Effective Separation of Acetylene/Ethylene by the Mesoporous MIL-100(Cr) MOF

Acetylene plays a key role in diverse commercial chemicals and high-quality fuel applications, yet its storage poses significant challenges due to its explosive nature. In-situ plasma-assisted CH4 coupling conversion presents a promising alternative for the safe production of C2 chemicals, including acetylene, assuming that efficient downstream separation processes are feasible. This study focuses on the adsorptive separation of acetylene from ethylene to achieve high-purity acetylene with the use of mesoporous metal-organic frameworks (MOFs) as effective selective adsorbents. Herein, we systematically investigate the acetylene/ethylene separation performance of a series of MIL-100 (M = Al, Fe, V, Cr) MOFs. Single-component sorption data first evidenced that MIL-100(Cr) shows the highest affinity to acetylene, supported by Operando Infrared spectroscopy and Density Functional Theory calculations. These analysis revealed the crucial role played by the Cr3+ coordinatively unsaturated sites and the counter-anions (OH-/F-) bound to 1 of the 3 Cr3+ atoms of the oxo-trimer. Grand Canonical Monte Carlo simulations further elucidated the microscopic adsorption mechanisms for each single-component and equimolar binary acetylene/ethylene mixtures. Breakthrough experiments demonstrated that MIL-100(Cr) achieves selectivity ranging from 5 to 23, suggesting its potential for dual high-purity acetylene and ethylene production. Vacuum Pressure Swing Adsorption (VPSA) cycle tests indicated that MIL-100(Cr) achieves high acetylene recovery and moderate purity without a rinse step, while an acetylene rinse step enhances purity for fine chemical raw materials. Overall, this study paves the way toward the promotion of MIL-100(Cr) for future large-scale industrial applications in acetylene harvesting and purification.

Optimizing the pore environment in biological metal-organic frameworks through the incorporation of hydrogen bond acceptors for inverse ethane/ethylene separation

The development of efficient adsorbents for the selective separation of ethane (C2H6) and ethylene (C2H4) is essential for the cost-effective production of high-purity ethylene. Here, we employ a pore engineering strategy to optimize the pore environment of biological metal-organic frameworks (MOFs) by incorporating hydrogen bond receptors to enhance the inverse separation efficiency of C2H6 and C2H4. Compared to the isomorphic Cu-AD-SA, the methyl-functionalized Cu-AD-MSA and Cu-AD-DMSA not only provide suitable pore confinement but also offer additional binding sites, thus creating an optimal environment for strong interactions with C2H6 (AD = adenine, SA = succinic acid, MSA = 2-methylsuccinic acid, and DMSA = 2,2-dimethylsuccinic acid). Adsorption results show that Cu-AD-DMSA exhibits remarkable C2H6/C2H4 selectivity (up to 2.4) as well as outstanding C2H6 adsorption capacity (3.63 mmol g-1), surpassing most reported C2H6-selective MOFs. Theoretical calculations combined with in situ infrared spectroscopy reveal that the synergetic effect of suitable pore confinement, amino groups, and functional surfaces decorated with multiple methyl binding sites provides strong and multipoint interactions for C2H6. Breakthrough experiments demonstrate that Cu-AD-DMSA exhibits exceptional performance in separating binary C2H6/C2H4 gas mixtures. The high chemical and thermal stability, scalable synthesis, and economic viability of Cu-AD-DMSA illustrate its potential as a candidate for C2H6/C2H4 separation application.

Recent advances and challenges of metal-organic frameworks for CO2 capture

Carbon dioxide (CO2) emissions resulting from extensive fossil fuel consumption have become an increasingly critical global challenge, underscoring the importance of carbon capture and separation technologies. As emerging porous materials, metal-organic frameworks (MOFs) exhibit remarkable potential for CO2 capture due to their unique structures and tunable properties. Current MOF-based CO2 capture methods have been broadly categorized into two major mechanisms: chemisorption and physisorption. By precisely tailoring MOF pore size and shape, creating unsaturated metal sites, and introducing functional groups, researchers significantly boost CO2 capture efficiency. This Frontier article discussed these two mechanisms and highlighted the latest advances in MOF-based CO2 capture, offering valuable guidelines for the development of novel MOF-related technologies.

Bioinspired Water-Stable Sc-MOF with Amino-Barb Vigreux-Type Channels for One-Step Ethylene Purification

We report a bioinspired Sc-MOF NTUniv-77 with Vigreux-type channels and amino-barb protrusions that enable selective gas adsorption. The unique amino group arrangement facilitates multistage cascade separation, enhancing C2H2 and C2H6 adsorption while allowing high-purity C2H4 purification in a single step. NTUniv-77 shows outstanding separation performance, with a C2H2/C2H4 (1:99) selectivity of 42 and C2H6/C2H4 (1:9) selectivity of 3.6, surpassing benchmark MOFs. GCMC simulations reveal that hydrogen bonding interactions at amino-barb sites are key to its efficiency. Breakthrough experiments confirmed the efficient separation of C2 gases, yielding high-purity C2H4 with a production capacity of 1.29 mmol g-1.

