Enhanced hydrolytic stability of self-assembling alkylated two-dimensional covalent organic frameworks

The stability and bulk properties of two-dimensional boronate ester-linked covalent organic frameworks (COFs) were investigated upon exposure to aqueous environments. Enhanced stability was observed for frameworks with alkylation in the pores of the COF compared to nonalkylated, bare-pore frameworks. COF-18? and COF-5 were analyzed as "bare-pore" COFs, while COF-16? (methyl), COF-14? (ethyl), and COF-11? (propyl) were evaluated as "alkylated-pore" materials. Upon submersion in aqueous media, the porosity of alkylated COFs decreased ～25%, while the nonalkylated COFs were almost completely hydrolyzed, virtually losing all porosity. Similar trends were observed for the degree of crystallinity for these materials, with ～40% decrease for alkylated COFs and 95% decrease for nonalkylated COFs. SEM was used to probe the particle size and morphology for these hydrolyzed materials. Stability tests, using absorbance spectroscopy and (1)H NMR, monitored the release of monomers as the COF degraded. While nonalkylated COFs were stable in organic solvent, hydrolysis was rapid in aqueous environments, more so in basic compared to neutral or acidic aqueous media (minutes to hours, respectively). Notably, alkylation in the pores of COFs slows hydrolysis, exhibiting up to a 50-fold enhancement in stability for COF-11? over COF-18?.     

Reticular synthesis of covalent organic borosilicate frameworks

This paper reports the synthesis and characterization of a new crystalline 3D covalent organic framework, COF-202: [C(C6H4)4]3[B3O6 (tBuSi)2]4, formed from condensation of a divergent boronic acid, tetra(4-dihydroxyborylphenyl)methane, and tert-butylsilane triol, tBuSi(OH)3. This framework is constructed through strong covalent bonds (Si-O, B-O) that link triangular and tetrahedral building units to form a structure based on the carbon nitride topology. COF-202 demonstrates high thermal stability, low density, and high porosity with a surface area of 2690 m2 g-1. The design and synthesis of COF-202 expand the type of linkage that could be used to crystallize new materials with extended covalent organic frameworks.     

Covalent organic frameworks as exceptional hydrogen storage materials

We report the H2 uptake properties of six covalent organic frameworks (COFs) from first-principles-based grand canonical Monte-Carlo simulations. The predicted H2 adsorption isotherm is in excellent agreement with the only available experimental result (3.3 vs 3.4 wt % at 50 bar and 77 K for COF-5), also reported here, validating the predictions. We predict that COF-105 and COF-108 lead to a reversible excess H2 uptake of 10.0 wt % at 77 K, making them the best known storage materials for molecular hydrogen at 77 K. We predict that the total H2 uptake for COF-108 is 18.9 wt % at 77 K. COF-102 shows the best volumetric performance, storing 40.4 g/L of H2 at 77 K. These results indicate that the COF systems are most promising candidates for practical hydrogen storage.     

Design of covalent organic frameworks for methane storage

We designed 14 new covalent organic frameworks (COFs), which are expected to adsorb large amounts of methane (CH(4)) at 298 K and up to 300 bar. We have calculated their delivery uptake using grand canonical Monte Carlo (GCMC) simulations. We also report their thermodynamic stability based on 7.5 ns molecular dynamics simulations. Two new frameworks, COF-103-Eth-trans and COF-102-Ant, are found to exceed the DOE target of 180 v(STP)/v at 35 bar for methane storage. Their performance is comparable to the best previously reported materials: PCN-14 and Ni-MOF-74. Our results indicate that using thin vinyl bridging groups aid performance by minimizing the interaction methane-COF at low pressure. This is a new feature that can be used to enhance loading in addition to the common practice of adding extra fused benzene rings. Most importantly, this report shows that pure nonbonding interactions, van der Waals (vdW) and electrostatic forces in light elements (C, O, B, H, and Si), can rival the enhancement in uptake obtained for microporous materials derived from early transition metals.     

