Selective Ethane/Ethylene Separation in a Robust Microporous Hydrogen-Bonded Organic Framework

Pore-Window Partitions in Metal-Organic Frameworks for Highly Efficient Reversed Ethylene/Ethane Separations

The development of paraffin-selective adsorbents is desirable but extremely challenging because adsorbents usually prefer olefin over paraffin. Herein, a new pore-window-partition strategy is proposed for the rational design of highly efficient paraffin-preferred metal-organic framework (MOF) adsorbents. The power of this strategy is demonstrated by stepwise installations of linear bidentate N-donor linkers into a prototype MOF (SNNU-201) to produce a series of partitional MOF adsorbents (SNNU-202-204). With continuous pore-window partitions from SNNU-201 to SNNU-204, the isosteric heat of adsorption can be tuned from -34.4 to -19.4 kJ mol^-1 for ethylene and from -25.5 to -20.7 kJ mol^-1 for ethane. Accordingly, partitional MOFs exhibit much higher ethane adsorption capacities, especially for SNNU-204 (104.6 cm³ g^-1), representing nearly 4 times as much ethane as the prototypical counterpart (SNNU-201; 27.5 cm³ g^-1) under ambient conditions. The C₂H₆/C₂H₄ ideal adsorbed solution theory selectivity, dynamic breakthrough experiments, and theoretical simulations further indicate that pore-window partition is a promising and universal strategy for the exploration of highly efficient paraffin-selective MOF adsorbents.

Design Rules of Hydrogen-Bonded Organic Frameworks with High Chemical and Thermal Stabilities

Hydrogen-bonded organic frameworks (HOFs), self-assembled from strategically pre-designed molecular tectons with complementary hydrogen-bonding patterns, are rapidly evolving into a novel and important class of porous materials. In addition to their common features shared with other functionalized porous materials constructed from modular building blocks, the intrinsically flexible and reversible H-bonding connections endow HOFs with straightforward purification procedures, high crystallinity, solution processability, and recyclability. These unique advantages of HOFs have attracted considerable attention across a broad range of fields, including gas adsorption and separation, catalysis, chemical sensing, and electrical and optical materials. However, the relatively weak H-bonding interactions within HOFs can potentially limit their stability and potential use in further applications. To that end, this Perspective highlights recent advances in the development of chemically and thermally robust HOF materials and systematically discusses relevant design rules and synthesis strategies to access highly stable HOFs.

Adsorption in Reversed Order of C2 Hydrocarbons on an Ultramicroporous Fluorinated Metal-Organic Framework

Metal-organic frameworks have been widely studied in the separation of C₂ hydrocarbons, which usually preferentially bind unsaturated hydrocarbons with the order of acetylene (C₂ H₂ )>ethylene (C₂ H₄ )>ethane (C₂ H₆ ). Herein, we report an ultramicroporous fluorinated metal-organic framework Zn-FBA (H₂ FBA=4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), shows a reversed adsorption order characteristic for C₂ hydrocarbons, that the uptake for C₂ hydrocarbons of the framework and the binding affinity between the guest molecule and the framework follows the order C₂ H₆ >C₂ H₄ >C₂ H₂ . Density-functional theory calculations confirm that the completely reversed adsorption order behavior is attributed to the close van der Waals interactions and multiple cooperative C-H⋅⋅⋅F hydrogen bonds between the framework and C₂ H₆ . Moreover, Zn-FBA exhibits a high selectivity of about 2.9 for C₂ H₆ over C₂ H₄ at 298 K and 1 bar. The experimental breakthrough studies show that the high-purity C₂ H₄ can be obtained from C₂ H₆ and C₂ H₄ mixtures in one step.

A Microporous Hydrogen-Bonded Organic Framework for Efficient Xe/Kr Separation

Separation of xenon/krypton gas mixtures is one of the valuable but challenging processes in the gas industries due to their close molecular size and similar physical properties. Here, we report a novel ultramicroporous hydrogen-bonded organic framework (termed as HOF-40) constructed from a cyano-based organic building unit of 1,2,4,5-tetrakis(4-cyanophenyl)benzene (TCPB), exhibiting superior separation performance for Xe/Kr mixtures, as clearly demonstrated by dynamic breakthrough curves. GCMC simulation results indicate that the pore confinement effect and abundant accessible binding sites play a synergistic role in this challenging gas separation. Furthermore, this cyano-based HOF displays excellent chemical stability from 12 M HCl to 20 M NaOH aqueous solutions.

