Halogen–C 2 H 2 Binding in Ultramicroporous Metal–Organic Frameworks (MOFs) for Benchmark C 2 H 2 /CO 2 Separation Selectivity

One-Step Butadiene Purification in a Sulfonate-Functionalized Metal-Organic Framework through Synergistic Separation Mechanism

Porous materials that could recognize specific molecules from complex mixtures are of great potential in improving the current energy-intensive multistep separation processes. However, due to the highly similar structures and properties of the mixtures, the design of desired porous materials remains challenging. Herein, a sulfonate-functionalized metal-organic framework ZU-609 with suitable pore size and pore chemistry is designed for 1,3-butadiene (C4H6) purification from complex C4 mixtures. The sulfonate anions decorated in the channel achieve selective recognition of C4H6 from other C4 olefins with subtle polarity differences through C-H⋅⋅⋅O-S interactions, affording recorded C4H6/trans-2-C4H8 selectivity (4.4). Meanwhile, the shrunken mouth of the channel with a suitable pore size (4.6 Å) exhibits exclusion effect to the larger molecules cis-2-C4H8, iso-C4H8, n-C4H10 and iso-C4H10. Benefiting from the moderate C4 olefins binding affinity exhibited by sulfonate anions, the adsorbed C4H6 could be easily regenerated near ambient conditions. Polymer-grade 1,3-butadiene (99.5 %) is firstly obtained from 7-component C4 mixtures via one adsorption-desorption cycle. The work demonstrates the great potential of synergistic recognition of size-sieving and thermodynamically equilibrium in dealing with complex mixtures.

Crystal Engineering of a New Hexafluorogermanate Pillared Hybrid Ultramicroporous Material Delivers Enhanced Acetylene Selectivity

Hybrid ultramicroporous materials (HUMs), metal-organic platforms that incorporate inorganic pillars, are a promising class of porous solids. A key area of interest for such materials is gas separation, where HUMs have already established benchmark performances. Thanks to their ready compositional modularity, we report the design and synthesis of a new HUM, GEFSIX-21-Cu, incorporating the ligand pypz (4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, 21) and GeF62- pillaring anions. GEFSIX-21-Cu delivers on two fronts: first, it displays an exceptionally high C2H2 adsorption capacity (≥5 mmol g-1) which is paired with low uptake of CO2 (<2 mmol g-1), and, second, a low enthalpy of adsorption for C2H2 (ca. 32 kJ mol-1). This combination is rarely seen in the C2H2 selective physisorbents reported thus far, and not observed in related isostructural HUMs featuring pypz and other pillaring anions. Dynamic column breakthrough experiments for 1:1 and 2:1 C2H2/CO2 mixtures revealed GEFSIX-21-Cu to selectively separate C2H2 from CO2, yielding ≥99.99% CO2 effluent purities. Temperature-programmed desorption experiments revealed full sorbent regeneration in <35 min at 60 °C, reinforcing HUMs as potentially technologically relevant materials for strategic gas separations.

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.

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).

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.

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 .

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal-Organic Framework for Efficient C2 H2 /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 -H₂ O)₂ (CO₂ )₄ ] as the node which was capped by the deprotonated organic ligand of H₄ L (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 C₂ H₂ /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 C₂ H₂ /CO₂ separation performance is contributed to the strong π-complexation interactions between the C₂ H₂ molecules and framework pore surfaces, leading to its more C₂ H₂ uptakes over CO₂ molecules.

Rational regulation of acetylene adsorption and separation for ultra-microporous copper-1,2,4-triazolate frameworks by halogen hydrogen bonds

