Incorporation of multiple supramolecular binding sites into a robust MOF for benchmark one-step ethylene purification

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%).

Regulating the Dynamics of Interpenetrated Porous Frameworks for Inverse C2H6/C2H4 Separation at Elevated Temperature

Selective adsorption of ethane (C2H6) from mixtures containing ethylene (C2H4) is of interest for the direct production of high purity C2H4. However, the extremely similar molecular properties of these gases make this process challenging, particularly at elevated temperatures, an implication of saved energy consumption. To address such challenge, we present a new approach for regulating the temperature-dependent dynamics in hydrogen-bonded interpenetrated frameworks. As a single H-bond linked interpenetrated porous framework, NTU-101-NH2 exhibits emerging structural dynamics in response to C2H6 (37 kPa) and C2H4 (53 kPa) and has shown a record ability to produce polymer-grade C2H4 (15.7 mL g-1) at 328 K, as the shifting of the interpenetrated frameworks here requires a relatively weak stimulus, allowing the optimization of adsorption at a higher temperatures range. Meanwhile, the robust and conveniently prepared NTU-101-NH2 shows good cyclic separation performance. In comparison, the framework response of the percussor NTU-101, connected by three H-bonds, occurs at 293 K and has a moderate separation ability (10.2 mL g-1). This work showcases the first adsorbent for direct C2H4 purification at elevated temperatures, and the insights into the hydrogen-bonded frameworks will pave the way for designing soft families capable of challenging separations with reduced energy requirements.

Superhydrophobic Molecular Selector for Efficient Separation of Ethane over Ethylene under Dry and Humid Conditions

Exploring humidity-resistant, ethane-selective adsorbents for the one-step purification of polymer-grade (>99.95%) ethylene from ethane-ethylene mixtures is of great importance, yet remains a significant challenge. To address this challenge, we present a novel strategy for constructing a "superhydrophobic molecular selector" (SMS) based on a porous organic cage (POC), which features a superhydrophobic outer surface and an inner cavity with multiple ethane-selective functional sites. The resulting SMS-POC-1 demonstrates excellent C2H6 adsorption capacity (97 cm3 g-1 at 298 K) and C2H6/C2H4 selectivity (Sads = 2.40 at 298 K), offering a superior trade-off between ethane adsorption capacity and C2H6/C2H4 adsorption selectivity among all C2H6-selective adsorbents. Especially, breakthrough experiments demonstrate that SMS-POC-1 efficiently produces polymer-grade C2H4 from C2H6/C2H4 mixtures at 60% relative humidity (RH), making it the highest-selectivity adsorbent reported to date that can stably operate in a humid environment. The combination of experimental results and theoretical calculations reveals that the coexistence of a superhydrophobic outer surface and synergistic C-H···π interactions and hydrogen-bonding sites accounts for the high C2H6/C2H4 separation performance under humid conditions for SMS-POC-1. Our work thus not only demonstrates a general strategy for guiding the design of humidity-resistant adsorption-separation materials but also presents a promising candidate for potential applications in hydrocarbon separation.

Engineering Supramolecular Binding Sites in an Ultrastable and Hydrophobic Metal-Organic Framework for C2H6/C2H4 Separation

The separation of ethane (C2H6) from ethylene (C2H4) is critical for obtaining polymer-grade C2H4. Adsorptive separation with C2H6-selective MOFs offers a viable alternative to energy-intensive cryogenic distillation, enabling the direct production of high-purity C2H4. In this study, we developed an ultrastable ethane-selective metal-organic framework, UiO-67-(CH3)2, which demonstrates enhanced C2H6 adsorption (4.10 mmol g-1 at 1 bar and 298 K), higher C2H6/C2H4 selectivity of 1.70, and an increased C2H6/C2H4 adsorption ratio of 1.53 compared to unmodified UiO-67. GCMC simulations demonstrate that C2H6 forms more C-H···π interactions with the surrounding benzene rings and more C-H···C interactions with methyl groups compared to C2H4, highlighting the synergistic effects of supramolecular interactions. Furthermore, the hydrophobic pore environment also minimizes water interference, with exceptionally low water uptake (0.019 g g-1 at 60% RH), ensuring robust separation capacity under high humid conditions. The introduction of methyl groups not only significantly enhances C2H6 adsorption performance and C2H6/C2H4 separation selectivity but also improves material's hydrophobicity.

