Fine-Tuned Ultra-Microporous Metal-Organic Framework in Mixed-Matrix Membrane: Pore-Tailoring Optimization for C2 H2 /C2 H4 Separation.

Effective separation of ethyne from ethyne/ethylene (C2 H2 /C2 H4 ) mixtures is a challenging and crucial industrial process. Herein, an ultra-microporous metal-organic framework (MOF) platform, Cd(dicarboxylate)2 (ditriazole), with triangular channels is proposed for high-efficiency separation of C2 H2 from C2 H4 . The targeted structures are constructed via a mixed-ligand strategy by selecting different-sized ligands, allowing for tunable pore sizes and volumes. The pore properties can be further optimized by additional modification via pore environment tailoring. This concept leads to the successful synthesis of three ultra-microporous Cd-MOFs (JLU-MOF87-89). As intended, C2 H2 uptake and C2 H2 /C2 H4 selectivity gradually increase with progressively optimizing the pore structure by adjusting ligand length and substituents. JLU-MOF89, functionalized with methyl groups, features the most optimal pore chemistry and shows selective recognition of C2 H2 over C2 H4 , owing to the framework-C2 H2 host-guest interactions. Furthermore, JLU-MOFs are fabricated into mixed-matrix membranes for C2 H2 /C2 H4 separation. C2 H2 permeability and C2 H2 /C2 H4 permselectivity are substantially enhanced by ≥400% and ≥200%, respectively, after hybridization of JLU-MOF88 and JLU-MOF89 with a polyimide polymer (6FDA-ODA). These membranes can work efficiently and are stable under different conditions, demonstrating their potential in actual ethyne separation.

Asymmetric pore windows in MOF membranes for natural gas valorization.

To use natural gas as a feedstock alternative to coal and oil, its main constituent, methane, needs to be isolated with high purity1. In particular, nitrogen dilutes the heating value of natural gas and is, therefore, of prime importance for removal2. However, the inertness of nitrogen and its similarities to methane in terms of kinetic size, polarizability and boiling point pose particular challenges for the development of energy-efficient nitrogen-removing processes3. Here we report a mixed-linker metal-organic framework (MOF) membrane based on fumarate (fum) and mesaconate (mes) linkers, Zr-fum67-mes33-fcu-MOF, with a pore aperture shape specific for effective nitrogen removal from natural gas. The deliberate introduction of asymmetry in the parent trefoil-shaped pore aperture induces a shape irregularity, blocking the transport of tetrahedral methane while allowing linear nitrogen to permeate. Zr-fum67-mes33-fcu-MOF membranes exhibit record-high nitrogen/methane selectivity and nitrogen permeance under practical pressures up to 50 bar, removing both carbon dioxide and nitrogen from natural gas. Techno-economic analysis shows that our membranes offer the potential to reduce methane purification costs by about 66% for nitrogen rejection and about 73% for simultaneous removal of carbon dioxide and nitrogen, relative to cryogenic distillation and amine-based carbon dioxide capture.

Designing Multicomponent Metal-Organic Frameworks with Hierarchical Structure-Mimicking Distribution for High CO2 Capture Performance.

By utilizing a mixed-ligand strategy, a novel multicomponent Cu-metal-organic framework (MOF) (JLU-MOF107) has been successfully synthesized. JLU-MOF107 has an unusual hierarchical structure-mimicking distribution structure. The triangular 4,4',4″-benzene-1,3,5-triyl-tribenzoate (BTB) ligand and the binuclear Cu cluster form a threefold interpenetration layer, while the linear ligand 1,4-phenylene-4,4'-bis(1,2,4-triazole) (p-tr2ph) and tetranuclear Cu cluster form a noninterpenetration pillared-layer structure. Then, the two types of layers are connected by tetranuclear Cu clusters to construct the final sandwichlike framework. JLU-MOF107 exhibits good water and humidity stability. Due to the presence of various active sites and pores, JLU-MOF107 shows an outstanding performance for CO2 capture (171.0 cm3 g-1 at 273 K). Density functional theory (DFT)-based calculations further prove the interactions between CO2 molecules and multiple active sites. The innovative synthesis of this multicomponent structure offers a new perspective on making hierarchical porous materials and multifunctional MOFs.