It is well known that the introduction of exposed fluorine (F) sites into metal-organic frameworks (MOFs) can effectively promote acetylene (C₂H₂) adsorption via C-H⋯F hydrogen bonds. However, such super strong hydrogen bonding interactions usually lead to very high acetylene adsorption enthalpy and thus require more energy during the adsorbent regeneration process. As the same group elements, chlorine (Cl), bromine (Br) and iodine (I) also can act as hydrogen bond acceptors but with relatively weak forces. So, it is speculated that the decoration of Cl, Br or I sites on the pore surface of MOF adsorbents may enhance acetylene adsorption but with lower energy consumption. Herein, ultra-microporous MOFs constructed by Cu₄X₄ (X = Cl, Br, I) motifs and 1,2,4-triazolate linkers, namely, [Cu₈X₄(TRZ)₄]_n (TRZ = 3,5-diethyl-1,2,4-triazole or detrz for SNNU-313-X, and 3,5-dipropyl-1,2,4-triazole or dptrz for SNNU-314-X), provide an ideal platform to investigate the effect of C-H⋯X (X = Cl, Br, I) hydrogen bonding on C₂H₂ adsorption and purification performance. Benefiting from the small pore size and pore environment, the C₂H₂ uptake and separation properties of this series of MOFs are systematically regulated. Detailed gas adsorption results show that with the same organic linker, the C₂H₂ uptake and separation (C₂H₂/C₂H₄ and C₂H₂/CO₂) performance decrease clearly with the electronegativity of halogen ions (SNNU-313-Cl > SNNU-313-Br > SNNU-313-I). With the same halogen ion, the gas adsorption decreases with the bulk of decorated alkyl groups (SNNU-313-Cl > SNNU-314-Cl). Remarkably, SNNU-313/314 series MOF adsorbents exhibit moderate C₂H₂ uptake capacity and high separation ability, but the C₂H₂ adsorption enthalpies are much lower than those of MOF materials with exposed F sites. Dynamic fixed-bed column breakthrough experiments and Grand Canonical Monte Carlo (GCMC) simulations further indicate the critical effects of halogen hydrogen bonds on acetylene adsorption and separation. Overall, this work demonstrated an effective regulation of acetylene adsorption and separation by rational C-H⋯X hydrogen bonding, which may provide a new route for the exploration of energy-efficient acetylene adsorbent materials.

The Complexity of Comparative Adsorption of C6 Hydrocarbons (Benzene, Cyclohexane, n-Hexane) at Metal-Organic Frameworks

The relatively stable MOFs Alfum, MIL-160, DUT-4, DUT-5, MIL-53-TDC, MIL-53, UiO-66, UiO-66-NH₂, UiO-66(F)₄, UiO-67, DUT-67, NH₂-MIL-125, MIL-125, MIL-101(Cr), ZIF-8, ZIF-11 and ZIF-7 were studied for their C₆ sorption properties. An understanding of the uptake of the larger C₆ molecules cannot simply be achieved with surface area and pore volume (from N₂ sorption) but involves the complex micropore structure of the MOF. The maximum adsorption capacity at p p₀^-1 = 0.9 was shown by DUT-4 for benzene, MIL-101(Cr) for cyclohexane and DUT-5 for n-hexane. In the low-pressure range from p p₀^-1 = 0.1 down to 0.05 the highest benzene uptake is given by DUT-5, DUT-67/UiO-67 and MIL-101(Cr), for cyclohexane and n-hexane by DUT-5, UiO-67 and MIL-101(Cr). The highest uptake capacity at p p₀^-1 = 0.02 was seen with MIL-53 for benzene, MIL-125 for cyclohexane and DUT-5 for n-hexane. DUT-5 and MIL-101(Cr) are the MOFs with the widest pore window openings/cross sections but the low-pressure uptake seems to be controlled by a complex combination of ligand and pore-size effect. IAST selectivities between the three binary mixtures show a finely tuned and difficult to predict interplay of pore window size with (critical) adsorptive size and possibly a role of electrostatics through functional groups such as NH₂.

C2H2 capture and separation in a MOF based on Ni6 trigonal-prismatic units

A honeycomb MOF, based on rare Ni₆ trigonal-prismatic supermolecular building blocks, was fabricated by utilizing an unexploited [1,1'-biphenyl]-3,3',5,5'-tetracarboxylic acid linker with -NH₂ substituent groups. The MOF contains novel building blocks and an enchanting structure, and also exhibits water-stable characteristics. Uniquely, the accessible adsorption sites, arising due to the high-density Lewis-basic amino-coordinated groups and uncoordinated carboxylate O atoms in the pores, endow the MOF with excellent capture and separation capabilities for C₂H₂.