Purification of Xe and SF6 through Adaptive Contractions in a Flexible Metal-Organic Framework

Overcoming the trade-off effects between adsorption capacity, adsorption selectivity, and adsorption enthalpy of an adsorbent is very important but remains a huge challenge. Here, we report a flexible metal-organic framework (FJI-H36); it can selectively adsorb Xe from Xe/Kr mixtures with high adsorption capacity but very low adsorption enthalpy. Structural analyses show that such excellent adsorption performances come from the adaptive contraction of the flexible framework; pore shrinkage can enhance the interactions between adsorbed Xe and the framework and offset some of the adsorption heats. For SF6/N2 mixtures, FJI-H36 can also enhance the adsorption performance of SF6 through adaptive contraction, resulting in both high adsorption selectivity and low adsorption enthalpy. This not only provides a new adsorbent for the purification of Xe/Kr/SF6 but also offers a potential solution to overcome the trade-offs among adsorption capacity, adsorption selectivity, and adsorption enthalpy of a specific adsorbent.

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.

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.

Kinetic Separation of Butane Isomers Using a Formate Metal-Organic Framework

n-butane (n-C4H10) and isobutane (i-C4H10) are important raw materials in chemical industry. The separation of the two hydrocarbon isomers via distillation is challenging and energy-consuming. Herein we report the adsorption behavior of a microporous cobalt formate framework [Co3(HCOO)6] for potential kinetic separation of butane isomers. Under ambient condition, [Co3(HCOO)6] shows near adsorption capacity for n-C4H10 (1.77 mmol g-1) and i-C4H10 (1.36 mmol g-1) with different adsorption kinetics. Study on the adsorption kinetics for butane indicates that the smaller isomer is adsorbed at a higher diffusion rate, resulting in a high kinetic selectivity of 193 for n-C4H10/i-C4H10 separation. Analyses of adsorption kinetics and breakthrough experiment have validated the separation potential of [Co3(HCOO)6] for butane purification.

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.

Topology-Oriented Assembly of Iron-2,5-Furandicarboxylate Coordination Cubes for Highly Selective CO2/SF6/N2 Capture

As typical greenhouse gases, selective capture of CO2 (carbon dioxide) and SF6 (sulfur hexafluoride) is of great importance. Herein, on the basis of a typical six-connected pcu topology, three isomorphic Fe-2,5-furandicarboxylate (Fe-FDC) metal-organic framework (MOF) adsorbents (SNNU-133-135) were successfully prepared via a rational assembly of {[Fe3O]8(FDC)12} cubic building blocks. With dihedral angles in Fe-FDC cubes varying from 80° (SNNU-133), 87° (SNNU-134), to 90°(SNNU-135), three MOF isomers show step-by-step enhancement of selective CO2 and SF6 capture performance. For SNNU-135, at 298 K and 1 bar, the adsorption capacities for CO2 and SF6 are 83.6 and 66.7 cm3/g, and the CO2/N2 and SF6/N2 selectivity values are up to 29.4 and 509.1, respectively. Furthermore, the practical breakthrough interval time of SNNU-135 can reach 75 and 185 min g-1 (298 K, 1 bar, 1 mL min-1, CO2/N2 = 15:85 and SF6/N2 = 10:90) with the captured CO2 and SF6 amounts of 1.24 and 2.34 mmol/g, and the SF6 purity greater than 99.9%. The most regular Fe-FDC cubes, all available Fe-OMSs together with multiple weak interactions, cause SNNU-135 to have the highest CO2 and SF6 adsorption capacity, best CO2/N2 and SF6/N2 selectivity performance, and one-step separation ability for CO2/SF6/N2 ternary mixtures.

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.

