Porous Polymers as Multifunctional Material Platforms toward Task‐Specific Applications

Exploring advanced porous materials is of critical importance in the development of science and technology. Porous polymers, being famous for their all‐organic components, tailored pore structures, and adjustable chemical components, have attracted an increasing level of research interest in a large number of applications, including gas adsorption/storage, separation, catalysis, environmental remediation, energy, optoelectronics, and health. Recent years have witnessed tremendous research breakthroughs in these fields thanks to the unique pore structures and versatile skeletons of porous polymers. Here, recent milestones in the diverse applications of porous polymers are presented, with an emphasis on the structural requirements or parameters that dominate their properties and functionalities. The Review covers the following applications: i) gas adsorption, ii) water treatment, iii) separation, iv) heterogeneous catalysis, v) electrochemical energy storage, vi) precursors for porous carbons, and vii) other applications (e.g., intelligent temperature control textiles, sensing, proton conduction, biomedicine, optoelectronics, and actuators). The key requirements for each application are discussed and an in‐depth understanding of the structure–property relationships of these advanced materials is provided. Finally, a perspective on the future research directions and challenges in this field is presented for further studies.     

Photothermal‐Responsive Microporous Nanosheets Confined Ionic Liquid for Efficient CO2 Separation

2D materials hold promising potential for novel gas separation. However, a lack of in‐plane pores and the randomly stacked interplane channels of these membranes still hinder their separation performance. In this work, ferrocene based‐MOFs (Zr‐Fc MOF) nanosheets, which contain abundant of in‐plane micropores, are synthesized as porous supports to fabricate Zr‐Fc MOF supported ionic liquid membrane (Zr‐Fc‐SILM) for highly efficient CO₂ separation. The micropores of Zr‐Fc MOF nanosheets not only provide extra paths for CO₂ transportation, and thus increase its permeance up to 145.15 GPU, but also endow the Zr‐Fc‐SILM with high selectivity (216.9) of CO₂/N₂ through the nanoconfinement effect, which is almost ten times higher than common porous polymer SILM. Furthermore, based on the photothermal‐responsive properties of Zr‐Fc MOF, the performance is further enhanced (35%) by light irradiation through a photothermal heating process. This provides a brand new way to design light facilitating gas separation membranes.     

Anion Substitution in Porous Aromatic Frameworks: Boosting Molecular Permeability and Selectivity for Membrane Acetylene Separation

Precise tailoring of pore chemistry is indispensable for efficient membrane gas separation, particularly for the challenging acetylene system. Here, a strategy called “anion substitution” is reported, to strengthen the interaction between anions and acetylene within the pores, for radically improving gas selectivity and permeability. The anions F⁻ and OH⁻ are infixed in iPAF-1 to replace the original Cl⁻ ion. Their small anionic radii allow retention of the original high porosity of iPAF-1-Cl in iPAF-1-F and iPAF-1-OH. Highly basic F⁻ and OH⁻ confined in the pores attract acidic acetylene strongly and preferentially. Nanoparticles of iPAF-1 are processed to form mixed matrix membranes, represented by iPAF-1-OH/6FDA-ODA. The prepared membranes exhibit remarkable performance in separating acetylene from ethylene and ethane. Transplantation of porous and functional iPAF-1-OH into 6FDA-ODA significantly enhances both acetylene permeability (sevenfold) and permselectivity (fivefold) for acetylene over ethylene and ethane, which is crucial for membrane acetylene gas separation.     

新型多孔材料在惰性气体Xe/Kr分离中的应用

惰性气体氙与氪的分离在大气放射性核素监测、惰性气体工业制备和乏燃料处理等领域中均有重要应用。常规的方法是利用低温精馏将氙与氪从大气中分离,需要耗费大量能源,成本高。因此,作为替代方法在常温下通过多孔材料高效吸附分离氙与氪具有重要意义。近年来发展的以金属有机框架材料、多孔有机分子笼材料等为代表的新型多孔材料在惰性气体氙与氪的分离中展现出了优异的性能与良好的应用前景。系统地综述了新型多孔材料在Xe/Kr分离中的研究进展,从计算模拟在Xe/Kr分离研究中的应用、高浓度氙/氪分离研究与极低浓度Xe/Kr分离研究3个方面进行论述与总结,最后对未来研究趋势进行了总结与展望。     

Polymer nanosieve membranes for CO2-capture applications

Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes.     

