Scalable Green Synthesis of Robust Ultra-Microporous Hofmann Clathrate Material with Record C3H6 Storage Density for Efficient C3H6/C3H8 Separation

Developing porous materials for C₃H₆/C₃H₈ separation faces the challenge of merging excellent separation performance with high stability and easy scalability of synthesis. Herein, we report a robust Hofmann clathrate material (ZJU-75a), featuring high-density strong binding sites to achieve all the above requirements. ZJU-75a adsorbs large amount of C₃H₆ with a record high storage density of 0.818 g mL⁻¹, and concurrently shows high C₃H₆/C₃H₈ selectivity (54.2) at 296 K and 1 bar. Single-crystal structure analysis unveil that the high-density binding sites in ZJU-75a not only provide much stronger interactions with C₃H₆ but also enable the dense packing of C₃H₆. Breakthrough experiments on gas mixtures afford both high separation factor of 14.7 and large C₃H₆ uptake (2.79 mmol g⁻¹). This material is highly stable and can be easily produced at kilogram-scale using a green synthesis method, making it as a benchmark material to address major challenges for industrial C₃H₆/C₃H₈ separation.     

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

The separation of acetylene (C₂H₂) 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 C₂H₂-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/C₂H₂ separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi-M′MOF , pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm⁻³, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂-capture amount of 4.54 mol L⁻¹, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi-M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M′MOF as a promising material for C₂H₂/CO₂ separation.     

Gram-Scale Synthesis of an Ultrastable Microporous Metal-Organic Framework for Efficient Adsorptive Separation of C2H2/CO2 and C2H2/CH4

A highly water and thermally stable metal-organic framework (MOF) Zn₂(Pydc)(Ata)₂ (1, H₂Pydc = 3,5-pyridinedicarboxylic acid; HAta = 3-amino-1,2,4-triazole) was synthesized on a large scale using inexpensive commercially available ligands for efficient separation of C₂H₂ from CH₄ and CO₂. Compound 1 could take up 47.2 mL/g of C₂H₂ under ambient conditions but only 33.0 mL/g of CO₂ and 19.1 mL/g of CH₄. The calculated ideal absorbed solution theory (IAST) selectivities for equimolar C₂H₂/CO₂ and C₂H₂/CH₄ were 5.1 and 21.5, respectively, comparable to those many popular MOFs. The Q_st values for C₂H₂, CO₂, and CH₄ at a near-zero loading in 1 were 43.1, 32.1, and 22.5 kJ mol⁻¹, respectively. The practical separation performance for C₂H₂/CO₂ mixtures was further confirmed by column breakthrough experiments.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi‐M′MOF , pyz=pyrazine), with multiple functional sites and compact one‐dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm^?3, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂‐capture amount of 4.54 mol L^?1, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi‐M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi‐M′MOF as a promising material for C₂H₂/CO₂ separation.     

Dynamic Entangled Porous Framework for Hydrocarbon (C2–C3) Storage,CO2 Capture,and Separation

Storage and separation of small (C1–C3) hydrocarbons are of great significance as these are alternative energy resources and also can be used as raw materials for many industrially important materials. Selective capture of greenhouse gas, CO₂ from CH₄ is important to improve the quality of natural gas. Among the available porous materials, MOFs with permanent porosity are the most suitable to serve these purposes. Herein, a two‐fold entangled dynamic framework {[Zn₂(bdc)₂(bpNDI)]?4DMF}_n with pore surface carved with polar functional groups and aromatic π clouds is exploited for selective capture of CO₂, C2, and C3 hydrocarbons at ambient condition. The framework shows stepwise CO₂ and C₂H₂ uptake at 195 K but type I profiles are observed at 298 K. The IAST selectivity of CO₂ over CH₄ is the highest (598 at 298 K) among the MOFs without open metal sites reported till date. It also shows high selectivity for C₂H₂, C₂H₄, C₂H₆, and C₃H₈ over CH₄ at 298 K. DFT calculations reveal that aromatic π surface and the polar imide (RNC=O) functional groups are the primary adsorption sites for adsorption. Furthermore, breakthrough column experiments showed CO₂/CH₄ C₂H₆/CH₄ and CO₂/N₂ separation capability at ambient condition.     