Molecular Mechanism Behind the Capture of Fluorinated Gases by Metal-Organic Frameworks

Fluorinated gases (F-gases) play a vital role in the chemical industry and in the fields of air conditioning, refrigeration, health care, and organic synthesis. However, the direct emission of waste gases containing F-gases into the atmosphere contributes to greenhouse effects and generates toxic substances. Developing porous materials for the energy-efficient capture, separation, and recovery of F-gases is highly desired. Recently, as a highly designable porous adsorbents, metal-organic frameworks (MOFs) exhibit excellent selective sorption performance toward F-gases, especially for the recognition and separation of different F-gases with highly similar properties, showing their great potential in F-gases control and recovery. In this review, we discuss the capture and separation of F-gases and their azeotropic, near-azeotropic, and isomeric mixtures in various application scenarios by MOFs, specifically classify and analyze molecular interaction between F-gases and MOFs, and interpret the mechanisms underlying their high performance regarding both adsorption capacity and selectivity, providing a repertoire for future materials design. Challenges faced in the transformation research roadmap of MOFs adsorbent separation technologies toward F-gases are also discussed, and areas for future research endeavors are highlighted.

An MOF-Based Single-Molecule Propylene Nanotrap for Benchmark Propylene Capture from Ethylene

Highly selective capture and separation of propylene (C3H6) from ethylene (C2H4) presents one of the most crucial processes to obtain pure C2H4 in the petrochemical industry. The separation performance of current physisorbents is commonly limited by insufficient C3H6 binding affinity, resulting in poor low-pressure C3H6 uptakes or inadequate C3H6/C2H4 selectivities. Herein, we realize a unique single-molecule C3H6 nanotrap in an ultramicroporous MOF material (Co(pyz)[Pd(CN)4], ZJU-74a-Pd), exhibiting the benchmark C3H6 capture capacity at low-pressure regions. This MOF-based nanotrap features the sandwichlike strong multipoint binding sites and the perfect size match with C3H6 molecules, providing an ultrastrong C3H6 binding affinity with the maximal Q st value (55.8 kJ mol-1). This affords the nanotrap to exhibit one of the highest C3H6 uptakes at low pressures (60.5 and 103.8 cm3 cm-3 at 0.01 and 0.1 bar) and record-high C3H6/C2H4 selectivity (23.4). Theoretical calculations reveal that the perfectly size-matched pore cavities combined with sandwichlike multibinding sites enable this single-molecule C3H6 nanotrap to maximize the C3H6 binding affinity, mainly accounting for its record low-pressure C3H6 capture capacity and selectivity. Breakthrough experiments further confirm its excellent separation capacity for actual 1/99 and 50/50 C3H6/C2H4 mixtures, affording the remarkably high pure C2H4 productivities of 17.1 and 3.4 mol kg-1, respectively.

Amino-Functionalized Metal-Organic Frameworks Featuring Ultra-Strong Ethane Nano-Traps for Efficient C2H6/C2H4 Separation

Developing high-performance porous materials to separate ethane from ethylene is an important but challenging task in the chemical industry, given their similar sizes and physicochemical properties. Herein, a new type of ultra-strong C2H6 nano-trap, CuIn(3-ain)4 is presented, which utilizes multiple guest-host interactions to efficiently capture C2H6 molecules and separate mixtures of C2H6 and C2H4. The ultra-strong C2H6 nano-trap exhibits the high C2H6 (2.38 mmol g-1) uptake at 6.25 kPa and 298 K and demonstrates a remarkable selectivity of 3.42 for C2H6/C2H4 (10:90). Additionally, equimolar C2H6/C2H4 exhibited a superior high separation potential ∆Q (2286 mmol L-1) at 298 K. Kinetic adsorption tests demonstrated that CuIn(3-ain)4 has a high adsorption rate for C2H6, establishing it as a new benchmark material for the capture of C2H6 and the separation of C2H6/C2H4. Notably, this exceptional performance is maintained even at a higher temperature of 333 K, a phenomenon not observed before. Theoretical simulations and single-crystal X-ray diffraction provide critical insights into how selective adsorption properties can be tuned by manipulating pore dimensions and geometry. The excellent separation performance of CuIn(3-ain)4 has been confirmed through breakthrough experiments for C2H6/C2H4 gas mixtures.

