Electrostatically Driven Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Material

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.

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

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

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

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

An adsorbate biased dynamic 3D porous framework for inverse CO2 sieving over C2H2

Separating carbon dioxide (CO2) from acetylene (C2H2) is one of the most critical and complex industrial separations due to similarities in physicochemical properties and molecular dimensions. Herein, we report a novel Ni-based three-dimensional framework {[Ni4(μ3-OH)2(μ2-OH2)2(1,4-ndc)3](3H2O)}n (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å2), that perfectly matches with the molecular size of CO2 and C2H2. The dehydrated framework shows structural transformation, decorated with an unsaturated Ni(ii) centre and pendant oxygen atoms. The dynamic nature of the framework is evident by displaying a multistep gate opening type CO2 adsorption at 195, 273, and 298 K, but not for C2H2. The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO2 selectivity over C2H2, attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, in situ spectroscopic inspection, and selectivity approximations. In situ DRIFTS measurements and DFT-based theoretical calculations confirm CO2 binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.

A Microporous Mn(II) MOF Based on 5-(4H-1,2,4-triazol-4-yl) Isophthalic Acid for CO2/N2 Separation

Removal of carbon dioxide (CO2) from a CO2/N2 mixture by utilizing CO2-selective sorbents is important from the perspective of energy security and environmental sustainability. Herein, a microporous metal-organic framework (MOF) composed of manganese(II) and a bifunctional linker 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid (H2L), [Mn(HL)2] (1) is designed and synthesized using a hydrothermal method. Characterized by single-crystal X-ray diffraction (SCXRD), a microporous channel was found in the structure of compound 1 along the a-axis. Attributed to hydrogen-binding interactions between CO2 molecules and N- and O-donor ligands in its microporous one-dimensional (1D) channel, compound 1 exhibits favorable adsorption of CO2 over N2. Further, verified by experimental breakthrough tests, the CO2/N2 mixture can be separated efficiently. This work provides potential guidance for designing CO2-selective MOFs for CO2/N2 separation.

Maximizing Electrostatic Interaction in Ultramicroporous Metal-Organic Frameworks for the One-Step Purification of Acetylene from Ternary Mixture

Developing efficient adsorbents for acetylene purification from multicomponent mixtures is of critical significance in the chemical industry, but the trade-off between regenerability and selectivity significantly restricts practical industrial applications. Here, we report ultramicroporous metal-organic frameworks with acetylene-affinity channels to enhance electrostatic interaction between C2H2 and frameworks for the efficient one-step purification of C2H2 from C2H2/CO2/C2H4 mixtures, in which the electrostatic interaction led to high regenerability. The obtained SNNU-277 exhibits significantly higher adsorption capacity for C2H2 than that for both C2H4 and CO2 at 298 K and 0.1 bar, while an ultrahigh selectivity of C2H2/C2H4 (100.6 at 298 K) and C2H2/CO2 (32.8 at 298 K) were achieved at 1 bar. Breakthrough experiments validated that SNNU-277 can efficiently separate C2H2 from C2H2/C2H4/CO2 mixtures. CO2 and C2H4 broke through the adsorption column at 4 and 14.8 min g-1, whereas C2H2 was detected until 177.6 min g-1 at 298 K. Theoretical calculations suggest that the framework is electrostatically compatible with C2H2 and electrostatically repels C2H4 and CO2 in the mixed components. This work highlights the importance of rational pore engineering for maximizing the electrostatic effect with the preferentially absorbed guest molecule for efficient multicomponent separation.

Anionic Ni-Based Metal-Organic Framework with Li(I) Cations in the Pores for Efficient C2H2/CO2 Separation

Acetylene (C2H2) is widely used as a raw material for producing various downstream commodities in the petrochemical and electronic industry. Therefore, the acquisition of high-purity C2H2 from a C2H2/CO2 mixture produced by partial methane combustion or thermal hydrocarbon cracking is of great significance yet highly challenging due to their similar physical and chemical properties. Herein, we report an anionic metal-organic framework (MOF) named LIFM-210, which has Li+ cations in the pores and shows a higher adsorption affinity for C2H2 than CO2. LIFM-210 is constructed by a unique tetranuclear Ni(II) cluster acting as a 10-connected node and an organic ligand acting as a 5-connected node. Single-component adsorption and transient breakthrough experiments demonstrate the good C2H2 selective separation performance of LIFM-210. Theoretical calculations revealed that Li+ ions strongly prefer C2H2 to CO2 and are primary adsorption sites, playing vital roles in the selective separation of C2H2/CO2.

