共价有机框架材料的离子化改性及其催化合成环碳酸酯的性能研究（英文）

共价有机框架(COFs)材料是继金属-有机框架材料之后,在拓扑学基础上发展起来的又一类多孔材料.这类材料是由轻质元素(C,H,O,N,B,Si等)通过可逆共价键连接而成的结晶性有机多孔聚合物,具有比表面积大、骨架密度低、孔道结构规整、可人为设计以及表面易修饰改性等特点,自2005年首次报道以来就引起了人们的广泛关注.经过十多年的发展,COFs材料已经被广泛用于气体吸附/分离、光电、能量存储、非均相催化等研究领域.由于材料的多孔性以及相对稳定的特点,近年来COFs材料作为催化剂或催化剂载体用于多相催化反应已经成为该领域的一个研究热点.但是到目前为止,COFs材料的离子化改性用于异相催化相关研究还相对较少.本文选择二维骨架中含有羟基基团的H2P-DHPhCOF作为载体,通过两步接枝反应成功地将咪唑型离子液体引入到COF材料的孔道中;采用红外光谱、核磁共振、粉末X射线衍射、热失重分析等方法详细地表征了COF材料在后修饰过程中的变化.研究发现,1,4-二溴丁烷与N-甲基咪唑基团的引入占据了部分孔道,导致框架材料的孔径和孔容减小.同时,我们还将该改性后的离子型COF材料在DMSO/盐酸溶液中消解,利用核磁共振波谱计算了离子化程度.实验结果表明,N-甲基咪唑的接枝率约为4.9wt%.在既定的反应条件下,将该离子化的COF材料作为多相催化剂用于CO2和环氧化合物之间的环加成反应.以环氧氯丙烷作为测试底物,发现该离子型催化剂的催化性能与H2P-DHPhCOF相比有大副度提高,转化率达到了91%(120°C,24 h,CO2压力位1.0 MPa).在相同的条件下,该催化剂还对其他的环氧化合物具有一定的催化效果,其中环氧丙烷的转化率高达95%,且目标产物碳酸丙烯酯的选择性为100%.然而,对于大分子的环氧化合物,转化率和产率均较低,表明催化剂具有明显的尺寸选择性.此外,我们还以环氧氯丙烷的环加成反应为例考察了催化剂的循环稳定性,经过连续的5次循环,催化剂的催化活性得到了有效保持.我们的研究表明COF材料作为异相催化剂用于多相催化具有潜在的应用前景.而且,由于离子型多孔材料具有可交换的性质,我们可以通过将不同功能的反离子交换到孔道中,从而得到具有不同功能特性的多孔材料.因此,离子化共价有机框架材料是一类集多孔、高比表面积、可人为设计等性质于一体的新型多孔材料,有望应用于更加广泛的研究领域.     

3D Microporous Base‐Functionalized Covalent Organic Frameworks for Size‐Selective Catalysis

The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base‐functionalized COFs, termed BF‐COF‐1 and BF‐COF‐2, by the use of a tetrahedral alkyl amine, 1,3,5,7‐tetraaminoadamantane (TAA), combined with 1,3,5‐triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF‐COFs showed remarkable conversion (96 % for BF‐COF‐1 and 98 % for BF‐COF‐2), high size selectivity, and good recyclability in base‐catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape‐selective catalysts.     

