A molecular sieve with ultrafast adsorption kinetics for propylene separation

Toward Molecular Simulation Guided Design of Next-Generation Membranes: Challenges and Opportunities

Membranes provide energy-efficient solutions for separating ions from water, ion-ion separation, neutral or charged molecules, and mixed gases. Understanding the fundamental mechanisms and design principles for these separation challenges has significant applications in the food and agriculture, energy, pharmaceutical, and electronics industries and environmental remediation. In situ experimental probes to explore Angstrom-nanometer length-scale and pico-nanosecond time-scale phenomena remain limited. Currently, molecular simulations such as density functional theory, ab initio molecular dynamics (MD), all-atom MD, and coarse-grained MD provide physics-based predictive models to study these phenomena. The status of molecular simulations to study transport mechanisms and state-of-the-art membrane separation is discussed. Furthermore, limitations and open challenges in molecular simulations are discussed. Finally, the importance of molecular simulations in generating data sets for machine learning and exploration of membrane design space is addressed.

Modulating Adsorption Kinetics in a 3D-Interconnected Nanocavity Framework with Narrow Apertures for Enhanced Propylene Separation

The energy-intensive distillation currently used for C3H6/C3H8 separation─challenged by their small boiling point difference─could be improved via adsorption. However, most porous materials face a trade-off among C3H6 adsorption capacity, selectivity, and kinetics. Herein, we report the synthesis and characterization of a novel metal-organic framework, denoted NiPz4Bim, constructed from a weak Lewis-base pyrazole-based ligand Pz4Bim and the weak Lewis-acid Ni2+, featuring 3D pore structures with nanocavities (∼1 nm) connected by very narrow apertures (∼5 Å). This framework enables efficient C3H6/C3H8 separation by combining selective adsorption with enhanced diffusion kinetics for C3H6. Specifically, adsorption capacities at 298 K and 1 bar were recorded as 3.24 mmol g-1 for C3H6 and 2.74 mmol g-1 for C3H8, with selectivity ratios of up to 2.42. Kinetic uptake analysis using the effective diffusion coefficient (D') revealed a significant difference in the adsorption rates of the two gases, corresponding to a kinetic selectivity of 51.96. Neutron powder diffraction, coupled with grand canonical Monte Carlo simulations and density functional theory calculations, directly visualizes the binding domains of adsorbed gases and the dynamics and energetics of the host-guest interactions. These studies reveal that the unique nanosized cavities with narrow apertures in NiPz4Bim facilitates van der Waals and π-π interactions with C3H6, enabling selective trapping over C3H8. Crucially, NiPz4Bim exhibits high stability and reusability in multicycle tests, demonstrating its practical viability. This work highlights the importance of pore-geometry engineering in framework materials for the efficient separation of structurally similar molecules, with immediate implications for sustainable olefin production.

Zinc Pyrazolate Framework with Knotted-Like Chains for Separation of Propylene/Ethylene Mixtures

Ethylene and propylene are important raw chemicals that are in high demand. Methanol-to-olefins (MTO) is a promising alternative approach for producing ethylene from non-petroleum feedstocks, in which the separation of propylene/ethylene is particularly crucial. In this study, a metal azolate framework (MAF) [Zn7(μ-H2O)(tppa)4(HCOO)2] (MAF-68, where H3tppa = tris(4-(1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazol-4-yl)phenyl)amine) has been synthesized with rare zinc pyrazolate chains comprising μ-H2O bridges, namely Zn7(μ-H2O)(Rpz)12(HCOO)2 (Rpz- denotes pyrazolate groups), for the separation of propylene/ethylene mixtures. Sorption experiments indicated that MAF-68 shows a remarkable uptake of 4.19 mmol g-1 for propylene (at 10 kPa), which is significantly higher than those of many other reported porous materials for C3H6/C2H4 separation. MAF-68 also shows a high selectivity of 9.5 for 2/5 C3H6/C2H4. Breakthrough experiments further confirm the separation potential of this material for high-purity C3H6 (99.9999%) and C2H4 (99.9999%).

Reticular Chemistry within Crystalline Porous Gas Adsorbents and Membranes

ConspectusAdsorptive and membrane separations are recognized as highly energy-efficient technologies, critically dependent on the properties of adsorbent and membrane materials. Crystalline porous materials (CPMs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), metal-organic cages (MOCs), and hydrogen-bonded organic frameworks (HOFs), have emerged as exceptional candidates for high-performance adsorbents and membranes due to their intrinsic structural tunability. Their orderly pore structure, high porosity, and large surface facilitate gas storage and separation processes. Furthermore, modifying the inner surface, controlling the pore size, and regulating the framework flexibility can significantly enhance CPMs' adsorption capacity and separation selectivity. Therefore, the precise structure regulation of CPMs is the key to optimizing gas separation and purification.Reticular chemistry is the use of strong chemical bonds to connect discrete molecular structures (molecules or molecular clusters) to create extended structures, such as CPMs. It allows precise atomic-level control and offers a method for regulating the structures of CPMs, enabling tailored pore environments that enhance selectivity for target separations. This approach is crucial to designing effective gas separation materials. For example, by functionalizing organic ligands, regulating metal ions, and modifying secondary building units, the pore size, porosity, and functionality of CPMs can be finely controlled while keeping the framework topology unchanged, thereby optimizing the gas separation performance.In this Account, we present an overview of our group's research efforts on optimizing gas separation by fine-tuning CPM adsorbents and membranes. Using reticular chemistry, we have developed strategies such as multiple cooperative regulation, adaptive pore control, pore environment engineering, preprocessed monomer interfacial polymerization, and precursor solution processing to create highly selective CPM adsorbents and membranes. Additionally, we elucidate the underlying mechanism of multiple hydrogen bonding and dipole-dipole interactions between CPMs and hydrocarbon molecules. By precise structural regulation, we further optimize the gas separation performance and broaden CPMs' applications. Finally, we discuss the challenges and future directions for CPM adsorbents and membranes, including material design, synthesis, stability, performance, and the structure-activity relationship. We also propose a membrane-adsorptive separation coupling technology as a potential solution for achieving high-purity gas separation. By utilizing CPM-based adsorbents and membranes, we aim to establish an energy-intensive and environmentally friendly pathway for the separation of low-carbon hydrocarbons, hydrogen, and natural gas, providing a sustainable alternative to conventional high-energy gas separation processes.