A new type of C2H2 binding site in a cis-bridging hexafluorosilicate ultramicroporous material that offers trace C2H2 capture

Hybrid ultramicroporous materials (HUMs) comprising hexafluorosilicate (SiF6 2-, SIFSIX) and their variants are promising physisorbents for trace acetylene (C2H2) capture and separation, where the inorganic anions serve as trans-bridging pillars. Herein, for the first time, we report a strategy of fluorine binding engineering in these HUMs via switching the coordination mode of SIFSIX from traditional trans to rarely explored cis. The first example of a rigid HUM involving cis-bridging SIFSIX, SIFSIX-bidmb-Cu (bidmb = 1,4-bis(1-imidazolyl)-2,5-dimethylbenzene), is reported. The resulting self-interpenetrated network is found to be water stable and exhibits strong binding to C2H2 but weak binding to C2H4 and CO2, affording a high Q st of 55.7 kJ mol-1 for C2H2, a high C2H2 uptake of 1.86 mmol g-1 at 0.01 bar and high ΔQ st values. Breakthrough experiments comprehensively demonstrate that SIFSIX-bidmb-Cu can efficiently capture and recover C2H2 from 50/50 or 1/99 C2H2/CO2 and C2H2/C2H4 binary mixtures. In situ single crystal X-ray diffraction (SCXRD) combined with dispersion-corrected density functional theory (DFT-D) calculations reveals that the C2H2 binding site involves two cis-SiF6 2- anions in close proximity (F⋯F distance of 7.16 Å), creating a new type of molecular trap that affords six uncoordinated fluoro moieties to chelate each C2H2 via sixfold C-H⋯F hydrogen bonds. This work therefore provides a new strategy for binding site engineering with selective C2H2 affinity to enable trace C2H2 capture.

Inversed Benzene/Cyclohexene/Cyclohexane Adsorption Selectivities for One-Step Purification of Cyclohexene and Beyond

Separation of benzene/cyclohexene/cyclohexane (Bz/Cye/Cya) mixtures, especially purification of Cye, is crucial but challenging in the petrochemical industry. Here, we report two new metal-organic frameworks with opposite adsorption selectivities for on-demand separation/purification of Bz/Cye/Cya mixtures. Although they possess similar frameworks and pore structures, their pore surfaces are functionalized by hydrophobic ethyl and hydrophilic hydroxymethyl groups, which interact conversely with Bz/Cye/Cya, giving a record-high Bz selectivity (129) and the first example of Cya/Cye/Bz selectivity (18.6), respectively. Equimolar ternary mixture breakthrough experiments showed that they could directly produce high-purity Cya (99.5%+, 0.39 mmol g-1) or Bz (99.5%+, 0.25 mmol g-1), and the tandem connection of two adsorbents enabled direct production of high-purity Cye (99.5%+, 0.37 mmol g-1) in a one-step adsorption process. Further, a bypass-tandem strategy is proposed to not only greatly improve Cye productivity (99.5%+, 0.57 mmol g-1) but also simultaneously produce high-purity Cya (99.5%+, 0.36 mmol g-1).

Heterometallic Aluminum Metal-Organic Frameworks

From spinel gemstone (MgAl2O4) to layered double hydroxides, nature has long relied on combinations between charge-complementary metal ions such as divalent metal ions (M2+) and Al3+ to create diverse valuable materials. However, for metal-organic frameworks (MOFs), heterometallic combinations such as Mg-Al are conspicuously absent. Here, we report a breakthrough in the synthesis of heterometallic Al-MOFs containing M2+/Al3+ trimeric clusters (M = Mg, Mn, Co, Ni). The synergistic effect between M(II) chlorides and aluminum lactate plays a critical role in the cooperative crystallization of M2+ and Al3+ into pore-space-partitioned MOFs (partitioned acs topology) with fast crystallization kinetics (about 3 h). New M2+/Al3+ MOFs exhibit highly tunable porosity and extraordinarily high uptakes for CO2 and small hydrocarbon molecules (112 cm3/g for CO2, 176 cm3/g for C2H2, 156 cm3/g for C2H4, and 163 cm3/g for C2H6) at 298 K and 1 bar. The high uptake capacity coupled with high selectivity (up to 8.5 for C2H2/CO2, 10.8 for C2H2/C2H4) gives rise to efficient separations of either C2H2/CO2 or C2H2/C2H4 gas mixtures, as confirmed by experimental breakthrough experiments.

Light- and Heat-Responsive Frustrated Lewis Pair Enables On-Demand Fixation of Ethylene

Frustrated Lewis pairs (FLPs) have been widely utilized as useful reagents and catalysts for activation of small molecules (SMs) through thermally controlled equilibrium formation of FLP-SM adducts. Herein, we report a light- and heat-responsive FLP system for on-demand fixation of ethylene. The system realizes capture and release of ethylene orthogonally triggered by visible light and heat, demonstrating potential utility as a nonmetallic and environmentally benign method for separation and storage of ethylene. The applicability to other alkenes is also demonstrated. Mechanistic investigations clarify that the photoexcited FLP enables stepwise radical addition to ethylene, followed by skeletal rearrangement to afford the FLP-ethylene adduct, which undergoes thermally promoted, concerted retro-cycloaddition to release ethylene and the free FLP. As a synthetic application, nonequilibrium, selective cis-to-trans isomerization of cyclooctene is achieved through the capture and release of cyclooctene with the FLP. This work discloses unique photochemical reactivity and application of FLPs, leading to further expansion of FLP chemistry into chemical science.

C2H2/CO2 Separation by a Carborane Hybrid 2D Metal-Organic Framework

The separation of acetylene (C2H2) from carbon dioxide (CO2) is important in industry but challenging due to their similar physical properties. Herein, a boron-rich 2D metal-organic framework ZNU-14 based on the carborane backbone was readily prepared by the supramolecular assembly of Zn2+, p-C2B10H10-(COOH)2, and di(pyridin-4-yl) amine under mild conditions for C2H2/CO2 separation. ZNU-14 displays a straight 1D channel (7.6 × 12.5 Å2) with an electronegative pore surface. Gas adsorption isotherms show that ZNU-14 has a good C2H2 adsorption capacity of 43.6 cm3 g-1, 181% of the CO2 uptake capacity. The calculated ideal adsorbed solution theory (IAST) selectivity is as high as 6.3-9.7, outperforming many popular materials. The moderate C2H2 adsorption heat of 34.3 kJ mol-1 facilitates the straightforward desorption and regeneration of ZNU-14. Furthermore, the theoretical study confirmed the stronger binding of C2H2 compared to that of CO2. The practical C2H2/CO2 separation performance was fully demonstrated by breakthrough experiments with excellent dynamic selectivity and recyclability under various conditions.