手性多孔材料在色谱分离分析中的应用

手性多孔有机骨架材料(Chiral porous organic frameworks,CPOFs)具有孔性质优异、比表面积高、稳定性好以及易功能化等诸多优点,已经在手性催化、识别和分离等领域中得到应用。手性多孔有机骨架材料主要有手性金属-有机骨架材料(Chiral metal-organic frameworks,CMOFs)和手性共价有机骨架材料(Chiral covalent organic frameworks,CCOFs)及其他材料,这类材料具有特殊的手性识别、吸附作用,在色谱分离分析领域中已成为研究热点之一。该文综述了手性多孔材料的合成及其在色谱分离和选择性吸附中的应用,展望了未来CPOFs材料可能的应用与发展方向。     

Direct-Space Structure Determination of Covalent Organic Frameworks from 3D Electron Diffraction Data

Structure determination of covalent organic frameworks (COFs) with atomic precision is a bottleneck that hinders the development of COF chemistry. Although three-dimensional electron diffraction (3D-ED) data has been used to solve structures of sub-micrometer-sized COFs, successful structure solution is not guaranteed as the data resolution is usually low. We demonstrate that the direct-space strategy for structure solution, implemented using a genetic algorithm (GA), is a successful approach for structure determination of COF-300 from 3D-ED data. Structural models with different geometric constraints were considered in the GA calculations, with successful structure solution achieved from room-temperature 3D-ED data with a resolution as low as ca. 3.78 Å. The generality of this strategy was further verified for different phases of COF-300. This study demonstrates a viable strategy for structure solution of COF materials from 3D-ED data of limited resolution, which may facilitate the discovery of new COF materials in the future.     

Recent advances of application of porous molecular cages for enantioselective recognition and separation

Porous materials with well‐defined pore structures have received considerable attention in the past decades due to their unique structures and wide applications. Most porous materials such as zeolites, metal‐organic frameworks, covalent organic frameworks, and porous organic polymers are extended to infinite frameworks or networks by robust covalent or coordination bonds. Porous molecular cages composed of discrete molecules with permanent cavities are an emerging class of porous material and the discrete molecules assemble into solids by weak intermolecular interaction. In comparison to porous extended solids such as metal‐organic frameworks and covalent organic frameworks, porous molecular cage solids are generally soluble in organic solvents thus allowing solution processing, making them more convenient to apply in many fields. This review mainly focuses on the recent advances of application of porous molecular cages (porous organic cages and metal‐organic cages) for enantioselective recognition and separation from 2010 to present, including gas chromatography, capillary electrochromatography, chiral fluorescent recognition, chiral potentiometric sensing, and enantioselective adsorption. Furthermore, the two important family members of porous molecular cages, porous organic cages and metal‐organic cages, are also discussed.     

Metallocenes@COF-102: organometallic host-guest chemistry of porous crystalline organic frameworks

The organometallic host-guest chemistry of porous covalent organic frameworks is explored by vapour phase infiltration of volatile organometallic precursors; namely, [Fe(η(5)-C(5)H(5))(2)], [Co(η(5)-C(5)H(5))(2)], and [Ru(cod)(cot)]. The unique arrangement of ferrocene molecules inside COF-102 is driven by π-π (host-guest) interactions and replicates the framework symmetry.     

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

Electroactive organic molecules have received a lot of attention in the field of electronics because of their fascinating electronic properties, easy functionalization and potential low cost towards their implementation in electronic devices. In recent years, electroactive organic molecules have also emerged as promising building blocks for the design and construction of crystalline porous frameworks such as metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs) for applications in electronics. Such porous materials present certain additional advantages such as, for example, an immense structural and functional versatility, combination of porosity with multiple electronic properties and the possibility of tuning their physical properties by post-synthetic modifications. In this Review, we summarize the main electroactive organic building blocks used in the past few years for the design and construction of functional porous materials (MOFs and COFs) for electronics with special emphasis on their electronic structure and function relationships. The different building blocks have been classified based on the electronic nature and main function of the resulting porous frameworks. The design and synthesis of novel electroactive organic molecules is encouraged towards the construction of functional porous frameworks exhibiting new functions and applications in electronics.     