Extraordinary Separation of Acetylene‐Containing Mixtures with Microporous Metal–Organic Frameworks with Open O Donor Sites and Tunable Robustness through Control of the Helical Chain Secondary Building Units

Acetylene separation is a very important but challenging industrial separation task. Here, through the solvothermal reaction of CuI and 5‐triazole isophthalic acid in different solvents, two metal–organic frameworks (MOFs, FJU‐21 and FJU‐22 ) with open O donor sites and controllable robustness have been obtained for acetylene separation. They contain the same paddle‐wheel {Cu₂(COO₂)₄} nodes and metal–ligand connection modes, but with different helical chains as secondary building units (SBUs), leading to different structural robustness for the MOFs. FJU‐21 and FJU‐22 are the first examples in which the MOFs’ robustness is controlled by adjusting the helical chain SBUs. Good robustness gives the activated FJU‐22 a , which has higher surface area and gas uptakes than the flexible FJU‐21 a . Importantly, FJU‐22 a shows extraordinary separation of acetylene mixtures under ambient conditions. The separation capacity of FJU‐22 a for 50:50 C₂H₂/CO₂ mixtures is about twice that of the high‐capacity HOF‐3, and its actual separation selectivity for C₂H₂/C₂H₄ mixtures containing 1 % acetylene is the highest among reported porous materials. Based on first‐principles calculations, the extraordinary separation performance of C₂H₂ for FJU‐22 a was attributed to hydrogen‐bonding interactions between the C₂H₂ molecules with the open O donors on the wall, which provide better recognition ability for C₂H₂ than other functional sites, including open metal sites and amino groups.     

Construction of a Stable Crystalline Polyimide Porous Organic Framework for C2H2/C2H4 and CO2/N2 Separation

Utilization of porous materials for gas capture and separation is a hot research topic. Removal of acetylene (C₂H₂) from ethylene (C₂H₄) is important in the oil refining and petrochemical industries, since C₂H₂ impurities deactivate the catalysts and terminate the polymerization of C₂H₄. Carbon dioxide (CO₂) emission from power plants contributes to global climate change and threatens the survival of life on this planet. Herein, 2D crystalline polyimide porous organic framework PAF-120, which was constructed by imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular 1,3,5-tris(4-aminophenyl)benzene, showed significant thermal and chemical stability. Low-pressure gas adsorption isotherms revealed that PAF-120 exhibits good selective adsorption of C₂H₂ over C₂H₄ and CO₂ over N₂. At 298 K and 1 bar, its C₂H₂ and CO₂ selectivities were predicted to be 4.1 and 68.7, respectively. More importantly, PAF-120 exhibits the highest selectivity for C₂H₂/C₂H₄ separation among porous organic frameworks. Thus PAF-120 could be a suitable candidate for selective separation of C₂H₂ over C₂H₄ and CO₂ over N₂.     

Halogen–C2H2 Binding in Ultramicroporous Metal–Organic Frameworks (MOFs) for Benchmark C2H2/CO2 Separation Selectivity

Acetylene (C₂H₂) capture is a step in a number of industrial processes, but it comes with a high-energy footprint. Although physisorbents have the potential to reduce this energy footprint, they are handicapped by generally poor selectivity versus other relevant gases, such as CO₂ and C₂H₄. In the case of CO₂, the respective physicochemical properties are so similar that traditional physisorbents, such as zeolites, silica, and activated carbons cannot differentiate well between CO₂ and C₂H₂. Herein, we report that a family of three isostructural, ultramicroporous (<7 Å) diamondoid metal–organic frameworks, [Cu(TMBP)X] (TMBP=3,3′,5,5′-tetramethyl-4,4′-bipyrazole), TCuX (X=Cl, Br, I), offer new benchmark C₂H₂/CO₂ separation selectivity at ambient temperature and pressure. We attribute this performance to a new type of strong binding site for C₂H₂. Specifically, halogen ⋅⋅⋅ HC interactions coupled with other noncovalent in a tight binding site is C₂H₂ specific versus CO₂. The binding site is distinct from those found in previous benchmark sorbents, which are based on open metal sites or electrostatic interactions enabled by inorganic fluoro or oxo anions.     