Novel Binary Ni-Based Mixed Metal-Organic Framework Nanosheets Materials and Their High Optical Power Limiting

With the rapid advance of laser technology in the photonicera, damage to precision optical instruments caused by exposure to sudden intense laser pulses has stimulated the search for effective optical power limiting materials exhibiting good dispersion, fast response speed, and good visible light transparency. In this study, novel binary Ni-based mixed MOF NSs (M = Mn, Zn, Co, Cd, Fe) were obtained, making the electronic transition more selective and changing the band gap to obtain an excellent reverse saturation absorption signal. The theoretical calculation results show that with the doping of the Fe element, the band gap of Ni-MOF NSs decreases from 3.12 to 0.66 eV of Ni-Fe-MOF NSs, indicating that the doping of the Fe element has a positive effect on the reverse saturated absorption. The experimental results prove that the optical limiting threshold of Ni-Fe-MOF NSs is better than the GNSs, indicating that the Ni-Fe-MOF NSs have a broad application prospect in the field of nonlinear optics and photonics.

An Adaptive Hydrogen-Bonded Organic Framework for the Exclusive Recognition of p-Xylene

Separation of xylene isomers is one of the most important but most challenging and energy-intensive separation processes in the petrochemical industry. Here, we report an adaptive hydrogen-bonded organic framework (HOF-29) constructed from a porphyrin based organic building block 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzonitrile (PTTBN), exhibiting the exclusive molecular recognition of p-xylene (pX) over its isomers of o-xylene (oX) and m-xylene (mX), as clearly demonstrated in the single crystal structure transformation and ¹ H NMR studies. Single crystal structure studies show that single-crystal-to-single-crystal transformation from the as-synthesized HOF-29 to the pX exclusively included HOF-29⊃pX is triggered by the encapsulation of pX molecules, accompanied by sliding of the 2D layers and local distortion of the ligand, which provides multiple C-H⋅⋅⋅π interactions.

HOFs Built from Hexatopic Carboxylic Acids: Structure, Porosity, Stability, and Photophysics

Hydrogen-bonded organic frameworks (HOFs) have attracted renewed attention as another type of promising candidates for functional porous materials. In most cases of HOF preparation, the applied molecular design principle is based on molecules with rigid π-conjugated skeleton together with more than three H-bonding groups to achieve 2D- or 3D-networked structures. However, the design principle does not always work, but results in formation of unexpected structures, where subtle structural factors of which we are not aware dictate the entire structure of HOFs. In this contribution, we assess recent advances in HOFs, focusing on those composed of hexatopic building block molecules, which can provide robust frameworks with a wide range of topologies and properties. The HOFs described in this work are classified into three types, depending on their H-bonded structural motifs. Here in, we focus on: (1) the chemical aspects that govern their unique fundamental chemistry and structures; and (2) their photophysics at the ensemble and single-crystal levels. The work addresses and discusses how these aspects affect and orient their photonic applicability. We trust that this contribution will provide a deep awareness and will help scientists to build up a systematic series of porous materials with the aim to control both their structural and photodynamical assets.

Organic microporous crystals driven by pure C-H⋯π interactions with vapor-induced crystal-to-crystal transformations

Organic porous crystals constructed by only a single kind of weak molecular interaction are invaluable to understanding the nature of the formation of organic porous materials and developing new types of porous materials. Here, we designed and synthesized two pure organic compounds of PBO and PBS through integrating planar dibenzothiophene/dibenzofuran and two phenothiazine groups together with twisted C-N bonds, which form organic microporous crystals with very good stability against strong acids and bases VIA pure C-H⋯π interactions. Accordingly, the effective absorption of toluene has been successfully realized with an adsorbing capacity of 6.20 mmol g^-1, regardless of the interference of water vapor. Excitingly, these microporous materials exhibit interesting crystal-to-crystal transformation (CCT) properties accompanied by changed pore size on being exposed to different organic vapors. Therefore, the desorption process of toluene could be completed through a simple exposure to dichloromethane (DCM) vapor and the second transformation of the crystal occurred in this process.

