Efficient C2H2/CO2 Separation in Ultramicroporous Metal-Organic Frameworks with Record C2H2 Storage Density

Zero- to One-Dimensional Transformation in a Highly Porous Metal-Organic Framework to Enhance Physicochemical Properties

The dynamic behaviors of metal-organic frameworks (MOFs) continue to expand the accessible architectures and properties within this material class. However, the dynamic behaviors that can be studied in MOFs are limited to the transitions, preserving their high crystallinity. For this reason, their significant structural changes involving coordination bond breakage and rearrangement remain largely underexplored. Herein, we report a three-step single-crystal-to-single-crystal (SCSC) phase transition in a new cerium-based MOF, HKU-9 [Ce2PET(DMF)2(H2O)2], transforming zero-dimensional (0D) secondary building units (SBUs) into one-dimensional (1D) chain SBUs in HKU-90 [Ce2(μ-H2O)PET(H2O)2]. Single-crystal X-ray diffraction studies unambiguously delineate the structural evolution at each stage of this multistep transition, revealing multiple coordination bond dissociations/associations and a significant lattice contraction─all while preserving single-crystal integrity. This dimensional transformation endows HKU-90 with enhanced chemical stability (pH 1-10) and a record-high Brunauer-Emmett-Teller (BET) surface area of 2660 m2 g-1 among reported Ce-based MOFs. Further, HKU-90 exhibits exceptional gas sorption performance, with one of the highest reported C2H2 storage capacities (184 cc g-1 at 273 K, 1 bar) and outstanding C2H2/CO2 selectivity (2.16) under these conditions. Notably, the formation of 1D chain SBUs, a structural motif found in many high-performance MOFs, highlights the potential of using the solid-state fusion of multinuclear metal clusters to tailor the properties of the framework.

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

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

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

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

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

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

Boosting Adsorption and Selectivity of Acetylene by Nitro Functionalisation in Copper(II)-Based Metal-Organic Frameworks

Purification and storage of acetylene (C2H2) are important to many industrial processes. The exploitation of metal-organic framework (MOF) materials to address the balance between selectivity for C2H2 vs carbon dioxide (CO2) against maximising uptake of C2H2 has attracted much interest. Herein, we report that the synergy between unsaturated Cu(II) sites and functional groups, fluoro (-F), methyl (-CH3), nitro (-NO2) in a series of isostructural MOF materials MFM-190(R) that show exceptional adsorption and selectivity of C2H2. At 298 K, MFM-190(NO2) exhibits an C2H2 uptake of 216 cm3 g-1 (320 cm3 g-1 at 273 K) at 1.0 bar and a high selectivity for C2H2/CO2 (up to ~150 for v/v = 2/1) relevant to that in the industrial cracking stream. Dynamic breakthrough studies validate and confirm the excellent separation of C2H2/CO2 by MFM-190(NO2) under ambient conditions. In situ neutron powder diffraction reveals the cooperative binding, packing and selectivity of C2H2 by unsaturated Cu(II) sites and free -NO2 groups.

Isoreticular Contraction in Dicopper Paddle-Wheel-Based Metal-Organic Frameworks to Enhance C2H2/CO2 Separation

Achieving a balance between high selectivity and uptake is a formidable challenge for the purification of acetylene from mixtures with carbon dioxide, particularly when seeking to maximize both C2H2 adsorption capacity and C2H2/CO2 separation selectivity in crystalline porous materials. In this study, leveraging the principles of reticular chemistry, we selected two tetracarboxylate-based linkers and combined them with Cu2+ ions to synthesize two isoreticular dicopper paddle-wheel-based metal-organic frameworks (MOFs): Cu-TPTC (terphenyl-3,3',5,5'-tetracarboxylic acid, H4TPTC) and Cu-ABTC (3,3,5,5-azobenzenetetracarboxylic acid, H4ABTC). The structural and sorption analyses revealed that Cu-ABTC, despite having slightly smaller pores due to the strategic replacement of a phenyl ring with an azo group between two tetratopic ligands, maintains high porosity compared to Cu-TPTC. Furthermore, Cu-ABTC outperforms Cu-TPTC in terms of C2H2 adsorption capacity (196 cm3 g-1 at 298 K and 1 bar) and C2H2/CO2 separation selectivity (16.5~5.6). These findings were corroborated by dynamic breakthrough experiments and computational modeling. This research highlights the potential of the isoreticular contraction strategy in enhancing MOFs for sophisticated gas adsorption and separation processes.