Contiguous layer based metal-organic framework with conjugated π-electron ligand for high iodine capture.

Herein, a novel 3-dimensional (3D) Cu(II) metal-organic framework (MOF), [Cu3(µ2-O)2(p-tr2Ph)2(HCOO)][NO3]·3DMF·3H2O (compound 1), which is constructed by directly interlocking regionalized hollow two-dimensional (2D) layers, has been conceived and solvothermally synthesized. Such a distinctive regionalized pore system effectively maintains the uniformity of the pore structure, isolates the counterions and bridging ligands in the partition layer, and endows compound 1 with high porosity. In consequence, compound 1 exhibits excellent adsorption ability of iodine in cyclohexane. The removal efficiency in cyclohexane solution (0.01 mol L-1) can reach up to 80% in 8 min, and the absorption ability towards iodine can reach about 1.15 g g-1. Moreover, iodine can also be controllably released in ethanol. The release rate was up to 4 × 10-5 mol L-1 min-1. Furthermore, compound 1 also showed prominent recyclability due to the high stability, and the maximum sorption amount could be retained after 3 cycles. This study paves a new way towards opening up MOFs' potential application in capturing radioactive iodine to protect the environment.

Recent Progress on Microfine Design of Metal-Organic Frameworks: Structure Regulation and Gas Sorption and Separation.

Metal-organic frameworks (MOFs) have emerged as an important and unique class of functional crystalline hybrid porous materials in the past two decades. Due to their modular structures and adjustable pore system, such distinctive materials have exhibited remarkable prospects in key applications pertaining to adsorption such as gas storage, gas and liquid separations, and trace impurity removal. Evidently, gaining a better understanding of the structure-property relationship offers great potential for the enhancement of a given associated MOF property either by structural adjustments via isoreticular chemistry or by the design and construction of new MOF structures via the practice of reticular chemistry. Correspondingly, the application of isoreticular chemistry paves the way for the microfine design and structure regulation of presented MOFs. Explicitly, the microfine tuning is mainly based on known MOF platforms, focusing on the modification and/or functionalization of a precise part of the MOF structure or pore system, thus providing an effective approach to produce richer pore systems with enhanced performances from a limited number of MOF platforms. Here, the latest progress in this field is highlighted by emphasizing the differences and connections between various methods. Finally, the challenges together with prospects are also discussed.

Quest for Zeolite-like Supramolecular Assemblies: Self-Assembly of Metal-Organic Squares via Directed Hydrogen Bonding.

Our conceived approach based on the directed assembly of functional metal-organic squares (MOSs), 4-membered ring (4MR) building units, permitted the construction of two novel zeolite-like supramolecular assemblies (ZSAs), namely [Co4 (ImDC)4 (En)4 ]⋅9 H2 O⋅1.5 DMF (ZSA-10) and [Co4 (ImDC)4 (En)4 ]⋅7 H2 O (ZSA-11) (H3 ImDC=4,5-imidazoledicarboxylic acid, En=ethylenediamine, DMF=N,N-dimethylformamide). The elected MOSs encompass both trans- and cis-coordinated nodes, offering complementary peripheral functional groups for their directed assembly into zeolite-like topologies via supramolecular hydrogen bonding interactions. Distinctly, ZSA-10 possesses the underling MER zeolite topology and is the only pure MER framework material (without any supporting templates) exhibiting permanent porosity up to now. ZSA-11 has the underlying ABW topology together with one type of narrow channel.

A Stable Mesoporous Zr-Based Metal Organic Framework for Highly Efficient CO2 Conversion.