Immobilization of Lewis Basic Sites into a Stable Ethane-Selective MOF Enabling One-Step Separation of Ethylene from a Ternary Mixture

Purification of C₂H₄ from a ternary C₂H₂/C₂H₆/C₂H₄ mixture by one-step adsorption separation is of prime importance but challenging in the petrochemical industry; however, effective strategies to design high-performance adsorbents are lacking. We herein report for the first time the incorporation of Lewis basic sites into a C₂H₆-selective MOF, enabling efficient one-step production of polymer-grade C₂H₄ from ternary mixtures. Introduction of amino groups into highly stable C₂H₆-selective UiO-67 can not only partition large pores into smaller cagelike pockets to provide suitable pore confinement but also offer additional binding sites to simultaneously enhance C₂H₂ and C₂H₆ adsorption capacities over C₂H₄. The amino-functionalized UiO-67-(NH₂)₂ thus exhibits exceptionally high C₂H₂ and C₂H₆ uptakes as well as benchmark C₂H₂/C₂H₄ and C₂H₆/C₂H₄ selectivities, surpassing all of the C₂H₂/C₂H₆-selective materials reported so far. Theoretical calculations combined with in situ infrared spectroscopy indicate that the synergetic effect of suitable pore confinement and functional surfaces decorated with amino groups provides overall stronger multipoint van der Waals interactions with C₂H₂ and C₂H₆ over C₂H₄. The exceptional performance of UiO-67-(NH₂)₂ was evidenced by breakthrough experiments for C₂H₂/C₂H₆/C₂H₄ mixtures under dry and wet conditions, providing a remarkable C₂H₄ productivity of 0.55 mmol g^-1 at ambient conditions.

Stimuli-Responsive Porous Molecular Crystal with Reversible Modulation of Porosity

Responsive materials have received much attention due to modulated properties under stimuli such as light, heat, and electricity. A photoresponsive porous molecular crystal (1) has been assembled from a racemic dithienylethene-cage (L) by multiple C-F···H-C hydrogen bonds and van der Waals forces according to crystallographic investigation. Electronic absorption spectroscopy reveals reversible photochromic behaviors of the solution and film forms of enantiomeric L upon UV and visible light irradiation due to photoisomerization of dithienylethene units. X-ray photoelectron spectroscopy (XPS), in combination with NMR, discloses the quantitative photoisomerization of photochromic dithienylethene moieties. Moreover, the porosity of 1 is modulated by UV irradiation based on gas sorption data. Interestingly, heating the irradiated sample of 1 in 1,4-dioxane leads to recovered porosity due to the recovered cage molecular structure and maintained periodic frameworks.

Functionalization of a stable AIE-based hydrogen-bonded organic framework for white light-emitting diodes

Hydrogen-bonded organic frameworks (HOFs) have received tremendous attention in recent years due to the good designability. However, the pure organic nature of HOFs sometimes limits the application development and performance improvement. Functionalizing is an effective strategy to control and modulate material properties, which can achieve properties that cannot be achieved by a pristine material. Herein, a series of HOF-76⊃DSMI were synthesized through functionalizing the stable AIE-based HOF-76 by incorporating a red dye which complements the deficiency of the red component of HOF-76. Then, a single matrix white light-emitting diode (WLED) was fabricated by coating the HOF-76⊃DSMI material on a 460 nm blue LED with CIE chromaticity coordinates of (0.333, 0.329), a correlated colour temperature (CCT) of 5490 K and a colour rendering index (CRI) of 80.

We successfully fabricated a white light-emitting diode by coating functionalized AIE-based HOF-76 material on a 460 nm blue LED chip.

Luminescent organic porous crystals from non-cyclic molecules and their applications

Organic porous crystals from small and non-cyclic organic molecules can be constructed by various intermolecular weak interactions. Owing to their precise stacking types, intermolecular interaction and pore microstructure, the relationship...