Guest Cation Functionalized Metal Organic Framework for Highly Efficient C2H2/CO2 Separation

The removal of carbon dioxide (CO2) from acetylene (C2H2) production is critical yet difficult due to their similar physicochemical properties. Despite extensive research has been conducted on metal-organic frameworks (MOFs) for C2H2/CO2 separation, approaches to designing functionalized MOFs remain limited. Enhancing gas adsorption through simple pore modification holds great promise in molecular recognition and industrial separation processes. This study proposes a guest cation functionalization strategy using the anionic framework SU-102 as the prototype material. Specifically, the guest cation Li+ is introduced into the skeleton by ion exchange to obtain SU-102-Li+. This strategy generates strong interactions between Li+ and gas molecules, thereby elevating C2H2 uptake to 49.18 cm3 g-1 and CO2 uptake to 29.88 cm3 g-1, marking 20.3% and 36.9% improvements over the parent material, respectively. In addition, ideal adsorbed solution theory selectivity calculations and dynamic breakthrough experiments confirmed the superior and stable separation performance of SU-102-Li+ for C2H2/CO2 (25 min g-1) and C2H2 productivity (1.55 mmol g-1). Theoretical calculations further reveals the unique molecular recognition mechanism between gas molecules and guest cations.

Asymmetric Pore Windows in Pillar-Layered Metal-Organic Framework Membranes for H2/CO2 Separation

In this study, a novel ultramicroporous pillar-layered Ni-LAP-NH2 [Ni2(l-asp)2(Pz-NH2)] (l-asp = l-aspartic acid, Pz-NH2 = aminopyrazine) membranes on porous α-Al2O3 tubes with high performance and good thermal stability was first fabricated using isostructural Ni-LAP[Ni2(l-asp)2(Pz)] (Pz = pyrazine) crystals as seeds. Utilizing the principle of reticular chemistry, here, we introduced the active amino side group into the Ni-LAP frameworks by replacing the pillar-layered ligand Pz with Pz -NH2 while maintaining the original Ni-LAP small pore size, and the amino side group induced a "steric hindrance" effect and the physical adsorption affinity, which synergistically delayed CO2 penetration. It was found that the preferential (111) orientation Ni-LAP-NH2 membrane (Z10) exhibited a high H2/CO2 separation performance with a separation factor of 41.7 and H2 permeance of 9.08 × 10-8 mol·m-2·s-1·Pa-1 under optimal conditions. These MOF materials demonstrated potential for industrial H2 purification due to their tunable pore structure and remarkable stability. Moreover, this strategy offers an effective approach to tailoring pillar-layered MOF membranes with targeted molecular sieving ability.

Synergistic C2H2 Binding Sites in Hydrogen-Bonded Supramolecular Framework for One-Step C2H4 Purification from Ternary C2 Mixture

Purification of C2H4 from the ternary C2 hydrocarbon mixture in one step is of critical significance but still extremely challenging according to its intermediate physical properties between C2H6 and C2H2. Hydrogen-bonded organic frameworks (HOFs) stabilized by supramolecular interactions are emerging as a new kind of adsorbents that facilitate green separation. However, it remains a problem to efficiently realize the one-step C2H4 purification from C2H6/C2H4/C2H2 mixture because of the low C2H2/C2H4 selectivity. We herein report a robust microporous HOF (termed as HOF-TDCPB) with dense O atoms and aromatic rings distributed on the pore surface which provide C2H6 and C2H2 preferred environment simultaneously. Dynamic breakthrough experiments indicate that HOF-TDCPB can not only obtain high-purity C2H4 from binary C2 mixture, but also firstly realize one-step C2H4 purification from ternary C2H6/C2H4/C2H2 mixture, with the C2H4 productivity of 3.2 L/kg (>99.999 %) for one breakthrough cycle. Furthermore, HOF-TDCPB displays outstanding stability in air, organic solvents and water, which endow it excellent cycle performance even under high-humidity conditions. Theoretical calculations indicate that multiple O sites on pore channels can create synergistic binding sites for C2H2, thus affording overall stronger multipoint interactions.

A Stable Layered Microporous MOF Assembled with Y-O Chains for Separation of MTO Products

Benefiting from highly tunable pore environments, some metal-organic frameworks (MOFs) have recently shown promising prospects in the separation of methanol-to-olefin (MTO) products (mainly C3H6 and C2H4). However, the "trade-off" between gas storage capacity and selectivity always results in inefficient separation. In addition, poor stability of MOFs also limits practical separation applications. Herein, we have successfully assembled a layered Y-MOF (FJI-W9) with bent diisophthalate ligands (H4L), Y-O chains, and 2-fluorobenzoic acids. As expected, FJI-W9 not only exhibits good chemical stability but also shows significant potential for C3H6/C2H4 separation. For FJI-W9, the C3H6 uptake at 298 K and 10 kPa is 63 cm3/g, and the IAST selectivity of FJI-W9 for C3H6/C2H4 (V/V = 50/50) is calculated to be 20.5. To the best of our knowledge, both C3H6 uptake and selectivity of FJI-W9 surpass most porous materials. GCMC simulation indicates that the special supramolecular binding sites in FJI-W9 have much stronger interactions with C3H6 than C2H4 molecules. More importantly, practical breakthrough experiments demonstrate that FJI-W9 can effectively separate C3H6/C2H4 (50/50) mixtures, thus obtaining high-purity C2H4 and C3H6, respectively.

