Identifying the Gate-Opening Mechanism in the Flexible Metal-Organic Framework UTSA-300

Flexible Microporous Framework for One-Step Acquisition of Ethylene from Ternary C2 Hydrocarbons

One-step purification of ethylene (C2H4) from ternary C2 hydrocarbon mixtures is a crucial task and an enduring challenge because of their similar molecular size and physical properties. Owing to their intriguing structural dynamics, flexible MOFs have attracted more attention for gas adsorption and separation. Herein, we report a flexible MOF FJI-W-66 that exhibits rarely seen "breathing" behaviors for C2 hydrocarbons. Upon activation, the channels of guest-free FJI-W-66a significantly contract to a nearly closed-pore state. FJI-W-66a shows the stepwise adsorption isotherms for C2 hydrocarbons, which suggests the occurrence of structural transformation between less open and more open phases. Breakthrough experiments provide evidence that FJI-W-66a can selectively separate C2H4 from C2H2/C2H4/C2H6 mixtures with different ratios under ambient conditions, realizing the one-step acquisition of C2H4 from ternary C2 hydrocarbons.

Luminescent Porous Organic Crystals for Adsorptive Separation of Toluene and Methylcyclohexane

A butterfly-shaped phenothiazine derivative, PTTCN, was synthesized to obtain pure organic porous crystals for the highly efficient absorptive separation of toluene (Tol) and methylcyclohexane (Mcy). Due to the presence of three polar cyano groups and nonplanar conformation, these molecules self-assembled into a hydrogen-bonded organic framework (X-HOF-5) with distinct cavities capable of accommodating Tol molecules through multiple hydrogen-bonding interactions. Upon solvent removal via heating, the activated X-HOF-5 retained its cavity structure albeit with altered stacking arrangements, accompanied by a remarkable fluorescent color change from cyan to green. X-HOF-5a can undergo a phase transformation into X-HOF-5 upon reabsorption of Tol, while exhibiting no accommodation of Mcy due to the weak intermolecular interaction between PTTCN and Mcy. This suggests that the activated HOF material prefers Tol over Mcy. Moreover, X-HOF-5a may selectively accommodate Tol in a Tol/Mcy equimolar mixture, and the purity of Tol can reach 97% after release from the framework. Additionally, it is noteworthy that the HOF material exhibits recyclability without any discernible loss in performance.

Occurrence, toxicity, impact and removal of selected non-steroidal anti-inflammatory drugs (NSAIDs): A review

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most frequently used pharmaceuticals for human therapy, pet therapeutics, and veterinary feeds, enabling them to enter into water sources such as wastewater, soil and sediment, and seawater. The control of NSAIDs has led to the advent of the novel materials for treatment techniques. Herein, we review the occurrence, impact and toxicity of NSAIDs against aquatic microorganisms, plants and humans. Typical NSAIDs, e.g., ibuprofen, ketoprofen, diclofenac, naproxen and aspirin were detected at high concentrations in wastewater up to 2,747,000 ng L-1. NSAIDs in water could cause genotoxicity, endocrine disruption, locomotive disorders, body deformations, organs damage, and photosynthetic corruption. Considering treatment methods, among adsorbents for removal of NSAIDs from water, metal-organic frameworks (10.7-638 mg g-1) and advanced porous carbons (7.4-400 mg g-1) were the most robust. Therefore, these carbon-based adsorbents showed promise in efficiency for the treatment of NSAIDs.

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C₂H₂- and C₂H₆-selective adsorption behavior, resulting in the potential tandem separation of C₂H₄ from C₂H₂ and C₂H₆ mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Gate Opening without Volume Change Triggers Cooperative Gas Interactions, Underpins an Isotherm Step in Metal-Organic Frameworks

Three halogenated metal-organic frameworks (MOFs) reported recently exhibited a second step in their CO₂ gas adsorption isotherms. The emergence of halogen-bonding interactions beyond a threshold gas pressure between the framework halogen and the CO₂ guest was conjectured to be the underlying reason for the additional step in the isotherm. Our investigation employing periodic density functional theory calculations did not show significant interactions between the halogen and CO₂ molecules. Further, using a combination of DFT-based ab initio molecular dynamics and grand canonical Monte Carlo simulations, we find that the increased separation of framework nitrate pairs facing each other across the pore channel enables the accommodation of an additional CO₂ molecule which is further stabilized by cooperative interactions─an observation that facilely explains the second isotherm step. The increased separation between the nitrate groups can occur without any lattice expansion, consistent with experiments. The results point to a structural feature to achieve this isotherm step in MOFs that neither possess large pores nor exhibit large-scale structural changes such as breathing.