Synthesis and Modification of Formate Zr-MOF (ZrFA) Toward Scalable and Cost-Cutting Gas Separation

The mass production of metal-organic frameworks (MOFs) with affordable cost is highly demanding yet limited for commercial applications, e.g., purification of polymer-grade ethylene (C2H4) via acetylene (C2H2) and carbon dioxide (CO2) removal faces the challenge of developing low-cost and large-scale physisorbents with efficiency and recyclability. Herein, we developed a viable synthetic protocol to scale-up a series of ultramicroporous Zr-MOFs (ZrFA/ZrFA-D/ZrFA-D-Cu(I)) with the simplest monocarboxylate, formate (FA), through consecutive production by recycling solvent/modulator. Besides a size-exclusion effect disfavoring C2H4 adsorption, introduction of defective and Cu(I) sites was found to enhance gas affinity and uptake capacity. A comprehensive evaluation of C2H4 separation and economic efficiency has been proposed, suggesting the improvement of C2H2 uptake capacity is effective for the binary C2H2/C2H4 separation, while the separation process of the ternary C2H2/CO2/C2H4 mixtures depends on subtle tradeoff of complex factors and limited by challenging CO2/C2H4 separating. Notably, the large-scale separation has been testified to significantly improve separation efficiency, and the low-cost preparation benefits high economic efficiency. The distinct C2H2/C2H4/CO2 adsorption mechanism in ZrFA/ZrFA-D/ZrFA-D-Cu(I) has been elucidated by the theoretical calculations. This work may shed a light on the future C2H4 purification technology by pushing MOF-syntheses toward low-cost, scale-up, and recyclable production.

Tailored Polymer-Zeolite Imidazolate Framework Membranes for Aperture-Matched C4 Hydrocarbon Separation

The integration of metal-organic frameworks (MOFs) with polymers for efficient C4 hydrocarbon separation membranes remains challenging, primarily due to inherent phase incompatibility. This work presents an in-situ synthesis strategy for polymer-zeolitic-imidazolate frameworks (polyZIF), utilizing polymer-metal-ligand coordination bonds combined with structural directing agents to produce crystalline microporous frameworks. With an accessible BET surface area of 261 m2 g-1 and a permanent porosity of ca. 4.42 Å, polyZIF membrane demonstrates butadiene permeance (∼332 GPU) and the selectivity over n-butene, n-butane, iso-butene, and iso-butane (17.2, 28.1, 21.5, and 34.8) under mixed gas conditions, respectively. Demonstrating practical scalability, the improved dispersibility and reduced interfacial defects in polyZIF facilitates fabrication of large-area defect-free membranes (up to 80 cm2) while maintaining robust C4 separation performance. This advancement not only establishes a novel preparation for constructing polyZIF membranes with C4 hydrocarbon molecular-sieving capability but also provides critical insights into industrial application of ZIF-based polymer membranes.

Improving Light-Responsive Efficiency of Type II Porous Liquid by Tailoring the Functionality of Host

Light-responsive porous liquids (LPLs) attract significant attention for their controllable gas uptake under light irradiation, while their preparation has remained a great challenge. Here we report the fabrication of type II LPLs with enhanced light-responsive efficiency by tailoring the host's functionality for the first time. The functionality of light-responsive metal-organic cage (MOC-RL, constructed from dicopper and responsive ligands) is modified by introducing the second long-chain alkyl ligand, producing MOC-RL-AL as a new host. A spatially hindered solvent based on polyethylene glycol, IL-NTf2, is designed and can dissolve MOC-RL-AL due to the suitable interaction, creating a type II LPL (PL-RL-AL). Under light irradiation, the variation in propylene adsorption for PL-RL-AL increases by 58.0 % compared to PL-RL. The enhanced light-responsive efficiency is caused by easier control in accessibility of internal cavities within MOCs and increased number of external cavities between MOCs and IL-NTf2. This makes PL-RL-AL the first LPL with the probability for propylene/propane separation.

A Metal-Organic Framework with Tailored Shape-Matched Interactions Towards Ambient-Temperature Argon Removal for Oxygen Purification

High-purity oxygen (O2) is essential for high-value-added applications in the medical, aerospace, and electronics sectors. The production of high-purity O2 via non-thermal-driven pressure-swing adsorption has the advantages of portable operation and low energy consumption. However, effectively removing trace amounts of argon (Ar) impurities in this process is indispensable, and it is a fundamental challenge to achieve the preferential adsorption of inert Ar atoms over polar O2 molecules instead of traditional thermodynamic or molecule sieving strategies. Herein, we have demonstrated this problem was addressed by integrating spheroidal shape-matched interactions to fit the spheroid Ar atoms while repulsing the linear O2 molecules. Using this strategy, customized TYUT-20 enables the exceptional recognition of Ar atoms over O2 molecules, demonstrating an unprecedented Ar adsorption capacity of up to 14.5 cm3 g-1 and a top-performing Ar/O2 (1.54) selectivity at 298 K and 1 bar. The Ar atom recognition mechanism on this adsorbent has been investigated using Ar-loaded single crystal diffraction analysis and molecular simulation studies. The productivity of high-purity O2 (>99.99%) from a 5/95 Ar/O2 mixture breakthrough experiment reached 6.6 L kg-1 under ambient conditions, which highlighted TYUT-20 as a very promising adsorbent in ready-to-use high-purity O2 production.

Electrostatic Potential Matching in an Anion-Pillared Framework for Benchmark Hexafluoroethane Purification from Ternary Mixture

One-step purification of CF3CF3 from ternary CF3CH2F/CF3CHF2/CF3CF3 mixture is crucial since its vital role in the semiconductor industry. However, efficient separation of chemically inert CF₃CF₃ remains challenging due to the difficulty in creating specific recognition sites in porous materials. In this work, we report the first example of anion-pillared MOFs to the separation of fluorinated electronic specialty gases, utilizing the unique electrostatic potential matching in the bipolar pores of SIFSIX-1-Cu to realize a benchmark CF3CH2F/CF3CHF2/CF3CF3 separation. SIFSIX-1-Cu exhibits the highest CF3CH2F and CF3CHF2 adsorption capacity at 0.01 bar, as well as the highest CF3CH2F/CF3CF3 and CF3CHF2/CF3CF3 IAST selectivity. Additionally, high-purity (≥ 99.995%) CF3CF3 with record productivity (882.9 L kg-1) can be acquired through one-step breakthrough experiment of CF3CH2F/CF3CHF2/CF3CF3 (5/5/90). Theoretical calculations further reveal that the coexistence of electronegative SiF6 2- and partially electropositive H sites promotes SIFSIX-1-Cu to effectively anchor CF3CH2F and CF3CHF2 through multiple supramolecular interactions.