Separation of High-Purity C2H2 from Binary C2H2/CO2 Using Robust Al-Based MOFs Comprising Nitrogen-Containing Heterocyclic Dicarboxylate

In this study, three nitrogen-containing aluminum-based metal-organic frameworks (Al-MOFs), namely, CAU-10pydc, MOF-303, and KMF-1, were investigated for the efficient separation of a C2H2/CO2 gas mixture. Among these three Al-MOFs, KMF-1 demonstrated the highest selectivity for C2H2/CO2 separation (6.31), primarily owing to its superior C2H2 uptake (7.90 mmol g-1) and lower CO2 uptake (2.82 mmol g-1) compared to that of the other two Al-MOFs. Dynamic breakthrough experiments, using an equimolar binary C2H2/CO2 gas mixture, demonstrated that KMF-1 achieved the highest separation performance. It yielded 3.42 mmol g-1 of high-purity C2H2 (>99.95%) through a straightforward desorption process under He purging at 298 K and 1 bar. To gain insights into the distinctive characteristics of the pore surfaces of structurally similar CAU-10pydc and KMF-1, we conducted computational simulations using canonical Monte Carlo and dispersion-corrected density functional theory methods. These simulations revealed that the secondary amine (C2N-H) groups in KMF-1 played a more significant role in differentiating between C2H2 and CO2 compared to that of the N atoms in CAU-10pydc and MOF-303. Consequently, KMF-1 emerged as a promising adsorbent for the separation of high-purity C2H2 from binary C2H2/CO2 gas mixtures.

Optimizing Sieving Effect for CO2 Capture from Humid Air Using an Adaptive Ultramicroporous Framework

Excessive CO2 in the air can not only lead to serious climate problems but also cause serious damage to humans in confined spaces. Here, a novel metal-organic framework (FJI-H38) with adaptive ultramicropores and multiple active sites is prepared. It can sieve CO2 from air with the very high adsorption capacity/selectivity but the lowest adsorption enthalpy among the reported physical adsorbents. Such excellent adsorption performances can be retained even at high humidity. Mechanistic studies show that the polar ultramicropore is very suitable for molecular sieving of CO2 from N2 , and the distinguishable adsorption sites for H2 O and CO2 enable them to be co-adsorbed. Notably, the adsorbed-CO2 -driven pore shrinkage can further promote CO2 capture while the adsorbed-H2 O-induced phase transitions in turn inhibit H2 O adsorption. Moreover, FJI-H38 has excellent stability and recyclability and can be synthesized on a large scale, making it a practical trace CO2 adsorbent. This will provide a new strategy for developing practical adsorbents for CO2 capture from the air.

A Microporous Hydrogen Bonded Organic Framework for Highly Selective Separation of Carbon Dioxide over Acetylene

The separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) is a very important but challenging task due to their similar molecular dimensions and physical properties. In terms of porous adsorbents for this separation, the CO2 -selective porous materials are superior to the C2 H2 -selective ones because of the cost- and energy-efficiency but have been rarely achieved. Herein we report our unexpected discovery of the first hydrogen bonded organic framework (HOF) constructed from a simple organic linker 2,4,6-tri(1H-pyrazol-4-yl)pyridine (PYTPZ) (termed as HOF-FJU-88) as the highly CO2 -selective porous material. HOF-FJU-88 is a two-dimensional HOFs with a pore pocket of about 7.6 Å. The activated HOF-FJU-88 takes up a high amount of CO2 (59.6 cm3  g-1 ) at ambient conditions with the record IAST selectivity of 1894. Its high performance for the CO2 /C2 H2 separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.

