Improving Ethane/Ethylene Separation Performance of Isoreticular Metal-Organic Frameworks via Substituent Engineering

Amino-Functionalized Metal-Organic Frameworks Featuring Ultra-Strong Ethane Nano-Traps for Efficient C2H6/C2H4 Separation

Developing high-performance porous materials to separate ethane from ethylene is an important but challenging task in the chemical industry, given their similar sizes and physicochemical properties. Herein, a new type of ultra-strong C2H6 nano-trap, CuIn(3-ain)4 is presented, which utilizes multiple guest-host interactions to efficiently capture C2H6 molecules and separate mixtures of C2H6 and C2H4. The ultra-strong C2H6 nano-trap exhibits the high C2H6 (2.38 mmol g-1) uptake at 6.25 kPa and 298 K and demonstrates a remarkable selectivity of 3.42 for C2H6/C2H4 (10:90). Additionally, equimolar C2H6/C2H4 exhibited a superior high separation potential ∆Q (2286 mmol L-1) at 298 K. Kinetic adsorption tests demonstrated that CuIn(3-ain)4 has a high adsorption rate for C2H6, establishing it as a new benchmark material for the capture of C2H6 and the separation of C2H6/C2H4. Notably, this exceptional performance is maintained even at a higher temperature of 333 K, a phenomenon not observed before. Theoretical simulations and single-crystal X-ray diffraction provide critical insights into how selective adsorption properties can be tuned by manipulating pore dimensions and geometry. The excellent separation performance of CuIn(3-ain)4 has been confirmed through breakthrough experiments for C2H6/C2H4 gas mixtures.

Metal-Organic Framework Featuring Cubic Caged Structures for One-Step Ethylene Purification from Ethylene/Ethane Mixtures

Separation of C2H6/C2H4 mixtures is of significant importance in the chemical industry but remains a challenge due to the physicochemical similarities of C2H6 and C2H4. Herein, a metal-organic framework (MOF), [Zn4(μ4-O)(PCTF)3]n (Zn-PCTF) (PCTF2-= 5-trifluoromethyl-1H-pyrazole-4-carboxylic), is provided for the removal of C2H6 from C2H6/C2H4 mixtures. Zn-PCTF displays a three-dimensional framework featuring one-dimensional pore channels with periodic bottleneck segments. The well-balanced C2H6 adsorption capacity (79.0 cm3 g-1 at 298 K) and C2H6/C2H4 selectivity (1.8) for Zn-PCTF under ambient conditions boost Zn-PCTF with highly promising potentials for efficient purification of C2H4 from C2H6/C2H4 mixtures, which is verified by the dynamic column breakthrough experiments. The well-matched caged pores and suitable pore chemistry (particularly the presence of abundant Lewis base sites (N, O, and F) on the pore surfaces) for C2H6 account for the high-performance C2H6/C2H4 separation of Zn-PCTF unveiled by computational simulations.

Tailorable Multi-Modular Pore-Space-Partitioned Vanadium Metal-Organic Frameworks for Gas Separation

Currently, few porous vanadium metal-organic frameworks (V-MOFs) are known and even fewer are obtainable as single crystals, resulting in limited information on their structures and properties. Here this work demonstrates remarkable promise of V-MOFs by presenting an extensible family of V-MOFs with tailorable pore geometry and properties. The synthesis leverages inter-modular synergy on a tri-modular pore-partitioned platform. New V-MOFs show a broad range of structural features and sorption properties suitable for gas storage and separation applications for C2H2/CO2, C2H6/C2H4, and C3H8/C3H6. The c/a ratio of the hexagonal cell, a measure of pore shape, is tunable from 0.612 to 1.258. Other tunable properties include pore size from 5.0 to 10.9 Å and surface area from 820 to 2964 m2 g-1. With C2H2/CO2 selectivity from 3.3 to 11 and high uptake capacity for C2H2 from 65.2 to 182 cm3 g-1 (298K, 1 bar), an efficient separation is confirmed by breakthrough experiments. The near-record high uptake for C2H6 (166.8 cm3 g-1) contributes to the promise for C2H6-selective separation of C2H6/C2H4. The multi-module pore expansion enables transition from C3H6-selective to more desirable C3H8-selective separation with extraordinarily high C3H8 uptake (254.9 cm3 g-1) and high separation potential (1.25 mmol g-1) for C3H8/C3H6 (50:50 v/v) mixture.