An ionic ultramicroporous polymer with engineered nanopores enables enhanced acetylene/carbon dioxide separation

A nanopore engineering approach enhances acetylene (C2H2) over carbon dioxide (CO2) selectivity in ionic ultramicroporous polymers (IUPs), an understudied class of sorbents. Extending the cationic arm of a prototypical IUP nearly doubles its C2H2/CO2 selectivity from 4.9 to 8.5 (at 298 K, 1 bar), underpinned by further observations from dynamic separation experiments and bespoke computational insights.

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.

Robust Anion-Pillared Ultramicroporous Material for C2H2/C2H4 Separation with High C2H2 Uptake and Selectivity

Removing trace amounts of C2H2 from C2H2/C2H4 mixtures for C2H4 purification is crucial but extremely challenging. In this work, by introducing SiF62- with specific recognition for C2H2, we constructed a robust adsorbent, FJI-W88, with a high C2H2 adsorption capacity and excellent C2H2/C2H4 separation selectivity. FJI-W88 not only exhibits ultrahigh C2H2 uptake at 0.01 bar (2.80 mmol g-1) but also shows exceptional C2H2/C2H4 (1/99) IAST selectivity of 698. Column breakthrough experiments further demonstrate that FJI-W88 can obtain C2H4 of high purity (≥99.95%) and high yield (230.0 mol kg-1) from C2H2/C2H4 (1/99) mixtures. Additionally, the C2H2/C2H4 (1/99) separation performance of FJI-W88 is basically unaffected under harsh conditions, such as high temperature and humidity.

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.

Precise C2H2 Adsorption Affinity Modulation by Nitrogen Functionalization in Isostructural Coordination Networks

Meticulous regulation of pore chemistry is essential for elucidating the intricate mechanism of the adsorption efficacy of porous materials. However, it is a great challenge to address the functionalization of pore chemistry while preserving pore size and geometry. In this study, the robust NPU-1 series network is selected as a platform to address this challenge. By regulating the nitrogen distribution in bilayer-pyridine ligands, a series of coordination networks (NPU-1-TPB/TPP/TPT) with the same pore size and geometry but different pore polarity is obtained, affording an increase in C2H2 enthalpies from -28.3 to -33.1 kJ mol-1. In situ, infrared spectroscopy uncovers the enhanced C2H2 interaction with the central phenyl ring of bilayer-pyridine ligands with the extent of nitrogen functionalization.

Efficient Separation of Dibranched Hexane from its Linear and Monobranched Isomers via the Synergistic Molecular Sieving and Pore Shape-Matching Strategy

The efficient separation of dibranched hexane from its linear and monobranched isomers is crucial but challenging for the production of high-RON (Research Octane Number) gasoline. Here, a strategy is presented to realize the efficient separation of high-purity (99.8%) dibranched 2,2-dimethylbutane from a ternary mixture of n-hexane/3-methylpentane/2,2-dimethylbutane by combining the sieving aperture and shape-matching cavity within the ultramicroporous metal-organic framework, Zn4O(NTB)2 (H3NTB = 4,4',4″-Nitrilotrisbenzoic acid). The static adsorption isotherms exhibit both high capacity for linear n-hexane (2.72 mmol g-1) and monobranched 3-methylpentane (2.59 mmol g-1). Dynamic breakthrough experiment shows that Zn4O(NTB)2 is capable of completely separating high-RON dibranched 2,2-dimethylbutane with a record-high productivity (0.98 mmol g-1), which is ≈1.6 times that of the previous benchmark material. Single-crystal X-ray diffraction of guest-loaded Zn4O(NTB)2 reveals that there exist high-density elongated cavities that match well with the shape of both n-hexane and 3-methylpentane, which can account for the high adsorption capacity for both of them. This work demonstrates the effectiveness of the synergistic effect of molecular sieving and shape matching in the efficient production of dibranched hexane from complex mixture.

One-Step Ethylene Purification from Ternary Mixture through Adaptive Recognition Sites

One-step adsorptive purification of ethylene (C2H4) from ternary mixture comprising of acetylene (C2H2), ethylene (C2H4) and carbon dioxide (CO2) is a great challenge in the chemical industry. Herein, a microporous metal-organic framework (FJI-H38) has been reported, which possesses high-density electronegative O/N binding sites and appropriate pore size. Notably, at 0.01 bar and 298 K FJI-H38 shows excellent trapping capability for C2H2 (1.64 mmol/g) and CO2 (2.33 mmol/g), while the uptake of C2H4 is only 0.41 mmol/g, which endows FJI-H38 high C2H2/C2H4 and top-level CO2/C2H4 selectivity simultaneously. Polymer-grade C2H4 (≥99.95 %) with record-high productivity can be successfully obtained from ternary C2H2/CO2/C2H4 mixture in one step under various conditions. Even at 318 K, the separation performance has no obvious decrease. Such excellent separation performance is due to the adaptive recognition of C2H2 and CO2 by FJI-H38 through the synergistic effect of appropriate pore size and the match of electrostatic potentials, where C2H2 and CO2 can be stabilized by the O/N and aromatic ring sites.