一种用于光催化氧化硫醚成亚砜的超薄卟啉的共价有机骨架纳米片

单线态氧(~1O_2)可将硫醚化合物选择性氧化为亚砜,而开发具有高~1O_2量子产率的高效光敏剂至关重要。本文中我们报道了超薄二维共价有机骨架(COFs)纳米片(NSs)COF-367 NSs的制备和表征。COF-367 NSs在各种有机溶剂中的良好分散性和高效率的光收集赋予其在可见光照射下产生~1O_2的显著性能,且远优于块体COF-367。我们还证明了COF-367 NSs是硫醚化合物光催化氧化成亚砜的优良非均相催化剂,具有高效率和选择性以及良好的循环稳定性。     

Metal@COFs: Covalent Organic Frameworks as Templates for Pd Nanoparticles and Hydrogen Storage Properties of Pd@COF-102 Hybrid Material

Three-dimensional covalent organic frameworks (COFs) have been demonstrated as a new class of templates for nanoparticles. Photodecomposition of the [Pd(η(3) -C(3) H(5) )(η(5) -C(5) H(5) )]@COF-102 inclusion compound (synthesized by a gas-phase infiltration method) led to the formation of the Pd@COF-102 hybrid material. Advanced electron microscopy techniques (including high-angle annular dark-field scanning transmission electron microscopy and electron tomography) along with other conventional characterization techniques unambiguously showed that highly monodisperse Pd nanoparticles ((2.4±0.5)?nm) were evenly distributed inside the COF-102 framework. The Pd@COF-102 hybrid material is a rare example of a metal-nanoparticle-loaded porous crystalline material with a very narrow size distribution without any larger agglomerates even at high loadings (30?wt?%). Two samples with moderate Pd content (3.5 and 9.5?wt?%) were used to study the hydrogen storage properties of the metal-decorated COF surface. The uptakes at room temperature from these samples were higher than those of similar systems such as Pd@metal-organic frameworks (MOFs). The studies show that the H(2) capacities were enhanced by a factor of 2-3 through Pd impregnation on COF-102 at room temperature and 20?bar. This remarkable enhancement is not just due to Pd hydride formation and can be mainly ascribed to hydrogenation of residual organic compounds, such as bicyclopentadiene. The significantly higher reversible hydrogen storage capacity that comes from decomposed products of the employed organometallic Pd precursor suggests that this discovery may be relevant to the discussion of the spillover phenomenon in metal/MOFs and related systems.     

Highly Efficient Enrichment of Volatile Iodine by Charged Porous Aromatic Frameworks with Three Sorption Sites

The targeted synthesis of a series of novel charged porous aromatic frameworks (PAFs) is reported. The compounds PAF‐23, PAF‐24, and PAF‐25 are built up by a tetrahedral building unit, lithium tetrakis(4‐iodophenyl)borate (LTIPB), and different alkyne monomers as linkers by a Sonogashira–Hagihara coupling reaction. They possess excellent adsorption properties to organic molecules owing to their “breathing” dynamic frameworks. As these PAF materials assemble three effective sorption sites, namely the ion bond, phenyl ring, and triple bond together, they exhibit high affinity and capacity for iodine molecules. To the best of our knowledge, these PAF materials give the highest adsorption values among all porous materials (zeolites, metal–organic frameworks, and porous organic frameworks) reported to date.     

Computer simulation of the adsorption of light gases in covalent organic frameworks

Grand canonical Monte Carlo simulations of argon, hydrogen, and methane adsorption in four covalent organic frameworks are presented. Argon adsorption isotherms from computer simulations overestimate the amount adsorbed by 25% upon saturation, with respect to the available experiments at T = 87 K. Hydrogen adsorption isotherms show that these materials might attain a 30% increase for the uptake when compared with analogous simulations performed for metal organic frameworks at T = 77 K and T = 298 K. Methane adsorption isotherms give a strong indication that at least one material in this class, COF-102, could meet or exceed the Department of Energy's target of 180 cm3 (STP)/cm3 for P = 35 bar and room temperature. The origin of this large affinity for methane is investigated by analyzing the structure of the potential energy surface of interaction between the adsorbate and the adsorbent.     

In Situ Enzyme Immobilization by Covalent Organic Frameworks

Enzyme immobilization is a widely reported method to favor the applicability of enzymes by enhancing their stability and re-usability. Among the various existing solid supports and immobilization strategies, the in situ encapsulation of enzymes within crystalline porous matrices is a powerful tool to design biohybrids with a stable and protected catalytic activity. However, to date, only a few metal–organic frameworks (MOFs) and hydrogen-bonded organic frameworks (HOFs) have been reported. Excitingly, for the first time, Y. Chen and co-workers expanded the in situ bio-encapsulation to a new class of crystalline porous materials, namely covalent organic frameworks (COFs). The enzyme@COF materials not only exhibited high enzyme loading with minimal leaching, high catalytic activity and selectivity, chemical and long-term stability and recyclability but could also be scaled up to a few grams. Undoubtedly, this work opens new striking opportunities for enzymatic immobilization and will stimulate new research on COF-based matrices.     