共价有机框架材料在多相催化领域的研究进展（英文）

共价有机框架(COFs)材料是近年来在拓扑学基础上发展起来的一类新型有机多孔聚合物,是有机单体通过可逆共价键连接而形成的晶型多孔材料,具有拓扑结构"可设计"、比表面积大、结构规整、孔道均一、孔径可调节以及易于修饰和功能化等优点.与金属有机框架材料(MOFs)相比,由于COFs是以共价键连接形成空间网络结构,具有较好的热稳定性和化学稳定性,又被称为"有机分子筛".COFs的构筑单体为有机小分子,有机小分子来源广泛而且种类繁多,使得构筑单体多样化,便于通过构筑单体来调控目标材料的结构和功能.自2005年首次报道以来,COFs以其独特的结构和优越的性能,吸引了广大科研工作者的极大兴趣,对其结构设计、可控合成、结构解析以及功能探索成为了研究热点,在气体吸附与分离、光电材料等领域展现出了广阔的应用前景.特别是在催化领域,由于COFs材料的多孔性、敞开的孔道结构、良好的稳定性以及易于修饰的特点,采用COFs作为催化剂以及催化剂载体受到了人们普遍的关注.作为催化剂,COFs可分为本征型催化剂和负载型催化剂.本征型催化剂的设计方法是基于"自下而上"策略将催化活性中心嵌入材料骨架之中;负载型催化剂的设计方法是以COFs为载体,通过后修饰方式负载金属颗粒或离子来构建多相催化剂.本征型COFs催化剂是在分子水平上引入催化活性中心,具有活性位点均匀分散、数量可控的特点,而且COFs规整均一的孔道结构有利于底物的传质,也为择形催化提供了可能;负载型催化剂通过后修饰方式引入催化活性中心,由于COFs以共价键连接,催化剂稳定性较高.COFs载体具有较大的比表面积,使得催化活性位点分散性好,也有利于底物与催化活性位点的结合.本文综述了COFs作为多相催化剂在催化领域的发展状况,按照COFs引入催化活性位点的类别,如单催化位点、双催化位点以及负载的金属纳米粒子进行了细致的阐述,重点讨论了COFs催化剂的设计理念、制备方式、功能化策略、材料的稳定性、催化活性以及选择性等内容.此外,对COFs作为光催化剂以及电催化剂方面的研究也进行了详细的介绍.最后,我们讨论了COFs在未来催化领域所面临的问题及挑战,并展望了COFs在超分子催化以及酶催化等方面的应用前景.     

Embedding Hydrogen Atom Transfer Moieties in Covalent Organic Frameworks for Efficient Photocatalytic C−H Functionalization

Covalent organic frameworks (COFs) have emerged as efficient heterogeneous photocatalysts for a wide range of relatively simple organic reactions, whereas their application in complex organic transformations, like site-selective functionalization of unactivated C−H bonds, is underexplored, which can be mainly attributed to the lack of highly active organophotocatalytic cores. Herein through bonding oxygen atoms at the N-terminus of quinolines in nonsubstituted quinoline-linked COFs (NQ−COFs), we successfully realized the embedding of active hydrogen atom transfer (HAT) moieties into the skeleton of COFs. This novel designed COF (NQ−COF_E5−O), serving as both an excellent photosensitizer and HAT catalyst, exhibited much higher efficiency in C−H functionalization than the corresponding NQ−COF_E5. Specially, we evaluated the photocatalytic performance of NQ−COF_E5−O on ten different substrates, including quinolines, benzothiazole, and benzoxazole, all of which were transferred to desired products in moderate to high yields (up to 93 %). Furthermore, the as-synthesized NQ−COF_E5−O displayed excellent photostability and could be reused with negligible loss of activity for five catalytic cycles.     

离子型共价有机框架材料的合成及其催化性能（英文）

共价有机框架(COFs)材料是在拓扑学基础上发展起来的一类新型有机晶体多孔聚合物.由于COFs材料具有较高的比表面积、良好的热稳定性和化学稳定性、可设计的孔结构以及容易修饰改性的特点,目前广泛用作催化剂或催化剂载体.COFs的构筑单体为有机小分子,其来源广泛且种类繁多,使得构筑单体多样化,便于通过构筑单体来调控目标材料的结构和功能.近年来对COFs的研究已经引起人们广泛关注.离子框架材料在气体分子的吸附与分离领域展示了良好性能,通过简单的离子交换过程,可以容易地将具有特定尺寸和功能的反离子引入到框架结构中来调控孔的尺寸大小,从而实现混合气体的有效分离.然而,在催化领域目前尚未见将具有特定催化功能的反离子基团引入到框架之中,研究离子框架材料的催化性能.本文设计合成了一种负电荷为骨架结构的离子型COFs材料.我们首先选取一种化学结构稳定的COF作为骨架前驱体,其中的单体具有可反应的活性基团酚羟基,然后通过与1,3-丙烷磺酸内酯进行开环反应,将烷基磺酸引入到孔中,经过弱碱处理后得到阴离子型COFs(I-COFs),然后通过简单的离子交换过程将具有催化活性的Mn2+以及[Mn(bpy)2]2+配位阳离子分别引入到COFs框架中,得到具有催化功能的新材料.我们考察了两种I-COFs对烯烃氧化制环氧化合物的催化性能,发现所得离子COFs对不同的反应底物均展示了较高的环氧化催化性能.结果证实了离子I-COF催化反应为多相催化,还表现出I-COFs催化剂具有较高的稳定性以及循环使用性能.我们认为,通过简单的离子交换过程,能够赋予I-COFs材料各种不同的功能,从而实现COFs在不同领域的应用.这为多孔材料的功能化设计提供了新的化学平台.     