Inverse CO2/C2H2 Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange

Although many porous materials, including metal–organic frameworks (MOFs), have been reported to selectively adsorb C₂H₂ in C₂H₂/CO₂ separation processes, CO₂-selective sorbents are much less common. Here, we report the remarkable performance of MFU-4 (Zn₅Cl₄(bbta)₃, bbta=benzo-1,2,4,5-bistriazolate) toward inverse CO₂/C₂H₂ separation. The MOF facilitates kinetic separation of CO₂ from C₂H₂, enabling the generation of high purity C₂H₂ (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C₂H₂ is excluded from MFU-4 by narrow pore windows formed by Zn−Cl groups. Postsynthetic F⁻/Cl⁻ ligand exchange was used to synthesize an analogue ( MFU-4-F ) with expanded pore apertures, resulting in equilibrium C₂H₂/CO₂ separation with reversed selectivity compared to MFU-4 . MFU-4-F also exhibits a remarkably high C₂H₂ adsorption capacity (6.7 mmol g⁻¹), allowing fuel grade C₂H₂ (98 % purity) to be harvested from C₂H₂/CO₂ mixtures by room temperature desorption.     

Ultramicropore Engineering by Dehydration to Enable Molecular Sieving of H2 by Calcium Trimesate

The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3–0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal–organic framework Ca‐trimesate, Ca(HBTC)?H₂O (H₃BTC=trimesic acid), bnn‐1‐Ca‐H₂O, affords a narrow pore variant, Ca(HBTC), bnn‐1‐Ca. Whereas bnn‐1‐Ca‐H₂O (pore diameter 0.34 nm) exhibits ultra‐high CO₂/N₂, CO₂/CH₄, and C₂H₂/C₂H₄ binary selectivity, bnn‐1‐Ca (pore diameter 0.31 nm) offers ideal selectivity for H₂/CO₂ and H₂/N₂ under cryogenic conditions. Ca‐trimesate, the first physisorbent to exhibit H₂ sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.     

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal–Organic Framework for Efficient C2H2/CO2 Separation

Rational design of high nuclear copper cluster-based metal–organic frameworks has not been established yet. Herein, we report a novel MOF ( FJU-112 ) with the ten-connected tetranuclear copper cluster [Cu₄(PO₃)₂(μ₂-H₂O)₂(CO₂)₄] as the node which was capped by the deprotonated organic ligand of H₄L (3,5-Dicarboxyphenylphosphonic acid). With BPE (1,2-Bis(4-pyridyl)ethane) as the pore partitioner, the pore spaces in the structure of FJU-112 were divided into several smaller cages and smaller windows for efficient gas adsorption and separation. FJU-112 exhibits a high separation performance for the C₂H₂/CO₂ separation, which were established by the temperature-dependent sorption isotherms and further confirmed by the lab-scale dynamic breakthrough experiments. The grand canonical Monte Carlo simulations (GCMC) studies show that its high C₂H₂/CO₂ separation performance is contributed to the strong π-complexation interactions between the C₂H₂ molecules and framework pore surfaces, leading to its more C₂H₂ uptakes over CO₂ molecules.     

Overcoming the Trade-Off between C2H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks

Designing porous materials for C₂H₂ purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of Pd^II and Pt^II on C₂H₂ sorption and C₂H₂/CO₂ separation in two isostructural NbO metal–organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA . The experimental investigations and systematic theoretical calculations reveal that Pd^II in Pd/Cu-PDA undergoes spontaneous chemical reaction with C₂H₂, leading to irreversible structural collapse and loss of C₂H₂/CO₂ sorption and separation. Contrarily, Pt^II in Pt/Cu-PDA shows strong di-σ bond interaction with C₂H₂ to form specific π-complexation, contributing to high C₂H₂ capture (28.7 cm³ g⁻¹ at 0.01 bar and 153 cm³ g⁻¹ at 1 bar). The reusable Pt/Cu-PDA efficiently separates C₂H₂ from C₂H₂/CO₂ mixtures with satisfying selectivity and C₂H₂ capacity (37 min g⁻¹). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.     

