Ideal Cage-like Pores for Molecular Sieving of Butane Isomers with High Purity and Record Productivity

n-C4H10 and iso-C4H10 are both important petrochemical raw materials. Considering the coexistence of the isomers in the production process, it is necessary to achieve their efficient separation through an economical way. However, to obtain high-purity n-C4H10 and iso-C4H10 in one-step separation process, developing iso-C4H10-exclusion adsorbents with high n-C4H10 adsorption capacity is crucial. Herein, we report a cage-like MOF (SIFSIX-Cu-TPA) with small windows and large cavities which can selectively allow smaller n-C4H10 enter the pore and accommodate a large amount of n-C4H10 simultaneously. Adsorption isotherms reveal that SIFSIX-Cu-TPA not only completely excludes iso-C4H10 in a wide temperature range, but also exhibits a very high n-C4H10 adsorption capacity of 94.2 cm3 g-1 at 100 kPa and 298 K, which is the highest value among iso-C4H10-exclusion-type adsorbents. Breakthrough experiments show that SIFSIX-Cu-TPA has excellent n/iso-C4H10 separation performance and can achieve a record-high productivity of iso-C4H10 (3.2 mol kg-1) with high purity (>99.95 %) as well as 3.0 mol kg-1 of n-C4H10 (>99 %) in one separation circle. More importantly, SIFSIX-Cu-TPA can realize the efficient separation of butanes at different flow rates, temperatures, as well as under high humid condition, which indicates that SIFSIX-Cu-TPA can be deemed as an ideal platform for industrial butane isomers separation.

Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure with dia topology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could not only stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility due to its weak intermolecular interactions (so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was exclusively confirmed by gas sorption isotherms and single-crystal X-ray diffraction studies, showing that the flexible pore pockets can be opened by C3H8 and n-C4H10 molecules rather by C2H6 and CH4. This leads to notably higher C3H8 and n-C4H10 uptakes with enhanced selectivities than C2H6 over CH4 under ambient conditions, affording one of the highest n-C4H10/CH4 selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-C4H10 can induce an obvious framework expansion along with pore pocket opening to improve n-C4H10 uptake and selectivity, while not for C2H6 adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.

Theoretical investigation of C1-C4 hydrocarbons adsorption and separation in a porous metallocavitand

The purification of light hydrocarbons is one of the most important chemical processes globally which consumes substantial energy. Porous materials are likely to improve the efficiency of the separation process by acting as regenerable solid adsorbents. To investigate such translational systems, the underlying mechanism of adsorption in the porous materials must be taken into account. Herein we report the adsorption and selective separation of C1-C4 hydrocarbons in the coinage metal-based macrocyclic metallocavitand Pillarplex, which exhibits excellent performance in the adsorption of CH4 at the ambient conditions with a binding energy of -17.9 kcal mol-1. In addition, the endohedral adsorption of C2-C4 hydrocarbon is impressive. The CH4, C2H4, C3H4, and 1,3-butadiene have potential uptake of 2.57, 4.26, 3.60, and 2.95 mmol g-1, respectively at ambient conditions are highest from their respective isomers. Selective separation of C1-C4 hydrocarbons is studied using ideal adsorption solution theory demonstrating its potential for one-step purification of C1-C3 hydrocarbons.

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.

Rational Construction and Performance Regulation of an In(III)-Tetraisophthalate Framework for One-Step Adsorption-Phase Purification of C2H4 from C2 Hydrocarbons