Destruction of 4-chlorophenol by the hydrogen-accelerated catalytic Fenton system enhanced by Pd/NH2-MIL-101(Cr)

4-chlorophenol (4-CP) could be rapidly mineralized by using Fenton reaction. However, massive iron sludge will be generated because of the excessive consumption of iron salt and poor recycling of Fe^III back to Fe^II. In this paper, by introducing hydrogen gas and solid catalyst Pd/NH₂-MIL-101(Cr) to classic Fenton reactor, the novel system named MHACF-NH₂-MIL-101(Cr) was constructed. Much less Fe^II was needed in this system because the hydrogen could significantly accelerate the regeneration of Fe^II. The catalyst improved the utilization of H₂. The degradation reaction of 4-CP could be driven by using only trace amount of Fe^II. It could be rapidly degraded by the hydroxyl radical detected by the 4-Hydroxy-benzoicacid which is the oxidative product of benzoic acid and hydroxyl radical. The effects of dosage of ferrous salt, H₂O₂ and catalyst, H₂ flow, Pd content, and initial pH of and concentration of 4-CP aqueous solution were investigated. The robustness and morphology changes of this catalytic material were also systematically analysed. By clarifying the role of this solid MOFs material in this hydrogen-mediated Fenton reaction system, it will provide a new direction for the research and development of advanced oxidation processes with high efficiency and low sludge generation in future.

Uncoordinated Hexafluorosilicates in a Microporous Metal-Organic Framework Enabled C2H2/CO2 Separation

Metal-organic frameworks (MOFs) represent a kind of low-energy physisorbent with modifiable pores and framework structures; however, a deep understanding of how these structural features influence properties is a prerequisite for the rational design and development of tailor-made materials for advanced applications. In this report, a MOF, [Ni₂(TCPP-Ni)_1/4(TPIM)₂(COOH)F][(Me₂NH₂)SiF₆]·xS (SDU-CP-1; S = solvent molecules, SDU = Shandong University, and CP = coordination polymer), assembled by tetrakis(4-carboxyphenyl)porphyrin (TCPP-Ni) and 2,4,5-tris(4-pyridyl)imidazole (TPIM) ligands as well as Ni²⁺ cations is reported. Interestingly, inorganic SiF₆^2- anions do not serve as the pillars like precedents in the framework but are just counterions, which endows SDU-CP-1 with high uptake for C₂H₂ and adsorption selectivity (2.5-4.2) for C₂H₂/CO₂ at room temperature, as certified by gas adsorption and separation experiments and grand canonical Monte Carlo calculation.

A new boron cluster anion pillared metal organic framework with ligand inclusion and its selective acetylene capture properties

A novel microporous boron cluster pillared metal–organic framework BSF-10 was synthesized with ligand inclusion for efficient C2H2/CO2 and C2H2/C2H4 adsorption separation.

An ato-topology metal–organic framework with large C2H2 adsorption and C2H2/CO2 separation capacity

The industrial separation of C2H2/CO2 is an energy-intensive process due to their similar molecular shapes. Here we demonstrate an ato-topology MOF with not only large C2H2 adsorption capacity but also high C2H2/CO2 selectivity.

Investigation on the catalytic behavior of a novel thulium-organic framework with a planar tetranuclear {Tm4} cluster as the active center for chemical CO2 fixation

Herein, the exquisite combination of coplanar [Tm₄(CO₂)₁₀(μ₃-OH)₂(μ₂-HCO₂)(OH₂)₂] clusters ({Tm₄}) and structure-oriented functional BDCP^5- leads to the highly robust nanoporous {Tm₄}-organic framework {(Me₂NH₂)[Tm₄(BDCP)₂(μ₃-OH)₂(μ₂-HCO₂)(H₂O)₂]·7DMF·5H₂O}_n (NUC-37, H₅BDCP = 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine). To the best of our knowledge, NUC-37 is the first anionic {Ln₄}-based three-dimensional framework with embedded hierarchical microporous and nanoporous channels, among which each larger one is shaped by six rows of coplanar {Tm₄} clusters and characterized by plentiful coexisting Lewis acid-base sites on the inner wall including open Tm^III sites, N_pyridine atoms, μ₃-OH and μ₂-HCO₂. Catalytic experimental studies exhibit that NUC-37 possesses highly selective catalytic activity on the cycloaddition of epoxides with CO₂ as well as high recyclability under gentle conditions, which should be ascribed to its nanoscale channels, rich bifunctional active sites, and stable physicochemical properties. This work offers an effective means for synthesizing productive cluster-based Ln-MOF catalysts by employing structure-oriented ligands and controlling the solvothermal reaction conditions.

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.