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

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

Multifunctional and Ultrastable Co-MOF Effectively Separates Various Different Component Gas Mixtures

Developing low-cost and multifunctional adsorbents for adsorption separation to obtain high-purity (>99.9%) gases is intriguing yet challenging. Notably, the ongoing trade-off between adsorption capacity and selectivity in separating multicomponent mixed gases still persists as a pressing scientific challenge requiring urgent attention. Herein, the ultrastable TJT-100 exhibits unique structural characteristics including uncoordinated carboxylate oxygen atoms, coordinated water molecules directed toward the pore surface, and sufficient Me2NH2+ cations in channels. TJT-100 exhibits a high adsorption capacity and exceptional separation performance, particularly notable for its high C2H2 capacity of 127.7 cm3/g and remarkable C2H2 selectivity over CO2 (5.4) and CH4 (19.8), which makes it a standout material for various separation applications. In a breakthrough experiment with a C2H2/CO2 mixture (v/v = 50/50), TJT-100 achieved a record-high C2H2 productivity of 69.33 L/kg with a purity of 99.9%. Additionally, TJT-100 demonstrates its effectiveness in separating CO2 from natural gas and flue gas. Its exceptional selectivity for CO2/CH4 (10.7) and CO2/N2 (11.9) results in a high CO2 productivity of 21.23 and 22.93 L/kg with 99.9% purity from CO2/CH4 (v/v = 50/50) and CO2/N2 (v/v = 15/85) mixtures, respectively.

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

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

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.

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.

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.

Decorating the Node of a Zirconium-Based Metal-Organic Framework to Tune Adsorption Behavior and Surface Permeation

Surface barriers are commonly observed in nanoporous materials. Although researchers have explored methods to repair defects or create flawless crystals to mitigate surface barriers, these approaches may not always be practical or readily achievable in targeted metal-organic frameworks (MOFs). In our study, we propose an alternative approach focusing on the introduction of diverse ligands onto a MOF-808 node to finely adjust its adsorption and mass transport characteristics. Significantly, our findings indicate that while adsorption curves can be inferred based on the MOF's chemical composition and the probing molecule, surface permeabilities exhibit variations dependent on the specific probe utilized and the incorporated ligand. Our investigation, considering van der Waals forces exclusively between the adsorbate (e.g., n-hexane, propane, and benzene) and the adsorbent, revealed that augmenting these interactions can indeed improve surface permeation to a certain extent. Conversely, strong adsorption resulting from hydrogen bonding interactions, particularly with water in modified MOFs, led to compromised permeation within the MOF crystals. These outcomes provide valuable insights for the porous materials community and offer guidance in the development of adsorbents with enhanced affinity and superior mass transport properties for gases and vapors.

Synthesis Strategies, Preparation Methods, and Applications of Chiral Metal-Organic Frameworks

Chiral Metal-Organic Frameworks (CMOFs) is a kind of material with great application value in recent years. Formed by the coordination of metal ions or metal clusters with organic ligands. It has ordered and adjustable pores, multi-dimensional network structure, large specific surface area and excellent adsorption properties. This material structure combines the properties of metal-organic frameworks (MOFs) with the chiral properties of chiral molecules. It has great advantages in catalysis, adsorption, separation and other fields. Therefore, it has a wide range of applications in chemistry, biology, medicine and materials science. In this paper, various synthesis strategies and preparation methods of chiral metal-organic frameworks are reviewed from different perspectives, and the advantages of each method are analyzed. In addition, the applications of chiral metal-organic framework materials in enantiomer recognition and separation, circular polarization luminescence and asymmetric catalysis are systematically summarized, and the corresponding mechanisms are discussed. Finally, the challenges and prospects of the development of chiral metal-organic frame materials are analyzed in detail.

In situ generated 2,5-pyrazinedicarboxylate and oxalate ligands leading to a Eu-MOF for selective capture of C2H2 from C2H2/CO2

The separation of C2H2/CO2 mixtures is a very important but highly challenging task due to their comparable physical natures and relative sizes. Herein, we report a europium-based 3D microporous MOF with a 4-connected two-nodal net with {4·53·62}2{42·62·82} topology, {[Eu2(pzdc)(ox)2(H2O)4]·5H2O}n (1) (H2pzdc = 2,5-pyrazinedicarboxylic acid, H2ox = oxalic acid), prepared by a hydrothermal method involving in situ generation of 2,5-pyrazinedicarboxylate and oxalate ligands. Two different temperatures were utilized to create two porous materials (1a and 1b) with channels of 4.8 × 5.4 Å and 4.1 × 6.3 Å, and 4.8 × 5.4 and 4.6 × 8.7 Å2, respectively. 1b shows a superior ability to selectively capture C2H2 from C2H2/CO2 as compared with 1a. At 1 bar and 298 K, 1b takes up 4.10 mmol g-1 C2H2 and 1.84 mmol g-1 CO2, respectively. In addition, at 298 K and 1 bar, 1b has a high selectivity for C2H2 over CO2, with an IAST selectivity of 12.7 while the value for 1a is 3.2. The separation of C2H2/CO2 with 1b also exhibits good reusability.