Designed Synthesis of a 2D Porphyrin‐Based sp2 Carbon‐Conjugated Covalent Organic Framework for Heterogeneous Photocatalysis

The construction of stable covalent organic frameworks (COFs) for various applications is highly desirable. Herein, we report the synthesis of a novel two‐dimensional (2D) porphyrin‐based sp² carbon‐conjugated COF (Por‐sp²c‐COF), which adopts an eclipsed AA stacking structure with a Brunauer—Emmett—Teller surface area of 689 m² g^?1. Owing to the C=C linkages, Por‐sp²c‐COF shows a high chemical stability under various conditions, even under harsh conditions such as 9 m HCl and 9 m NaOH solutions. Interestingly, Por‐sp²c‐COF can be used as a metal‐free heterogeneous photocatalyst for the visible‐light‐induced aerobic oxidation of amines to imines. More importantly, in comparison to imine‐linked Por‐COF, the inherent structure of Por‐sp²c‐COF equips it with several advantages as a photocatalyst, including reusability and high photocatalytic performance. This clearly demonstrates that sp² carbon‐linked 2D COFs can provide an interesting platform for heterogeneous photocatalysis.     

Thiophene-based covalent organic frameworks for highly efficient iodine capture

Development of adsorbent materials for highly efficient iodine capture is high demand from the perspective of ecological environment and human health. Herein, the two kinds of thiophene-based covalent organic frameworks (COFs) with different morphologies were synthesized by solvothermal reaction using thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) as the aldehyde monomer and tri(4-aminophenyl)benzene (PB) or tris(4-aminophenyl)amine (PA) as the amino monomer (denoted as PB-TT COF and PA-TT COF) and the as-prepared two heteroatoms-rich COFs possessed many excellent properties, including high thermal stability and abundant binding sites. Among them, PB-TT COF exhibited ultra-high iodine uptake up to 5.97 g/g in vapor, surpassing most of adsorbents previously reported, which was ascribed to its high specific surface (1305.3 m²/g). Interestingly, PA-TT COF with low specific surface (48.6 m²/g) showed good adsorption ability for iodine in cyclohexane solution with uptake value of 750 mg/g, which was 2.38 times higher than that obtained with PB-TT COF due to its unique sheet-like morphology. Besides, the two COFs possessed good reusability, high selectivity and iodine retention ability. Based on experimental results, the adsorption mechanisms of both COFs were studied, revealing that iodine was captured by the physical-chemical adsorption. Furthermore, the both COFs showed excellent adsorption ability in real radioactive seawater treated safely, demonstrating their great potential in real environment.     

Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three‐dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy‐functionalized COF through postsynthetic modification of a hydroxy‐functionalized COF, and for the first time exploration of the 3D carboxy‐functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy‐functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd³⁺ over Sr²⁺ and Fe³⁺ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.     

Site-Selective Synthesis and Concurrent Immobilization of Imine-Based Covalent Organic Frameworks on Electrodes Using an Electrogenerated Acid

Imine-based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine-based COFs, including a three-dimensional (3D) COF structure.     