A nanosized anionic MOF with rich thiadiazole groups for controlled oral drug delivery

Controlling the crystal size and surface chemistry of MOF materials, and understanding their multifunctional effect are of great significance for the biomedical applications of MOF systems. Herein, we designed and synthesized a new anionic MOF, ZJU-64-NSN, which features 1D channels decorated with highly polarized thiadiazole groups, and its crystal size could be systematically tuned from 200 ​μm to 300 ​nm through a green and simple approach. As a result, the optimal nanosized ZJU-64-NSN is found to enable an ultrafast loading of cationic drug procainamide (PA) (21.2 ​wt% within 1 ​min). Moreover, the undesirable chemical stability of PA@ZJU-64-NSN is greatly improved by the surface coating of polyethylene glycol (PEG) biopolymer. The final drug delivery system PEG/PA@ZJU-64-NSN is found to effectively prevent PA from premature release under the harsh stomach environments due to the intense host-guest interaction, and mainly release PA to the targeted intestinal surroundings. Such controlled drug delivery is proved to be triggered by endogenic Na⁺ ions instead of H⁺ ions, well revealed by the study on the dynamics behavior of drug release and UV–Vis absorption spectrum. Good biocompatibility of ZJU-64-NSN and PEG-coated ZJU-64-NSN has been fully demonstrated by MTT assay as well as confocal microscopy imaging.

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A new anionic MOF enables an ultrafast drug loading.

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The crystal size of such MOF could be well size-controlled.

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The surface coating of PEG improves the chemical stability of drug carrier.

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The drug delivery system reveals an endogenic Na ​⁺ ​-triggered procainamide release.

Chemically-Engineered Porous Molecular Coatings as Reactive Oxygen Species Generators and Reservoirs for Long-Lasting Self-Cleaning Textiles

Wearable personal protective equipment that is decorated with photoactive self-cleaning materials capable of actively neutralizing biological pathogens is in high demand. Here, we developed a series of solution-processable, crystalline porous materials capable of addressing this challenge. Textiles coated with these materials exhibit a broad range of functionalities, including spontaneous ROS generation upon absorption of daylight, and long-term ROS storage in dark conditions. The ROS generation and storage abilities of these materials can be further improved through chemical engineering of the precursors without altering the three-dimensional assembled superstructures. In comparison with traditional TiO 2 or C 3 N 4 self-cleaning materials, the fluorinated molecular coating material HOF-101-F shows a 10- to 60-fold enhancement of ROS generation and 10- to 20- fold greater ROS storage ability. Our results pave the way for further developing self-cleaning textile coatings for the rapid deactivation of highly infectious pathogenic bacteria under both daylight and light-free conditions.

Pore-Space Partition and Optimization for Propane-Selective High-Performance Propane/Propylene Separation

The development of effective propane (C3H8)-selective adsorbents for the purification of propylene (C3H6) from C3H8/C3H6 mixture is a promising alternative to replace the energy-intensive cryogenic distillation. However, few materials possess the dual desirable features of propane selectivity and high uptake capacity. Here, we report a family of pore-space-partitioned crystalline porous materials (CPM) with remarkable C3H8 uptake capacity (up to 10.9 mmol/g) and the highly desirable yet uncommon C3H8 selectivity (up to 1.54 at 0.1 bar and 1.44 at 1 bar). The selectivity-capacity synergy endows them with record-performing C3H8/C3H6 separation potential (i.e., C3H6 recovered from the mixture). Moreover, these CPMs exhibit outstanding properties including high stability, low regeneration energy, and multimodular chemical and geometrical tunability within the same isoreticular framework. The high C3H8/C3H6 separation performance was further confirmed by the breakthrough experiments.

Ethylene/ethane separation in a stable hydrogen-bonded organic framework through a gating mechanism

Porous materials are very promising for the development of cost- and energy-efficient separation processes, such as for the purification of ethylene from ethylene/ethane mixture-an important but currently challenging industrial process. Here we report a microporous hydrogen-bonded organic framework that takes up ethylene with very good selectivity over ethane through a gating mechanism. The material consists of tetracyano-bicarbazole building blocks held together through intermolecular CN···H-C hydrogen bonding interactions, and forms as a threefold-interpenetrated framework with pores of suitable size for the selective capture of ethylene. The hydrogen-bonded organic framework exhibits a gating mechanism in which the threshold pressure required for guest uptake varies with the temperature. Ethylene/ethane separation is validated by breakthrough experiments with high purity of ethylene (99.1%) at 333 K. Hydrogen-bonded organic frameworks are usually not robust, yet this material was stable under harsh conditions, including exposure to strong acidity, basicity and a variety of highly polar solvents.