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.

Precise Pore Engineering of Zirconium Metal-Organic Cages for One-Step Ethylene Purification from Ternary Mixtures

One-step purification of ethylene from ternary mixtures (C2H2, C2H4, and C2H6) can greatly reduce the energy consumption of the separation process, but it is extremely challenging. Herein, we use crystal engineering and reticular chemistry to introduce unsaturated bonds (ethynyl and alkyne) into ligands, and successfully design and synthesized two novel Zr-MOCs (ZrT-1-ethenyl and ZrT-1-alkyne). The introduction of carbon-carbon unsaturated bonds provides abundant adsorption sites within the framework while modulating the pore window size. Comprehensive characterization techniques including single crystal and powder X-ray diffraction, as well as electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) confirm that ZrT-1-ethenyl and ZrT-1-alkyne possess an isostructural framework with ZrT-1 and ZrT-1-Me, respectively. Adsorption isotherms and breakthrough experiments combined with theoretical calculations demonstrate that ZrT-1-ethenyl can effectively remove trace C2H2 and C2H6 in C2H4 and achieve separation of C2H2 from C2H4 and CO2. ZrT-1-ethenyl can also directly purify C2H4 in liquid solutions. This work provides a benchmark for MOCs that one-step purification of ethylene from ternary mixtures.

A Propeller-Like Ligand-Directed Construction of a Tetranuclear Cerium-Organic Framework for Single-Step Ethylene Purification from Ternary C2 Mixtures

The efficient single-step purification of ethylene from ternary C2 mixtures containing ethane and acetylene is challenging and demanding. Herein, we introduce a novel cerium-based metal-organic framework (MOF) of Ce-NTB-rtk synthesized via a ligand-conformer strategy. The Ce-NTB-rtk features a rare tetranuclear cerium cluster and 2D kgd layers pillared by a 3D rtl framework concomitant with an extraordinary (3,3,12)-c network. The compound encompasses microporous cavities replete with a nonpolar microenvironment. Gas sorption and breakthrough experiments demonstrate its superior affinity for C2H6 and C2H2 over C2H4, enabling effective single-step ethylene purification. Computational simulations reveal that preferential adsorptions are facilitated by different interaction strengths of C-H···O hydrogen bonds. The performance of Ce-NTB-rtk in separation selectivity and regeneration capacity makes it a promising candidate for sustainable and cost-effective ethylene purification, showcasing the potential of MOFs in advanced gas separation applications.

Molten Guest-Mediated Metal-Organic Frameworks Featuring Multi-Modal Supramolecular Interaction Sites for Flame-Retardant Superionic Conductor in All-Solid-State Batteries

The development of solid-state electrolytes (SSEs) with outstanding comprehensive performance is currently a critical challenge for achieving high energy density and safer solid-state batteries (SSBs). In this study, a strategy of nano-confined in situ solidification is proposed to create a novel category of molten guest-mediated metal-organic frameworks, named MGM-MOFs. By embedding the newly developed molten crystalline organic electrolyte (ML20) into the nanocages of anionic MOF-OH, MGM-MOF-OH, characterized by multi-modal supramolecular interaction sites and continuous negative electrostatic environments within nano-channels, is achieved. These nanochannels promote ion transport through the successive hopping of Li+ between neighbored negative electrostatic environments and suppress anion movement through the chemical constraint of the hydroxyl-functionalized pore wall. This results in remarkable Li+ conductivity of 7.1 × 10-4 S cm-1 and high Li+ transference number of 0.81. Leveraging these advantages, the SSBs assembled with MGM-MOF-OH exhibit impressive cycle stability and a high specific energy density of 410.5 Wh kganode + cathode + electrolyte -1 under constrained conditions and various working temperatures. Unlike flammable traditional MOFs, MGM-MOF-OH demonstrates high robustness under various harsh conditions, including ignition, high voltage, and extended to humidity.