Three-in-One C2 H2 -Selectivity-Guided Adsorptive Separation across an Isoreticular Family of Cationic Square-Lattice MOFs

Energy-efficient selective physisorption driven C₂ H₂ separation from industrial C2-C1 impurities such as C₂ H₄ , CO₂ and CH₄ is of great importance in the purification of downstream commodity chemicals. We address this challenge employing a series of isoreticular cationic metal-organic frameworks, namely iMOF-nC (n=5, 6, 7). All three square lattice topology MOFs registered higher C₂ H₂ uptakes versus the competing C2-C1 gases (C₂ H₄ , CO₂ and CH₄ ). Dynamic column breakthrough experiments on the best-performing iMOF-6C revealed the first three-in-one C₂ H₂ adsorption selectivity guided separation of C₂ H₂ from 1:1 C₂ H₂ /CO₂ , C₂ H₂ /C₂ H₄ and C₂ H₂ /CH₄ mixtures. Density functional theory calculations critically examined the C₂ H₂ selective interactions in iMOF-6C. Thanks to the abundance of square lattice topology MOFs, this study introduces a crystal engineering blueprint for designing C₂ H₂ -selective layered metal-organic physisorbents, previously unreported in cationic frameworks.

Breaking the trade-off between selectivity and adsorption capacity for gas separation

The trade-off between selectivity and adsorption capacity with porous materials is a major roadblock to reducing the energy footprint of gas separation technologies. To address this matter, we report herein a systematic crystal engineering study of C₂H₂ removal from CO₂ in a family of hybrid ultramicroporous materials (HUMs). The HUMs are composed of the same organic linker ligand, 4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, pypz, three inorganic pillar ligands, and two metal cations, thereby affording six isostructural pcu topology HUMs. All six HUMs exhibited strong binding sites for C₂H₂ and weaker affinity for CO₂. The tuning of pore size and chemistry enabled by crystal engineering resulted in benchmark C₂H₂/CO₂ separation performance. Fixed-bed dynamic column breakthrough experiments for an equimolar (v/v = 1:1) C₂H₂/CO₂ binary gas mixture revealed that one sorbent, SIFSIX-21-Ni, was the first C₂H₂ selective sorbent that combines exceptional separation selectivity (27.7) with high adsorption capacity (4 mmol·g⁻¹).

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Six isostructural hybrid ultramicroporous materials are prepared and characterized

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Crystal engineering approach enabled fine-tuning of pore size and chemistry

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Weak CO₂/strong C₂H₂ affinity resulted in high C₂H₂/CO₂ separation selectivities

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SIFSIX-21-Ni: benchmark selectivity/uptake capacity for C₂H₂/CO₂ separation

It is generally recognized that porous solids (sorbents) with high selectivity and high adsorption capacity offer potential for energy-efficient gas separations. Unfortunately, there is generally a trade-off between capacity and selectivity, which represents a roadblock to the utility of sorbents in key industrial processes. For example, acetylene (C₂H₂), an important fuel and chemical intermediate, is produced with CO₂ as an impurity, and the similar physicochemical properties of C₂H₂ and CO₂ mean that most sorbents are poorly selective. Hybrid ultramicroporous materials (HUMs) are candidates for gas separations as they exhibit benchmark selectivity for several key gas pairs. Unfortunately, existing HUMs are handicapped by low capacity. We report a new HUM, SIFSIX-21-Ni, that addresses the trade-off between selectivity and capacity that has plagued sorbents, as its high uptake and high selectivity renders it the new benchmark for C₂H₂/CO₂ separation performance.

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

Physical separation of C₂H₂ from CO₂ on metal-organic frameworks (MOFs) has received substantial research interest due to the advantages of simplicity, security, and energy efficiency. However, that C₂H₂ and CO₂ exhibit very close physical properties makes their separation exceptionally challenging. Previous work appeared to mostly focused on introducing open metal sites that aims to enhance the C₂H₂ affinity at desired sites, whereas the reticular manipulation of organic components has rarely been investigated. In this work, by reticulating preselected amino and hydroxy functionalities into isostructural ultramicroporous chiral MOFs-Ni₂(l-asp)₂(bpy) (MOF-NH₂) and Ni₂(l-mal)₂(bpy) (MOF-OH)-we targeted efficient C₂H₂ uptake and C₂H₂/CO₂ separation, which outperforms most benchmark materials. Explicitly, MOF-OH adsorbs substantial amount of C₂H₂ with record storage density of 0.81 g mL^-1 at ambient conditions, which even exceeds the solid density of C₂H₂ at 189 K. In addition, MOF-OH gave IAST selectivity of 25 toward equimolar mixture of C₂H₂/CO₂, which is nearly twice higher than that of MOF-NH₂. Notably, the adsorption enthalpies for C₂H₂ at zero converge in both MOFs are remarkably low (17.5 kJ mol^-1 for MOF-OH and 16.7 kJ mol^-1 for MOF-NH₂), which to our knowledge are the lowest among efficient rigid C₂H₂ sorbents. The efficiencies of both MOFs for the separation of C₂H₂/CO₂ are validated by multicycle breakthrough experiments. DFT calculations provide molecular-level insight over the adsorption/separation mechanism. Moreover, MOF-OH can survive in boiling water for at least 1 week and can be easily scaled up to kilograms eco-friendly and economically, which is very crucial for potential industrial implementation.