A Highly Chemically Robust 3D Interpenetrated MOF Heterogeneous Catalyst for the Synthesis of Hantzsch 1,4-Dihydropyridines and Drug Molecules

Metal-organic frameworks (MOFs) have attracted immense attention as efficient heterogeneous catalysts over other solid catalysts, however, their chemical environment instability often limits their catalytic potential. Herein, utilizing a flexible unexplored tetra-acid ligand and employing the mixed ligand approach, a 3D interpenetrated robust framework is strategically developed, IITKGP-51 (IITKGP stands for Indian Institute of Technology Kharagpur), which retained its crystallinity over a wide range of pH solution (4-12). Having ample open metal sites (OMSs), IITKGP-51 is explored as a heterogeneous catalyst in one-pot Hantzsch condensation reaction, with low catalyst loading for a broad range of substrates. The synthesis of drug molecules remains one of the most significant and emergent areas of organic and medicinal chemistry. Considering such practical utility, biologically important Nemadipine B and Nifedipine drug molecules (calcium channel protein inhibitor) are synthesized for the first time by using this catalyst and fully characterized via SC-XRD and other spectroscopic methods. This report inaugurates the usage of a MOF material as a catalyst for the synthesis of drug molecules.

A Copper-Based Metal-Organic Framework for Selective Separation of C2 Hydrocarbons from Methane at Ambient Conditions: Experiment and Simulation

C2 hydrocarbon separation from methane represents a technological challenge for natural gas upgrading. Herein, we report a new metal-organic framework, [Cu2L(DEF)2]·2DEF (UNT-14; H4L = 4,4',4″,4‴-((1E,1'E,1″E,1‴E)-benzene-1,2,4,5-tetrayltetrakis(ethene-2,1-diyl))tetrabenzoic acid; DEF = N,N-diethylformamide; UNT = University of North Texas). The linker design will potentially increase the surface area and adsorption energy owing to π(hydrocarbon)-π(linker)/M interactions, hence increasing C2 hydrocarbon/CH4 separation. Crystallographic data unravel an sql topology for UNT-14, whereby [Cu2(COO)4]···[L]4- paddle-wheel units afford two-dimensional porous sheets. Activated UNT-14a exhibits moderate porosity with an experimental Brunauer-Emmett-Teller (BET) surface area of 480 m2 g-1 (vs 1868 m2 g-1 from the crystallographic data). UNT-14a exhibits considerable C2 uptake capacity under ambient conditions vs CH4. GCMC simulations reveal higher isosteric heats of adsorption (Qst) and Henry's coefficients (KH) for UNT-14a vs related literature MOFs. Ideal adsorbed solution theory yields favorable adsorption selectivity of UNT-14a for equimolar C2Hn/CH4 gas mixtures, attaining 31.1, 11.9, and 14.8 for equimolar mixtures of C2H6/CH4, C2H4/CH4, and C2H2/CH4, respectively, manifesting efficient C2 hydrocarbon/CH4 separation. The highest C2 uptake and Qst being for ethane are also desirable technologically; it is attributed to the greatest number of "agostic" or other dispersion C-H bond interactions (6) vs 4/2/4 for ethylene/acetylene/methane.

Exceptionally High Perfluorooctanoic Acid Uptake in Water by a Zirconium-Based Metal-Organic Framework through Synergistic Chemical and Physical Adsorption

Perfluorooctanoic acid (PFOA) is an environmental contaminant ubiquitous in water resources, which as a xenobiotic and carcinogenic agent, severely endangers human health. The development of techniques for its efficient removal is therefore highly sought after. Herein, we demonstrate an unprecedented zirconium-based MOF (PCN-999) possessing Zr6 and biformate-bridged (Zr6)2 clusters simultaneously, which exhibits an exceptional PFOA uptake of 1089 mg/g (2.63 mmol/g), representing a ca. 50% increase over the previous record for MOFs. Single-crystal X-ray diffraction studies and computational analysis revealed that the (Zr6)2 clusters offer additional open coordination sites for hosting PFOA. The coordinated PFOAs further enhance the interaction between coordinated and free PFOAs for physical adsorption, boosting the adsorption capacity to an unparalleled high standard. Our findings represent a major step forward in the fundamental understanding of the MOF-based PFOA removal mechanism, paving the way toward the rational design of next-generation adsorbents for per- and polyfluoroalkyl substance (PFAS) removal.

Three-Dimensional Homochiral Covalent Organic Frameworks with Intrinsic Chiral Topology

Although a variety of chiral porous framework materials have been reported, there are few examples known to combine molecular chirality, helicity, and three-dimensional (3D) intrinsically chiral topology in one structure, which is beneficial for chirality transfer and amplification. Here, we report the synthesis of the first two 3D covalent organic frameworks (COFs) with an intrinsic chiral qzd topology, which exhibit unusual integration of various homochiral and homohelical features. By imine condensation of 4-connected porphyrin tetraamines and 2-connected enantiopure diene dialdehyde, we prepared two isostructural COFs with a noninterpenetrated qzd topology. The specific geometry and conformation flexibility of the V-shaped diene linker control the alignment of square-planar porphyrin units with rotational linkages and facilitate the creation of homochiral extended porous structures that feature a helical arrangement of porphyrins. Post-synthetic metalation of CCOF 23 with Rh(I) affords a heterogeneous catalyst for the asymmetric Michael addition reaction of aryl boronic acids to 2-cyclohexenone, which shows higher enantioselectivities compared to their homogeneous counterparts, presumably due to the confined effect of helical channels. This finding will provide an impetus to explore multichirality materials, offering new insights into the generation and control of helicity, homochirality, and enantioselectivity in the solid state.

