Enhancing Multicomponent Metal–Organic Frameworks for Low Pressure Liquid Organic Hydrogen Carrier Separations

Redox-Active Mixed-Linker Metal-Organic Frameworks with Switchable Semiconductive Characteristics for Tailorable Chemiresistive Sensing

Metal-organic frameworks (MOFs), with diverse metal nodes and designable organic linkers, offer unique opportunities for the rational engineering of semiconducting properties. In this work, we report a mixed-linker conductive MOF system with both tetrathiafulvalene and Ni-bis(dithiolene) moieties, which allows the fine-tuning of electronic structures and semiconductive characteristics. By continuously increasing the molar ratio between tetrathiafulvalene and Ni-bis(dithiolene), the switching of the semiconducting behaviors from n-type to p-type was observed along with an increase in electrical conductivity by 3 orders of magnitude (from 2.88×10^-7  S m^-1 to 9.26×10^-5  S m^-1 ). Furthermore, mixed-linker MOFs were applied for the chemiresistive detection of volatile organic compounds (VOCs), where the sensing performance was modulated by the corresponding linker ratios, showing synergistic and nonlinear modulation effects.

Impact of Pore Flexibility in Imine-Linked Covalent Organic Frameworks on Benzene and Cyclohexane Adsorption

This work focuses on the impact of covalent organic frameworks' (COFs) pore flexibility in the adsorption and separation of benzene and cyclohexane. With this aim, we have selected the imine-linked 3D COFs COF-300 and LZU-111 as examples of flexible and rigid frameworks, respectively. Optimized syntheses at room temperature or in solvothermal conditions enabled us to selectively isolate the narrow-pore form of COF-300 (COF-300-rt) or a mixture of the narrow-pore and a larger-pore form (COF-300-st), respectively, with different textural properties (BET specific surface area = 39 or 1270 m²/g, respectively, from N₂ adsorption at 77 K). In the case of LZU-111, only the room temperature route was successful, leading to the known microporous framework. COF-300-rt, COF-300-st, and LZU-111 were studied for benzene and cyclohexane adsorption and separation in static and dynamic conditions. At 298 K and 1 bar, these COFs adsorb more benzene (251, 221, and 214 cm³/g STP, respectively) than cyclohexane (175, 133, and 164 cm³/g STP, respectively). Moreover, the benzene and cyclohexane isotherms of COF-300-rt and COF-300-st are characterized by steps, as expected with a flexible material. Indeed, in situ powder X-ray diffraction experiments on benzene- and cyclohexane-impregnated batches enabled us to trap, for the first time, a sequence of forms of COF-300 with different pore aperture, rationalizing the stepped hysteretic isotherms. Finally, benzene/cyclohexane separation was evaluated using a benzene/cyclohexane 50:50 v/v flow at different temperatures (T = 298, 323, and 348 K): LZU-111 does not selectively retain any of the two components, while COF-300 exhibits stronger benzene-COF interactions also in dynamic conditions.

Three-in-One C2 H2 -Selectivity-Guided Adsorptive Separation across an Isoreticular Family of Cationic Square-Lattice MOFs

Energy-efficient selective physisorption driven C₂ H₂ separation from industrial C2-C1 impurities such as C₂ H₄ , CO₂ and CH₄ is of great importance in the purification of downstream commodity chemicals. We address this challenge employing a series of isoreticular cationic metal-organic frameworks, namely iMOF-nC (n=5, 6, 7). All three square lattice topology MOFs registered higher C₂ H₂ uptakes versus the competing C2-C1 gases (C₂ H₄ , CO₂ and CH₄ ). Dynamic column breakthrough experiments on the best-performing iMOF-6C revealed the first three-in-one C₂ H₂ adsorption selectivity guided separation of C₂ H₂ from 1:1 C₂ H₂ /CO₂ , C₂ H₂ /C₂ H₄ and C₂ H₂ /CH₄ mixtures. Density functional theory calculations critically examined the C₂ H₂ selective interactions in iMOF-6C. Thanks to the abundance of square lattice topology MOFs, this study introduces a crystal engineering blueprint for designing C₂ H₂ -selective layered metal-organic physisorbents, previously unreported in cationic frameworks.

Harnessing Shape Complementarity for Upgraded Cyclohexane Purification through Adaptive Bottlenecked Pores in an Imidazole-Containing MOF

Shape complementarity is a biological craft for precisely binding substrates at protein-protein interfaces. An analogy to such a function can be drawn conceptually for crystalline porous solids; yet the manifested entities are rare in reticular chemistry. The bottleneck-shaped pores carved out of a metal-organic framework, Zn(MIBA)₂ (aka. MAF-stu-13), can perfectly accommodate benzene molecules. Remarkably, its framework adapts to the optimal guest binding-the enhanced host-guest interactions in the neck in turn minimize the guest-guest repulsion in the pore to the extent it turns into attraction-as demonstrated by the combined X-ray structural and DFT computational studies. This adaptive material can be used for liquid-phase production of ultrahigh-purity (≥99 %) cyclohexane, achieving a balance between uptake capacity and separation selectivity and surpassing the performances of other porous and nonporous crystals reported recently (e.g. product purity 99.4 % vs. 97.5 % to date).