Design and Solvothermal Synthesis of Polyoxometalate-Based Cu(II)-Pyrazolate Photocatalytic Compounds for Solar-Light-Driven Hydrogen Evolution

Polyoxometalates (POMs) are known for their photocatalytic hydrogen production activity, but their solubility and limited stability often restrict their practical applications. Herein, we designed and solvothermally synthesized two new Cu-H₂bpz (3,3',5,5'-tetramethyl-4,4'-bipyrazole, abbreviated as H₂bpz) compounds, namely, Cu_0.5(H₂bpz)(NO₃) (1) and Cu(Hbpz)(Cl)·DMF (2), and three new polyoxometalate-based Cu(II)-pyrazolate compounds, namely, Cu(PW₁₂O₄₀)_0.5(H₂bpz)₂(H₂O)·(OH)_0.5(H₂O)_5.5 (3), Cu(HPMo₁₂O₄₀)(H₂bpz)₂(H₂O)₂·(H₂O)₄ (4), and Cu₂(SiW₁₂O₄₀)(H₂bpz)₃(H₂O)₃·(H₂O)₆ (5). Compound 3 (Cu(PW₁₂O₄₀)_0.5(H₂bpz)₂(H₂O)·(OH)_0.5(H₂O)_5.5) exhibits the best photocatalytic activity of 44.4 μ L h^-1 g^-1, which may be related to the stability of compounds. Herein, the solvothermal method has been proven to be an effective method in synthesizing stable organic-inorganic hybrid compounds with soluble POMs, metal ions, and organic ligands. Thus, heterogeneous catalysts with outstanding solar-light-driven photocatalytic properties were obtained.

Interpenetration symmetry control within ultramicroporous robust boron cluster hybrid MOFs for benchmark purification of acetylene from carbon dioxide

The separation of C2H2/CO2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their similar physical properties and identical kinetic molecular size. Herein, we report the first example of symmetrically interpenetrated dodecaborate pillared MOF, ZNU-1, for benchmark selective separation of C2H2 from CO2 with a high C2H2 capacity of 76.3 cm3 g-1 and record C2H2/CO2 selectivity of 56.6 (298 K, 1 bar) among all the robust porous materials without open metal sites. Single crystal structure analysis and modelling study indicated that the interpenetration shifting from asymmetric to symmetric mode provided optimal pore chemistry with ideal synergistic "2+2" dihydrogen bonding sites for tight C2H2 trapping. The exceptional separation performance was further evidenced by simulated and experimental breakthroughs with excellent recyclability and high productivity (2.4 mol/kg) of 99.5% purity C2H2 during stepped desorption process.

Modulation of Topological Structures and Adsorption Properties of Copper-Tricarboxylate Frameworks Enabled by the Effect of the Functional Group and Its Position

To push forward the structural development and fully explore the potential utility, it is highly desired but challenging to regulate in a controllable manner the structures and properties of MOFs. In this work, we reported the structural and functional modulation of Cu(II)-tricarboxylate frameworks by employing a strategy of engineering the functionalities and their positions. Two pairs of unsymmetrical biaryl tricarboxylate ligands modified with a methyl group and a pyridinic-N atom at distinct positions were logically designed and synthesized, and their corresponding Cu(II)-based MOFs were solvothermally constructed. Diffraction analyses revealed that the variation of functionalities and their positions furnished three different types of topological structures, which we ascribed to the steric effect exerted by the methyl group and the chelating effect involving the pyridinic-N atom. Furthermore, gas adsorption studies showed that three of them are potential candidates as solid separation media for acetylene (C₂H₂) purification, with the separation potential tailorable by altering functionalities and their locations. At 106.7 kPa and 298 K, the C₂H₂ uptake capacity varies from 64.1 to 132.4 cm³ (STP) g^-1, while the adsorption selectivities of C₂H₂ over its coexisting components of CO₂ and CH₄ fall in the ranges of 3.28-4.60 and 14.1-21.9, respectively.