CO2-Based Stable Porous Metal-Organic Frameworks for CO2 Utilization

The transformation of carbon dioxide (CO2) into functional materials has garnered considerable worldwide interest. Metal-organic frameworks (MOFs), as a distinctive class of materials, have made great contributions to CO2 capture and conversion. However, facile conversion of CO2 to stable porous MOFs for CO2 utilization remains unexplored. Herein, we present a facile methodology of using CO2 to synthesize stable zirconium-based MOFs. Two zirconium-based MOFs CO2-Zr-DEP and CO2-Zr-DEDP with face-centered cubic topology were obtained via a sequential desilylation-carboxylation-coordination reaction. The MOFs exhibit excellent crystallinity, as verified through powder X-ray diffraction and high-resolution transmission electron microscopy analyses. They also have notable porosity with high surface area (SBET up to 3688 m2 g-1) and good CO2 adsorption capacity (up to 12.5 wt %). The resulting MOFs have abundant alkyne functional moieties, confirmed through 13C cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectra. Leveraging the catalytic prowess of Ag(I) in diverse CO2-involved reactions, we incorporated Ag(I) into zirconium-based MOFs, capitalizing on their interactions with carbon-carbon π-bonds of alkynes, thereby forming a heterogeneous catalyst. This catalyst demonstrates outstanding efficiency in catalyzing the conversion of CO2 and propargylic alcohols into cyclic carbonates, achieving >99% yield at room temperature and atmospheric pressure conditions. Thus, this work provides a dual CO2 utilization strategy, encompassing the synthesis of CO2-based MOFs (20-24 wt % from CO2) and their subsequent application in CO2 capture and conversion processes. This approach significantly enhances overall CO2 utilization.

Water-Resistant, Scalable, and Inexpensive Chiral Metal-Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

Physical separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) on metal-organic frameworks (MOFs) is crucial for achieving high-purity feed gases with minimal energy penalty. However, such processes are exceptionally challenging due to their close physical properties and are also critically restricted by the high cost of large-scale MOF synthesis. Here, we demonstrate the readily scalable synthesis of a highly water-resistant chiral Cu-MOF (TAMOF-1) based on an inexpensive proteogenic amino acid derivative bearing rich N/O sites. Notably, the unique coordination in this ultramicroporous MOF has resulted in the generation of rare global negative electrostatic potentials, which greatly facilitate the electrostatic interactions with C2H2 molecules, thus leading to their efficient separation from C2H2/CO2 and C2H2/C2H4 mixtures under ambient conditions. The separation efficiency and mechanism are unequivocally validated by breakthrough experiments and computational simulations. This work not only highlights the pivotal role of creating a negative electro-environment in confined spaces for boosting C2H2 capture and separation but also opens up new ways of employing cheap amino acid derivatives bearing rich electro-negative N and O sites as organic linkers to constructing high-performing MOF materials for gas separation purposes.

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.

Reversible Acid-Base Long Persistent Luminescence Switch Based on Amino-Functionalized Metal-Organic Frameworks

Metal-organic frameworks (MOFs) with long persistent luminescence (LPL) have attracted extensive research attention from researchers due to their potential applications in information encryption, anticounterfeiting technology, and security logic. In contrast to short-lived fluorescent materials, LPL materials offer a visible response that can be easily distinguished by the naked eye, thereby facilitating a much clearer visualization. However, there are few reports on functional LPL MOF materials as probes. In this article, two amino-functional LPL MOFs (VB4-2D and VB4-1D) were synthesized. They both exhibited adjustable fluorescence and phosphorescence from blue to green and from cyan to green, respectively. Notably, the MOFs emitted bright and adjustable LPL upon the removal of the different radiation sources. The basic amino functional groups in the MOFs exhibited acid and ammonia sensitivity, and fluorescence and phosphorescence emission intensities can be burst and restored in two atmospheres, respectively, which can be cycled multiple times. Furthermore, LPL intensity undergoes switching between two different conditions as well, which can be visually discerned by the naked eye, enabling visual sensing of volatiles by LPL. This combination of photoluminescence and the visual LPL switching behavior of acids and bases in functional MOFs may provide an effective avenue for stimulus response, anticounterfeiting, and encryption applications.

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.

Stepwise Synthesis of Cl-Decorated Trinuclear-Cu Cluster-Based Frameworks for C2H2/C2H4 and C2H2/CO2 Separation

A novel Cl-decorated trinuclear-Cu cluster-based MOF (NbU-7-Cl, NbU denotes Ningbo University) was synthesized by a stepwise synthesis strategy. Compared to one-step reactions, the strategy of combining cationic templates with single-crystal-to-single-crystal transformation provides more possibilities for the design and postsynthetic modification of multifunctional materials. Note that the chloride ions are attached to the copper ions of the planar trinuclear cluster nodes in a fully symmetric or partially asymmetric manner. The insertion of the chloride ion can alter the overall symmetry and adsorption energy in addition to occupying the appropriate asymmetric orbit and reducing the effective active sites of metal. The activated NbU-7-Cl displays improved C2H2 uptake capacity and C2H2/C2H4 and C2H2/CO2 separation performance, which is proved by breakthrough experiments.