Hydrogen-Localization Transfer Regulation in 3D COFs Enhances Photocatalytic Acetylene Semi-Hydrogenation to Ethylene

In this work, a series of new crystalline three-dimensional covalent organic frameworks (3D COFs) based on [8+4] construction was designed and successfully realized efficient photocatalytic acetylene (C2H2) hydrogenation to ethylene (C2H4). By regulating the hydrogen-localization transfer effect in these 3D COFs, the Cz-Co-COF-H containing cobalt glyoximate active centers exhibited excellent C2H2-to-C2H4 performance, with an average C2H4 yield of 1755.33 μmol g-1 h-1 in pure C2H2, also showed near 100 % conversion of C2H2 in 1 % C2H2 contained crude C2H4 mixtures (industry-relevant conditions), and finally obtain polymer grade C2H4. In contrast, the Cz-Co-COF-BF2 only showed one fifth activity due to lack of hydrogen-localization transfer. The density functional theory (DFT), projected density of states (PDOS) and molecular dynamics "slow-growth" kinetic calculations based on precise 3D COF structures confirmed that the rapid hydrogen species transfer, enhanced water dissociation and suitable C2H2 adsorption in COFs jointly contributed efficient photocatalytic acetylene hydrogenation (PAH). This work provides new opportunity towards rational design and development of crystalline photocatalysts for C2H2 hydrogenation.

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.

Functional crystalline porous framework materials based on supramolecular macrocycles

Crystalline porous framework materials like metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) possess periodic extended structures, high porosity, tunability and designability, making them good candidates for sensing, catalysis, gas adsorption, separation, etc. Despite their many advantages, there are still problems affecting their applicability. For example, most of them lack specific recognition sites for guest uptake. Supramolecular macrocycles are typical hosts for guest uptake in solution. Macrocycle-based crystalline porous framework materials, in which macrocycles are incorporated into framework materials, are growing into an emerging area as they combine reticular chemistry and supramolecular chemistry. Organic building blocks which incorporate macrocycles endow the framework materials with guest recognition sites in the solid state through supramolecular interactions. Distinct from solution-state molecular recognition, the complexation in the solid state is ordered and structurally achievable. This allows for determination of the mechanism of molecular recognition through noncovalent interactions while that of the traditional recognition in solution is ambiguous. Furthermore, crystalline porous framework materials in the solid state are well-defined and recyclable, and can realize what is impossible in solution. In this review, we summarize the progress of the incorporation of macrocycles into functional crystalline porous frameworks (i.e., MOFs and COFs) for their solid state applications such as molecular recognition, chiral separation and catalysis. We focus on the design and synthesis of organic building blocks with macrocycles, and then illustrate the applications of framework materials with macrocycles. Finally, we propose the future directions of macrocycle-based framework materials as reliable carriers for specific molecular recognition, as well as guiding the crystalline porous frameworks with their chemistry, applications and commercialization.

Exploring the Fluorination and Hydroxylation of Pore-Space-Partitioned Metal-Organic Frameworks for C2H2/CH4 Separation

We report three novel pore-space-partitioned metal-organic frameworks (MOFs) functionalized with fluorine and hydroxyl groups using 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid (F4-BDC) and a new ligand 3,6-difluoro-2,5-dihydroxybenzene-1,4-dicarboxylic acid (F2(OH)2-BDC) as organic building blocks, with 1,3,5-tris(4-pyridyl)-2,4,6-triazine (TPT) as pore partition agent. With the polar fluorine and hydroxyl groups and the open metal sites being blocked by TPT, moderate molecule-framework interactions can be engineered. These three isoreticular microporous frameworks Mn-TPT-BDC-F4 (NCKU-21), Mn-TPT-BDC-F2(OH)2 (NCKU-22), and Mg-TPT-BDC-F2(OH)2 (NCKU-23) (NCKU=National Cheng Kung University) exhibit distinct single-component gas adsorption behaviors. Although NCKU-22 uptakes a much lower amount of C2H2 compared to NCKU-21 and -23, dynamic breakthrough experiments show that these three materials are all capable of efficient C2H2/CH4 separations. These MOFs possess moderate isosteric heat of adsorption for C2H2 (25.7-32.1 kJ mol-1), allowing easy regeneration and energy-efficient C2H2/CH4 separations.

A Fluorinated Zinc-based Metal-Organic Framework for Efficient Separation of Butane Isomers via Pore Engineering

Separating n-butane/iso-butane is a challenging and energy-intensive task in the petrochemical industry. There have been only several adsorbents reported for C4 paraffins separation while they are confronted in real-world applications with either poor selectivity or low n-butane uptake capacity. In this study, a fluorinated zinc-based metal-organic framework (MOF), Znpyc-CF3, derived from Znpyc-CH3 is developed, which has fluorine-containing functional groups on the pore surface that can enhance the interaction with the linear n-butane. Remarkably, this fluorinated porous material demonstrates both high n-butane uptake (55.5 cm3 g⁻¹) and excellent selectivity (IAST selectivity = 187) at ambient temperature. Multicycle breakthrough experiments confirmed its practical performance for real gas mixtures. Znpyc-CF3 exhibits outstanding stability, maintaining its structural integrity after repeated sorption cycles and dynamic breakthrough tests under both dry and highly humid conditions. The preferential adsorption mechanism of n-butane is further elucidated through Grand Canonical Monte Carlo (GCMC) simulations and Density Functional Theory (DFT) calculations. Overall, this research presents an efficient and stable adsorbent for the separation of butane isomers.

Asymmetric rotations slow down diffusion under confinement

Translation and rotation are the two most fundamental forms of diffusion, yet their coupling mechanism is not clear, especially under confinement. Here, we provided evidence of the coupling between rotation and translation using a substituted benzene molecule as an example. A counterintuitive behavior was observed where the movement of the smaller molecule with an asymmetric shape was unexpectedly slower than the larger one with a symmetric shape in confined channels of zeolite. We showed that this diffusion behavior was caused by the presence of the specific and selective interaction of the asymmetric guest with the pores, which increased the local restricted residence time, thus inhibiting the translation under confinement, as further confirmed by dynamic breakthrough curves, uptake measurements, quasi-elastic neutron scattering, and 2H solid-state NMR techniques. Our work correlated asymmetric rotation and diffusion under a confined environment, which enriched our understanding of the coupling between rotation and translation and could shed light on a fundamental understanding of the diffusion process.