Electroactive Covalent Organic Frameworks: Design,Synthesis, and Applications

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailorable compositions, porosities, functionalities, and intrinsic chemical stability. The incorporation of electroactive moieties in the structure transforms COFs into electroactive materials with great potential for energy-related applications. Herein, the recent advances in the design and use of electroactive COFs as capacitors, batteries, conductors, fuel cells, water-splitting, and electrocatalysis are addressed. Their remarkable performance is discussed and compared with other porous materials; hence, perspectives in the development of electroactive COFs are presented.     

A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Propyne/propylene (C₃H₄/C₃H₆) separation is a critical process for the production of polymer‐grade C₃H₆. However, optimization of the structure of porous materials for the highly efficient removal of C₃H₄ from C₃H₆ remains challenging due to their similar structures and ultralow C₃H₄ concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF₆^2? = SIFSIX, NbOF₅^2? = NbOFFIVE) can serve as highly selective C₃H₄ traps for the removal of trace C₃H₄ from C₃H₆. Especially, it is revealed that the pyrazine‐based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1–0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single‐molecule trap for C₃H₄ molecule. The pyrazine‐based single‐molecule trap enables extremely high C₃H₄ uptake under ultralow concentration (2.65 mmol g^?1 at 3000 ppm, one C₃H₄ per unit cell) and record selectivity over C₃H₆ at 298 K (>250). The single‐molecule binding mode for C₃H₄ within ultramicroporous material is validated by X‐ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion‐pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C₃H₄ (1000 ppm on SIFSIX‐3‐Ni, and 10 000 ppm on SIFSIX‐2‐Cu‐i) from C₃H₆.     

Nanoporous polymeric materials: A new class of materials with enhanced properties

Nanoporous polymeric materials are porous materials with pore sizes in the nanometer range (i.e., below 200 nm), processed as bulk or film materials, and from a wide set of polymers. Over the last several years, research and development on these novel materials have progressed significantly, because it is believed that the reduction of the pore size to the nanometer range could strongly influence some of the properties of porous polymers, providing unexpected and improved properties compared to conventional porous and microporous polymers and non-porous solids.In this review, the key properties of these nanoporous polymeric materials (mechanical, thermal, dielectric, optical, filtration, sensing, etc.) are analyzed. The experimental and theoretical results obtained up to date related to the structure–property relations are presented. In several sections, in order to present a more compressive approach, the trends obtained for nanoporous polymers are compared to those for metallic and ceramic nanoporous systems. Moreover, some specific characteristics of these materials, such as the consequences of the confinement of both gas and solid phases, are described. Likewise, the main production methods are briefly described. Finally, some of the potential applications of these materials are also discussed in this paper.     

Breath Figures法制备漆酚铜聚合物多孔膜

以漆酚铜聚合物(UCP)有机溶液为铸膜液,采用Breath Figures法制备漆酚铜聚合物多孔膜,探讨了溶剂、环境相对湿度和潮湿气体流速等因素对多孔膜形貌的影响,并使用红外光谱和扫描电镜等进行表征。结果表明,以二硫化碳为溶剂,在静态(潮湿气体流速为0mL/min,湿度为95%)或动态(潮湿气体流速为400mL/min,湿度为85%)时,均可制得孔分布均匀、孔型规整、优良耐热性和耐酸碱性的疏水性UCP多孔膜,其平均孔径分别为1.5和0.85μm。     

Engineering porous materials for fuel cell applications

Porous materials play an important role in fuel cell engineering. For example, they are used to support delicate electrolyte membranes, where mechanical integrity and effective diffusivity to fuel gases is critical; they are used as gas diffusion layers, where electronic conductivity and permeability to both gas and water is critical; and they are used to construct fuel cell electrodes, where an optimum combination of ionic conductivity, electronic conductivity, porosity and catalyst distribution is critical. The paper will discuss these characteristics, and introduce the materials and processing methods used to engineer porous materials within two of the leading fuel cell variants, the solid oxide fuel cell and the polymer electrolyte membrane fuel cell.     