Discriminatory Gate-Opening Effect in a Flexible Metal-Organic Framework for Inverse CO2 /C2 H2 Separation

Considering the significant application of acetylene (C2 H2 ) in the manufacturing and petrochemical industries, the selective capture of impurity carbon dioxide (CO2 ) is a crucial task and an enduring challenge. Here, a flexible metal-organic framework (Zn-DPNA) accompanied by a conformation change of the Me2 NH2 + ions in the framework is reported. The solvate-free framework provides a stepped adsorption isotherm and large hysteresis for C2 H2 , but type-I adsorption for CO2 . Owing to their uptakes difference before gate-opening pressure, Zn-DPNA demonstrated favorable inverse CO2 /C2 H2 separation. According to molecular simulation, the higher adsorption enthalpy of CO2 (43.1 kJ mol-1 ) is due to strong electrostatic interactions with Me2 NH2 + ions, which lock the hydrogen-bond network and narrow pores. Furthermore, the density contours and electrostatic potential verifies the middle of the cage in the large pore favors C2 H2 and repels CO2 , leading to the expansion of the narrow pore and further diffusion of C2 H2 . These results provide a new strategy that optimizes the desired dynamic behavior for one-step purification of C2 H2 .

Immobilization of the Polar Group into an Ultramicroporous Metal-Organic Framework Enabling Benchmark Inverse Selective CO2/C2H2 Separation with Record C2H2 Production

One-step harvest of high-purity light hydrocarbons without the desorption process represents an advanced and highly efficient strategy for the purification of target substances. The separation and purification of acetylene (C₂H₂) from carbon dioxide (CO₂) by CO₂-selective adsorbents are urgently demanded yet are very challenging owing to their similar physicochemical properties. Here, we employ the pore chemistry strategy to adjust the pore environment by immobilizing polar groups into an ultramicroporous metal-organic framework (MOF), achieving one-step manufacture of high-purity C₂H₂ from CO₂/C₂H₂ mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz) not only changes the pore environment but also improves the discrimination of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO₂/C₂H₂ uptake ratio of 12.6 (123.32/9.79 cm³ cm^-3) and an exceptionally high equimolar CO₂/C₂H₂ selectivity of 1064.9 at ambient conditions. Molecular simulations reveal that the synergetic effect of pore confinement and surfaces decorated with methyl groups provides high recognition of CO₂ molecules through multiple van der Waals interactions. The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification capacity of C₂H₂ from the CO₂/C₂H₂ mixture with a record C₂H₂ productivity of 2091 mmol kg^-1, surpassing all of the CO₂-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical stability under different pH values of aqueous solutions (pH = 1-12). Moreover, the highly stable framework and excellent inverse selective CO₂/C₂H₂ separation performance showcase its promising application as a C₂H₂ splitter for industrial manufacture. This work paves the way to developing reverse-selective adsorbents for the challenging gas separation process.

Exclusive Recognition of CO2 from Hydrocarbons by Aluminum Formate with Hydrogen-Confined Pore Cavities

Exclusive capture of carbon dioxide (CO₂) from hydrocarbons via adsorptive separation is an important technology in the petrochemical industry, especially for acetylene (C₂H₂) production. However, the physicochemical similarities between CO₂ and C₂H₂ hamper the development of CO₂-preferential sorbents, and CO₂ is mainly discerned via C recognition with low efficiency. Here, we report that the ultramicroporous material Al(HCOO)₃, ALF, can exclusively capture CO₂ from hydrocarbon mixtures, including those containing C₂H₂ and CH₄. ALF shows a remarkable CO₂ capacity of 86.2 cm³ g^-1 and record-high CO₂/C₂H₂ and CO₂/CH₄ uptake ratios. The inverse CO₂/C₂H₂ separation and exclusive CO₂ capture performance from hydrocarbons are validated via adsorption isotherms and dynamic breakthrough experiments. Notably, the hydrogen-confined pore cavities with appropriate dimensional size provide an ideal pore chemistry to specifically match CO₂ via a hydrogen bonding mechanism, with all hydrocarbons rejected. This molecular recognition mechanism is unveiled by in situ Fourier-transform infrared spectroscopy, X-ray diffraction studies, and molecular simulations.

Engineering Pore Environments of Sulfate-Pillared Metal-Organic Framework for Efficient C2 H2 /CO2 Separation with Record Selectivity