New Supercage Metal–Organic Framework Based on Allopurinol Ligands Showing Acetylene Storage and Separation

To develop efficient adsorbent materials for storage and separation of C₂H₂, an unprecedented supercage MOF, [Me₂NH₂]⋅[Zn₃(ALP)(TDC)_2.5]⋅3.5DMF⋅2 H₂O ( 1 ) was constructed through medicinal molecule allopurinol (ALP) and S-containing 2,5-thiophenedicarboxylic acid (H₂TDC). 1 contains a novel linear trinuclear cluster that is composed by ALP and carboxylates and forms a final uncommon 5-connected yfy topological framework. The framework possesses three types of interlinked cages decorated by rich functional sites, and reveals not only high adsorption capacity for C₂H₂ but also excellent selective separation for C₂H₂/CO₂ and C₂H₂/CH₄ at 298 K. Dynamic breakthrough experiments on C₂H₂/CO₂ (1:1) mixture and C₂H₂/CH₄ (1:1) mixture also demonstrated the potential of the material to separate C₂H₂ from CO₂ or CH₄ mixtures. Molecular simulations were also studied to identify the different CO₂- and C₂H₂- binding sites in 1 , such as carboxylate groups, S atoms and carbonyl groups.     

New Microporous Materials for Acetylene Storage and C2H2/CO2 Separation: Insights from Molecular Simulations

Force‐field based grand‐canonical Monte Carlo simulations are used to investigate the acetylene and carbon dioxide uptake capacity, as well as the C₂H₂/CO₂ adsorption selectivity of three novel microporous materials: Magnesium formate, Cu₃(btc)₂, and cucurbit[6]uril. Because no comparable computational studies of acetylene adsorption have been reported so far, the study focuses on systems for which experimental data are available to permit a thorough validation of the simulation results. The results for magnesium formate are in excellent agreement with experiment. The simulation predicts a high selectivity for acetylene over CO₂, which can be understood from a detailed analysis of the structural features that determine the affinity of Mg‐formate towards C₂H₂. For Cu₃(btc)₂, preliminary calculations reveal the necessity to include the interaction of the sorbate molecules with the unsaturated metal sites, which is done by means of a parameter adjustment based on ab‐initio calculations. In spite of the high C₂H₂ storage capacity, the C₂H₂/CO₂ selectivity of this material is very modest. The simulation results for the porous organic crystal cucurbit[6]uril show that the adsorption characteristics that have been observed experimentally, particularly the very high isosteric heat of adsorption, cannot be understood when an ideal structure is assumed. It is postulated that structural imperfections play a key role in determining the C₂H₂ adsorption behavior of this material, and this proposition is supported by additional calculations.     

A unique 3D microporous MOF constructed by cross-linking 1D coordination polymer chains for effectively selective separation of CO_2/CH_4 and C_2H_2/CH_4

Selective separation of CO_2/CH_4 and C_2 H_2/CH_4 are promising for their high-purity industrial demand and scientific research on account of the similar molecular radius and physical properties.In this work,a unique 3 D microporous MOF material [Cu(SiF_6)(sdi)_2]·solvents(1,sdi=1,1'-sulfonyldiimidazole) was successfully constructed by cross-linking 1 D coordination polymer chains.The dense functional active sites on the inner walls of the channel of la can provide strong binding affinities to CO_2,C_2 H_2,and thus effectively improve the gas separation performance of CO_2/CH_4 and C_2 H_2/CH_4.     

Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

Separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C₂H₂ from CO₂ and C₂H₄. Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C₂H₂ capacity (7.94 mmol/g) and a high C₂H₂/CO₂ (10.3) or C₂H₂/C₂H₄ (11.6) selectivity. The calculated capacity of C₂H₂ per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF₆²⁻ anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C₂H₂/CO₂ mixtures and 1/99 C₂H₂/C₂H₄ mixtures under various conditions with excellent recyclability and benchmark productivity of pure C₂H₂ (5.13 mmol/g) or C₂H₄ (48.57 mmol/g).     