新型无机二维材料在气体分离膜领域的研究进展

气体膜分离技术是过滤与分离工业的重要技术之一, 相比于传统分离技术更加高效、节能、环保。新型无机二维材料在分离膜领域的应用, 有望同时实现高选择性和高渗透率, 突破商业聚合物膜渗透率和选择性相互制约的瓶颈, 极大地促进高性能分离膜的发展。本文简述了膜的气体分离机制, 综述了石墨烯基、过渡金属硫族化物(TMDs)和二维过渡金属碳化物/氮化物(MXene)等新型无机二维材料近年来在气体分离膜领域的研究进展, 包括其设计、制造和应用, 探讨了不同材料分离膜的特点、面临的挑战和发展前景。此外, 本文对其他新兴二维材料——层状双氢氧化物(LDHs)、六方氮化硼(h-BN)、云母纳米片等的分离膜研究也进行了概述。最后, 对新型无机二维材料在气体分离膜领域的研究方向及面临的挑战作出了评价。     

Polymer-coated fibrous materials as the stationary phase in packed capillary gas chromatography

Synthetic polymer filaments have been introduced as the support material in packed capillary gas chromatography (GC). The filaments of the heat-resistant polymers, Zylon, Kevlar, Nomex, and Technora, were longitudinally packed into a short fused-silica capillary, followed by the conventional coating process for open-tubular GC columns. The separation of several test mixtures such as n-alkylbenzenes and n-alkanes was carried out with these polymer-coated fiber-packed capillary columns. With the coating by various polymeric materials on the surface of these filaments, the retentivity was significantly improved over the parent fiber-packed column (without polymer coating) as well as a conventional open-tubular capillary of the same length. The results demonstrated a good combination of Zylon as the support and poly(dimethylsiloxane)-based materials as the coating liquid-phase for the successful GC separation of n-alkanes and polycyclic aromatic hydrocarbons (PAHs), while successful applications for other separations such as poly(ethylene glycol) coating for the separation of alcohols were also obtained. From the results it has been suggested that the selectivity of the fiber-packed column could be tuned by selecting different coating materials, indicating the promising possibility for a novel usage of fine fibrous polymers as the support material that can be combined with newly synthesized coating materials specially designed for particular separations. Taking advantage of good thermal stability of the fibers, the column temperature could be elevated to higher than 350 degrees C with the combination of a short metallic capillary.     

Freeforming of polymers

Rapid prototyping and freeform fabrication methods are being increasingly used as a stage in the design cycle of polymers. They also represent new ways of processing materials and particularly provide much closer coupling between materials synthesis and materials processing. Freeforming techniques also allow new combinations of materials to be formed, such as functional gradients, oriented composites, porous structures and devices.     

含金刚烷聚合物的研究进展

含金刚烷聚合物在气体分离、液晶显示材料、通讯技术、微电子、生物医学等高新技术领域已显示出潜在用途。文中对以金刚烷衍生物为单体的聚合物的合成、结构与性能等方面的研究进展做了分析和评述,对这一领域的发展趋势进行了展望。     

混合超微孔材料中CO2/N2吸附与分离的理论研究

碳捕获与封存技术是一种具有前景的CO₂减排策略。本工作采用巨正则蒙特卡洛模拟研究了温度为298 K、压强在0~5 kPa范围内三种混合超微孔材料SIFSIX-X-Cu(以SiF₆ ^2-排列, Cu为金属中心, X=2, 3, O)中CO₂/N₂吸附与分离的行为。结果显示, 相比于SIFSIX-2-Cu, SIFSIX-3-Cu和SIFSIX-O-Cu中CO₂在0.5 kPa就达到吸附饱和, 且在1 kPa下的吸附量分别达到了2.70与2.39 mmol·g ^-1。CO₂/N₂混合气体中CO₂的吸附量几乎没有下降。SIFSIX-3-Cu和SIFSIX-O-Cu具有接近于CO₂分子动力学直径的孔径, 对CO₂亲和力较大, 吸附热分别达到了59和66 kJ·mol ^-1。密度泛函理论分析发现, 在两种结构中每个孔隙只吸附一个CO₂分子, 且几乎处于孔道的中心。本工作为低压下吸附与分离CO₂的混合超微孔材料的开发提供了理论指导。     

Engineering Homochiral Metal‐Organic Frameworks for Heterogeneous Asymmetric Catalysis and Enantioselective Separation

Owing to the potential applications in technological areas such as gas storage, catalysis, separation, sensing and nonlinear optics, tremendous efforts have been devoted to the development of porous metal‐organic frameworks (MOFs) over the past ten years. Homochiral porous MOFs are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds due to the lack of homochiral inorganic porous materials such as zeolites. In this review, we summarize the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and latest advances in asymmetric heterogeneous catalysis and enantioselective separation.     