Engineering pore environments exhibit great potential in improving gas adsorption and separation performances but require specific means for acetylene/carbon dioxide (C₂ H₂ /CO₂ ) separation due to their identical dynamic diameters and similar properties. Herein, a novel sulfate-pillared MOF adsorbent (SOFOUR-TEPE-Zn) using 1,1,2,2-tetra(pyridin-4-yl) ethene (TEPE) ligand with dense electronegative pore surfaces is reported. Compared to the prototype SOFOUR-1-Zn, SOFOUR-TEPE-Zn exhibits a higher C₂ H₂ uptake (89.1 cm³ g^-1 ), meanwhile the CO₂ uptake reduces to 14.1 cm³ g^-1 , only 17.4% of that on SOFOUR-1-Zn (81.0 cm³ g^-1 ). The high affinity toward C₂ H₂ than CO₂ is demonstrated by the benchmark C₂ H₂ /CO₂ selectivity (16 833). Furthermore, dynamic breakthrough experiments confirm its application feasibility and good cyclability at various flow rates. During the desorption cycle, 60.1 cm³ g^-1 C₂ H₂ of 99.5% purity or 33.2 cm³ g^-1 C₂ H₂ of 99.99% purity can be recovered by stepped purging and mild heating. The simulated pressure swing adsorption processes reveal that 75.5 cm³ g^-1 C₂ H₂ of 99.5+% purity with a high gas recovery of 99.82% can be produced in a counter-current blowdown process. Modeling studies disclose four favorable adsorption sites and dense packing for C₂ H₂ .

Low-concentration CO2 capture using metal-organic frameworks - current status and future perspectives

The ever-increasing atmospheric CO₂ level is considered to be the major cause of climate change. Although the move away from fossil fuel-based energy generation to sustainable energy sources would significantly reduce the release of CO₂ into the atmosphere, it will most probably take time to be fully implemented on a global scale. On the other hand, capturing CO₂ from emission sources or directly from the atmosphere are robust approaches that can reduce the atmospheric CO₂ concentration in a relatively short time. Here, we provide a perspective on the recent development of metal-organic framework (MOF)-based solid sorbents that have been investigated for application in CO₂ capture from low-concentration (<10 000 ppm) CO₂ sources. We summarized the different sorbent engineering approaches adopted by researchers, both from the sorbent development and processing viewpoints. We also discuss the immediate challenges of using MOF-based CO₂ sorbents for low-concentration CO₂ capture. MOF-based materials, with tuneable pore properties and tailorable surface chemistry, and ease of handling, certainly deserve continued development into low-cost, efficient CO₂ sorbents for low-concentration CO₂ capture.

Synthesis of Carborane-Backbone Metallacycles for Highly Selective Capture of n-Pentane

The specific recognition and separation of alkanes with similar molecular structures and close boiling points face significant scientific challenges and industrial demands. Here, rectangular carborane-based metallacycles were designed to selectively encapsulate n-pentane from n-pentane, iso-pentane, and cyclo-pentane mixtures in a simple-to-operate and more energy-efficient way. Metallacycle 1, bearing 1,2-di(4-pyridyl) ethylene, can selectively separate n-pentane from these three-component mixtures with a purity of 97%. The selectivity is ascribed to the capture of the preferred guest with matching size, C-H···π interactions, and potential B-H^δ-···H^δ+-C interactions. Besides, the removal of n-pentane gives rise to original guest-free carborane-based metallacycles, which can be recycled without losing performance. Considering the variety of substituted carborane derivatives, metal ions, and organic linkers, these new carborane-based supramolecular coordination complexes (SCCs) may be broadly applicable to other challenging recognition and separation systems with good performance.

Spatial disposition of square-planar mononuclear nodes in metal-organic frameworks for C2H2/CO2 separation

The efficient separation of acetylene (C2H2) from its mixture with carbon dioxide (CO2) remains a challenging industrial process due to their close molecular sizes/shapes and similar physical properties. Herein, we report a microporous metal-organic framework (JNU-4) with square-planar mononuclear copper(ii) centers as nodes and tetrahedral organic linkers as spacers, allowing for two accessible binding sites per metal center for C2H2 molecules. Consequently, JNU-4 exhibits excellent C2H2 adsorption capacity, particularly at 298 K and 0.5 bar (200 cm3 g-1). Detailed computational studies confirm that C2H2 molecules are indeed predominantly located in close proximity to the square-planar copper centers on both sides. Breakthrough experiments demonstrate that JNU-4 is capable of efficiently separating C2H2 from a 50 : 50 C2H2/CO2 mixture over a broad range of flow rates, affording by far the largest C2H2 capture capacity (160 cm3 g-1) and fuel-grade C2H2 production (105 cm3 g-1, ≥98% purity) upon desorption. Simply by maximizing accessible open metal sites on mononuclear metal centers, this work presents a promising strategy to improve the C2H2 adsorption capacity and address the challenging C2H2/CO2 separation.