Efficient CO2/CO separation in a stable microporous hydrogen-bonded organic framework

We herein realize the first example of using a microporous HOF material (ZJU-HOF-1) with suitable pore cavities for highly efficient CO₂/CO separation under dry and humid conditions.

A Solid Transformation into Carboxyl Dimers Based on a Robust Hydrogen-Bonded Organic Framework for Propyne/Propylene Separation

Self-assembly of N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine with the help of different solvents provides isostructural hydrogen-bonded organic frameworks (HOF-30). Single-crystal X-ray diffraction (SCXRD) analysis reveals HOF-30 possesses 3D ten-fold interpenetrated dia nets connected by two kinds of hydrogen bonds, namely solvent-bridged carboxyl dimers and carboxyl⋅⋅⋅carboxyl dimers. Degassing treatment for HOF-30 yields HOF-30a with 3D ten-fold interpenetrated dia nets but linked with sole carboxyl⋅⋅⋅carboxyl dimers. Reversible hydrogen-bond-to-hydrogen-bond transformation between solvent-bridged carboxyl dimers in HOF-30 and carboxyl⋅⋅⋅carboxyl dimers in HOF-30a has been unveiled by single-crystal and powder X-ray diffraction. In addition, HOF-30a enables the selective adsorption of propyne over propylene according to single-component sorption and breakthrough experiments. The preferred propyne location in HOF has also been identified by SCXRD test.

Separation and Purification of Hydrocarbons with Porous Materials

This Minireview focuses on the developments of the adsorptive separation of methane/nitrogen, ethene/ethane, propene/propane mixtures as well as on the separation of C8 aromatics (i.e. xylene isomers) with a wide variety of materials, including carbonaceous materials, zeolites, metal-organic frameworks, and porous organic frameworks. Some recent important developments for these adsorptive separations are also highlighted. The advantages and disadvantages of each material category are discussed and guidelines for the design of improved materials are proposed. Furthermore, challenges and future developments of each material type and separation processes are discussed.

A Microporous Hydrogen-Bonded Organic Framework for the Efficient Capture and Purification of Propylene

Adsorptive separation of propylene/propane (C₃ H₆ /C₃ H₈ ) mixture is desired for its potential energy saving on replacing currently deployed and energy-intensive cryogenic distillation. Realizing efficient C₃ H₆ /C₃ H₈ separation in the emerging hydrogen-bonded organic frameworks (HOFs) is very challenging owing to the lack of functional sites for preferential gas binding. By virtue of crystal engineering, we herein report a functionalized HOF (HOF-16) with free -COOH sites for the efficient separation of C₃ H₆ /C₃ H₈ mixtures. Under ambient conditions, HOF-16 shows a significant C₃ H₆ /C₃ H₈ uptake difference (by 76 %) and selectivity (5.4) in contrast to other carboxylic acid-based HOFs. Modeling studies indicate that free -COOH groups together with the suitable pore confinement facilitate the recognition and high-density packing of gas molecules. The separation performance of HOF-16 was validated by breakthrough experiments. HOF-16 is stable towards strong acidity and water.

Construction of isostructural hydrogen-bonded organic frameworks: limitations and possibilities of pore expansion

The library of isostructural porous frameworks enables a systematic survey to optimize the structure and functionality of porous materials. In contrary to metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), a handful of isostructural frameworks have been reported for hydrogen-bonded organic frameworks (HOFs) due to the weakness of the bonds. Herein, we provide a rule-of-thumb to develop isostructural HOFs, where we demonstrate the construction of the third and fourth generation of isostructural HAT-based HOFs (TolHAT-1 and ThiaHAT-1) by considering three important structural factors, that are (1) directional H-bonding, (2) shape-fitted docking of the HAT core, and (3) modulation of peripheral moieties. Their structural and photo-physical properties including HCl vapor detection are presented. Moreover, TolHAT-1, ThiaHAT-1, and other isostructural HOFs (CPHAT-1 and CBPHAT-1) were thoroughly compared from the viewpoints of structures and properties. Importantly, molecular dynamics (MD) simulation proves to be rationally capable of evaluating the stability of isostructural HOFs. These results can accelerate the development of various isostructural molecular porous materials.