Proton Conduction in Metal–Organic Frameworks and Related Modularly Built Porous Solids

Proton‐conducting materials are an important component of fuel cells. Development of new types of proton‐conducting materials is one of the most important issues in fuel‐cell technology. Herein, we present newly developed proton‐conducting materials, modularly built porous solids, including coordination polymers (CPs) or metal–organic frameworks (MOFs). The designable and tunable nature of the porous materials allows for fast development in this research field. Design and synthesis of the new types of proton‐conducting materials and their unique proton‐conduction properties are discussed.     

Hydrogen sorption in functionalized metal-organic frameworks

Five porous metal-organic frameworks based on linking zinc oxide clusters with benzene-1,4-dicarboxylate, naphthalene-2,6-dicarboxylate, 4,5,9,10-tetrahydropyrene-2,7-dicarboxylate, 2,3,5,6-tetramethylbenzene-1,4-dicarboxylate, or benzene-1,3,5-tris(4-benzoate) were synthesized in gram-scale quantities to measure their hydrogen uptake properties. Hydrogen adsorption isotherms measured at 77 K show a distinct dependence of uptake on the nature of the link. At 1 atm, the materials sorb between 4.2 and 9.3 molecules of H2 per formula unit. The results imply a trend in hydrogen uptake with the number of rings in the organic moiety.     

Hydrogen‐Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton‐Conducting Materials

Two porous hydrogen‐bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra‐high proton conduction values (σ) 0.75× 10^?2 S cm^?1 and 1.8×10^?2 S cm^?1 under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic‐based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen‐bonded porous organic frameworks as solid‐state proton conducting materials.     

A Porous Crystalline Nitrone-Linked Covalent Organic Framework**

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N′, N′, N′′′-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid-state ¹³C multi cross-polarization magic angle spinning NMR spectroscopy of the ¹³C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N₂, CO₂, and H₂ sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO₂ capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.     

衍生多孔碳材料在固相微萃取中的应用研究进展

固相微萃取是一种集采样、萃取、富集和进样于一体的样品前处理技术,其萃取效果与涂层材料密切相关。多孔碳材料具有比表面积大、多孔结构可控、活性位点多和化学稳定性好等优点,广泛应用于电池、超级电容器、催化、吸附和分离等领域,也是一种热门的用作固相微萃取探针的涂层材料。衍生多孔碳材料因种类丰富、可设计性强被广泛研究,研究主要集中在对衍生多孔碳材料的结构优化方面。但是衍生多孔碳材料在固相微萃取中的应用还存在如下问题:(1)共价有机框架衍生多孔碳材料的制备已取得较大进展,但将其应用于固相微萃取领域的研究仍较少;(2)有待进一步明确制备出的衍生多孔碳材料用作固相微萃取涂层表现出优异提取能力的机理;(3)有待进一步深入研究将衍生多孔碳材料用作固相微萃取涂层以实现对不同物理化学性质污染物的广谱高灵敏度分析。文章综述了近3年衍生多孔碳材料在固相微萃取中的应用研究,并展望了未来衍生多孔碳材料在固相微萃取中的研究前景。引用文献共56篇,主要来源于Elsevier。     

Porous Solids Arising from Synergistic and Competing Modes of Assembly: Combining Coordination Chemistry and Covalent Bond Formation

Design and synthesis of porous solids employing both reversible coordination chemistry and reversible covalent bond formation is described. The combination of two different linkage modes in a single material presents a link between two distinct classes of porous materials as exemplified by metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). This strategy, in addition to being a compelling material‐discovery method, also offers a platform for developing a fundamental understanding of the factors influencing the competing modes of assembly. We also demonstrate that even temporary formation of reversible connections between components may be leveraged to make new phases thus offering design routes to polymorphic frameworks. Moreover, this approach has the striking potential of providing a rich landscape of structurally complex materials from commercially available or readily accessible feedstocks.