Impact of Pore Size and Defects on the Selective Adsorption of Acetylene in Alkyne-Functionalized Nickel(II)-Pyrazolate-Based MOFs

C₂H₂/CO₂ separation is a highly challenging process as a consequence of their similar physicochemical properties. In this work we have explored, by static and dynamic gas sorption techniques and computational modelling, the suitability of a series of two isoreticular robust Ni(II)pyrazolate-based MOFs, bearing alkyne moieties on the ligand backbones, for C₂H₂/CO₂ separation. The results are consistent with high adsorption capacity and selectivity of the essayed systems towards C₂H₂ molecules. Furthermore, a post-synthetic treatment with KOH ethanolic solution gives rise to linker vacancy defects and incorporation of extraframework potassium ions. Creation of defects is responsible for increased adsorption capacity for both gases, however, strong interactions of the cluster basic sites and extraframework potassium cations with CO₂ molecules are responsible for a lowering of C₂H₂ over CO₂ selectivity.     

Structure and gas transport characteristics of triethylene oxide-grafted polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene

Polymeric membrane-based gas separation technology has significant advantages compared with traditional amine-based CO₂ separation method. In this work, SEBS block copolymer is used as a polymer matrix to incorporate triethylene oxide (TEO) functionality. The short ethylene oxide segment is chosen to avoid crystallization, which is confirmed by differential scanning calorimetry and wide-angle X-ray scattering characterizations. The gas permeability results reveal that CO₂/N₂ selectivity increased with increasing content of TEO functional group. The highest CO₂ permeability (281 Barrer) and CO₂/N₂ selectivity (31) were obtained for the membrane with the highest TEO incorporation (57 mol%). Increasing the TEO content in these copolymers results in an increase in CO₂ solubility and a decrease in C₂H₆ solubility. For example, as the grafted TEO content increased from 0 to 57 mol%, the CO₂ solubility and CO₂/C₂H₆ solubility selectivity increased from 0.72 to 1.3 cm³(STP)/cm³ atm and 0.47 to 1.3 at 35°C, respectively. The polar ether linkage in TEO-grafted SEBS copolymers exhibits favorable interaction with CO₂ and unfavorable interaction with nonpolar C₂H₆, thus enhancing CO₂/C₂H₆ solubility selectivity.     

Facilitated Transport of C<Subscript>2</Subscript>H<Subscript>4</Subscript> in a SiO<Subscript>2</Subscript>-poly(N-vinylpyrrolidone)-Ag<Superscript>+</Superscript> Inorganic-Organic Hybrid Membrane

Inorganic-organic hybrid membranes containing silica as the structure matrix, poly(N-vinylpyrrolidone) (PVP) as the organic mediating agent and silver ions as olefinic carriers were prepared using sol–gel method and dip-coating process. The structure and permeances of the membranes for N₂, He, C₂H₄, C₂H₆ at different temperatures indicated that defect-free membranes were obtained and the transportation of the C₂H₄ through the membranes followed the dissolution and diffusion mechanism. Ideal separation factors of C₂H₄/C₂H₆ through the membranes were evaluated at the temperature of 298, 373 and 423 K respectively using mixture gas of 50% C₂H₄-50% C₂H₆. The results showed that the ideal separation factors of C₂H₄/C₂H₆ through the membranes were obviously greater than the ratio of PC₂H₄/PC₂H₆ obtained from the single gas measurement due to the hindering effect by the adsorbed C₂H₄. The ideal separation factors of C₂H₄/C₂H₆ increased with temperature and reached 10 at 423 K, which suggested that C₂H₄ and C₂H₆ could be separated at lower humidity compared to the reported organic polymer/silver salt membranes in which humidified gases and higher silver loading were usually used. The transport of C₂H₄ in the inorganic-organic hybrid membrane was proposed to follow the hopping mechanism, that is, olefins moved across the fixed silver sites.