Cyclotetrabenzoin Acetate: A Macrocyclic Porous Molecular Crystal for CO2 Separations by Pressure Swing Adsorption*

A porous molecular crystal (PMC) assembled by macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for CO₂ separations. The 7.1×7.1 Å square pore of PMC and its ester C=O groups play important roles in improving its affinity for CO₂ molecules. The benzene walls of macrocycle engage in an apparent [π⋅⋅⋅π] interaction with the molecule of CO₂ at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0×5.0 Å square, which offers kinetic selectivity for CO₂ capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. Most importantly, the moderate adsorbate-adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption processes. The eluted N₂ and CH₄ are obtained with over 99.9 % and 99.8 % purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, cyclotetrabenzoin acetate is a promising adsorbent for CO₂ separations from flue and natural gases.

Highly Stable Single Crystals of Three-Dimensional Porous Oligomer Frameworks Synthesized under Kinetic Conditions

Various robust, crystalline, and porous organic frameworks based on in situ-formed imine-linked oligomers were investigated. These oligomers self-assembled through collaborative intermolecular hydrogen bonding interactions via liquid-liquid interfacial reactions. The soluble oligomers were kinetic products with multiple unreacted aldehyde groups that acted as hydrogen bond donors and acceptors and directed the assembly of the resulting oligomers into 3D frameworks. The sequential formation of robust covalent linkages and highly reversible hydrogen bonds enforced long-range symmetry and facilitated the production of large single crystals, with structures that were unambiguously determined by single-crystal X-ray diffraction. The unique hierarchical arrangements increased the steric hindrance of the imine bond, which prevented attacks from water molecules, greatly improving the stability. The multiple binding sites in the frameworks enabled rapid sequestration of micropollutant in water.

Efficient ethylene purification by a robust ethane-trapping porous organic cage

The removal of ethane (C₂H₆) from its analogous ethylene (C₂H₄) is of paramount importance in the petrochemical industry, but highly challenging due to their similar physicochemical properties. The use of emerging porous organic cage (POC) materials for C₂H₆/C₂H₄ separation is still in its infancy. Here, we report the benchmark example of a truncated octahedral calix[4]resorcinarene-based POC adsorbent (CPOC-301), preferring to adsorb C₂H₆ than C₂H₄, and thus can be used as a robust absorbent to directly separate high-purity C₂H₄ from the C₂H₆/C₂H₄ mixture. Molecular modelling studies suggest the exceptional C₂H₆ selectivity is due to the suitable resorcin[4]arene cavities in CPOC-301, which form more multiple C–H···π hydrogen bonds with C₂H₆ than with C₂H₄ guests. This work provides a fresh avenue to utilize POC materials for highly selective separation of industrially important hydrocarbons.

The removal of ethane from ethylene is of importance in the petrochemical industry, but similar physicochemical properties of these molecules makes separation a challenging task. Here, the authors demonstrate that a robust octahedral calix[4]resorcinarene-based porous organic cage can separate high-purity ethylene from ethane/ethylene mixtures.

Benchmark C2 H2 /CO2 Separation in an Ultra-Microporous Metal-Organic Framework via Copper(I)-Alkynyl Chemistry

Separation of acetylene from carbon dioxide remains a daunting challenge because of their very similar molecular sizes and physical properties. We herein report the first example of using copper(I)-alkynyl chemistry within an ultra-microporous MOF (Cu^I @UiO-66-(COOH)₂ ) to achieve ultrahigh C₂ H₂ /CO₂ separation selectivity. The anchored Cu^I ions on the pore surfaces can specifically and strongly interact with C₂ H₂ molecule through copper(I)-alkynyl π-complexation and thus rapidly adsorb large amount of C₂ H₂ at low-pressure region, while effectively reduce CO₂ uptake due to the small pore sizes. This material thus exhibits the record high C₂ H₂ /CO₂ selectivity of 185 at ambient conditions, significantly higher than the previous benchmark ZJU-74a (36.5) and ATC-Cu (53.6). Theoretical calculations reveal that the unique π-complexation between Cu^I and C₂ H₂ mainly contributes to the ultra-strong C₂ H₂ binding affinity and record selectivity. The exceptional separation performance was evidenced by breakthrough experiments for C₂ H₂ /CO₂ gas mixtures. This work suggests a new perspective to functionalizing MOFs with copper(I)-alkynyl chemistry for highly selective separation of C₂ H₂ over CO₂ .