Construction of Negative Electrostatic Pore Environments in a Scalable, Stable and Low-Cost Metal-organic Framework for One-Step Ethylene Purification from Ternary Mixtures

One-step separation of C2 H4 from ternary C2 mixtures by physisorbents remains a challenge to combine excellent separation performance with high stability, low cost, and easy scalability for industrial applications. Herein, we report a strategy of constructing negative electrostatic pore environments in a stable, low-cost, and easily scaled-up aluminum MOF (MOF-303) for efficient one-step C2 H2 /C2 H6 /C2 H4 separation. This material exhibits not only record high C2 H2 and C2 H6 uptakes, but also top-tier C2 H2 /C2 H4 and C2 H6 /C2 H4 selectivities at ambient conditions. Theoretical calculations combined with in situ infrared spectroscopy indicate that multiple N/O sites on pore channels can build a negative electro-environment to provide stronger interactions with C2 H2 and C2 H6 over C2 H4 . Breakthrough experiments confirm its exceptional separation performance for ternary mixtures, affording one of the highest C2 H4 productivity of 1.35 mmol g-1 . This material is highly stable and can be easily synthesized at kilogram-scale from cheap raw materials using a water-based green synthesis. The benchmark combination of excellent separation properties with high stability and low cost in scalable MOF-303 has unlocked its great potential in this challenging industrial separation.

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

One-step adsorption separation of C2H4 from ternary C2 hydrocarbon mixtures remains an important and challenging goal for petrochemical industry. Current physisorbents either suffer from unsatisfied separation performance, poor stability, or are difficult to scale up. Herein, we report a strategy of constructing multiple supramolecular binding sites in a robust and scalable MOF (Al-PyDC) for highly efficient one-step C2H4 purification from ternary mixtures. Owing to suitable pore confinement with multiple supramolecular binding sites, Al-PyDC exhibits one of the highest C2H2 and C2H6 uptakes and selectivities over C2H4 at ambient conditions. The gas binding sites have been visualized by single-crystal X-ray diffraction studies, unveiling that the low-polarity pore surfaces with abundant electronegative N/O sites provide stronger multiple supramolecular interactions with C2H2 and C2H6 over C2H4. Breakthrough experiments showed that polymer-grade C2H4 can be separated from ternary mixtures with a maximum productivity of 1.61 mmol g-1. This material can be prepared from two simple reagents using a green synthesis method with water as the sole solvent, and its synthesis can be easily scaled to multikilogram batches. Al-PyDC achieves an effective combination of benchmark separation performance, high stability/recyclability, green synthesis and easy scalability to address major challenges for industrial one-step C2H4 purification.

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

Separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) or ethylene (C2 H4 ) 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 C2 H2 from CO2 and C2 H4 . 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 C2 H2 capacity (7.94 mmol/g) and a high C2 H2 /CO2 (10.3) or C2 H2 /C2 H4 (11.6) selectivity. The calculated capacity of C2 H2 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 SiF6 2- 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 C2 H2 /CO2 mixtures and 1/99 C2 H2 /C2 H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2 H2 (5.13 mmol/g) or C2 H4 (48.57 mmol/g).

Closo-[B12 H12 ]2- Derivatives with Polar Groups As Promising Building Blocks in Metal-Organic Frameworks for Gas Separation

Engineering design of metal organic frameworks (MOFs) for gas separation applications is nowadays a thriving field of investigation. Based on the recent experimental studies of dodecaborate-hybrid MOFs as potential materials to separate industry-relevant gas mixtures, we herein present a systematic theoretical study on the derivatives of the closo-dodecaborate anion [B12 H12 ]2- , which can serve as building blocks for MOFs. We discover that amino functionalization can impart a greater ability to selectively capture carbon dioxide from its mixtures with other gases such as nitrogen, ethylene and acetylene. The main advantage lies in the polarization effect induced by amino group, which favors the localization of the negative charges on the boron-cluster anion and offers a nucleophilic anchoring site to accommodate the carbon atom in carbon dioxide. This work suggests an appealing strategy of polar functionalization to optimize the molecule discrimination ability via preferential adsorption.

3D ZnII-Based coordination polymer: Synthesis, structure and fluorescent sensing property for nitroaromatic compounds