Hopping Diffusion in Wiggling Nanopore Architecture of MOF Enabling Synergistic Equilibrium-Kinetic Separation of Fluorinated Propylene and Propane

The separation of octafluoropropane (C3F8) from hexafluoropropylene (C3F6) is an industrially important yet challenging process due to their similar physicochemical properties and stringent purity demands in industrial applications. Herein, we address this task through precise pore architecture in a zirconium-based metal-organic framework (Zr-PMA), which exhibits unique "wiggling nanopores" with narrow windows and large cavities. The narrow windows act as diffusion barriers, selectively restricting C3F8 transport, while the large cavities provide strong adsorption sites for C3F6, enabling an equilibrium-kinetic synergistic separation. This dual functionality results in a ∼450-fold difference in diffusion rates and exceptional kinetic selectivity for C3F6 over C3F8, as demonstrated by adsorption isotherms, time-resolved kinetics, and dynamic breakthrough experiments. Theoretical calculations coupled with in situ spectroscopy elucidate the pore geometry-dependent hopping diffusion mechanism responsible for the separation. This work establishes wiggling pore geometry as a versatile paradigm for advanced adsorbents targeting energy-efficient separations of structurally similar fluorocarbon mixtures.

Tailoring Metal-Organic Frameworks for One-Step Separation of Alkane/Alkene/Alkyne Mixtures

The purification of polymer-grade olefins (>99.9 %), primarily C2 and C3, is a significant yet challenging process in the petrochemical industry. The conventional method for hydrocarbon separation typically involves heat-driven distillation. In contrast, adsorptive separation using porous solids presents a promising alternative, offering the potential for olefin purification under ambient conditions, thus providing substantial energy and environmental benefits. Particularly, one-step purification of alkenes through the selective adsorption of their corresponding alkanes and alkynes has gained attention as an effective approach. Metal-organic frameworks (MOFs), with their tunable pore structures, such as pore size, shape, and internal chemical environment, hold considerable potential for this process. This review discusses recent advancements in the development of MOFs for the one-step adsorptive purification of alkenes from ternary mixtures of alkanes, alkenes, and alkynes, with a focus on the rational design of pore structures to achieve the desired separation.

Pore Space Partition Enabled by Lithium(I) Chelation of a Metal-Organic Framework for Benchmark C2H2/CO2 Separation

Adsorptive separation of acetylene (C2H2) from carbon dioxide (CO2) offers a promising approach to purify C2H2 with low-energy footprints. However, the development of ideal adsorbents with simultaneous high C2H2 adsorption and selectivity remains a great challenge due to their very small molecular sizes and physical properties. Herein, we report a lithium(I)-chelation strategy for pore space partition (PSP) in a microporous MOF (Li+@NOTT-101-(COOH)2) to achieve simultaneous high C2H2 uptake and selectivity. The chelation model of Li+ ions within the framework was visually identified by single-crystal X-ray diffraction studies. The immobilized Li+ ions were found to have two functions: (1) partitioning large pore cages into smaller ones while maintaining high surface area and (2) providing specific binding sites to selectively take up C2H2 over CO2. The resulting Li+@NOTT-101-(COOH)2 exhibits a rare combination of a simultaneous high C2H2 capture capacity (205 cm3 g-1) and C2H2/CO2 selectivity (13) at ambient conditions, far surpassing that of NOTT-101-(COOH)2 (148 cm3 g-1 and 3.8, respectively) and most top-tier materials reported. Theoretical calculations and gas-loaded SCXRD studies reveal that the chelated Li+ ions combined with the segmented small cages can selectively bind with a large amount of C2H2 through the unique π-complexation, accounting for the improved C2H2 uptake and selectivity. Breakthrough experiments validated its excellent separation capacity for actual C2H2/CO2 mixtures, providing one of the highest C2H2 productivities of 118.9 L kg-1 (>99.5% purity) in a single adsorption-desorption cycle.

Lowering Linker Symmetry to Access Zirconium Metal-Organic Frameworks for Inverse Alkane/Alkene Separations

Enriching the structural diversity of metal-organic frameworks (MOFs) is of great importance in developing functional porous materials with specific properties. New MOF structures can be accessed through the rational design of organic linkers with diverse geometric conformations, and their structural complexity can be enhanced by choosing linkers with reduced symmetry. Herein, a series of Zr-based MOFs with unprecedented topologies were developed through a linker desymmetrization and conformation engineering approach. A tritopic carboxylate linker with reduced symmetry and flexible triangular geometry was designed to construct three Zr-based MOFs (denoted as NU-57, NU-58, and NU-59) by modulating synthetic conditions. Notably, the conformational flexibility and reduced symmetry of the linker generated two unprecedented topologies in NU-58 and NU-59. Furthermore, solvent removal in NU-58 via thermal activation process produced missing linker defects. Finally, the adsorption behavior of these MOFs toward alkanes and alkenes was studied to gain insights into their structure-property relationships, which demonstrated that NU-57 and NU-58 exhibit unusual reverse selectivity for alkanes in alkane/alkene separations. Overall, this work highlights the rational design of linkers using a desymmetrization strategy as a powerful method to enrich the structural diversity of MOFs and to access novel MOFs with unique properties.

Ionic porous materials: from synthetic strategies to applications in gas separation and catalysis

Ionic porous materials possess a unique combination of tunable pore sizes and task-specific interactions between guest molecules and the charged frameworks, which endow them with versatility across diverse domains in chemistry and materials science. Significant advancements in their applications for gas separation and catalysis have been achieved in recent years due to the incorporation of ionic functionalities and ultra-microporous structures that enable molecular-scale recognition of guest molecules. This review summarizes recent advancements in the synthetic strategies of ionic porous materials, establishing design guidelines for the incorporation of ionic moieties into the backbone to fine-tune pore sizes and chemistry. It highlights the synergistic interplay of task-specific interactions with custom-designed pore structures in key applications, including adsorption separation, membrane separation, and gas conversion. Additionally, it examines structure-property relationships, offering deeper insights into enhancing performance. The report also addresses the current challenges in the practical application of these materials. Finally, the review provides future perspectives on ionic porous materials from both scientific and industrial viewpoints. Overall, this review aims to provide insights into pore structure and chemistry, supporting the precise placement of ionic functionalities.