Zirconium-mediated metathesis of imines: a study of the scope, longevity, and mechanism of a complicated catalytic system

By kinetically stabilizing imidozirconocene complexes through the use of a sterically demanding ligand, or by generating a more thermodynamically stable resting state with addition of diphenylacetylene, we have developed transition metal-catalyzed imine metathesis reactions that are mechanistically analogous to olefin metathesis reactions catalyzed by metal carbene complexes. When 5 mol % of Cp*Cp(THF)Zr=N(t)Bu is used as the catalyst precursor in the metathesis reaction between PhCH=NPh and p-TolCH=N-p-Tol, a 1:1:1:1 equilibrium mixture with the two mixed imines p-TolCH=NPh and PhCH=N-p-Tol is generated in C(6)D(6) at 105 degrees C. The catalyst was still active after 20 days with an estimated 847 turnovers (t(1/2) 170 m; TON = 1.77 h(-1)). When the azametallacyclobutene Cp(2)Zr(N(Tol)C(Ph)=C(Ph)) is used as the catalyst precursor under similar reaction conditions, a total of 410 turnovers are obtained after 4 days (t(1/2) 170 m; TON = 4.3 h(-1)). An extensive kinetic and equilibrium analysis of the metallacyclobutene-catalyzed metathesis of PhCH=N-p-Tol and p-F-C(6)H(4)CH=N-p-F-C(6)H(4) was carried out by monitoring the concentrations of imines and observable metal-containing intermediates over time. Numerical integration methods were used to fit these data to a detailed mechanism involving coordinatively unsaturated (16-electron) imido complexes as critical intermediates. Examination of the scope of reaction between different organic imines revealed characteristic selectivity that appears to be unique to the zirconium-mediated system. Several zirconocene complexes that could generate the catalytically active "CpCp'Zr=NAr" (Cp' = Cp or Cp*) species in situ were found to be effective agents in the metathetical exchange between different N-aryl imines. N-Alkyl aldimines were found to be completely unreactive toward metathesis with N-aryl aldimines, and metathesis reactions involving the two N-alkyl imines TolCH=NPr and PhCH=NMe gave slow or erratic results, depending on the catalyst used. Metathesis was observed between N-aryl ketimines and N-aryl aldimines, but for N-aryl ketimine substrates, the catalyst resting state consists of zirconocene enamido complexes, generated by the formal C-H activation of the alpha position of the ketimine substrates.     

Designing Thiophene-Enriched Fully Conjugated 3D Covalent Organic Framework as Metal-Free Oxygen Reduction Catalyst for Hydrogen Fuel Cells

The application of three-dimensional (3D) covalent organic frameworks (COFs) in renewable energy fields is greatly limited due to their non-conjugated skeletons. Here, we design and successfully synthesize a thiophene-enriched fully conjugated 3D COF (BUCT-COF-11) through an all-thiophene-linked saddle-shaped building block (COThTh-CHO). The BUCT-COF-11 exhibits excellent semiconducting property with intrinsic metal-free oxygen reduction reaction (ORR) activity. Using the COF as cathode catalyst, the assembled anion-exchange membrane fuel cells (AEMFCs) exhibited a high peak power density up to 493 mW cm⁻². DFT calculations reveal that thiophene introduction in the COF not only improves the conductivity but also optimizes the electronic structure of the sample, which therefore boosts the ORR performance. This is the first report on the application of COFs as metal-free catalysts in fuel cells, demonstrating the great potential of fully conjugated 3D COFs as promising semiconductors in energy fields.     

Porphyrin-based donor–acceptor COFs as efficient and reusable photocatalysts for PET-RAFT polymerization under broad spectrum excitation

Covalent organic frameworks (COFs) are crystalline and porous organic materials attractive for photocatalysis applications due to their structural versatility and tunable optical and electronic properties. The use of photocatalysts (PCs) for polymerizations enables the preparation of well-defined polymeric materials under mild reaction conditions. Herein, we report two porphyrin-based donor–acceptor COFs that are effective heterogeneous PCs for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT). Using density functional theory (DFT) calculations, we designed porphyrin COFs with strong donor–acceptor characteristics and delocalized conduction bands. The COFs were effective PCs for PET-RAFT, successfully polymerizing a variety of monomers in both organic and aqueous media using visible light (λ_max from 460 to 635 nm) to produce polymers with tunable molecular weights (MWs), low molecular weight dispersity, and good chain-end fidelity. The heterogeneous COF PCs could also be reused for PET-RAFT polymerization at least 5 times without losing photocatalytic performance. This work demonstrates porphyrin-based COFs that are effective catalysts for photo-RDRP and establishes design principles for the development of highly active COF PCs for a variety of applications.