Negative electrostatic potentials in a Hofmann-type metal-organic framework for efficient acetylene separation

Efficient adsorptive separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) is industrially important but challenging due to the identical dynamic diameter or the trace amount. Here we show an electrostatic potential compatible strategy in a nitroprusside-based Hofmann-type metal-organic framework, Cu(bpy)NP (NP = nitroprusside, bpy = 4,4'-bipyridine), for efficient C2H2 separation. The intruding cyanide and nitrosyl groups in undulating one-dimensional channels induce negative electrostatic potentials for preferential C2H2 recognition instead of open metal sites in traditional Hofmann-type MOFs. As a result, Cu(bpy)NP exhibits a 50/50 C2H2/CO2 selectivity of 47.2, outperforming most rigid MOFs. The dynamic breakthrough experiment demonstrates a 99.9% purity C2H4 productivity of 20.57 mmol g-1 from C2H2/C2H4 (1/99, v/v) gas-mixture. Meanwhile, C2H2 can also be captured and recognized from ternary C2H2/CO2/C2H4 (25/25/50, v/v/v) gas-mixture. Furthermore, computational studies and in-situ infrared spectroscopy reveal that the selective C2H2 binding arises from the compatible pore electro-environment generated by the electron-rich N and O atoms from nitroprusside anions.

Efficient One-Step Purification of C1 and C2 Hydrocarbons over CO2 in a New CO2-Selective MOF with a Gate-Opening Effect

Removing CO2 impurity is an essential industrial process in the purification of hydrocarbons. The most promising strategy is the one-step collection of high-purity hydrocarbons by employing CO2-selective adsorbents, which requires improving the CO2 adsorption and separation behavior of adsorbents, especially the low-pressure performance under actual industrial conditions. Herein, we constructed a new flexible metal-organic framework [Zn(odip)0.5(bpe)0.5(CH3OH)]·0.5NMF·H2O (1) (H4odip = 5,5'-oxydiisophthalic acid, bpe = 1,2-bi(4-pyridyl)ethylene, and NMF = N-methylformamide) containing rich ether O adsorption sites in the channels that exhibits remarkable adsorption capacity for CO2 (118.7 cm3 g-1) due to the only gate-opening-type abrupt adsorption of CO2 at room temperature. Its low affinity for other competing gases enables it to deliver high selectivity for the adsorption of CO2 over C1 and C2 hydrocarbons. For equimolar mixtures of CO2-CH4 and CO2-C2H2, the selectivities are 376.0 and 13.2, respectively. Molecular simulations disclose more abundant adsorption sites for CO2 than hydrocarbons in 1. The breakthrough separation performances combined with remarkable stability and recyclability further verify that 1 is a promising adsorbent that can efficiently extract high-purity hydrocarbons through selective capture of CO2.

Binary Solvent Regulated Architecture of Ultra-Microporous Hydrogen-Bonded Organic Frameworks with Tunable Polarization for Highly-Selective Gas Separation

A binary solvent synthetic strategy is proposed for the construction of C₂ -symmetric molecule-based hydrogen-bonded organic frameworks (HOFs) with permanent ultra-micropores and surface polarization derived from tunable coplanar open oxygen atoms. The activated HOFs BTBA-1 a and PTBA-1 a show highly selective separation of CO₂ /N₂ with a record high ideal adsorbed solution theory (IAST) selectivity >2000 under ambient temperature and pressure.

Recent progress on porous MOFs for process-efficient hydrocarbon separation, luminescent sensing, and information encryption

Metal-organic frameworks (MOFs), as an emerging class of porous materials, excel in designability, regulatability, and modifiability in terms of their composition, topology, pore size, and surface chemistry, thus affording a huge potential for addressing environment and energy-related challenges. In particular, MOFs can be applied as porous adsorbents for the purification of industrially important hydrocarbons through certain process-efficient separation schemes based on selectivity-reversed adsorption and multicomponent separation. Moreover, the vast combination possibilities and controllable and engineerable luminescent units of MOFs make them a versatile platform to develop functionally tailored materials for luminescent sensing and optical data encryption. In this feature article, we summarize the recent progress in the use of porous MOFs for the separation and purification of acetylene (C₂H₂) and ethylene (C₂H₄) based on selectivity-reversed adsorption and multicomponent separation strategies. Moreover, we highlight the advances over the past three years in the field of MOF-based luminescent materials for thermometry, turn-on sensing, and information encryption.