The development of porous materials for ethylene (C₂H₄) separation and purification, a very important separation process in the chemical industry, is urgently needed but quite challenging. In particular, the realization of selectivity-reversed adsorption (namely, C₂H₄ is not preferentially adsorbed) and the simultaneous capture of multinary coexisting impurities such as ethane (C₂H₆) and acetylene (C₂H₂) will significantly simplify process design and reduce energy and cost consumption, but such porous materials are quite difficult to design and have not yet been fully explored. In this work, by employing an aromatic-rich bithiophene-based tetraisophthalate ligand, we solvothermally fabricated an anionic In(III)-based framework termed ZJNU-115 featuring In(COO)₄ as an inorganic secondary building unit as well as one-dimensional channels. Due to the absence of unsaturated metallic sites, together with aromatic-rich channel surface decorated with abundant hydrogen-bonding acceptors of carboxylate oxygen and thiophene sulfur atoms, desolvated ZJNU-115 exhibited an unusual adsorption relationship with respect to C₂ hydrocarbons, namely, simultaneous and preferable capture of C₂H₆ and C₂H₂ over C₂H₄ at the temperatures investigated, thus representing a rare metal-organic framework (MOF) with the promising potential for one-step adsorption-phase purification of C₂H₄ from a trinary C₂ hydrocarbon mixture. Compared to a few of the MOFs reported for such an application, ZJNU-115 displayed simultaneously good adsorption selectivities of both C₂H₂ and C₂H₆ over C₂H₄. Furthermore, its separation potential can be postsynthetically tailored by substituting dimethylammonium (Me₂NH₂⁺) counterions with tetraalkyl ammonium ions (NR₄⁺; R = Me, Et, or n-Pr). More importantly, ZJNU-115 was stable in various organic solvents as well as aqueous solutions with pH values ranging from 5 to 9, thus laying a solid foundation for its practical applications. The design principle and the performance regulation strategy adopted in this work will offer valuable guidance for the contrapuntal construction of porous MOFs employed for direct multicomponent purification of C₂H₄ with improved performance.

Two Pyrene-Based Metal-Organic Frameworks for Chemiluminescence

Fluorescent agents play an important role in the peroxyoxalate chemiluminescence system. However, the effect of different frameworks on chemiluminescence (CL) has not been explored. Herein two pyrene-based metal-organic frameworks (MOFs), [Pb₂L]_n·2nDMA·2nH₂O (1) and [(Ca₂L)·(DMF)₃]_n·2.5nDMF·6nH₂O (2) (H₄L = 5,5'-(-pyrene-1,6-diyl)-diisophthalic acid; DMA = N,N'-dimethylacetamide; DMF = N,N'-dimethylformamide), have been successfully synthesized and are applied to CL. They both exhibit strong and lasting emission that is visible to the naked eye and is significantly stronger than that of the ligand. More importantly, compared with 2, 1 has notably better CL performance. We infer that the reason may be that 1 has higher stability and larger open channels, which can avoid the aggregation of organic ligands as well as provide an effective pathway for the active substance to diffuse into the channels.

Building a robust 3D Ca-MOF by a new square Ca4O SBU for purification of natural gas

For the first time, a new square Ca4O SBU is introduced into a 3D Ca-MOF, ([MeNH2]2[Ca4O(MTB)2(EtOH)4])·(solvent)n (1), to generate a (4,8)-connected flu-topology structure. Compound 1 exhibits selective adsorption of C3 and C2 hydrocarbons and CO2 over CH4 with especially high IAST selectivities for C3 hydrocarbons over CH4 (at 15/85 and 50/50 ratio) at 298K and 1 bar.

Ti4(embonate)6 Cage-Ligand Strategy on the Construction of Metal-Organic Frameworks with High Stability and Gas Sorption Properties

Herein we report an efficient strategy to construct cage-based metal-organic frameworks (MOFs) via the assembly of Ti₄L₆ (L = embonate) cages and N-contained ligands with Mn²⁺ and Zn²⁺ ions, respectively, and two Ti₄L₆-cage-based MOFs (PTC-219 and PTC-220) with high stability and gas sorption properties have been generated through two-step reactions, respectively.

Rational construction and remarkable gas adsorption properties of a HKUST-1-like tbo-type MOF based on a tetraisophthalate linker

A condensed version of tetraisophthalate MOF MFM-181 was rationally designed and synthesized based on ligand contraction and conformation preorganization strategy, exhibiting the promising potential for the separation of C₂H₂ and CO₂ from CH₄.