A water-stable Zn^II-based coordination polymer (CP) with excellent photophysical behavior, namely [Zn₂L(atez)(H₂O)₂] (compound 1; H₃L = 4-(2',3'-dicarboxylphenoxy); atez = 5-aminotetrazole), was successfully prepared by the solvothermal reaction of Zn ions with a π-conjugated and semi-rigid multicarboxylate ligand H₃L in the presence of N-containing linker atez. Compound 1 displays a hierarchically pillared three-dimensional (3D) (3,4,5)-connected (4·6²) (4²·6⁴) (4³·6⁴·8³) net which is based on two-dimensional (2D) multicarboxylate- Zn^II layers strutted by the atez ligands. Sensing investigations of compound 1 reveal that this material can selectively and sensitively detect nitroaromatic compounds in water suspension through fluorescence quenching effect. In particular, it is worth noting that it shows highly specific detection of nitrobenzene (NB) and 2,4,6-trinitrophenol (TNP) with remarkable quenching constants (K_SV = 7.5 × 10⁴ M^-1 for NB and K_SV = 1.9 × 10⁵ M^-1 for TNP) and low limit of detection (LOD = 0.93 μM for NB and LOD = 0.36 μM for TNP). Investigations reveal that the probable mechanisms for such sensing processes are the concurrent presence of fluorescence resonance energy transfer (FRET) as well as photoinduced electron transfer (PET) between the CP and nitroaromatic molecules. This work not only offers an effective route to improve the application of fluorescent CPs but also provide one novel probable fluorescence probe for nitroaromatic compounds.

Crystal Engineering of a Chiral Crystalline Sponge That Enables Absolute Structure Determination and Enantiomeric Separation

Chiral metal-organic materials (CMOMs), can offer molecular binding sites that mimic the enantioselectivity exhibited by biomolecules and are amenable to systematic fine-tuning of structure and properties. Herein, we report that the reaction of Ni(NO₃)₂, S-indoline-2-carboxylic acid (S-IDECH), and 4,4'-bipyridine (bipy) afforded a homochiral cationic diamondoid, dia, network, [Ni(S-IDEC)(bipy)(H₂O)][NO₃], CMOM-5. Composed of rod building blocks (RBBs) cross-linked by bipy linkers, the activated form of CMOM-5 adapted its pore structure to bind four guest molecules, 1-phenyl-1-butanol (1P1B), 4-phenyl-2-butanol (4P2B), 1-(4-methoxyphenyl)ethanol (MPE), and methyl mandelate (MM), making it an example of a chiral crystalline sponge (CCS). Chiral resolution experiments revealed enantiomeric excess, ee, values of 36.2-93.5%. The structural adaptability of CMOM-5 enabled eight enantiomer@CMOM-5 crystal structures to be determined. The five ordered crystal structures revealed that host-guest hydrogen-bonding interactions are behind the observed enantioselectivity, three of which represent the first crystal structures determined of the ambient liquids R-4P2B, S-4P2B, and R-MPE.

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.

Molecular Mechanisms behind Acetylene Adsorption and Selectivity in Functional Porous Materials

Since its first industrial production in 1890s, acetylene has played a vital role in manufacturing a wide spectrum of materials. Although current methods and infrastructures for various segments of acetylene industries are well-established, with emerging functional porous materials that enabled desired selectivity toward target molecules, it is of timely interest to develop new efficient technologies to promote safer acetylene processes with a higher energy efficiency and lower carbon footprint. In this Minireview, we, from the perspective of materials chemistry, review state-of-the-art examples of advanced porous materials, namely metal-organic frameworks and decorated zeolites, that have been applied to the purification and storage of acetylene. We also discuss the challenges on the roadmap of translational research in the development of new solid sorbent-based separation technologies and highlight areas which require future research efforts.

Facile Synthesis of Ultra-microporous Pillar-Layered Metal-Organic Framework Membranes for Highly H2-Selective Separation

Recently, pillar-layered MOF materials have attracted much attention and shown great potential in separation application due to their fine pore size/channel and pore surface chemistry tunability and designability. In this work, we reported an effective and universal synthesis strategy for preparing ultra-microporous Ni-based pillar-layered MOF [Ni₂(L-asp)₂(bpy)] (Ni-LAB) and [Ni₂(L-asp)₂(pz)] (Ni-LAP) (L-asp = L-aspartic acid, bpy = 4,4'-bipyridine, pz = pyrazine) membranes on a porous α-Al₂O₃ substrate with high performance and good stability by secondary growth. Through this strategy, the seed size reduction and screening engineering (SRSE) is proposed to obtain uniform sub-micron size MOF seeds by high-energy ball milling-combined solvent deposition. This strategy not only effectively addresses the issue of obtaining the uniform small seeds being significant for secondary growth but also provides an approach for the preparation of Ni-based pillar-layered MOF membranes where the freedom of synthesizing small crystals is lacking. Based on reticular chemistry, the pore size of Ni-LAB was narrowed by making use of shorter pillar ligands of pz instead of the longer pillar ligand of bpy. The prepared ultra-microporous Ni-LAP membranes exhibited a high H₂/CO₂ separation factor of 40.4 with H₂ permeance of 9.69 × 10^-8 mol m^-2 s^-1 Pa^-1 under ambient conditions and good mechanical and thermal stability. The superiority of the tunable pore structure and the remarkable stability of these MOF materials showed great potential for industrial H₂ purification. More importantly, our synthesis strategy demonstrated the generality for preparation of MOF membranes, enabling the regulation of membrane pore size and surface functional groups by reticular chemistry.