Bioinspired supramolecular liquid crystals

A brief account on the historical events leading to the discovery of self-assembling dendrons that generate self-organizable supramolecular dendrimers, or supramolecular polymers, and self-organizable dendronized polymers is provided. These building blocks were accessed by an accelerated design strategy that involves structural and retrostructural analysis of periodic and quasi-periodic assemblies. This design strategy mediated the discovery of porous helical supramolecular structures that self-assembled from dendritic dipeptides. Helical porous columns are the closest mimics of biologically related structures, such as tobacco mosaic virus coat, porous transmembrane proteins, porous pathogens and antibiotics. It is expected that this concept will allow one to investigate the structural origin of functions in synthetic supramolecular materials.     

Recent Advances of Solid-State NMR Spectroscopy for Microporous Materials

Microporous materials have attracted a rapid growth of research interest in materials science and the multidisciplinary area because of their wide applications in catalysis, separation, ion exchange, gas storage, drug release, and sensing. A fundamental understanding of their diverse structures and properties is crucial for rational design of high-performance materials and technological applications in industry. Solid-state NMR (SSNMR), capable of providing atomic-level information on both structure and dynamics, is a powerful tool in the scientific exploration of solid materials. Here, advanced SSNMR instruments and methods for characterization of microporous materials are briefly described. The recent progress of the application of SSNMR for the investigation of microporous materials including zeolites, metal–organic frameworks, covalent organic frameworks, porous aromatic frameworks, and layered materials is discussed with representative work. The versatile SSNMR techniques provide detailed information on the local structure, dynamics, and chemical processes in the confined space of porous materials. The challenges and prospects in SSNMR study of microporous and related materials are discussed.     

On the molecular origin of supercapacitance in nanoporous carbon electrodes

Lightweight, low-cost supercapacitors with the capability of rapidly storing a large amount of electrical energy can contribute to meeting continuous energy demands and effectively levelling the cyclic nature of renewable energy sources. The excellent electrochemical performance of supercapacitors is due to a reversible ion adsorption in porous carbon electrodes. Recently, it was demonstrated that ions from the electrolyte could enter sub nanometre pores, greatly increasing the capacitance. However, the molecular mechanism of this enhancement remains poorly understood. Here we provide the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes. We show how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values (125 F g(-1)) than with simpler electrode geometries. The proposed mechanism opens the door for the design of materials with improved energy storage capabilities. It also sheds new light on situations where ion adsorption in porous structures or membranes plays a role.     

Polymers with Side Chain Porosity for Ultrapermeable and Plasticization Resistant Materials for Gas Separations

Polymer membranes with ultrahigh CO₂ permeabilities and high selectivities are needed to address some of the critical separation challenges related to energy and the environment, especially in natural gas purification and postcombustion carbon capture. However, very few solution‐processable, linear polymers are known today that access these types of characteristics, and all of the known structures achieve their separation performance through the design of rigid backbone chemistries that concomitantly increase chain stiffness and interchain spacing, thereby resulting in ultramicroporosity in solid‐state chain‐entangled films. Herein, the separation performance of a porous polymer obtained via ring‐opening metathesis polymerization is reported, which possesses a flexible backbone with rigid, fluorinated side chains. This polymer exhibits ultrahigh CO₂ permeability (>21 000 Barrer) and exceptional plasticization resistance (CO₂ plasticization pressure > 51 bar). Compared to traditional polymers of intrinsic microporosity, the rate of physical aging is slower, especially for gases with small effective diameters (i.e., He, H₂, and O₂). This structural design strategy, coupled with studies on fluorination, demonstrates a generalizable approach to create new polymers with flexible backbones and pore‐forming side chains that have unexplored promise for small‐molecule separations.