Spatially Confined π-Complexation within Pore-Space-Partitioned Metal-Organic Frameworks for Enhanced Light Hydrocarbon Separation and Purification

Ultramicroporous metal-organic frameworks (MOFs) are demonstrated to be advantageous for the separation and purification of light hydrocarbons such as C2H2, C2H4, and CH4. The introduction of transition metal sites with strong π-complexation affinity into MOFs is more effective than other adsorption sites for the selective adsorption of π-electron-rich unsaturated hydrocarbon gases from their mixtures. However, lower coordination numbers make it challenging to produce robust MOFs directly utilizing metal ions with π-coordination activity, such as Cu+, Ag+, and Pd2+. Herein, a series of novel π-complexing MOFs (SNNU-33s) with a pore size of 4.6 Å are precisely constructed by cleverly introducing symmetrically matched C3-type [Cu(pyz)3] (pyz = pyrazine) coordinated fragments into 1D hexagonal channels of MIL-88 prototype frameworks. Benifit from the spatial confinement combined with π-complex-active Cu+ of [Cu(pyz)3], pore-space-partitioned SNNU-33 MOFs all present excellent C2H2/CH4, C2H4/CH4, and CO2/CH4 separation ability. Notably, the optimized SNNU-33b adsorbent demonstrates top-level IAST selectivity values for C2H2/CH4 (597.4) and C2H4/CH4 (69.8), as well as excellent breakthrough performance. Theoretical calculations further reveal that such benchmark light hydrocarbon separation and purification ability is mainly ascribed to the extra-strong binding affinity between Cu+ and π-electron donor molecules via a spatially confined π-complexation process.

Cu-MOFs with Rich Open Metal and F Sites for Separation of C2H2 from CO2 and CH4

Herein, we used the 4-fluoro-[1,1'-biphenyl]-3,4',5-tricarboxylic acid (H₃fbptc) ligand to design and construct a new metal-organic framework (MOF), [Cu₃(fbptc)₂(H₂O)₃]·3NMP (1), which possesses rich accessible metal sites and F functional groups in the porous walls and shows high uptake for C₂H₂ (119.3 cm³ g^-1) and significant adsorption selectivity for C₂H₂ over CH₄ (14.4) and CO₂ (3.6) at 298 K and 100 kPa. In particular, for the gas mixtures of C₂H₂-CH₄ and C₂H₂-CO₂, the MOF reveals large breakthrough time ratios (C₂H₂/CH₄ = 13, C₂H₂/CO₂ = 5.9), which are particularly prominent in dynamic breakthrough experiments, also confirming the excellent potential for the practical separation of C₂H₂ from two-component mixtures (C₂H₂-CH₄ and C₂H₂-CO₂) and even three-component mixtures (C₂H₂-CO₂-CH₄).

A novel trigonal bipyramidal cage-based Zn(ii)-MOF featuring two types of trinuclear clusters with high gas sorption properties

A unique trigonal bipyramidal cage-based Zn(ii)-MOF built from a linear trinuclear pin-wheel cluster and a triangular trinuclear cluster was prepared and shows a moderate gas adsorption amounts and high selectivities towards C2Hn/CH4 and C2H2/CO2.

A new 3D 8-connected Cd(ii) MOF as a potent photocatalyst for oxytetracycline antibiotic degradation

1 exhibits the best photocatalytic decomposition efficiency towards antibiotic OXY. The plausible photocatalytic mechanism has been explained with the help of the density of states calculations and Hirshfeld surface analysis.

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

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

Synergistic Effect of Active Sites and a Multiple-Micropore System for a Metal-Organic Framework Exhibiting High Separation of CO2/CH4 and C2H2/CH4

Efficient gas separation and purification play a vital role in the current advanced development of industry, and the application of MOF adsorbents in this area with highly technical materials shows obvious advantages. On the basis of reticular chemistry, the 4-c lvt MOF adsorbent [CuDTTA]·3DMF·CH₃CN has been constructed (CuDTTA; H₂DTTA = 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalic acid). CuDTTA reveals a multiple-micropore system and high-density active sites decorated on the channel surfaces, which are conducive to its extraordinary selectivity of CO₂/CH₄ and C₂H₂/CH₄ (29 and 166, 1:1). In combination with an analysis of Q_st values, CuDTTA possesses the synergistic effect of size sieving and abundant functional sites, significantly improving the gas adsorption and separation performance. Meanwhile, the results also reveal that functional sites have a stronger binding affinity toward C₂H₂ with respect to CO₂. Such a conclusion renders CuDTTA to be a promising adsorbent material for industrial applications.

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.

