Rui Biao Lin

UTSA-74: A MOF-74 Isomer with Two Accessible Binding Sites per Metal Center for Highly Selective Gas Separation

A new metal-organic framework Zn2(H2O)(dobdc)·0.5(H2O) (UTSA-74, H4dobdc = 2,5-dioxido-1,4-benzenedicarboxylic acid), Zn-MOF-74/CPO-27-Zn isomer, has been synthesized and structurally characterized. It has a novel four coordinated fgl topology with one-dimensional channels of about 8.0 Å. Unlike metal sites in the well-established MOF-74 with a rod-packing structure in which each of them is in a five coordinate square pyramidal coordination geometry, there are two different Zn(2+) sites within the binuclear secondary building units in UTSA-74 in which one of them (Zn1) is in a tetrahedral while another (Zn2) in an octahedral coordination geometry. After activation, the two axial water molecules on Zn2 sites can be removed, generating UTSA-74a with two accessible gas binding sites per Zn2 ion. Accordingly, UTSA-74a takes up a moderately high and comparable amount of acetylene (145 cm(3)/cm(3)) to Zn-MOF-74. Interestingly, the accessible Zn(2+) sites in UTSA-74a are bridged by carbon dioxide molecules instead of being terminally bound in Zn-MOF-74, so UTSA-74a adsorbs a much smaller amount of carbon dioxide (90 cm(3)/cm(3)) than Zn-MOF-74 (146 cm(3)/cm(3)) at room temperature and 1 bar, leading to a superior MOF material for highly selective C2H2/CO2 separation. X-ray crystal structures, gas sorption isotherms, molecular modeling, and simulated and experimental breakthroughs comprehensively support this result.

Flexible-Robust Metal-Organic Framework for Efficient Removal of Propyne from Propylene

The removal of trace amounts of propyne from propylene is critical for the production of polymer-grade propylene. We herein report the first example of metal-organic frameworks of flexible-robust nature for the efficient separation of propyne/propylene mixtures. The strong binding affinity and suitable pore confinement for propyne account for its high uptake capacity and selectivity, as evidenced by neutron powder diffraction studies and density functional theory calculations. The purity of the obtained propylene is over 99.9998%, as demonstrated by experimental breakthrough curves for a 1/99 propyne/propylene mixture.

An Ideal Molecular Sieve for Acetylene Removal from Ethylene with Record Selectivity and Productivity

Realization of ideal molecular sieves, in which the larger gas molecules are completely blocked without sacrificing high adsorption capacities of the preferred smaller gas molecules, can significantly reduce energy costs for gas separation and purification and thus facilitate a possible technological transformation from the traditional energy-intensive cryogenic distillation to the energy-efficient, adsorbent-based separation and purification in the future. Although extensive research endeavors are pursued to target ideal molecular sieves among diverse porous materials, over the past several decades, ideal molecular sieves for the separation and purification of light hydrocarbons are rarely realized. Herein, an ideal porous material, SIFSIX-14-Cu-i (also termed as UTSA-200), is reported with ultrafine tuning of pore size (3.4 Å) to effectively block ethylene (C2 H4 ) molecules but to take up a record-high amount of acetylene (C2 H2 , 58 cm3 cm-3 under 0.01 bar and 298 K). The material therefore sets up new benchmarks for both the adsorption capacity and selectivity, and thus provides a record purification capacity for the removal of trace C2 H2 from C2 H4 with 1.18 mmol g-1 C2 H2 uptake capacity from a 1/99 C2 H2 /C2 H4 mixture to produce 99.9999% pure C2 H4 (much higher than the acceptable purity of 99.996% for polymer-grade C2 H4 ), as demonstrated by experimental breakthrough curves.

Separation of C2/C1 hydrocarbons through a gate-opening effect in a microporous metal–organic framework

A flexible metal–organic framework (MOF) [Mn(INA)2]·MeOH (1) (INA− = isonicotinate) has been solvothermally synthesized. Single-crystal X-ray diffraction reveals that compound 1 features a 3D microporous framework containing one-dimensional channels. The activated phase 1a displays permanent porosity with a Brunauer–Emmett–Teller (BET) surface area of 236 m2 g−1. Gas sorption analyses reveal that 1a exhibits interesting gate-opening hydrocarbon sorption behavior with considerable C2 uptake capacities but a negligible amount for CH4 under ambient conditions. Selectivity calculation and breakthrough experiment comprehensively demonstrate that 1a has remarkably high selectivity towards C2 hydrocarbons over CH4 under ambient conditions.