Impact of Grafting Density on the Assembly and Mechanical Properties of Self-Assembled Metal-Organic Framework Monolayers

Polymer-grafted metal-organic frameworks (MOFs) can be used to form free-standing self-assembled MOF monolayers (SAMMs). Polymer chains can be introduced onto MOF surfaces through either the ligands or metal nodes using both grafting-to and grafting-from approaches. However, controlling the grafting density of polymer-grafted MOFs has not yet been achieved, because a means to control the density of grafting sites on the MOF surface has not been developed. In this study, the grafting density of polymer-grafted UiO-66 (UiO = University of Oslo) was controlled by functionalizing a portion of the Zr(IV) secondary building units (SBUs) on a UiO-66 surface with a so-called blocking agent. The remaining sites on the UiO-66 SBUs were functionalized with polymerization initiation groups, and polymers were grown from these sites to obtain particles with variable grafting densities and chain lengths that form SAMMs at an air-water interface. Even under conditions of low grafting density, these materials retain the ability to form SAMMs and their free-standing ability. Changes in particle arrangement within the monolayers were investigated using SEM imaging, and the toughness of the monolayers was evaluated using a film-on-water (FOW) method. Furthermore, coarse-grained molecular dynamics simulations were carried out to elucidate the morphology and mechanical properties of the monolayers. Findings from both experiments and simulations indicate that the toughness of SAMMs is more heavily influenced by the chain length of the grafted polymers than by the overall polymer content in the composite.

A Lewis basic site rich metal-organic framework featuring a hydrogen-bonded acetylene nano-trap for the efficient separation of C2H2/CO2

The physical separation of C2H2 from CO2 on metal-organic frameworks (MOFs) has received a substantial amount of research interest due to its advantages of simplicity, security, and energy efficiency. However, the exploitation of ideal MOF adsorbents for C2H2/CO2 separation remains a challenging task due to their similar physical properties and molecular sizes. Herein, we report a unique C2H2 nano-trap constructed using accessible oxygen and nitrogen sites, which exhibits energetic favorability toward C2H2 molecules. This material exhibits a good acetylene capacity of 55.31 cm3 g-1 and high C2H2/CO2 selectivity of 7.0 under ambient conditions. We have combined in situ IR spectroscopy and in-depth theoretical calculations to unravel the synergistic interactions driven by the high density of accessible oxygen and nitrogen sites. Furthermore, dynamic breakthrough experiments confirmed the capability of TUTJ-201Ni for the separation of binary C2H2/CO2 mixtures. This study on Ni-based MOFs will enrich Lewis basic site rich MOFs for gas adsorption and separation applications.

Ethane Triggered Gate-Opening in a Flexible-Robust Metal-Organic Framework for Ultra-High Purity Ethylene Purification

Priority recognition separation of inert and larger ethane molecules from high-concentration ethylene mixtures instead of the traditional thermodynamic or size sieving strategy is a fundamental challenge. Herein, we report ethane triggered gate-opening in the flexible-robust metal-organic framework Zn(ad)(min), the 3-methylisonicotinic acid ligand can spin as a flexible gate when adsorbing the cross-section well-matched ethane molecule, achieving an unprecedented ethane adsorption capacity (62.6 cm3 g-1) and ethane/ethylene uptake ratio (3.34) under low-pressure region (0.1 bar and 298 K). The ethane-induced structural transition behavior has been uncovered by a collaboration of single-crystal X-ray diffraction, in situ variable pressure X-ray diffraction and theoretical calculations, elucidating the synergetic mechanism of cross-section matching and multiple supramolecular interactions within the tailor-made pore channels. Dynamic breakthrough experiments have revealed the outstanding separation performance of Zn(ad)(min) during the production of ultra-high purity ethylene (>99.995 %) with a productivity of up to 39.2 L/kg under ambient conditions.

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.

Energy-Level Alignment at TiO2@NH2-MIL-125 Interface for High-Performance Gas Sensing

Metal oxide (MO)-based chemiresistive sensors have great potential in environmental monitoring, security protection, and disease diagnosis. However, the thermally activated sensing mechanism in pristine MOs leads to high working temperature and poor selectivity, which are the main challenges impeding practical applications. Precise modulation of the band structure at the heterojunction interfaces of MOs offers the opportunity to unlock unique electrical and optical properties, enabling us to overcome these challenges. Metal-organic frameworks (MOFs) with tunable structures are promising materials for aligning the energy levels at the heterojunctions of MOs. Herein, we report the energy-level structural engineering of MO@MOF heterojunctions to optimize chemiresistive sensing performance. The interface was flexibly modulated from a straddling gap to a staggered gap by -NH2 functionalization of TiO2@(NH2)x-MIL-125, varying x from 0 to 1 and 2, respectively. TiO2@(NH2)x-MIL-125 combines the advantages of MOs and MOFs to synergistically improve gas-sensing properties. As a result, TiO2@NH2-MIL-125 is the first light-activated material to detect NO2 at 1 ppb with a response time of < 0.3 min at room temperature. It also exhibited excellent selectivity and long-term stability. Our study underscores the potential of energy band engineering in creating high-performance sensors, offering a strategy to overcome current material limits.

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.