Multiple Functions of Gas Separation and Vapor Adsorption in a New MOF with Open Tubular Channels

Separation or purification is one of the difficult problems in the petrochemical industry. To help solve the difficulty of separation or purification for C₂H₂/CO₂ and C₂H_n/CH₄ in the chemical industry, we synthesized a new metal-organic framework (MOF), [Ni(dpip)]·2.5DMF·H₂O (1), by a bipyridyl-substituted isophthalic acid ligand. The MOF includes two types of one-dimensional (1D) tubular channels with different sizes and porous environments. The unique tubular channels lead to not only remarkable gas sorption capacity of C₂H₄, C₂H₂, and CO₂, but also good selectivity for C₂H₂/CH₄, C₂H₂/CH₄, CO₂/CH₄, and C₂H₂/CO₂, as demonstrated by single-component sorption isotherm results, ideal adsorbed solution theory calculations, and dynamic breakthrough curves. Grand canonical Monte Carlo (GCMC) simulation reveals preferential adsorption sites in the MOF for CO₂, C₂H₂, and C₂H₄. The MOF also exhibits an obvious size-selective absorption effect on vapor molecules.

Two new CdII MOFs of 1,4-bis(1H-benzimidazol-1-yl)butane and flexible dicarboxylate ligands: luminescence sensing towards Fe3

Two new Cd^II MOFs, namely, two-dimensional (2D) poly[[[μ₂-1,4-bis(1H-benzimidazol-1-yl)butane](μ₂-heptanedioato)cadmium(II)] tetrahydrate], {[Cd(C₇H₁₀O₄)(C₁₈H₁₈N₄)]·4H₂O}_n or {[Cd(Pim)(bbimb)]·4H₂O}_n (1), and 2D poly[diaqua[μ₂-1,4-bis(1H-benzimidazol-1-yl)butane](μ₄-decanedioato)(μ₂-decanedioato)dicadmium(II)], [Cd₂(C₁₀H₁₆O₄)₂(C₁₈H₁₈N₄)(H₂O)₂]_n or [Cd(Seb)(bbimb)_0.5(H₂O)]_n (2), have been synthesized hydrothermally based on the 1,4-bis(1H-benzimidazol-1-yl)butane (bbimb) and pimelate (Pim^2-, heptanedioate) or sebacate (Seb^2-, decanedioate) ligands. Both MOFs were structurally characterized by single-crystal X-ray diffraction. In 1, the Cd^II centres are connected by bbimb and Pim^2- ligands to generate a 2D sql layer structure with an octameric (H₂O)₈ water cluster. The 2D layers are further connected by O-H...O hydrogen bonds, resulting in a three-dimensional (3D) supramolecular structure. In 2, the Cd^II centres are coordinated by Seb^2- ligands to form binuclear Cd₂ units which are linked by bbimb and Seb^2- ligands into a 2D hxl layer. The 2D layers are further connected by O-H...O hydrogen bonds, leading to an 8-connected 3D hex supramolecular network. IR and UV-Vis spectroscopy, thermogravimetric analysis and solid-state photoluminescence analysis were carried out on both MOFs. Luminescence sensing experiments reveal that both MOFs have good selective sensing towards Fe³⁺ in aqueous solution.

Crystal engineering of porous coordination networks to enable separation of C2 hydrocarbons

Crystal engineering, the field of chemistry that studies the design, properties, and applications of crystals, is exemplified by the emergence over the past thirty years of porous coordination networks (PCNs), including metal-organic frameworks (MOFs) and hybrid coordination networks (HCNs). PCNs have now come of age thanks to their amenability to design from first principles and how this in turn can result in new materials with task-specific features. Herein, we focus upon how control over the pore chemistry and pore size of PCNs has been leveraged to create a new generation of physisorbents for efficient purification of light hydrocarbons (LHs). The impetus for this research comes from the need to address LH purification processes based upon cryogenic separation, distillation, chemisorption or solvent extraction, each of which is energy intensive. Adsorptive separation by physisorbents (in general) and PCNs (in particular) can offer two advantages over these existing approaches: improved energy efficiency; lower plant size/cost. Unfortunately, most existing physisorbents suffer from low uptake and/or poor sorbate selectivity and are therefore unsuitable for trace separations of LHs including the high volume C2 LHs (C₂H_x, x = 2, 4, 6). This situation is rapidly changing thanks to PCN sorbents that have set new performance benchmarks for several C2 separations. Herein, we review and analyse PCN sorbents with respect to the supramolecular chemistry of sorbent-sorbate binding and detail the crystal engineering approaches that have enabled the exquisite control over pore size and pore chemistry that affords highly selective binding sites. Whereas the structure-function relationships that have emerged offer important design principles, several development roadblocks remain to be overcome.