Deciphering Mechanisms of CO2-Selective Recognition over Acetylene within Porous Materials

Reverse adsorption of carbon dioxide (CO2) from acetylene (C2H2) presents both significant importance and formidable challenges, particularly in the context of carbon capture, energy efficiency, and environmental sustainability. In this Review, we delve into the burgeoning field of reverse CO2/C2H2 adsorption and separation, underscoring the absence of a cohesive materials design strategy and a comprehensive understanding of the CO2-selective capture mechanisms from C2H2, in contrast to the quite mature methodologies available for C2H2-selective adsorption. Focusing on porous materials, the latest advancements in CO2-selective recognition mechanisms are highlighted. The review establishes that the efficacy of CO2 recognition from C2H2 relies intricately on a myriad of factors, including pore architecture, framework flexibility, functional group interactions, and dynamic responsive behaviors under operating conditions. It is noted that achieving selectivity extends beyond physical sieving, necessitating meticulous adjustments in pore chemistry to exploit the subtle differences between CO2 and C2H2. This comprehensive overview seeks to enhance the understanding of CO2-selective recognition mechanisms, integrating essential insights crucial for the advancement of future materials. It also lays the groundwork for innovative porous materials in CO2/C2H2 separation, addressing the pressing demand for more efficient molecular recognition within gas separation technologies.

Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure with dia topology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could not only stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility due to its weak intermolecular interactions (so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was exclusively confirmed by gas sorption isotherms and single-crystal X-ray diffraction studies, showing that the flexible pore pockets can be opened by C3H8 and n-C4H10 molecules rather by C2H6 and CH4. This leads to notably higher C3H8 and n-C4H10 uptakes with enhanced selectivities than C2H6 over CH4 under ambient conditions, affording one of the highest n-C4H10/CH4 selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-C4H10 can induce an obvious framework expansion along with pore pocket opening to improve n-C4H10 uptake and selectivity, while not for C2H6 adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.

Systemic regulation of binding sites in porous coordination polymers for ethylene purification from ternary C2 hydrocarbons

The global demand for poly-grade ethylene (C2H4) is increasing annually. However, the energy-saving purification of this gas remains a major challenge due to the similarity in molecular properties among the ternary C2 hydrocarbons. To address this challenge, we report an approach of systematic tuning of the pore environment with organic sites (from -COOH to -CF3, then to -CH3) in porous coordination polymers (PCPs), of which NTU-73-CH3 shows remarkable capability for the direct production of poly-grade C2H4 from ternary C2 hydrocarbons under ambient conditions. In comparison, the precursor structure of NTU-73-COOH is unable to purify C2H4, while NTU-73-CF3 shows minimal ability to harvest C2H4. This is because the changed binding sites in the NTU-73-series not only eliminate the channel obstruction caused by the formation of gas clusters, but also enhance the interaction with acetylene (C2H2) and ethane (C2H6), as validated by in situ crystallographic and Raman analysis. Our findings, in particular the systematic tuning of the pore environment and the efficient C2H4 purification by NTU-73-CH3, provide a blueprint for the creation of advanced porous families that can handle desired tasks.

Balanced Mass Transfer and Active Sites Density in Hierarchical Porous Catalytic Metal-Organic Framework for Enhancing Redox Reaction in Lithium-Sulfur Batteries

Developing highly efficient catalysts, characterized by controllable pore architecture and effective utilization of active sites, is paramount in addressing the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs), which, however, remains a formidable challenge. In this study, a hierarchical porous catalytic metal-organic framework (HPC-MOF) with both appropriate porosity and abundant exposed catalytic sites is achieved through time-controlled precise pore engineering. It is revealed that the evolution of the porous structure and catalytic site density is time-dependent during the etching processes. The moderately etched HPC-MOF-M attains heterogeneous pores at various scales, where large apertures ensure fast mass transfer and micropores inherit high-density catalytic sites, enhancing utilization and catalytic kinetics at internal catalytic sites. Capitalizing on these advantages, LSB incorporating the HPC-MOF-M interlayer demonstrates a 164.6% improvement in discharge capability and an 83.3% lower decay rate over long-term cycling at 1.0C. Even under high sulfur loading of 7.1 mg cm-2 and lean electrolyte conditions, the LSB exhibits stable cycling for over 100 cycles. This work highlights the significance of balancing the relationship between mass transfer and catalytic sites through precise chemical regulation of the porous structure in catalytic MOFs, which are anticipated to inspire the development of advanced catalysts for LSBs.