A Scalable Pore-space-partitioned Metal-organic Framework Powered by Polycatenation Strategy for Efficient Acetylene Purification

Efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is a significant challenge in the petrochemical industry due to their similar physicochemical properties. Pore space partition (PSP) has shown promise in enhancing gas adsorption capacity and selectivity by reducing pore size and increasing the density of guest binding sites. Herein, we firstly employ the 2D→3D polycatenation strategy to construct a PSP metal-organic framework (MOF) Ni-dcpp-bpy, incorporating functional N/O sites to enhance C2H2 purification. The polycatenated framework with optimized pore size and regularity, exhibiting significant improvements over traditional PSP MOFs by resolving the critical contradiction of balancing C2H2 uptake (98.5 cm3 g-1 at 298 K, 100 kPa) and selectivity of C2H2/CO2 (3.4), C2H2/C2H4 (5.9), and C2H2/CH4 (96.4) in a MOF. Breakthrough experiments confirm high-purity C2H4 (>99.9 %) and high C2H2 productivity from binary and ternary mixtures. Notably, Ni-dcpp-bpy exhibits excellent water stability, scalability, and regenerability after 20 cycles for separating C2H2/CO2. Theoretical calculations verify that the strong binding of C2H2 is mainly attributed to the C-H⋅⋅⋅O/N interactions between host Ni-dcpp-bpy and guest C2H2 molecules. The polycatenation strategy not only improved industrial C2H2 purification efficiency but also enriched the design diversity of customized MOFs for other gas separation applications.

In Situ Stimulus Response Study on the Acetylene/Ethylene Purification Process in MOFs

Efficient removal of acetylene (C2H2) impurities from polymer-grade ethylene (C2H4) in a simple, clean manner remains a challenging goal in industry. The use of porous materials such as metal-organic frameworks (MOFs) is promising for this aim but the acquisition of high purification performance is still hindered by few knowledge on the purification process because the previous conclusions were derived basically from the non-breakthrough tests or ignored the influence of structural difference (crystal structure, morphology, or defect). Here we propose an unprecedented in situ stimulus response strategy to minimize the influence of structural difference, obtain the gas-loading crystal structures of the same MOF before and after light or heat stimulation, directly observe the evolution of pore charge distribution and pore⋅⋅⋅gas interactions under light/heat induction, and finally summarizes the favorable structure for highly efficient purification of C2H4. This study opens a new route to understand the relationship between the structure and separation performance for porous materials.

A Pillared-Layer Coordination Network for One-Step Ethylene Production from Ternary CO2/C2H2/C2H4 Gas Mixture

One-step separation of ethylene (C2H4) from multicomponent mixtures poses significant challenges in the petrochemical industry due to the high similarity of involved gas molecules. Herein, we report a pillared-layer coordination network named Zn-fa-mtrz (H2fa = fumaric acid; Hmtrz = 3-methyl-1,2,4-triazole) possessing pore surfaces decorated with methyl groups and electronegative N/O atoms. Molecular modeling reveals that the pore surface of Zn-fa-mtrz provides more and stronger multiple interaction sites to simultaneously enhance the adsorption affinity for CO2 and C2H2 other than C2H4. The experimental and simulated breakthrough experiments demonstrate the ability to produce high-purity C2H4 (>99.97%) in one-step from ternary CO2/C2H2/C2H4 gas mixtures.

Experimental and Theoretical Insights on Gas Trapping of Noble Gases in MFU-4-Type Metal-Organic Frameworks

Isostructural metal-organic frameworks (MOFs), namely MFU-4 and MFU-4-Br, in which the pore apertures are defined by anionic side ligands (Cl- and Br-, respectively), were synthesized and loaded with noble gases. By selecting the type of side ligand, one can fine-tune the pore aperture size, allowing for precise regulation of the entry and release of gas guests. In this study, we conducted experiments to examine gas loading and release using krypton and xenon as model gases, and we complemented our findings with computational modeling. Remarkably, the loaded gas guests remained trapped inside the pores even after being exposed to air under ambient conditions for extended periods, in some cases for up to several weeks. Therefore, we focused on determining the energy barrier preventing gas release using both theoretical and experimental methods. The results were compared in relation to the types of hosts and guests, providing valuable insights into the gas trapping process in MOFs, as well as programmed gas release in air under ambient conditions. Furthermore, the crystal structure of MFU-4-Br was elucidated using the three-dimensional electron diffraction (3DED) technique, and the bulk purity of the sample was subsequently verified through Rietveld refinement.

Removal of Trace Benzene from Cyclohexane Using a MOF Molecular Sieve

Cyclohexane (Cy), commonly produced by the catalytic hydrogenation of benzene (Bz), is used in large quantities as a solvent or feedstock for nylon polymers. Removing trace unreacted Bz from the Cy product is technically difficult due to their similar molecular structures and physical properties. Herein, we report that a metal-organic framework (MOF) adsorbent shows a molecular sieving effect for Bz and Cy with record-high Bz/Cy adsorption selectivities (216, 723, and 1027) in their liquid mixtures (v/v = 1:1, 1:10, and 1:20), and traps Bz molecules effectively even at low partial pressure in the vapor phase (e.g., 2.49 mmol/g at 8.2 Pa) or at low content in liquid-phase Cy (e.g., 128 mg/g at 20 ppm). Over 99% removal of trace Bz (1000 ppm) from liquid Cy could be achieved in one simple stripping step at room temperature using this sorbent, producing a Cy with >99.999% purity. Single-crystal structure analyses for guest-free and Bz-loaded phases of the MOF disclosed that a narrow slit-like pore aperture and the strong uniting of multiple weak host-guest and guest-guest interactions are the co-origin of its distinct adsorption property for Bz and Cy.

Imidazole-Functionalized Zn-MOFs for One-Step C2H4 Purification from C2H2/C2H4/C2H6 Ternary Mixture

The discovery of new structures is very important for metal-organic framework (MOF) adsorbents and their application in gas separation, where the design of ligands and the selection of metal ions play a decisive role. Herein, we synthesized two isoreticular Zn-MOFs, UPC-250 and UPC-251, composed of imidazole-based tricarboxylic acid ligands and binuclear zinc clusters. The pore environment was regulated via modifying fluorine atoms at different positions of ligands, and one-step purification of ethylene from acetylene/ethylene/ethane ternary mixture was realized in UPC-251.