Fine pore engineering in a series of isoreticular metal-organic frameworks for efficient C2H2/CO2 separation

The separation of C₂H₂/CO₂ is not only industrially important for acetylene purification but also scientifically challenging owing to their high similarities in physical properties and molecular sizes. Ultramicroporous metal-organic frameworks (MOFs) can exhibit a pore confinement effect to differentiate gas molecules of similar size. Herein, we report the fine-tuning of pore sizes in sub-nanometer scale on a series of isoreticular MOFs that can realize highly efficient C₂H₂/CO₂ separation. The subtle structural differences lead to remarkable adsorption performances enhancement. Among four MOF analogs, by integrating appropriate pore size and specific binding sites, [Cu(dps)₂(SiF₆)] (SIFSIX-dps-Cu, SIFSIX = SiF₆^2-, dps = 4.4'-dipyridylsulfide, also termed as NCU-100) exhibits the highest C₂H₂ uptake capacity and C₂H₂/CO₂ selectivity. At room temperature, the pore space of SIFSIX-dps-Cu significantly inhibits CO₂ molecules but takes up a large amount of C₂H₂ (4.57 mmol g^-1), resulting in a high IAST selectivity of 1787 for C₂H₂/CO₂ separation. The multiple host-guest interactions for C₂H₂ in both inter- and intralayer cavities are further revealed by dispersion-corrected density functional theory and grand canonical Monte Carlo simulations. Dynamic breakthrough experiments show a clean C₂H₂/CO₂ separation with a high C₂H₂ working capacity of 2.48 mmol g^-1.

Robust metal–organic framework with abundant large electronegative sites for removal of CO2 from a ternary C2H2/C2H4/CO2 mixture

Herein, a MOF with cavities decorated with high-density electronegative F and O sites for the challenging separation of a ternary equimolar mixture of C2H2, C2H4, and CO2 is presented.

Old Materials for New Functions: Recent Progress on Metal Cyanide Based Porous Materials

Cyanide is the simplest ligand with strong basicity to construct open frameworks including some of the oldest compounds reported in the history of coordination chemistry. Cyanide can form numerous cyanometallates with different transition metal ions showing diverse geometries. Rational design of robust extended networks is enabled by the strong bonding nature and high directionality of cyanide ligand. By virtue of a combination of cyanometallates and/or organic linkers, multifunctional framework materials can be targeted and readily synthesized for various applications, ranging from molecular adsorptions/separations to energy conversion and storage, and spin-crossover materials. External guest- and stimuli-responsive behaviors in cyanide-based materials are also highlighted for the development of the next-generation smart materials. In this review, an overview of the recent progress of cyanide-based multifunctional materials is presented to demonstrate the great potential of cyanide ligands in the development of modern coordination chemistry and material science.

The First Sulfate-Pillared Hybrid Ultramicroporous Material, SOFOUR-1-Zn, and its Acetylene Capture Properties

Hybrid ultramicroporous materials, HUMs, are comprised of metal cations linked by combinations of inorganic and organic ligands. Their modular nature makes them amenable to crystal engineering studies, which have thus far afforded four HUM platforms (as classified by the inorganic linkers). HUMs are of practical interest because of their benchmark gas separation performance for several industrial gas mixtures. We report herein design and gram‐scale synthesis of the prototypal sulfate‐linked HUM, the fsc topology coordination network ([Zn(tepb)(SO₄)]_n), SOFOUR‐1‐Zn, tepb=(tetra(4‐pyridyl)benzene). Alignment of the sulfate anions enables strong binding to C₂H₂ via O⋅⋅⋅HC interactions but weak CO₂ binding, affording a new benchmark for the difference between C₂H₂ and CO₂ heats of sorption at low loading (ΔQ_st=24 kJ mol⁻¹). Dynamic column breakthrough studies afforded fuel‐grade C₂H₂ from trace (1 : 99) or 1 : 1 C₂H₂/CO₂ mixtures, outperforming its SiF₆²⁻ analogue, SIFSIX‐22‐Zn.