Multivariate Metal-Organic Frameworks Prepared by Simultaneous Metal/Ligand Exchange for Enhanced C2-C3 Selective Recovery from Natural Gas

Recovering light alkanes from natural gas is a critical but challenging process in petrochemical production. Herein, we propose a postmodification strategy via simultaneous metal/ligand exchange to prepare multivariate metal-organic frameworks with enhanced capacity and selectivity of ethane (C2H6) and propane (C3H8) for their recovery from natural gas with methane (CH4) as the primary component. By utilizing the Kuratowski-type secondary building unit of CFA-1 as a scaffold, namely, {Zn5(OAc)4}6+, the Zn2+ metal ions and OAc- ligands were simultaneously exchanged by other transition metal ions and halogen ligands under mild conditions. Inspiringly, this postmodification treatment can give rise to improved capacity for C2H6 and C3H8 without a noticeable increase in CH4 uptake, and consequently, it resulted in significantly enhanced selectivity toward C2H6/CH4 and C3H8/CH4. In particular, by adjusting the species and amount of the modulator, the optimal sample CFA-1-NiCl2-2.3 demonstrated the maximum capacities of C2H6 (5.00 mmol/g) and C3H8 (8.59 mmol/g), increased by 29 and 32% compared to that of CFA-1. Moreover, this compound exhibited excellent separation performance toward C2H6/CH4 and C3H8/CH4, with high uptake ratios of 6.9 and 11.9 at 298 K and 1 bar, respectively, superior to the performance of a majority of the reported MOFs. Molecular simulations were applied to unravel the improved separation mechanism of CFA-1-NiCl2-2.3 toward C2H6/CH4 and C3H8/CH4. Furthermore, remarkable thermal/chemical robustness, moderate isosteric heat, and fully reproducible breakthrough experiments were confirmed on CFA-1-NiCl2-2.3, indicating its great potential for light alkane recovery from natural gas.

Substituent Engineering-Enabled Structural Rigidification and Performance Improvement for C2/CO2 Separation in Three Isoreticular Coordination Frameworks

Construction of porous solid materials applied to the adsorptive removal of CO₂ from C₂ hydrocarbons is highly demanded thanks to the important role C₂ hydrocarbons play in the chemical industry but quite challenging owing to the similar physical parameters between C₂ hydrocarbons and CO₂. In particular, the development of synthetic strategies to simultaneously enhance the uptake capacity and adsorption selectivity is very difficult due to the trade-off effect frequently existing between both of them. In this work, a combination of the dicopper paddlewheel unit and 4-pyridylisophthalate derivatives bearing different substituents afforded an isoreticular family of coordination framework compounds as a platform. Their adsorption properties toward C₂ hydrocarbons and CO₂ were systematically investigated, and subsequent IAST and density functional theory calculations combined with column breakthrough experiments verified their promising potential for C₂/CO₂ separations. Furthermore, the substituent engineering endowed the resulting compounds with simultaneous enhancement of uptake capacity and adsorption selectivity and thus better C₂/CO₂ separation performance compared to their parent compound. The substituent introduction not only mitigated the framework distortion via fixing the ligand conformation for establishment of better permanent porosity required for gas adsorption but also polarized the framework surface for host-guest interaction improvement, thus resulting in enhanced separation performance.

Engineering a Series of Isoreticular Pillared Layer Ultramicroporous MOFs for Gas and Vapor Uptake

The accurate design and systematic engineering of MOFs is a large challenge due to the randomness of the synthesis process. Isoreticular chemistry provides a powerful approach for the regulation of pore environment in a more predictable and precise way to systematically control gas/vapor adsorption performances. Herein, utilizing an effective strategy of altering the "pillared" motifs of pillared layer structures, three isoreticular ultramicroporous MOFs were successfully constructed. Combined with the reported parent MOFs and two other recorded isoreticular MOFs modified with -NH₂ and -CH₃, gas and vapor uptake performances of this family of isoreticular pillared layer MOFs were systematically explored.