Integration of ordered porous materials for targeted three-component gas separation

Separation of multi-component mixtures in an energy-efficient manner has important practical impact in chemical industry but is highly challenging. Especially, targeted simultaneous removal of multiple impurities to purify the desired product in one-step separation process is an extremely difficult task. We introduced a pore integration strategy of modularizing ordered pore structures with specific functions for on-demand assembly to deal with complex multi-component separation systems, which are unattainable by each individual pore. As a proof of concept, two ultramicroporous nanocrystals (one for C2H2-selective and the other for CO2-selective) as the shell pores were respectively grown on a C2H6-selective ordered porous material as the core pore. Both of the respective pore-integrated materials show excellent one-step ethylene production performance in dynamic breakthrough separation experiments of C2H2/C2H4/C2H6 and CO2/C2H4/C2H6 gas mixture, and even better than that from traditional tandem-packing processes originated from the optimized mass/heat transfer. Thermodynamic and dynamic simulation results explained that the pre-designed pore modules can perform specific target functions independently in the pore-integrated materials.

Metal-Organic Framework with Polar Pore Surface Designed for Purification of Both Natural Gas and Ethylene

The advancement of high-value CH4 purification technology within the natural gas industry is paramount for industrial processes. Herein, we constructed ZJNU-402, a new porous material characterized by permanent porosity, as an effective adsorbent for separating C3H8/CH4 and C2H6/CH4 mixtures. The findings reveal an outstanding C3H8 adsorption capacity of 68 cm3 g-1 and a moderate C2H6 adsorption rate of 42 cm3 g-1, with a notably lower CH4 adsorption rate of 11 cm3 g-1. Noteworthy is the exceptional selectivity of ZJNU-402 for C3H8/CH4 and C2H6/CH4, standing at 375 and 31, respectively, surpassing many previously documented high-performance adsorbents and breaking the traditional trade-off between adsorption capacity and separation selectivity. Adsorption heat calculations show that compared with CH4 molecules, C3H8 and C2H6 molecules form stronger bonds with the skeleton, resulting in excellent separation performance. In addition, the breakthrough experiment of ZJNU-402 can also completely separate the ternary component C3H8/C2H6/CH4 mixture to obtain 99.95 % high-purity methane. At the same time, ZJNU-402 also has excellent structural stability, excellent recyclability, and low isosteric adsorption heat. Consequently, ZJNU-402 exhibits substantial potential for augmenting the efficacy of natural gas enrichment processes.

Construction of a Fluorinated-Anion Pillared Metal-Organic Framework Exhibiting Dual-Pore Architecture for Simultaneous Enhancement of C2H2 Adsorption Capacity and Selectivity

Physisorption-based separation processes represents a promising alternative to the conventional thermally driven methods, such as cryogenic separation. However, a significant challenge lies in balancing the trade-off between adsorption capacity and selectivity of adsorbents. In this study, we introduce a novel fluorinated-anion pillared metal-organic frameworks (APMOFs) featuring a dual-pore architecture, constructed using a pyridine-oxazole bifunctional ligand. The inherent low symmetry of the ligand leads to significant distortion of the fluorinated-anion pillars, resulting in a distinctive type of APMOFs characterized by dual-pore architecture. On pore structure with constrict pore width is enriched with a high density of anion fluorinated pillars, offering numerous active sites advantageous for enhancing separation selectivity. Concurrently, the other pore structure exhibits larger dimensions, facilitating increased gas molecule accommodation and thereby augmenting adsorption capacity. Gas sorption studies reveal a substantial C2H2 adsorption capacity and a high C2H2/CO2 separation selectivity. Breakthrough experiments confirm its exceptional separation performance, while theoretical investigations elucidate a sequential adsorption process within these APMOFs, underscoring the efficacy of this strategy in overcoming trade-off limits in adsorbents.

A Fluorine-Functionalized Tb(III)-Organic Framework for Ba2+ Detection

The development of lanthanide-organic frameworks (Ln-MOFs) using for luminescence sensing and selective gas adsorption applications is of great significance from an energy and environmental perspective. This study reports the solvothermal synthesis of a fluorine-functionalized 3D microporous Tb-MOF with a face-centered cubic (fcu) topology constructed from hexanuclear clusters (Tb6O30) bridged by fdpdc ligands, formulated as {[Tb6(fdpdc)6(μ3-OH)8(H2O)6]·4DMF}n (1), (fdpdc = 3-fluorobiphenyl-4,4'-dicarboxylate). Complex 1 displays a 3D framework with the channel of 7.2 × 7.2 Å2 (measured between opposite atoms) perpendicular to the a-axis. With respect to Ba2+ cation, the framework of activated 1 (1a) exhibits high selectivity and reversibility in luminescence sensing function, with an LOD of 4.34665 mM. According to the results of simulations, compared to other small gas molecules (CO2, N2, H2, CO, and CH4), activated 1 (1a) shows a high adsorption selectivity for C2H2 at 298 K.

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.

Isolation of Polyethylene Glycol with Larger Molecular Weights via Metal-Organic Frameworks

Polymer products typically present as mixtures with a range of molecular weights, which notably influence the expression of their properties. In this study, a technique is proposed to separate polyethylene glycol (PEG) mixtures of varying molecular weights using metal-organic frameworks (MOFs), thereby narrowing down their molecular weight distribution. Due to the hydrogen bond interactions between PEG and -OH groups in the pores of NU-1000, NU-1000 can selectively adsorb PEG with larger molecular weights from PEG mixture. This separation method consistently yields with narrower molecular weight distribution across multiple cycles. This is the first application of MOFs in regulating the dispersity (Ð) of polymers in solution, providing a novel approach for separating and purifying mixed molecular weight polymers.