Acetylene Separation by a Ca-MOF Containing Accessible Sites of Open Metal Centers and Organic Groups

Efficient separation of acetylene from a ternary acetylene-containing mixture is an important and vital task in petrochemical industry, which is difficult to achieve using a single material. Herein, a new Ca²⁺-based metal-organic framework (MOF) [Ca(dtztp)_0.5(DMA)]·2H₂O (1) was constructed using the N,O-donor ligand 2,5-di(2H-tetrazol-5-yl)terephthalic acid and the less-studied alkaline earth Ca²⁺ ions. The MOF shows a 3D honeycomb framework based on unique metal-carboxylate-azolate rod secondary building units. Owing to the presence of high-density organic hydrogen-bonding acceptors and open metal sites (OMSs), the activated MOF shows high adsorption capacity for C₂H₂ and selectivity for C₂H₂ over CO₂, C₂H₄, C₂H₆, and CH₄. Dynamic breakthrough experiments indicated the actual C₂H₂ separation potential of the MOF from binary (C₂H₂-C₂H₄ and C₂H₂-CO₂) and ternary (C₂H₂-C₂H₄-CO₂ and C₂H₂-C₂H₄-C₂H₆) mixtures. Simulations revealed that the synergistic interactions between the OMSs and N atoms in MOF and C₂H₂ molecules play an important role in the separation of C₂H₂.

Achieving High Performance Metal-Organic Framework Materials through Pore Engineering

Achieving high performance functional materials has been a long-term goal for scientists and engineers that can significantly promote science and technology development and thus benefit our society and human beings. As well-known porous materials, metal-organic frameworks (MOFs) are crystalline open frameworks made up of molecular building blocks linked by strong coordination bonds, affording pore space for storing and trapping guest molecules. In terms of porosity, MOFs outperform traditional porous materials including zeolites and activated carbon, showing exceptional porosity with internal surface area up to thousands of square meters per gram of sample and with periodic pore sizes ranging from sub-nanometer to nanometers. Numerous MOFs have been synthesized with potential applications ranging from storing gaseous fuels to separating intractable industrial gas mixtures, sensing physical and chemical stimulus, and transmitting protons for conduction. Compared to traditional porous materials, MOFs are distinguished for their exceptional capability for pore adjustment and interior modification through pore engineering, which have made them a preeminent platform for exploring functional materials with high performance.Rational combinations of rigid building units of different geometry and multibranched organic linkers have provided MOFs with diverse pore structures, ranging from spherical to cylindrical, slit, and tubular ones isolating or interconnecting in different directions, which can be optimized for high-capacity gas storage. Based on the isoreticular principle and building blocks approach in MOF chemistry, the pore adjustment of porous materials can be performed with exquisite precision, making them suitable to address industrially important gas separation. The large pore cavities in MOFs are readily available for encapsulation of different functional guest species, resulting in novel MOF composite materials with various functions.In this Account, we summarize our recent research progress on pore engineering to achieve high-performance MOF materials. We have been able to tune and optimize pore structures, immobilize specific functional sites, and incorporate guest species into target MOF materials for hydrogen storage, methane storage, light-hydrocarbon purification, and proton conduction, especially for various industrially important gas separations including acetylene removal and ethylene and propylene purification. By engineering the porosity and pore chemistry that endows MOFs with multiple functionalities, our research endeavors have brought about the customization of high-performance MOF materials for corresponding application scenarios.

Photoinduced Electron-Transfer (PIET) Strategy for Selective Adsorption of CO2 over C2 H2 in a MOF

Similarities in sizes, shapes, and physical properties between carbon dioxide (CO₂ ) and acetylene (C₂ H₂ ) make it a great challenge to separate the major impurity CO₂ from products in C₂ H₂ production. The use of porous materials is an appealing path to replace current very costly and energy-consuming technologies, such as solvent extraction and cryogenic distillation; however, high CO₂ /C₂ H₂ uptake ratio with minor adsorption of C₂ H₂ at standard pressure was only unexpectedly observed in scarce examples in recent years although the related research started early at 1950s, and general design strategies to realize this aim are still absent. This work has successfully developed an efficient PIET strategy and obtained the second highest CO₂ /C₂ H₂ adsorption ratio for porous materials in a proof-of-concept MOF with a photochromism-active bipyridinium zwitterion. An unprecedented photocontrollable gate effect, owing to change of interannular dihedral after photoinduced generation of radical species, was also observed for the first time. These findings will inspire design and synthesis of porous materials for high efficient gas adsorption and separation.