Search

Cage‐like metal–organic frameworks (MOFs) are promising for hexane isomer separation, but their aperture sizes are difficult to control precisely. Herein, a molecular valve strategy is proposed to fine‐tune the aperture of cage‐like MOFs, thereby enhancing their separation performance for hexane isomers. Three novel isostructural cage‐like MOFs, namely Cu‐MO4‐TPA, are synthesized using different oxometallate anions (MO42−, M = Cr, Mo, and W) and the ligand tri(pyridin‐4‐yl)amine (TPA). The different oxometallate anions induce varying degrees of twisting in the TPA ligand, leading to sub‐angstrom tuning in the aperture size of the MOFs. The materials can separate hexane isomers based on their degree of branching, with the smallest aperture material (Cu‐MoO4‐TPA) showing molecular sieving of di‐branched isomers. Adsorption isotherms, kinetic, and breakthrough measurements, Monte Carlo, and density functional theory calculations confirm the aperture size differences result in superior separation of hexane isomers by molecular sieving on Cu‐MoO4‐TPA. The results demonstrate the effectiveness of molecular valve strategy for fine‐tuning MOF aperture size for selective separation applications. [ABSTRACT FROM AUTHOR]

The designability and ultrahigh stability of zirconium–organic frameworks make them attractive adsorbents for noble gases xenon (Xe) and krypton (Kr), but their Xe/Kr separation performance needs to be further enhanced. In this study, we rationally control the topology and porosity of zirconium–fumarate frameworks by simply changing the synthesis conditions, and successfully construct an adsorbent (named as MIP‐203‐F) with one‐dimensional pore instead of the original cage‐like fcu metal–organic framework MOF‐801. The Xe/Kr separation performance of MIP‐203‐F is thoroughly evaluated by isotherm measurements and breakthrough experiments, while the adsorption mechanism is elucidated in detail by Monte Carlo and density functional theory calculations. Due to the uniform pore with suitable size and abundant polarization groups, MIP‐203‐F can differentially polarize and recognize atomic Xe/Kr gases, and establishes a new record among zirconium–organic frameworks for the capture and separation of Xe/Kr. [ABSTRACT FROM AUTHOR]

Efficient separation of acetylene (C2H2)/ethylene (C2H4) and acetylene/carbon dioxide (CO2) by adsorption is an industrially promising process, but adsorbents capable of simultaneously capturing trace acetylene from ethylene and carbon dioxide are scarce. Herein, a gate‐opening effect on three isomorphous flexible metal–organic frameworks (MOFs) named Co(4‐DPDS)2MO4 (M = Cr, Mo, W; 4‐DPDS = 4,4‐dipyridyldisulfide) is modulated by anion pillars substitution. The shortest CrO42− strengthens intraframework hydrogen bonding and thus blocks structural transformation after activation, striking a good balance among working capacity, separation selectivity, and trace impurity removal of flexible MOFs out of nearly C2H2/C2H4 and C2H2/CO2 molecular sieving. The exceptional separation performance of Co(4‐DPDS)2CrO4 is confirmed by dynamic breakthrough experiments. It reveals the specific threshold pressures control in anion‐pillared flexible materials enabled elimination of the impurity leakage to realize high purity products through precise control of the intraframework interaction. The adsorption mechanism and multimode structural transformation property are revealed by both calculations and crystallography studies. This work demonstrates the feasibility of modulating flexibility for controlling gate‐opening effect, especially for some cases of significant aperture shrinkage after activation. [ABSTRACT FROM AUTHOR]

Adsorbents executing molecular sieving mechanisms for the efficient separation of n‐hexane (C6) alkane isomers require delicate pore size control, but afford unsatisfactory single‐component separations according to their branch degrees. Herein, we report a novel oxygenate‐pillared microporous adsorbent, MoOFOUR‐Co‐tpb, ([Co(tpb)2MoO4], tpb = 1,2,4,5‐tetra(pyridin‐4‐yl) benzene), with three gourd‐shaped channels for dual pore‐size sieving of C6 isomers. In particular, MoOFOUR‐Co‐tpb excludes 2,2‐dimethylbutane, while 3‐methylpentane (3MP) can enter one channel showing a high uptake of 82.6 mg g−1, contrasting to the n‐hexane (nHEX) adsorption by two channels (136 mg g−1). This dual pore‐size control strategy renders a record high equilibrium–kinetic combined selectivity for nHEX/3MP (30.2). Moreover, three‐ and five‐component breakthrough experiments confirm the practical separation performances and cycling stability. Multiple theoretical simulations reveal the separation mechanism and adsorption sites. [ABSTRACT FROM AUTHOR]

Adsorptive separation of xenon (Xe) and krypton (Kr) is a promising technique but remains a daunting challenge since they are atomic gases without dipole or quadruple moments. Herein we report a strategy for fabricating angular anion‐pillared materials featuring shell‐like Xe nano‐traps, which provide a cooperative effect conferred by the pore confinement and multiple specific interactions. The perfect permanent pore channel (4–5 Å) of Ni(4‐DPDS)2MO4 (M=Cr, Mo, W) can host Xe atoms efficiently even at ultra‐low concentration (400 ppm Xe), showing the second‐highest selectivity of 30.2 in Ni(4‐DPDS)2WO4 and excellent Xe adsorption capacity in Ni(4‐DPDS)2CrO4 (15.0 mmol kg−1). Crystallography studies and DFT‐D calculations revealed the energy favorable binding sites and angular anions enable the synergism between optimal pore size and polar porosity for boosting Xe affinity. Dynamic breakthrough experiments demonstrated three MOFs as efficient adsorbents for Xe/Kr separation. [ABSTRACT FROM AUTHOR]