Two-Dimensional Anion-Pillared Metal-Organic Framework for Sieving Separation of Propylene from Propane with Ultrahigh Kinetic Performance

Adsorptive separation of propylene/propane using porous materials offers a promising alternative to energy-intensive cryogenic distillation. Molecular sieving-type adsorbents are considered the most ideal materials due to their superior selectivity and efficiency, but many suffer from limited adsorption capacity and slow diffusion due to small pore sizes. Here, we present a solvent-blocking strategy on NbOFFIVE-1-Ni (KAUST-7), the inaugural reported metal-organic framework for propylene/propane separation based on molecular sieving. By use of solvents of varying sizes, KAUST-7 with different framework strain energies and crystal morphologies was synthesized. Notably, methanol and ethanol facilitated the formation of well-defined rectangular nanosheets (designated as KAUST-7(MeOH) and KAUST-7(EtOH)), which have a high aspect ratio that shortens mass transfer paths and markedly augments gas diffusion. In comparison to the original sample, KAUST-7(MeOH) exhibits enhanced adsorption kinetics, with the propylene adsorption equilibrium time being curtailed by over 20-fold, along with a significantly enhanced adsorption capacity by 60% to 48 cm3 g-1, while the propane adsorption remains nearly unaltered. Molecular dynamics simulations reveal that methanol inhibits (0 0 2) faces more strongly, leading to faster lateral crystal growth. Its improved adsorption capacity, fast adsorption kinetics and regeneration, and excellent moisture stability make it a promising candidate for industrial application.

Sight into a Rare-Earth-Based Catalyst with Spatial Confinement Effect from the Perspective of Electronic Structure

Rare-earth elements include 15 kinds of lanthanides as well as Sc and Y elements. Interestingly, the special electronic configuration of a lanthanide rare earth is [Xe]4fn5d0-16s2 (n = 0-14), which results in rare-earth materials' unique activity in such areas as thermal catalysis, electrocatalysis, photocatalysis, etc. It is worth noting that a class of materials with spatial confinement effects are playing an increasingly important role in the catalytic performance; especially, the construction of hollow multishelled structures (HoMSs) can further enhance the activity of rare-earth catalytic materials. In this review, we discuss in depth the important roles of the rare-earth 4f5d electronic structure. Subsequently, this review systematically summarizes the synthesis methods of rare-earth HoMSs and their research progress in the field of catalysis and specifically introduces the advanced characterization and analysis methods of rare-earth HoMSs. Finally, the research directions, application prospects, and challenges that need to be focused on in the future of rare-earth-based HoMSs are discussed and anticipated. We believe that this review will not only inspire more creativity in optimizing the local electronic structure and spatial confinement structure design of rare-earth-based catalysts but also provide valuable insights for designing other types of catalysts.

A Hydrolytically Stable Metal-Organic Framework for Simultaneous Desulfurization and Dehydration of Wet Flue Gas

Metal-organic frameworks (MOFs) have great prospects as adsorbents for industrial gas purification, but often suffer from issues of water stability and competitive water adsorption. Herein, we present a hydrolytically stable MOF that could selectively capture and recover trace SO2 from flue gas, and exhibits remarkable recyclability in the breakthrough experiments under wet flue-gas conditions, due to its excellent resistance to the corrosion of SO2 and the water-derived capillary forces. More strikingly, its SO2 capture efficiency is barely influenced by the increasing humidity, even if the pore filling with water is reached. Mechanistic studies demonstrate that the delicate pore structure with diverse pore dimensions and chemistry leads to different adsorption kinetics and thermodynamics as well as segregated adsorption domains of SO2 and H2O. Significantly, this non-competitive adsorption mechanism enables simultaneous desulfurization and dehydration by a single adsorbent, opening an avenue toward cost-effective and simplified processing flowcharts for flue gas purification.

A Microporous Hydrogen-Bonded Organic Framework with Open Pyrene Sites Isolated by Hydrogen-Bonded Helical Chains for Efficient Separation of Xenon and Krypton

Achieving efficient xenon/krypton (Xe/Kr) separation in emerging hydrogen-bonded organic frameworks (HOFs) is highly challenging because of the lack of gas-binding sites on their pore surfaces. Herein, we report the first microporous HOF (HOF-FJU-168) based on hydrogen-bonded helical chains, which prevent self-aggregation of the pyrene core, thereby preserving open pyrene sites on the pore surfaces. Its activated form, HOF-FJU-168a is capable of separating Xe/Kr under ambient conditions while achieving an excellent balance between adsorption capacity and selectivity. At 296 K and 1 bar, the Xe adsorption capacity of HOF-FJU-168a reached 78.31 cm3/g, with an Xe/Kr IAST selectivity of 22.0; both values surpass those of currently known top-performing HOFs. Breakthrough experiments confirmed its superior separation performance with a separation factor of 8.6 and a yield of high-purity Kr (>99.5 %) of 184 mL/g. Furthermore HOF-FJU-168 exhibits excellent thermal and chemical stability, as well as renewability. Single-crystal X-ray diffraction and molecular modeling revealed that the unique electrostatic surface potential around the open pyrene sites creates a micro-electric field, exerting a stronger polarizing effect on Xe than on Kr, thereby enhancing host-Xe interactions.

Optimizing Propylene/Propane Sieving Separation through Gate-Pressure Control within a Flexible Organic Framework

The separation of propylene (C3H6) and propane (C3H8) is of great significance in the chemical industry, which poses a challenge due to their almost identical kinetic diameters and similar physical properties. In this work, we synthesized an ultramicroporous flexible hydrogen-bonded organic framework (named HOF-FJU-106) by using molecule 2,3,6,7-tetra (4-cyanophenyl) tetrathiafulvalene (TTF-4CN). The formation of the dimer causes the TTF-4CN molecular to bend and weaken π-stacked interactions, coupled with the flexibility of C≡N ⋯ ${\cdots }$ H-C hydrogen bonds, which leads to reversible conversion between open and closed frameworks through the mutual slip of adjacent layers/columns under activation and stimulation of gas molecules. Through gas adsorption isotherms and adsorption enthalpy, HOF-FJU-106a exhibited adaptive adsorption and stronger binding affinity for C3H6, and presented a recorded gas uptake ratio of C3H6/C3H8 (23.77) among presentative HOF materials at room temperature to date. Importantly, the flexible HOF-FJU-106a shows an interesting phenomenon about the reversible gate pressure control under variable temperature, which realized the gas adsorption and separation performance enhancement for the binary C3H6/C3H8 mixtures. This strategy through designing HOFs with thermoregulatory gating effect is a powerful way to maximize the performance of materials.