Porphyrin-based donor–acceptor COFs are effective heterogeneous photocatalysts for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT), including for aqueous polymerizations and under red-light excitation.     

Covalent Organic Frameworks Based Single-site Electrocatalysts for Oxygen Reduction Reaction

Single site catalysts(SSCs) are a new type of heterogeneous catalysts formed by isolated metal atoms supported on kinds of substrates. SSCs have shown great potential for energy conversion and storage in recent years, especially for oxygen reduction reactions(ORR). Typically, SSCs are confined on the substrate by strong chemical interactions, such as coordination bonds. Therefore, the surface chemical environment and porous properties of the supports are crucial to the performance of SSCs. In recent years, COFs have become excellent candidates for preparing SSCs as they can precisely assemble monomers into highly ordered crystalline porous materials with a fine structure and definite components. In this review, we not only summarize the characteristics and advantages of COFs based SSCs, but also highlight the applications of COFs constructed from different single active sites for ORR in recent years. Finally, challenges in practical application, feasible strategies and perspectives are proposed for the of COFs based SSCs.     

Irreversible Amide-Linked Covalent Organic Framework for Selective and Ultrafast Gold Recovery

Design of stable adsorbents for selective gold recovery with large capacity and fast adsorption kinetics is of great challenge, but significant for the economy and the environment. Herein, we show the design and preparation of an irreversible amide-linked covalent organic framework (COF) JNU-1 via a building block exchange strategy for efficient recovery of gold. JNU-1 was synthesized through the exchange of 4,4′-biphenyldicarboxaldehyde (BA) in mother COF TzBA consisting of 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and BA with terephthaloyl chloride. The irreversible amide linked JNU-1 gave good stability, unprecedented fast kinetics, excellent selectivity and outstanding adsorption capacity for gold recovery. X-ray photoelectron spectroscopy along with thermodynamic study and quantum mechanics calculation reveals that the excellent performance of JNU-1 for gold recovery results from the formation of hydrogen bonds C(N)−H⋅⋅⋅Cl and coordinate interaction of O and Au. The rational design of irreversible bonds as both inherent linkage and functional groups in COFs is a promising way to prepare stable COFs for diverse applications.     

Construction of novel benzoxazine-linked covalent organic framework with antimicrobial activity via postsynthetic cyclization

Organic framework materials have shown increasingly promising applications in biomedicine, such as drug delivery and release. In this work, we first synthesized a new hydroxyl-containing imine-linked two-dimensional covalent organic framework (COF) through solvothermal synthesis. Then, the imine group was converted into a benzoxazine group using a cyclization reaction. The results show that the postsynthetic modification did not change the basic framework of the original COF and did not affect the basic properties of the original COF. At the same time, the new benzoxazine group obtained by cyclization gave the COF good antibacterial activity against Escherichia coli and Staphylococcus aureus. The COF efficiency after cyclization was improved, and its antibacterial activity against both bacteria was over 90% compared with the imine-linked COF. Moreover, the benzoxazine-linked COF crystal structure and pore structures were retained, leaving the drug delivery and release functions unaffected. A benzoxazine-linked COF has never been reported because it cannot be synthesized by a direct reaction method. The work in this paper shows that the COFs that cannot be directly synthesized can be obtained through specific postsynthetic modification reactions. This means that more functional COFs can be obtained based on existing COFs, and the diversity of COF types and their potential applications can be further enriched and expanded.     

A general model for selectivity in olefin cross metathesis

In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with alpha-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using feedstock stoichiometries as low as 1:1. By employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electron-rich, electron-deficient, and sterically bulky olefins. Application of this model has allowed for the prediction and development of selective cross metathesis reactions, culminating in unprecedented three-component intermolecular cross metathesis reactions.     