Vertex Strategy in Layered 2D MOFs: Simultaneous Improvement of Thermodynamics and Kinetics for Record C2H2/CO2 Separation Performance

Developing adsorbents with multiple merits in capacity, selectivity, mass transfer, and stability toward C₂H₂/CO₂ separation is crucial and challenging for producing high-purity C₂H₂ for advanced polymers and the electronic industry. Here, we demonstrate a vertex strategy to create adsorbents combining these merits through rationally designing the vertex groups of a wavy-shaped framework in layered 2D metal-organic frameworks (MOFs) to finely regulate the local conformation and stacking interactions, which creates the optimal inter- and intralayer space to realize simultaneous improvement of adsorption thermodynamics and kinetics. Two new hydrolytically stable MOFs, ZUL-330 and ZUL-430, were prepared, and diverse experiments and modeling on both adsorption equilibrium and diffusion were performed. Record separation selectivities coupled with extraordinary dynamic C₂H₂ capacities were achieved for C₂H₂/CO₂ mixtures with different proportions (50/50 or 10/5, v/v), along with a small diffusion barrier and fast mass transfer. Consequently, polymer-grade (99.9%) and electronic-grade (99.99%) C₂H₂ were obtained with excellent productivities of up to ∼6 mmol cm^-3.

Scalable Green Synthesis of Robust Ultra-Microporous Hofmann Clathrate Material with Record C3 H6 Storage Density for Efficient C3 H6 /C3 H8 Separation

Developing porous materials for C₃ H₆ /C₃ H₈ 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 C₃ H₆ with a record high storage density of 0.818 g mL^-1 , and concurrently shows high C₃ H₆ /C₃ H₈ 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 C₃ H₆ but also enable the dense packing of C₃ H₆ . Breakthrough experiments on gas mixtures afford both high separation factor of 14.7 and large C₃ H₆ 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 C₃ H₆ /C₃ H₈ separation.

A Robust Molecular Porous Material for C2 H2 /CO2 Separation

A molecular porous material, MPM-2, comprised of cationic [Ni₂ (AlF₆ )(pzH)₈ (H₂ O)₂ ] and anionic [Ni₂ Al₂ F₁₁ (pzH)₈ (H₂ O)₂ ] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C₂ H₂ over CO₂ thanks to a high (ΔQ_st )_AC [Q_st (C₂ H₂ ) - Q_st (CO₂ )] of 13.7 kJ mol^-1 at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C₂ H₂ from a 1:1 C₂ H₂ /CO₂ mixture at 298 K with effluent CO₂ purity of 99.995% and C₂ H₂ purity of >95% after temperature-programmed desorption. C-H···F interactions between C₂ H₂ molecules and F atoms of AlF₆ ^3- are found to enable high selectivity toward C₂ H₂ , as determined by density functional theory simulations.

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2 H2 /C2 H4 and C2 H2 /CO2 Separations in Metal-Organic Frameworks

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal-organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M=Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C₂ H₂ uptake capacity under low and ambient pressures (175.3 cm³  cm^-3 @ 0.1 bar, 222.9 cm³  cm^-3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C₂ H₂ /C₂ H₄ , 22.7 for C₂ H₂ /CO₂ ). Remarkably, SNNU-98-Mn can efficiently separate C₂ H₂ from C₂ H₂ /CO₂ and C₂ H₂ /C₂ H₄ mixtures with a benchmark C₂ H₂ /C₂ H₄ (1/99) breakthrough time of 2325 min g^-1 , and produce 99.9999 % C₂ H₄ with a productivity up to 64.6 mmol g^-1 , surpassing values of reported MOF adsorbents.

Application of covalent organic frameworks and metal–organic frameworks nanomaterials in organic/inorganic pollutants removal from solutions through sorption-catalysis strategies

With the fast development of agriculture, industrialization and urbanization, large amounts of different (in)organic pollutants are inevitably discharged into the ecosystems. The efficient decontamination of the (in)organic contaminants is crucial to human health and ecosystem pollution remediation. Covalent organic frameworks (COFs) and metal–organic frameworks (MOFs) have attracted multidisciplinary research interests because of their outstanding physicochemical properties like high stability, large surface areas, high sorption capacity or catalytic activity. In this review, we summarized the recent works about the elimination/extraction of organic pollutants, heavy metal ions, and radionuclides by MOFs and COFs nanomaterials through the sorption-catalytic degradation for organic chemicals and sorption-catalytic reduction-precipitation-extraction for metals or radionuclides. The interactions between the (in)organic pollutants and COFs/MOFs nanomaterials at the molecular level were discussed from the density functional theory calculation and spectroscopy analysis. The sorption of organic chemicals was mainly dominated by electrostatic attraction, π-π interaction, surface complexation and H-bonding interaction, whereas the sorption of radionuclides and metal ions was mainly attributed to surface complexation, ion exchange, reduction and incorporation reactions. The porous structures, surface functional groups, and active sites were important for the sorption ability and selectivity. The doping or co-doping of metal/nonmetal, or the incorporation with other materials could change the visible light harvest and the generation/separation of electrons/holes (e−/h+) pairs, thereby enhanced the photocatalytic activity. The challenges for the possible application of COFs/MOFs nanomaterials in the elimination of pollutants from water were described in the end.