High-Throughput Discovery of Ni(IN)2 for Ethane/Ethylene Separation

Although ethylene (C2 H4 ) is one of the most critical chemicals used as a feedstock in artificial plastic chemistry fields, it is challenging to obtain high-purity C2 H4 gas without any trace ethane (C2 H6 ) by the oil cracking process. Adsorptive separation using C2 H6 -selective adsorbents is beneficial because it directly produces high-purity C2 H4 in a single step. Herein, Ni(IN)2 (HIN = isonicotinic acid) is computationally discovered as a promising adsorbent with the assistance of the multiscale high-throughput computational screening workflow and Computation-Ready, Experimental (CoRE) metal-organic framework (MOF) 2019 database. Ni(IN)2 is subsequently synthesized and tested to show the ideal adsorbed solution theory (IAST) selectivity of 2.45 at 1 bar for a C2 H6 /C2 H4 mixture (1:15), which is one of the top-performing selectivity values reported for C2 H6 -selective MOFs as well as excellent recyclability, suggesting that this material is a promising C2 H6 -selective adsorbent. Process-level simulation results based on experimental isotherms demonstrate that the material is one of the top materials reported to date for ethane/ethylene separation under the conditions considered in this work.

Solvatomorphism Influence of Porous Organic Cage on C2H2/CO2 Separation

Porous organic molecular (POM) materials can exhibit solvatomorphs via altering their crystallographic packing in the solid state, but investigating real gas mixture separation by porous materials with such a behavior is still very rare. Herein, we report that a lantern-shaped calix[4]resorcinarene-based porous organic cage (POC, namely, CPOC-101) can exhibit eight distinct solid-state solvatomorphs via crystallization in different solvents. This POC solvatomorphism has a significant influence on their gas sorption capacities as well as separation abilities. Specifically, the apparent Brunauer-Emmett-Teller (BET) surface area determined by nitrogen gas sorption at 77 K for CPOC-101α crystallized from toluene/chloroform is up to 406 m² g^-1, which is much higher than the rest of CPOC-101 solvatomorphs with BET values less than 40 m² g^-1. More interestingly, C₂H₂ and CO₂ adsorbed capacities, in addition to the C₂H₂/CO₂ separation ability at room temperature for CPOC-101α, are superior to those of CPOC-101β crystalized from nitrobenzene, the representative of POC solvatomorphs with low BET surface areas. These results indicate the possibility of adjusting gas sorption and separation properties of POC materials by controlling their solvatomorphs.

Organic molecular sieve membranes for chemical separations

Molecular separations that enable selective transport of target molecules from gas and liquid molecular mixtures, such as CO2 capture, olefin/paraffin separations, and organic solvent nanofiltration, represent the most energy sensitive and significant demands. Membranes are favored for molecular separations owing to the advantages of energy efficiency, simplicity, scalability, and small environmental footprint. A number of emerging microporous organic materials have displayed great potential as building blocks of molecular separation membranes, which not only integrate the rigid, engineered pore structures and desirable stability of inorganic molecular sieve membranes, but also exhibit a high degree of freedom to create chemically rich combinations/sequences. To gain a deep insight into the intrinsic connections and characteristics of these microporous organic material-based membranes, in this review, for the first time, we propose the concept of organic molecular sieve membranes (OMSMs) with a focus on the precise construction of membrane structures and efficient intensification of membrane processes. The platform chemistries, designing principles, and assembly methods for the precise construction of OMSMs are elaborated. Conventional mass transport mechanisms are analyzed based on the interactions between OMSMs and penetrate(s). Particularly, the 'STEM' guidelines of OMSMs are highlighted to guide the precise construction of OMSM structures and efficient intensification of OMSM processes. Emerging mass transport mechanisms are elucidated inspired by the phenomena and principles of the mass transport processes in the biological realm. The representative applications of OMSMs in gas and liquid molecular mixture separations are highlighted. The major challenges and brief perspectives for the fundamental science and practical applications of OMSMs are tentatively identified.