Solvothermal depolymerization and recrystallization of imine-linked two-dimensional covalent organic frameworks

Mechanistic understanding into the formation and growth of imine-linked two-dimensional (2D) covalent organic frameworks (COFs) is needed to improve their materials quality and access larger crystallite sizes, both of which limit the promise of 2D COFs and 2D polymerization techniques. Here we report a previously unknown temperature-dependent depolymerization of colloidal 2D imine-linked COFs, which offers a new means to improve their crystallinity. 2D COF colloids form at room temperature but then depolymerize when their reaction mixtures are heated to 90 °C. As the solutions are cooled back to room temperature, the 2D COFs repolymerize and crystallize with improved crystallinity and porosity, as characterized by X-ray diffraction, infrared spectroscopy and N₂ porosimetry. The evolution of COF crystallinity during the solvothermal depolymerization and repolymerization processes was characterized by in situ wide angle X-ray scattering, and the concentrations of free COF monomers as a function of temperature were quantified by variable temperature ¹H NMR spectroscopy. The ability of a 2D COF to depolymerize under these conditions depends on both the identity of the COF and its initial materials quality. For one network formed at room temperature (TAPB-PDA COF), a first depolymerization process is nearly complete, and the repolymerization yields materials with dramatically enhanced crystallinity and surface area. Already recrystallized materials partially depolymerize upon heating their reaction mixtures a second time. A related 2D COF (TAPB-DMTA COF) forms initially with improved crystallinity compared to TAPB-PDA COF and then partially depolymerizes upon heating. These results suggest that both high materials quality and network-dependent properties, such as interlayer interaction strength, influence the extent to which 2D COFs resist depolymerization. These findings offer a new means to recrystallize or solvent anneal 2D COFs and may ultimately inform crystallization conditions for obtaining large-area imine-linked two-dimensional polymers from solution.

Conditions for which imine-linked 2D COF polymerizations are temperature-sensitive are identified that enable a dissolution/repolymerization process akin to molecular recrystallization.     

Predicting of Covalent Organic Frameworks for Membrane-based Isobutene/1,3-Butadiene Separation: Combining Molecular Simulation and Machine Learning

Efficient separation of C4 olefins is of critical importance and a challenging task in petrochemical industry. Covalent organic frameworks(COFs) could be used as promising candidates for membrane-based isobutene/1,3-butadiene(i-C₄H₈/C₄H₆) separation. Owing to large amounts of COFs appearing, however, the rapid prediction of optimal COFs is imperative before experimental efforts. In this work, we combine molecular simulation and machine learning to study COF membranes for efficient isolation of i-C₄H₈ over C₄H₆. Using molecular simulation, four potential COF membranes, which possess both high membrane performance score (MPS) value and moderate membrane selectivity were screened out and the mechanism of membrane separation further revealed is an adsorption dominated process. Further, random forest(RF) model with high prediction accuracy(R²>0.84) was obtained and used for elucidating key factors in controlling the membrane selectivity and i-C₄H₈ permeability. Ultimately, the optimal COF features were obtained through structure-performance relationship study. Our results may trigger experimental efforts to accelerate the design of novel COFs with better i-C₄H₈/C₄H₆separation performance.     

Functionalized COFs with Quaternary Phosphonium Salt for Versatilely Catalyzing Chemical Transformations of CO2

Currently, it encounters great challenges to accomplish catalyzing various kinds of carbon dioxide(CO₂) conversion reactions efficiently with single catalyst, let alone control the interplay among catalytic efficiency and selectivity evenly. Here, we prepared a functional covalent organic framework, [PTPP]_X%-TD-COF[PTPP=3-bromopropyltriphenylphosphonium; TD=1,3,5-tri(4-aminophenyl)benzene-1,4-diformylbenzene], by immobilizing the quaternary phosphonium salt onto the skeleton of COFs through a post-synthesis strategy for versatilely catalyzing reduction of CO₂ and CO₂ fixation on epoxide and aziridine facilely. With the typical features of COFs(such as porosity and ordered structure) and catalytic activity of the quaternary phosphonium salt, [PTPP]_X%-TD-COF possesses an intensely synergistic effect for catalyzing the chemical transformations of CO₂. Noteworthily, the quaternary phosphonium salt functionalized COFs catalyze the CO₂ reduction reaction with amine and phenylsilane to produce formylated and methylated products under gentle reaction conditions with high selectivity and efficiency. Furthermore, [PTPP]_X%-TD-COF shows high catalytic ability in CO₂ chemical fixation reactions.