Highly Selective Ethylene/Ethane Separation in MOF Composites through Pore Contraction and Particle Size Enlargement Strategy

The discrimination of ethylene (C2H4) and ethane (C2H6) by the precise regulation of porous materials is important and challenging. In this work, the quasi-exclusion of C2H6 from C2H4 is realized through a facile polymer modification and shaping method of metal-organic framework ZnAtzPO4 (Atz = 3-amino-1,2,4-triazole). The polymer (carboxymethyl cellulose, CMC) modification and shaping of ZnAtzPO4@CMC result in pore contraction and particle size enlargement, which impedes the diffusion of larger C2H6 molecules and improves the kinetic separation of C2H4/C2H6. The C2H6 capacity decreases steeply from 1.63 (ZnAtzPO4 powder) to 0.27 mmol g-1 (ZnAtzPO4@CMC), and the resulting C2H4/C2H6 uptake ratio increases from 1.38 to 6.67. Kinetic adsorption experiments confirm that ZnAtzPO4@CMC presents a negligible C2H6 dynamic capacity and the diffusion difference between C2H4 and C2H6 is amplified significantly. The corresponding kinetic C2H4/C2H6 separation selectivity of ZnAtzPO4@CMC increases from 13.06 (ZnAtzPO4) to 34.67, superior to the most reported benchmark materials. Furthermore, ZnAtzPO4@CMC exhibits excellent breakthrough performance for equimolar C2H4/C2H6 mixture separation. This study provides guidance to discriminate similar gases through polymer modification of MOFs.

Construction of Multiple Nonpolar SF6 Nano-Traps by Highly Stable Pyrazole-Based MOFs for SF6 Recovery

Sulfur hexafluoride (SF6), widely used in electric power systems, is one of the most potent greenhouse gases. Efficient separation of SF6/N2 by adsorptive separation technology based on porous materials is of great significance in the industry yet remains a daunting challenge. Herein, a novel strategy is introduced to construct unique pore channels with multiple SF6 nano-traps by precisely selecting bipyrazole ligands to design the nonpolar surface of microporous metal-organic frameworks (MOFs), which significantly enhances the material's affinity for SF6. A series of ultra-stable bipyrazole-based MOFs, M(BPZ) (M═Co, Ni, Zn), are synthesized and investigated. Among these three materials, Co(BPZ) and Zn(BPZ) show excellent SF6 uptakes of 2.47 and 2.39 mmol g-1 at 298 K and 0.1 bar while Co(BPZ) exhibits the highest SF6/N2 (10/90, v/v) IAST selectivity of 748. Breakthrough experiments reveal that SF6/N2 mixtures can be efficiently separated by Co(BPZ) with a high SF6 (≥99.5 %) productivity of 46.1 L kg-1. Theoretical calculations suggest that SF6 preferably adsorbs in the channels through multiple S-F···π (pyrazole rings) van der Waals interactions. This work provides a straightforward approach for exploring adsorbents in efficient SF6/N2 separation.

Green and Scalable Preparation of an Isomeric CALF-20 Adsorbent with Tailored Pore Size for Molecular Sieving of Propylene from Propane

Molecular sieving of propylene (C3H6) from propane (C3H8) is highly demanded for C3H6 purification. However, delicate control over aperture size to achieve both high C3H6 uptake and C3H6/C3H8 selectivity with low cost remains a significant challenge. Herein, a green and scalable approach is reported for preparing an isomeric CALF-20 adsorbent, termed as NCU-20, using water as the only solvent with a cost of $10 per kilogram. NCU-20 features a contracted pore size (4.2 × 4.7 Å2) compared to CALF-20 (5.2 × 5.7 Å2), which enables molecular sieving of C3H6 (4.16 × 4.65 Å2) from C3H8 (4.20 × 4.80 Å2). Notably, NCU-20 exhibits record-high C3H6 adsorption capacity (94.41 cm3 cm-3) at 298 K and 1.0 bar, outperforming all C3H6/C3H8 molecular sieving adsorbents. The sieving performances of C3H6/C3H8 are well maintained at elevated temperatures. Therefore, a delicate balance between C3H6 adsorption capacity (91.62 cm3 cm-3) and C3H6/C3H8 selectivity (uptake ratio of 22.2) is obtained on NCU-20 at 298 K and 0.5 bar. Furthermore, dynamic breakthrough experiments demonstrate a high productivity of 65.39 cm3 cm-3 for high-purity C3H6 (>99.5%) from an equimolar C3H6/C3H8 gas-mixture.

Mathematical Expression and Prediction of VOCs Adsorption Capacity and Isotherm

Adsorption capacity prediction, which needs to be based on the precise structure-capacity relationship, is important for better adsorbent design. However, the precise adsorption contribution coefficients of pores of different sizes for volatile organic compound (VOC) adsorption remain unclear. Herein, a control variable method is employed as a generative model to realize the numerization of the precise structure-capacity relationship. For the first time, a concise equation is proposed that can predict the adsorption capacities/isotherms of unknown adsorbents through their pore structure parameters. Interestingly, practical VOC adsorption amounts aligned with predicted values obtained by simultaneously considering pore volume (which undergoes volume-filling adsorption) and surface area (which undergoes surface-covering adsorption) as input variables. Derivation of the equation is based on classical adsorption theories and mathematical expression of the precise structure-capacity relationship obtained from actual experimental results. Each parameter in the equation has a specific physical meaning. This unprecedented VOC adsorption capacity/isotherm prediction method provides in-depth insight for accurate quantification of VOC adsorption, with great potential for gas adsorption prediction and guidance in the development of adsorption materials and technologies.

Carbonaceous adsorbents in wastewater treatment: From mechanism to emerging application

Adsorption is of great significance in the water pollution control. Carbonaceous adsorbents, such as carbon quantum dots, carbon nanotubes, graphene, and activated carbons, have long been deployed in sustainable wastewater treatment due to their excellent physical structure and strong interaction with various pollutants; these features allow them to spark greater interest in environmental remediation. Although numerous eye-catch researches on carbon materials in wastewater treatment, there is a lack of comprehensive comparison and summary of the vivid structure-activity-application relationships of different types of carbonaceous adsorbents at the molecular and atomic level. Herein, this review aims to scrutinize and contrast the adsorption mechanisms of carbonaceous adsorbents with different dimensions, analyzing the qualitative differences in adsorption capacity from microscopic perspectives, structural diversity caused by preparation methods, and environmental external factors affecting adsorption occurrence. Then, a quantitatively in-depth critical appraisal of traditional and emerging contaminants in wastewater treatment using carbonaceous adsorbents, and innovative strategies for enhancing their adsorption capacity are discussed. Finally, in the context of growing imposed circularity and zero waste wishes, this review offers some promising insights for carbonaceous adsorbents in achieving sustainable wastewater treatment.

