. APC-COP acts as a smart, valuable and sustainable catalyst for efficient access to the amide bond under mild conditions at room temperature in 30 min. APC-COP exhibits selectivity towards carboxylic acids over esters. The key features of this protocol involve the variety of parameters, viz. wider substrate scope, no use of additive and recyclability, which makes this approach highly desirable in gramscale synthesis. Moreover, we have shown the practical utility of the present method in the catalytic synthesis of paracetamol.

A mesoporous cationic metal–organic framework with a high density of positive charge for enhanced removal of dichromate from water

A mesoporous cationic metal–organic framework (FJI-C11) was firstly employed to capture efficiently dichromate ions from water.

A fluorescent conjugated polymer photocatalyst based on Knoevenagel polycondensation for hydrogen production

An organic polymer photocatalyst (p-P) for hydrogen production was designed and synthesized through Knoevenagel condensation with a high yield.

Ag NPs decorated on a COF in the presence of DBU as an efficient catalytic system for the synthesis of tetramic acids via CO2 fixation into propargylic amines at atmospheric pressure

Ag NPs are decorated at the surface of a COF material TpPa-1 and the resulting Ag@TpPa-1 catalyzes efficiently for the synthesis of tetramic acids from a variety of propargylic amines using CO₂ as reagent.

Highly tunable periodic imidazole-based mesoporous polymers as cooperative catalysts for efficient carbon dioxide fixation

We designed new periodic imidazole-based mesoporous polymers for cooperative catalysis, revealing the structure–activity relationships in CO₂ cycloaddition.

Two cyclotriveratrylene metal-organic frameworks as effective catalysts for Knoevenagel condensation and CO2 cycloaddition with epoxides

By using a novel imidazole-functional cyclotriveratrylene ligand, two isostructural frameworks, [Cd3(HECTV)(bdc)3]·DMF·6H2O (1) and [Zn3(HECTV)(OH-bdc)3]·3DMF·4H2O (2) (HECTV = 5,6,12,13,19,20-hexaimidazolium-ethoxy-cyclotriveratrylene), were constructed. The two compounds exhibit fascinating 4-fold interpenetration three-dimensional frameworks. There are still large void spaces in the structures despite the interpenetration, which were filled with solvent molecules. Interestingly, 1 demonstrates a single-crystal to single-crystal transformation with the guests changed by a cycloalkane solvent. Strikingly, 1 and 2 feature highly heterogeneous catalytic activities for Knoevenagel condensation and CO2 cycloaddition, respectively. In particular, catalysts 1 and 2 could be reused with good catalytic performance.

Amine-functionalized Zn(ii) MOF as an efficient multifunctional catalyst for CO2 utilization and sulfoxidation reaction

Herein, a zinc(ii)-based 3D mixed ligand metal organic framework (MOF) was synthesized via versatile routes including green mechanochemical synthesis. The MOF {[Zn(ATA)(L)·H2O]}n (ZnMOF-1-NH2) has been characterized by various physico-chemical techniques, including SCXRD, and composed of the bipyridyl-based Schiff base (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and 2-aminoterephthalic acid (H2ATA) ligands as linkers. The MOF material has been explored as a multifunctional heterogeneous catalyst for the cycloaddition of alkyl and aryl epoxides with CO2 and sulfoxidation reactions of aryl sulfides. The influence of various reaction parameters is examined to optimize the performance of the catalytic reactions. It is found that solvent-free catalytic reaction conditions offer good catalytic conversion in the case of cyclic carbonates, and for sulfoxide, good conversion and selectivity are achieved in the presence of DCM as a solvent medium under ambient reaction conditions. The chemical and thermal stability of the catalyst are excellent and it is active for up to four catalytic cycles without significant loss in activity. Furthermore, based on the catalytic activity and structural evidence, a plausible mechanism for both catalytic reactions is proposed.