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework

Developing practical storage technologies for acetylene (C₂ H₂ ) is important but challenging because C₂ H₂ is useful but explosive. Here, a novel metal-organic framework (MOF) (FJI-H36) with adaptive channels was prepared. It can effectively capture C₂ H₂ (159.9 cm³  cm^-3 ) at 1 atm and 298 K, possessing a record-high storage density (561 g L^-1 ) but a very low adsorption enthalpy (28 kJ mol^-1 ) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C₂ H₂ can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C₂ H₂ . Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C₂ H₂ . This will provide a useful strategy for developing practical and efficient adsorbents for C₂ H₂ storage.

Programmed Polarizability Engineering in a Cyclen-Based Cubic Zr(IV) Metal-Organic Framework to Boost Xe/Kr Separation

Efficient separation of xenon (Xe) and krypton (Kr) mixtures through vacuum swing adsorption (VSA) is considered the most attractive route to reduce energy consumption, but discriminating between these two gases is difficult due to their similar properties. In this work, we report a cubic zirconium-based MOF (Zr-MOF) platform, denoted as NU-1107, capable of achieving selective separation of Xe/Kr by post-synthetically engineering framework polarizability in a programmable manner. Specifically, the tetratopic linkers in NU-1107 feature tetradentate cyclen cores that are capable of chelating a variety of transition-metal ions, affording a sequence of metal-docked cationic isostructural Zr-MOFs. NU-1107-Ag(I), which features the strongest framework polarizability among this series, achieves the best performance for a 20:80 v/v Xe/Kr mixture at 298 K and 1.0 bar with an ideal adsorbed solution theory (IAST) predicted selectivity of 13.4, placing it among the highest performing MOF materials reported to date. Notably, the Xe/Kr separation performance for NU-1107-Ag(I) is significantly better than that of the isoreticular, porphyrin-based MOF-525-Ag(II), highlighting how the cyclen core can generate relatively stronger framework polarizability through the formation of low-valent Ag(I) species and polarizable counteranions. Density functional theory (DFT) calculations corroborate these experimental results and suggest strong interactions between Xe and exposed Ag(I) sites in NU-1107-Ag(I). Finally, we validated this framework polarizability regulation approach by demonstrating the effectiveness of NU-1107-Ag(I) toward C₃H₆/C₃H₈ separation, indicating that this generalizable strategy can facilitate the bespoke synthesis of polarized porous materials for targeted separations.

Dative B←N bonds based crystalline organic framework with permanent porosity for acetylene storage and separation

The utilization of dative B←N bonds for the creation of crystalline organic framework (BNOF) has increasingly received intensive interest; however, the shortage of permanent porosity is an obstacle that must be overcome to guarantee their application as porous materials. Here, we report the first microporous crystalline framework, BNOF-1, that is assembled through sole monomers, which can be scalably synthesized by the cheap 4-pyridine boronic acid. The 2D networks of BNOF-1 were stacked in parallel to generate a highly porous supramolecular open framework, which possessed not only the highest BET surface area of 1345 m² g^-1 amongst all of the BNOFs but also features a record-high uptake of C₂H₂ and CO₂ in covalent organic framework (COF) materials to date. Dynamic breakthrough experiments demonstrated that BNOF-1 material can efficiently separate C₂H₂/CO₂ mixtures. In addition, the network can be regenerated in organic solvents with no loss in performance, making its solution processable. We believe that BNOF-1 would greatly diversify the reticular chemistry and open new avenues for the application of BNOFs.

Rational Pore Design of a Cage-like Metal-Organic Framework for Efficient C2H2/CO2 Separation

Considering the importance of C₂H₂ in industry, it is of great significance to develop porous materials for efficient C₂H₂/CO₂ separation. Besides the high selectivity, the C₂H₂ adsorption capacity is another vital factor in C₂H₂/CO₂ separation. However, the "trade-off" between these two factors is still perplexing. Rational pore design of metal-organic frameworks (MOFs) has been proven to be an effective way to solve the above problem. In this work, we have appropriately combined three kinds of strategies in the design of the MOF (FJI-H33), i.e., the introduction of open metal sites, construction of cage-like cavities, and adjustment of moderate pore size. As anticipated, FJI-H33 exhibits both outstanding C₂H₂ adsorption capacity and high C₂H₂/CO₂ selectivity. At 298 K and 100 kPa, the C₂H₂ storage capacity of FJI-H33 is 154 cm³/g, while the CO₂ uptake is only 80 cm³/g. The ideal adsorbed solution theory (IAST) selectivity of C₂H₂/CO₂ (50:50) is calculated as high as 15.5 at 298 K. More importantly, the excellent practical separation performance was verified by breakthrough experiments. In addition, the calculation of adsorption sites and relevant energy by density functional theory (DFT) provides a good explanation for the excellent separation performance and pore design strategy.

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.