Ultramicroporous Metal-Organic Framework Featuring Multiple Polar Sites for Efficient Xenon Capture and Xe/Kr Separation

Efficient adsorption separation of xenon/krypton (Xe/Kr) mixtures is an important technological challenge due to their similar sizes and shapes. Herein, we report an ultramicroporous metal-organic framework (MOF), ZJU-Bao-302a, with pore sizes close to the kinetic diameter of Xe and pore surfaces lined with a high density of polar sites, including methyl groups, amines, and uncoordinated oxygen atoms. The synergistic effect of these polar sites enables ZJU-Bao-302a to exhibit a high Xe uptake of 2.77 mmol g-1 and a balanced Xe/Kr selectivity of 14.6 under ambient conditions. Dynamic breakthrough experiments demonstrate the material's capability to efficiently separate Xe/Kr mixtures (20/80) as well as capture Xe at ultralow concentrations (400 ppmv) from nuclear reprocessing exhausts, achieving a superior dynamic Xe capacity of 24.2 mmol kg-1. Density functional theory calculations reveal that the localized polar groups/atoms in ZJU-Bao-302a provide more effective recognition sites for Xe than Kr, enhancing the thermodynamic selectivity. This study highlights the importance of integrating tailored pore sizes and dense polar sites in metal-organic frameworks for developing high-performance Xe/Kr separation adsorbents.

Cooperative Immobilization of Transition-Metal Clusters into Kagome-Type Metal-Organic Framework for C2H2/CO2 Separation

There has long been a pursuit for a metal-organic framework (MOF)-based adsorbent for various hydrocarbon separations. Herein, we utilized simple trimesic acid and 1,2,4-triazole, together with the heterometallic strategy to produce two quaternary MOFs with a kgm-type structure. The cooperative coordination allows the immobilization of metal clusters into the pore channels, creating an appropriate pore size and high density of open metal sites. The resulting material shows excellent C2H2/CO2 separation performance with good stability.

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.

Surface Chemistry Regulation in Cu4I4-Triazolate Metal-Organic Frameworks for One-Step C3H6 Purification from Quaternary C3 Mixtures

C3H6 is a crucial building block for many chemicals, yet separating it from other C3 hydrocarbons presents a significant challenge. Herein, we report a hydrolytically stable Cu4I4-triazolate metal-organic framework (MOF) (JNU-9-CH3) featuring 1D channels decorated with readily accessible iodine and nitrogen atoms from Cu4I4 clusters and triazolate linkers, respectively. The exposed iodine and nitrogen atoms allow for cooperative binding of C3 hydrocarbons, as evidenced by in situ single-crystal crystallography and Raman spectroscopy studies. As a result, JNU-9-CH3 exhibits substantially stronger binding affinity for C3H4, CH2═C═CH2, and C3H8 than that for C3H6. Breakthrough experiments confirm its ability to directly separate C3H6 (≥99.99%) from C3H4/CH2═C═CH2/C3H8/C3H6 mixtures at varying ratios and flow rates. Overall, we illustrate the cooperative binding of C3 hydrocarbons in a Cu4I4-triazolate MOF and its highly efficient C3H6 purification from quaternary C3 mixtures. The study highlights the potential of MOF adsorbents with metal-iodide clusters for cooperative bindings and hydrocarbon separations.

Achieving Record C2H2 Packing Density for Highly Efficient C2H2/C2H4 Separation with a Metal-Organic Framework Prepared by a Scalable Synthesis in Water

Adsorptive C2H2/C2H4 separation using metal-organic frameworks (MOFs) has emerged as a promising technology for the removal of C2H2 (acetylene) impurity (1 %) from C2H4 (ethylene). The practical application of these materials involves the optimization of separation performance as well as development of scalable and green production protocols. Herein, we report the efficient C2H2/C2H4 separation in a MOF, Cu(OH)INA (INA: isonicotinate) which achieves a record C2H2 packing density of 351 mg cm-3 at 0.01 bar through high affinity towards C2H2. DFT (density functional theory) calculations reveal the synergistic binding mechanism through pore confinement and the oxygen sites in pore wall. The weakly basic nature of binding sites leads to a relatively low heat of adsorption (Qst) of approximately 36 kJ/mol, which is beneficial for material regeneration and thermal management. Furthermore, a scalable and environmentally friendly synthesis protocol with a high space-time yield of 544 kg m-3 day-1 has been developed without using any modulating agents. This material also demonstrates enduring separation performance for multiple cycles, maintaining its efficacy after exposure to water or air for three months.

Bioinspired recognition in metal-organic frameworks enabling precise sieving separation of fluorinated propylene and propane mixtures

The separation of fluorinated propane/propylene mixtures remains a major challenge in the electronics industry. Inspired by biological ion channels with negatively charged inner walls that allow selective transport of cations, we presented a series of formic acid-based metal-organic frameworks (MFA) featuring biomimetic multi-hydrogen confined cavities. These MFA materials, especially the cobalt formate (CoFA), exhibit specific recognition of hexafluoropropylene (C3F6) while facilitating size exclusion of perfluoropropane (C3F8). The dual-functional adsorbent offers multiple binding sites to realize intelligent selective recognition of C3F6, as supported by theoretical calculations and in situ spectroscopic experiments. Mixed-gas breakthrough experiments validate the capability of CoFA to produce high-purity (>5 N) C3F8 in a single step. Importantly, the stability and cost-effective scalable synthesis of CoFA underscore its extraordinary potential for industrial C3F6/C3F8 separations. This bioinspired molecular recognition approach opens new avenues for the efficient purification of fluorinated electronic specialty gases.

Advanced Porous Nanomaterials: Synthesis, Properties, and Applications

Porous nanomaterials have emerged as one of the most versatile and valuable classes of materials, captivating the attention of both scientists and engineers due to their exceptional functional and structural properties [...].

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.