Robust Two-Dimensional Hydrogen-Bonded Organic Framework for Efficient Separation of C1-C3 Alkanes

Separating natural gas to obtain high-quality C1-C3 alkanes is an imperative process for supplying clean energy sources and high valued petrochemical feedstocks. However, developing adsorbents which can efficiently distinguish CH4, C2H6, and C3H8 molecules remains challenging. We herein report an ultra-stable layered hydrogen-bonded framework (HOF-NBDA), which features differential affinities and adsorption capacities for CH4, C2H6, and C3H8 molecules, respectively. Breakthrough experiments on ternary component gas mixture show that HOF-NBDA can achieve efficient separation of CH4/C2H6/C3H8 (v/v/v, 85/7.5/7.5). More importantly, HOF-NBDA can realize efficient C3H8 recovery from ternary CH4/C2H6/C3H8 gas mixture. After one cycle of breakthrough, 70.9 L·kg-1 of high-purity (≥ 99.95%) CH4 and 54.2 L·kg-1 of C3H8 (purity ≥99.5%) could be obtained. Furthermore, excellent separation performance under different flow rates, temperatures, and humidities could endow HOF-NBDA an ideal adsorbent for the future natural gas purification.

Modulator-Directed Counterintuitive Catenation Control for Crafting Highly Porous and Robust Metal-Organic Frameworks with Record High SO2 Uptake Capacity

Sulfur dioxide (SO2) is an important industrial feedstock that can be directly utilized or catalytically transformed to value-added chemicals such as sulfuric acid. The development of regenerable porous sorbents for the highly efficient storage and energy-minimal release of toxic SO2 operating under ambient conditions has attracted growing interest. Herein, we report the topology-guided construction of highly porous acs-type metal-organic frameworks (MOFs) through a counterintuitive modulator-directed catenation control approach. In contrast to the conventional modulator facilitated coordination competition that favors the thermodynamic catenated phase, we show that the elevation of modulator concentration can promote the formation of the noncatenated phase probably through a sublattice dissolution pathway. The assembly of a custom-designed trigonal prismatic triptycene-quinoxaline linker and trinuclear Fe3O cluster affords either the threefold catenated SJTU-219 or noncatenated SJTU-220 with desired acs net. Impressively, the synthetic approach is applicable to various metal ions, including Al3+, V3+, and even Ti4+. The noncatenated SJTU-220 exhibits an extraordinary SO2 sorption capacity of 29.6 mmol g-1 at 298 K and 1 bar, surpassing all reported solid sorbents. The uptake capacity can be further raised to 35.6 mmol g-1 via the replacement of Fe3+ with kinetically more inert Cr3+, resulting in a staggering ∼329-fold volume reduction compared with free ideal SO2 gas. Computational simulations suggest that unique Fe3+···S(SO2) interactions dominate the SO2 seeding process, facilitating the efficient packing of SO2 molecules in the large channels. Besides, the exceptionally low uptake at the low pressure region implies global weak framework-SO2 interactions, which offer great potential for practically implementing an "easy-on/easy-off" SO2 delivery system.

Pore configuration control in hybrid azolate ultra-microporous frameworks for sieving propylene from propane

Developing porous adsorbents for the complete sieving of propylene/propane mixtures represents an alternative method to energy-intensive cryogenic distillation processes. However, the similar physical properties of these molecules and the inherent trade-off among adsorption capacity, selectivity, diffusion kinetic and host-guest binding interactions in molecular sieving adsorbents makes their separation challenging. Here we report the separation of propylene/propane mixtures through a crystalline porous material (HAF-1) that features channels and shrinkage throats-the latter defined as narrower channels that connect the main channels and a molecular pocket-where the throat aperture is between the kinetic diameters of propylene and propane. Single-crystal X-ray diffraction and computational simulation reveal that the shrinkage channels and hanging molecular pockets are key to ensure high sieving efficiency and high propylene adsorption capacity. Dynamic breakthrough experiments show that HAF-1 enables the achievement of high-purity (≥99.7%) propylene with a productivity of 33.9 l kg-1 by just one adsorption-desorption circle from propylene/propane mixtures.

Highly Efficient Separation of Intermediate-Size m-Xylene from Xylenes via a Length-Matched Metal-Organic Framework with Optimal Oxygen Sites Distribution

Xylene separation is crucial but challenging, especially for the preferential separation of the intermediate-size m-xylene from xylene mixtures. Herein, exploiting the differences in molecular length and alkyl distribution among xylenes, we present a length-matched metal-organic framework, formulated as Al(OH)[O2C-C4H2O-CO2], featuring an effective pore size corresponding to m-xylene molecular length combined with multiple negative O hydrogen bond donors distribution, can serve as a molecular trap for efficient preferential separation of the intermediate-size m-xylene. Benchmark separation performance was achieved for separating m-xylene from a ternary mixture of m-xylene/o-xylene/p-xylene, with simultaneous record-high m-xylene uptake (1.3 mmol g-1) and m-xylene/p-xylene selectivity (5.3) in the liquid-phase competitive adsorption. Both vapor- and liquid-phase fixed-bed tests confirmed its practical separation capability with benchmark dynamic m-xylene/p-xylene and m-xylene/o-xylene selectivities, as well as excellent regenerability. The selective and strong m-xylene binding affinity among xylene molecules was further elucidated by simulations, validating the effectiveness of such a pore environment for the separation of intermediate-size molecules.

The Chemistry of Metal-Organic Frameworks for Multicomponent Gas Separation

Adsorbents-based gas separation technologies are regarded as the potential energy-efficient alternatives towards current thermal-driven methods, and the study on multi-component gas separation is essential to deepen our understanding of the adsorbents for practical use. Relative to the ideal two-component mixtures, both the adsorption behavior and separation mechanisms are obviously more complex in multiple gas mixtures due to their close or even overlapped sizes and properties. The emergence of metal-organic frameworks with controllable pore size and pore chemistry provides the platform for the tailor-made pore structure to satisfy the harsh requirements of multi-component gas separation. This minireview highlights the recent advance of multi-component gas separation using metal-organic frameworks, including multiple impurities removal and selective molecular capture. Combining with the typical cases of hydrocarbon separations (C2, C4, and C8), the detailed discussion about the developed strategies (e.g. self-adaptive binding sites, multiple binding spaces, synergistic binding sites, synergistic sorbent separation technology, gate-opening effect, size and thermodynamic combine effect) that are adaptive to different scenarios would be provided. The review will conclude with our perspective on the existing barriers and the future direction of this topic.