Treatment Activity of Ho(III)-Based Coordination Polymer on Liver Cancer by the Inhibition of Vascular Endothelial Growth Factor Signaling Pathway Activity

A new 0D dinuclear coordination polymer [Ho2(L)6(phen)2] (1) was hydrothermally synthesized based on HoCl3·6H2O, organic ligand HL = 3-hydroxybenzoic acid, and the auxiliary ligand phen = 1,10-phenanthroline (L− is the fully deprotonated organic ligand), and full characterization of the structure was performed via the X-ray single-crystal diffraction data. Once this newly synthesized novel compound was achieved, the way it acted inside the liver cancer was examined, and the corresponding mechanism was determined. First, the Cell Counting Kit-8 (CCK-8) method was conducted to analyze the compound activity after the treatment of liver cancer cells. In addition, real-time reverse-transcription polymerase chain reaction (RT-PCR) method was used to examine the in-cell vascular endothelial growth factor (VEGF) signaling pathway activity. The molecular docking simulation showed that the carboxyl and phenol groups contained active binding receptor sites, indicating that Ho complex has excellent biological activity.

Ligand Tailoring Strategy of a Metal-Organic Framework for Optimizing Methane Storage Working Capacities

Methane, as the main component of natural gas, shale gas, and marsh gas, is regarded as an ideal clean energy to replace traditional fossil fuels and reduce carbon emissions. Porous materials with superior methane storage capacities are the key to the wide application of adsorbed natural gas technology in vehicle transportation. In this work, we applied a ligand tailoring strategy to a metal-organic framework (NOTT-101) to fine-tune its pore geometry, which was well characterized by gas and dye sorption measurements. High-pressure methane sorption isotherms revealed that the methane storage performance of the modified NOTT-101 can be effectively improved by decreasing the unusable uptake at 5 bar and increasing the total uptake under high pressures, achieving a substantially high volumetric methane storage working capacity of 190 cm³ (STP) cm^-3 at 298 K and 5-80 bar.

Recent advances in metal-organic frameworks for gas adsorption/separation

The unique structural advantage of metal-organic frameworks (MOFs) determines the great prospect and developability in gas adsorption and separation. Both ligand design and microporous engineering based on crystal structure are significant lever for coping with new application exploration and requirements. Focusing on the designable pore and modifiable frameworks of MOFs, this review discussed the recent advances in the field of gas adsorption and separation, and analyzed the host-guest interaction, structure-performance relations, and the adsorption/separation mechanism from ligand design, skeleton optimization, metal node regulation, and active sites construction. Based on the function-oriented perspective, we summarized the main research recently, and made an outlook based on the focus of microporous MOFs that require further attention in the structure design and industrial application.

Incorporating Fullerenes in Nanoscale Metal-Organic Matrixes: An Ultrasensitive Platform for Impedimetric Aptasensing of Tobramycin

The rational design and preparation of available fullerene@metal-organic matrix hybrid materials are of profound significance in electrochemical biosensing applications due to their unique photoelectric properties. In this work, C₆₀@UiO-66-NH₂ nanocomposites serve as greatly promising materials to modify electrodes and fix aptamers, resulting in a remarkable electrochemical aptasensor for impedimetric sensing of tobramycin (TOB). Nanoscale composites have preferable electroactivity and small particle size with more exposed functional sites, such as Zr(IV) and -NH₂, to immobilize aptamers for enhanced detection performance. As we know, most of the electrochemical impedance aptasensors require a long time to complete the detection process, but this prepared biosensor shows the rapid quantitative identification of target TOB within 4 min. This work expands the synthesis of functional fullerene@metal-organic matrix hybrid materials in electrochemical biosensing applications.

Recent progress on porous MOFs for process-efficient hydrocarbon separation, luminescent sensing, and information encryption

Metal-organic frameworks (MOFs), as an emerging class of porous materials, excel in designability, regulatability, and modifiability in terms of their composition, topology, pore size, and surface chemistry, thus affording a huge potential for addressing environment and energy-related challenges. In particular, MOFs can be applied as porous adsorbents for the purification of industrially important hydrocarbons through certain process-efficient separation schemes based on selectivity-reversed adsorption and multicomponent separation. Moreover, the vast combination possibilities and controllable and engineerable luminescent units of MOFs make them a versatile platform to develop functionally tailored materials for luminescent sensing and optical data encryption. In this feature article, we summarize the recent progress in the use of porous MOFs for the separation and purification of acetylene (C₂H₂) and ethylene (C₂H₄) based on selectivity-reversed adsorption and multicomponent separation strategies. Moreover, we highlight the advances over the past three years in the field of MOF-based luminescent materials for thermometry, turn-on sensing, and information encryption.

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Construction of two novel non-penetrating Co-MOFs derived from designed 2,4,6-tri(2,4-dicarboxyphenyl) pyridine: synthesis, structure and gas adsorption properties

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