With the help of modulator synthesis method, a mesoporous Zr-based metal-organic framework, [Zr6O4(OH)8(H2O)4(TADIBA)4]·24DMF·45H2O (DMF = N, N-dimethylformamide, H2TADIBA = 4,4'-(2 H-1,2,4-triazole-3,5-diyl) dibenzoic acid), namely, JLU-MOF58, was successfully constructed. JLU-MOF58 having reo topology is constructed by the bent ligands with Lewis basic sites and 8-connected Zr6 clusters with Lewis and Brønsted acid sites. It not only possesses two types of mesoporous cages: octahedral and cuboctahedral (2.76 and 4.10 nm), with a pore volume of 1.76 cm3 g-1, but also displays excellent chemical stability in acid and base aqueous phase. Benefiting from the Brønsted and Lewis acid sites, Lewis basic sites, excellent chemical stability, and the mesoporous cages incorporated in the framework, JLU-MOF58 can be regarded as a remarkably efficient heterogeneous catalyst that exhibits excellent catalytic efficiency for CO2 conversion.

Supramolecular interactions induced distortion of BTB ligands: breaking convention to reproduce an unusual (3,4,4)-connected MOF topology.

An unusual (3,4,4)-connected MOF topology has been reproduced by a 4,4',4''-benzene-1,3,5-triyl-tribenzoate (BTB) ligand which was previously judged to be not feasible to form this network. The outcome demonstrates that supramolecular interactions play a key role in the formation of this highly distorted network. Moreover, this triple interpenetrated framework exhibits high BET surface area.

Mesoporous Hexanuclear Copper Cluster-Based Metal-Organic Framework with Highly Selective Adsorption of Gas and Organic Dye Molecules.

Despite many advances in the design and assembly of mesoporous metal-organic frameworks (meso-MOFs), it is still a challenge to obtain the desired structure. Here, we utilized an effective cluster cooperative assembly strategy by introducing SO42- ions as chelating binding sites to construct a novel mesoporous MOF, [Cu8(SO4)(TBA)6(OH)2( N,N-dimethylacetamide (DMA))4]·12DMA·12CH3OH [JLU-MOF51, H2TBA = 4-(1 H-tetrazol-5-yl)-benzoic acid]. Remarkably, the cooperative assembly of the infrequent hexanuclear [Cu6SO4(OH)2] cluster and the classical paddlewheel [Cu2(CO2)4] via linear hetero-N, O donor ligand results in an open three-dimensional framework, which possesses one-dimensional nanometer tube channels with the diameter of 24 and 28 Å. Fascinatingly, JLU-MOF51 displays an exceptionally large Langmuir surface area (5443 m2 g-1) and exhibits a high capacity for selective adsorption of C3H8 (C3H8: 348 cm3 g-1 at 273 K; C3H8/CH4 = 220 at 298 K). In addition, JLU-MOF51 can selectively adsorb fluorescein disodium salt dye among numerous organic dyes. An extremely high surface area and unique structural characteristics make JLU-MOF51 a promising meso-MOF material for the adsorption and separation of hydrocarbon gases and organic dyes. Moreover, this strategy will provide an effective means for constructing meso-MOFs via one-step synthesis.

Two Finite Binuclear [M2(µ2-OH)(COO)2] (M = Co, Ni) Based Highly Porous Metal-Organic Frameworks with High Performance for Gas Sorption and Separation.

Two highly porous MOFs, [Co2(µ2-OH)(bpdc)(Htpim)2][SiF6]·3.5DMA·2.5CH3OH (JLU-Liu37, H2bpdc = biphenyl-4,4'-dicarboxylate, Htpim = 2,4,5-tri(4-pyridyl)imidazole) and [Ni2(µ2-OH)(bpdc)(Htpim)2][SiF6]·7.5DMA·6CH3OH (JLU-Liu38), have been solvothermally synthesized by using the mixed ligand strategy. Both of the compounds possess finite binuclear [M2(µ2-OH)(COO)2] (M = Co, Ni) secondary building units (SBUs) which formed with a polar functional group, µ2-OH. JLU-Liu37 and JLU-Liu38 exhibit notable adsorption capacities for CO2 and light hydrocarbons (CH4, C2H6, and C3H8). Moreover, both of the materials exhibit arrestive natural gas selective separation ability, especially for C3H8/CH4 (206 for an equimolar mixture under 1 bar and 298 K, for JLU-Liu37). Both of the MOFs may be effectively applied in the separation of industrial light hydrocarbons.