The Reinforced Separation of Intractable Gas Mixtures by Using Porous Adsorbents

This review focuses on the mechanism and driving force in the intractable gas separation using porous adsorbents. A variety of intractable mixtures have been discussed, including air separation, carbon capture, and hydrocarbon purification. Moreover, the separation systems are categorized according to distinctly biased modes depending on the minor differences in the kinetic diameter, dipole/quadruple moment, and polarizability of the adsorbates, or sorted by the varied separation occasions (e.g., CO2 capture from flue gas or air) and driving forces (thermodynamic and kinetic separation, molecular sieving). Each section highlights the functionalization strategies for porous materials, like synthesis condition optimization and organic group modifications for porous carbon materials, cation exchange and heteroatom doping for zeolites, and metal node-organic ligand adjustments for MOFs. These functionalization strategies are subsequently associated with enhanced adsorption performances (capacity, selectivity, structural/thermal stability, moisture resistance, etc.) toward the analog gas mixtures. Finally, this review also discusses future challenges and prospects for using porous materials in intractable gas separation. Therein, the combination of theoretical calculation with the synthesis condition and adsorption parameters optimization of porous adsorbents may have great potential, given its fast targeting of candidate adsorbents and deeper insights into the adsorption forces in the confined pores and cages.

Hierarchically porous MOF@COF structures with ultrafast gas diffusion rate for C2H6/C2H4 separation

For ethylene purification, C2H6-selective metal-organic frameworks (MOFs) show great potential to directly produce polymer-grade C2H4 from C2H6/C2H4 mixtures. Most C2H6-traping MOFs are ultra-microporous structures so as to strengthen multiple supramolecular interactions with C2H6. However, the narrowed pore channels of C2H6-traping MOFs cause large guest diffusion barriers, greatly hampering their practical applications. Herein, we present a feasible strategy by precisely constructing hierarchically porous MOF@COF core-shell structures to address this issue. Additional mesoporous diffusion channels were incorporated between MOF crystals through the construction of the COF shell, thereby enhancing the gas adsorption kinetics. Notably, designing a core-shell MOF@COF structure with an optimal coating amount of mesoporous COF shell will further improve the gas diffusion rate. Breakthrough experiments reveal that the tailored MOF@COF composites can effectively achieve C2H6/C2H4 separation and maintain its separation performance over five continuous measurement cycles. This investigation opens up a new avenue to solve the diffusion/transfer issues and provides more opportunities and potentials for MOF@COF composites in practical separation applications.

Cross-Linking CdSO4-Type Nets with Hexafluorosilicate Anions to Form an Ultramicroporous Material for Efficient C2H2/CO2 and C2H2/C2H4 Separation

A 44.610.8 topology hybrid ultramicroporous material (HUM), {[Cu1.5F(SiF6)(L)2.5]·G}n, (L = 4,4'-bisimidazolylbiphenyl, G = guest molecules), 1, formed by cross-linking interpenetrated 3D four-connected CdSO4-type nets with hexafluorosilicate anions is synthesized and evaluated in the context of gas sorption and separation herein. 1 is the first HUM functionalized with two different types of fluorinated sites (SiF6 2- and F- anions) lining along the pore surface. The optimal pore size (≈5 Å) combining mixed and high-density electronegative fluorinated sites enable 1 to preferentially adsorb C2H2 over CO2 and C2H4 by hydrogen bonding interactions with a high C2H2 isosteric heat of adsorption (Qst) of ≈42.3 kJ mol-1 at zero loading. The pronounced discriminatory sorption behaviors lead to excellent separation performance for C2H2/CO2 and C2H2/C2H4 that surpasses many well-known sorbents. Dynamic breakthrough experiments are conducted to confirm the practical separation capability of 1, which reveal an impressive separation factor of 6.1 for equimolar C2H2/CO2 mixture. Furthermore, molecular simulation and density functional theory (DFT) calculations validate the strong binding of C2H2 stems from the chelating fix of C2H2 between SiF6 2- anion and coordinated F- anion.

Guest-Induced Helical Superstructure from a Gold Nanocluster-Based Supramolecular Organic Framework Enables Efficient Catalysis

Mimicking hierarchical assembly in nature to exploit atomically precise artificial systems with complex structures and versatile functions remains a long-standing challenge. Herein, we report two single-crystal supramolecular organic frameworks (MSOF-4 and MSOF-5) based on custom-designed atomically precise gold nanoclusters Au11(4-Mpy)3(PPh3)7, showing distinct and intriguing host-guest adaptation behaviors toward 1-/2-bromopropane (BPR) isomers. MSOF-4 exhibits sev topology and cylindrical channels with 4-mercaptopyridine (4-Mpy) ligands matching well with guest 1-BPR. Due to the confinement effect, solid MSOF-4 undergoes significant structural change upon selective adsorption of 1-BPR vapor over 2-BPR, resulting in strong near-infrared fluorescence. Single-crystal X-ray diffraction reveals that Au11(4-Mpy)3(PPh3)7 in MSOF-4 transforms into Au11Br3(PPh3)7 upon ligand exchange with 1-BPR, resulting in 1-BPR@MSOF-6 single crystals with a rarely reported helical assembly structure. Significantly, the double-helical structure of MSOF-6 facilitates efficient catalysis of the electron transfer (ET) reaction, resulting in a nearly 6 times increase of catalytic rates compared with MSOF-4. In sharp contrast, solid MSOF-5 possesses chb topology and cage-type channels with narrow windows, showing excellent selective physical adsorption toward 1-BPR vapor but a nonfluorescent feature upon guest adsorption. Our results demonstrate a powerful strategy for developing advanced assemblies with high-order complexity and engineering their functions in atomic precision.

Precise Construction of Nitrogen-Enriched Porous Ionic Polymers as Highly Efficient Sulfur Dioxide Adsorbent

Porous ionic polymers with unique features have exhibited high performance in various applications. However, the fabrication of functional porous ionic polymers with custom functionality and porosity for efficient removal of low-concentration SO2 remains challenging. Herein, a novel nitrogen-enriched porous ionic polymer NH2Py-PIP is prepared featuring high-content nitrogen sites (15.9 wt.%), adequate ionic sites (1.22 mmol g-1), and a hierarchical porous structure. The proposed construction pathway relies on a tailored nitrogen-functionalized cross-linker NH2Py, which effectively introduces abundant functional sites and improves the porosity of porous ionic polymers. NH2Py-PIP with a well-engineered SO2-affinity environment achieves excellent SO2/CO2 selectivity (1165) and high SO2 adsorption capacity (1.13 mmol g-1 at 0.002 bar), as well as enables highly efficient and reversible dynamic separation performance. Modeling studies further elucidate that the nitrogen sites and bromide anions collaboratively promote preferential adsorption of SO2. The unique design in this work provides new insights into constructing functional porous ionic polymers for high-efficiency separations.