Coordination sphere hydrogen bonding as a structural element in metal-organic Frameworks

In the design of new metal-organic frameworks, the constant challenges of framework stability and structural predictability continue to influence ligand choice in favour of well-studied dicarboxylates and similar ligands. However, a small subset of known MOF ligands contains suitable functionality for coordination sphere hydrogen bonding which can provide new opportunities in ligand design. Such interactions may serve to support and rigidity the coordination geometry of mononuclear coordination spheres, as well as providing extra thermodynamic and kinetic stabilisation to meet the challenge of hydrolytic stability in these materials. In this perspective, a collection of pyrazole, amine, amide and carboxylic acid containing species are examined through the lens of (primarily) inner-sphere hydrogen bonding. The influence of these interactions is then related to the overall structure, stability and function of these materials, to provide starting points for harnessing these interactions in future materials design.

Precise Pore Space Partitions Combined with High-Density Hydrogen-Bonding Acceptors within Metal-Organic Frameworks for Highly Efficient Acetylene Storage and Separation

The high storage capacity versus high selectivity trade-off barrier presents a daunting challenge to practical application as an acetylene (C₂ H₂ ) adsorbent. A structure-performance relationship screening for sixty-two high-performance metal-organic framework adsorbents reveals that a moderate pore size distribution around 5.0-7.5 Å is critical to fulfill this task. A precise pore space partition approach was involved to partition 1D hexagonal channels of typical MIL-88 architecture into finite segments with pore sizes varying from 4.5 Å (SNNU-26) to 6.4 Å (SNNU-27), 7.1 Å (SNNU-28), and 8.1 Å (SNNU-29). Coupled with bare tetrazole N sites (6 or 12 bare N sites within one cage) as high-density H-bonding acceptors for C₂ H₂ , the target MOFs offer a good combination of high C₂ H₂ /CO₂ adsorption selectivity and high C₂ H₂ uptake capacity in addition to good stability. The optimized SNNU-27-Fe material demonstrates a C₂ H₂ uptake of 182.4 cm³  g^-1 and an extraordinary C₂ H₂ /CO₂ dynamic breakthrough time up to 91 min g^-1 under ambient conditions.

A window-space-directed assembly strategy for the construction of supertetrahedron-based zeolitic mesoporous metal-organic frameworks with ultramicroporous apertures for selective gas adsorption

Despite their scarcity due to synthetic challenges, supertetrahedron-based metal-organic frameworks (MOFs) possess intriguing architectures, diverse functionalities, and superb properties that make them in-demand materials. Employing a new window-space-directed assembly strategy, a family of mesoporous zeolitic MOFs have been constructed herein from corner-shared supertetrahedra based on homometallic or heterometallic trimers [M3(OH/O)(COO)6] (M3 = Co3, Ni3 or Co2Ti). These MOFs consisted of close-packed truncated octahedral cages possessing a sodalite topology and large β-cavity mesoporous cages (∼22 Å diameter) connected by ultramicroporous apertures (∼5.6 Å diameter). Notably, the supertetrahedron-based sodalite topology MOF combined with the Co2Ti trimer exhibited high thermal and chemical stability as well as the ability to efficiently separate acetylene (C2H2) from carbon dioxide (CO2).

Engineering ligand conformation by substituent manipulation towards diverse copper-tricarboxylate frameworks with tuned gas adsorption properties

To expand the structural diversity and optimize the material performance, it is essential but challenging to regulate MOF structures in a predictable and controllable manner. In this work, by manipulating the substituents to engineer the ligand conformations, we designed and synthesized two asymmetric tricarboxylate ligands, and used them to successfully target two copper-tricarboxylate frameworks with diversified topologies depending on the ligand conformations. Besides, the ligand asymmetry induced the formation of two uncommon kinds of copper-carboxylate clusters, thus greatly expanding the library of copper-carboxylate secondary building units. Furthermore, the two compounds also displayed tunable gas adsorption properties pertinent to C2H2 separation and purification. At 298 K and 1 atm, the uptake capacity of C2H2 varies from 79.5 to 104.6 cm3 (STP) g-1, while the adsorption selectivities of C2H2 with respect to CO2 and CH4 are in the range of 2.3-3.8 and 15.3-21.6 for the equimolar components, respectively. Compared to the nitro counterpart, the methoxy MOF features higher C2H2 uptake capacity, larger C2H2/CO2 and C2H2/CH4 adsorption selectivities, and lower regeneration energy. This work demonstrates that simple ligand modification can be used to engineer the structures and tune gas adsorption properties of the resulting MOFs.