Tunable Low-Pressure Water Adsorption in Stable Multivariate Metal-Organic Frameworks for Boosting Water-Based Ultralow-Temperature-Driven Refrigeration

The green water-based adsorption refrigeration is considered as a promising strategy to realize near-zero-carbon cooling applications. Although many metal-organic frameworks (MOFs) have been developed as water adsorbents, their cooling performance are commonly limited by the insufficient water uptakes below P/P0 = 0.2. Herein, the development of multivariate MOFs (MTV-MOFs) is reported to highly modulate and boost the low-pressure water uptake for improving coefficient of performance (COP) for refrigeration. Through ligand exchange in the pristine MIL-125-NH2 , a series of MTV-MOFs with bare nitrogen sites are designed and synthesized. The resulting MIL-125-NH2 /MD-5% exhibits the significantly improved water uptake of 0.39 g g-1 at 298 K and P/P0 = 0.2, which is three times higher than MIL-125-NH2 (0.12 g g-1 ) and comparable to some benchmark materials including KMF-1 (0.4 g g-1 ) and MIP-200 (0.36 g g-1 ). Combined with its low-temperature regeneration, fast sorption kinetics and high stability, MIL-125-NH2 /MD-5% achieves one of the highest COP values (0.8) and working capacities (0.24 g g-1 ) for refrig-2 under an ultralow-driven temperature of 65 °C, which are higher than some best-performing MOFs such as MIP-200 (0.74 and 0.11 g g-1 ) and KMF-2 (0.62 and 0.16 g g-1 ), making it among the best adsorbents for efficient ultralow-temperature-driven refrigeration.

Multimodal Engineering of Catalytic Interfaces Confers Multi-Site Metal-Organic Framework for Internal Preconcentration and Accelerating Redox Kinetics in Lithium-Sulfur Batteries

The development of highly efficient catalysts to address the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) remains a formidable challenge. In this study, a series of multi-site catalytic metal-organic frameworks (MSC-MOFs) were elaborated through multimodal molecular engineering to regulate both the reactant diffusion and catalysis processes. MSC-MOFs were crafted with nanocages featuring collaborative specific adsorption/catalytic interfaces formed by exposed mixed-valence metal sites and surrounding adsorption sites. This design facilitates internal preconcentration, a coadsorption mechanism, and continuous efficient catalytic conversion toward polysulfides concurrently. Leveraging these attributes, LSBs with an MSC-MOF-Ti catalytic interlayer demonstrated a 62 % improvement in discharge capacity and cycling stability. This resulted in achieving a high areal capacity (11.57 mAh cm-2 ) at a high sulfur loading (9.32 mg cm-2 ) under lean electrolyte conditions, along with a pouch cell exhibiting an ultra-high gravimetric energy density of 350.8 Wh kg-1 . Lastly, this work introduces a universal strategy for the development of a new class of efficient catalytic MOFs, promoting SRR and suppressing the shuttle effect at the molecular level. The findings shed light on the design of advanced porous catalytic materials for application in high-energy LSBs.

Thiadiazole-Functionalized Th/Zr-UiO-66 for Efficient C2H2/CO2 Separation

Adsorptive separation technology provides an effective approach for separating gases with similar physicochemical properties, such as the purification of acetylene (C2H2) from carbon dioxide (CO2). The high designability and tunability of metal-organic framework (MOF) adsorbents make them ideal design platforms for this challenging separation. Herein, we employ an isoreticular functionalization strategy to fine-tune the pore environment of Zr- and Th-based UiO-66 by the immobilization of the benzothiadiazole group via bottom-up synthesis. The functionalized UPC-120 exhibits an enhanced C2H2/CO2 separation performance, which is confirmed by adsorption isotherms, dynamic breakthrough curves, and theoretical simulations. The synergy of ligand functionalization and metal ion fine-tuning guided by isoreticular chemistry provides a new perspective for the design and development of adsorbents for challenging gas separation processes.