Reverse Separation of Carbon Dioxide and Acetylene in Two Isostructural Copper Pyridine-Carboxylate Frameworks

Separating acetylene from carbon dioxide is important but highly challenging due to their similar molecular shapes and physical properties. Adsorptive separation of carbon dioxide from acetylene can directly produce pure acetylene but is hardly realized because of relatively polarizable acetylene binds more strongly. Here, we reverse the CO2 and C2H2 separation by adjusting the pore structures in two isoreticular ultramicroporous metal-organic frameworks (MOFs). Under ambient conditions, copper isonicotinate (Cu(ina)2), with relatively large pore channels shows C2H2-selective adsorption with a C2H2/CO2 selectivity of 3.4, whereas its smaller-pore analogue, copper quinoline-5-carboxylate (Cu(Qc)2) shows an inverse CO2/C2H2 selectivity of 5.6. Cu(Qc)2 shows compact pore space that well matches the optimal orientation of CO2 but is not compatible for C2H2. Neutron powder diffraction experiments confirmed that CO2 molecules adopt preferential orientation along the pore channels during adsorption binding, whereas C2H2 molecules bind in an opposite fashion with distorted configurations due to their opposite quadrupole moments. Dynamic breakthrough experiments have validated the separation performance of Cu(Qc)2 for CO2/C2H2 separation.

Topology Reconfiguration of Anion-Pillared Metal-Organic Framework from Flexibility to Rigidity for Enhanced Acetylene Separation

Flexible metal-organic framework (MOF) adsorbents commonly encounter limitations in removing trace impurities below gate-opening threshold pressures. Topology reconfiguration can fundamentally eliminate intrinsic structural flexibility, yet remains a formidable challenge and is rarely achieved in practical applications. Herein, a solvent-mediated approach is presented to regulate the flexible CuSnF6-dpds-sql (dpds = 4,4''-dipyridyldisulfide) with sql topology into rigid CuSnF6-dpds-cds with cds topology. Notably, the cds topology is unprecedented and first obtained in anion-pillared MOF materials. As a result, rigid CuSnF6-dpds-cds exhibits enhanced C2H2 adsorption capacity of 48.61 cm3 g-1 at 0.01 bar compared to flexible CuSnF6-dpds-sql (21.06 cm3 g-1). The topology transformation also facilitates the adsorption kinetics for C2H2, exhibiting a 6.5-fold enhanced diffusion time constant (D/r2) of 1.71 × 10-3 s-1 on CuSnF6-dpds-cds than that of CuSnF6-dpds-sql (2.64 × 10-4 s-1). Multiple computational simulations reveal the structural transformations and guest-host interactions in both adsorbents. Furthermore, dynamic breakthrough experiments demonstrate that high-purity C2H4 (>99.996%) effluent with a productivity of 93.9 mmol g-1 can be directly collected from C2H2/C2H4 (1/99, v/v) gas-mixture in a single CuSnF6-dpds-cds column.

Metal-Organic Framework with Space-Partition Pores by Fluorinated Anions for Benchmark C2H2/CO2 Separation

The efficient separation of C2H2 from C2H2/CO2 or C2H2/CO2/CH4 mixtures is crucial for achieving high-purity C2H2 (>99%), essential in producing contemporary commodity chemicals. In this report, we present ZNU-12, a metal-organic framework with space-partitioned pores formed by inorganic fluorinated anions, for highly efficient C2H2/CO2 and C2H2/CO2/CH4 separation. The framework, partitioned by fluorinated SiF62- anions into three distinct cages, enables both a high C2H2 capacity (176.5 cm3/g at 298 K and 1.0 bar) and outstanding C2H2 selectivity over CO2 (13.4) and CH4 (233.5) simultaneously. Notably, we achieve a record-high C2H2 productivity (132.7, 105.9, 98.8, and 80.0 L/kg with 99.5% purity) from C2H2/CO2 (v/v = 50/50) and C2H2/CO2/CH4 (v/v = 1/1/1, 1/1/2, or 1/1/8) mixtures through a cycle of adsorption-desorption breakthrough experiments with high recovery rates. Theoretical calculations suggest the presence of potent "2 + 2" collaborative hydrogen bonds between C2H2 and two hexafluorosilicate (SiF62-) anions in the confined cavities.

One-Step Butadiene Purification in a Sulfonate-Functionalized Metal-Organic Framework through Synergistic Separation Mechanism

Porous materials that could recognize specific molecules from complex mixtures are of great potential in improving the current energy-intensive multistep separation processes. However, due to the highly similar structures and properties of the mixtures, the design of desired porous materials remains challenging. Herein, a sulfonate-functionalized metal-organic framework ZU-609 with suitable pore size and pore chemistry is designed for 1,3-butadiene (C4H6) purification from complex C4 mixtures. The sulfonate anions decorated in the channel achieve selective recognition of C4H6 from other C4 olefins with subtle polarity differences through C-H⋅⋅⋅O-S interactions, affording recorded C4H6/trans-2-C4H8 selectivity (4.4). Meanwhile, the shrunken mouth of the channel with a suitable pore size (4.6 Å) exhibits exclusion effect to the larger molecules cis-2-C4H8, iso-C4H8, n-C4H10 and iso-C4H10. Benefiting from the moderate C4 olefins binding affinity exhibited by sulfonate anions, the adsorbed C4H6 could be easily regenerated near ambient conditions. Polymer-grade 1,3-butadiene (99.5 %) is firstly obtained from 7-component C4 mixtures via one adsorption-desorption cycle. The work demonstrates the great potential of synergistic recognition of size-sieving and thermodynamically equilibrium in dealing with complex mixtures.

Sulfonate Functional Ultramicroporous Materials with Suitable Pore Size and Layer-Stacked Structure for C4 Olefins Purification

Selective recognition of 1,3-butadiene from complex olefin isomers is vital for 1,3-butadiene purification, but the lack of porous materials with suitable pore structures results in poor selectivity and low capacity in C4 olefin separation. Herein, two sulfonate-functionalized organic frameworks, ZU-601 and ZU-602, are designed and show impressive separation performance toward C4 olefins. Benefiting from the suitable aperture size caused by the flexibility of coordinated organic ligand, ZU-601, ZU-602 that are pillared with different sulfonate anions could discriminate C4 olefin isomers with high uptake ratio: 1,3-butadiene/1-butene (207), 1,3-butadiene/trans-2-butene (10.1). Meanwhile, their layer-stacked structure enables the utilization of both intra- and interlayer space, enhancing the accommodation of guest molecules. ZU-601 exhibits record high 1,3-butadiene adsorption capacity of 2.90 mmol g-1 (0.5 bar, 298 K) among the reported flexible porous materials with high 1,3-butadiene/1-butene selectivity. The breakthrough experiments confirm their superior separation ability even for all five C4 olefin isomers, and the molecular-level structural change is well elucidated via powder, crystal analysis, and simulation studies. The work provides ideas toward advanced materials design with simultaneous high separation capacity and high separation selectivity for challenging separations.