A Robust Squarate-Based Metal–Organic Framework Demonstrates Record-High Affinity and Selectivity for Xenon over Krypton

Calcium-Based Metal-Organic Framework for Simultaneous Capture of Trace Propyne and Propadiene from Propylene

The simultaneous capture of trace propyne and propadiene from propylene is one of the important but energy demanding industrial processes because of their similar physicochemical properties as well as the ultralow concentration in the mixtures. Herein, a highly stable Ca-based MOF, constructed from an inexpensive precursor (CaCO₃) and rigid squaric acid, is capable of preferentially capturing trace propyne and propadiene with record-high uptake capacities of 2.44 and 2.64 mmol/g at pressures as low as 5 mbar, respectively. Direct multicomponent breakthrough experiments confirm that Ca-based MOF exhibits an excellent performance for simultaneous removal of trace propyne and propadiene from propylene. DFT simulation and in situ single-crystal X-ray diffraction of propadiene- and propyne-adsorbed Ca-based MOFs reveal that the strong affinity of the framework toward two species is ascribed to the multiple types of cooperative binding including π-π stacking and C-H···O interactions. The calcium squarate framework sets a new benchmark for adsorptive purification of propylene, showing great potential in the practical application.

A Semiconducting Bi2O2(C4O4) Coordination Polymer Showing a Photoelectric Response

Inorganic semiconductors are extensively considered to be among the most promising materials to convert solar light into electricity or chemical energy owing to their efficiency in the separation of photoinduced electron/hole. Bismuth oxides, and, in particular, those built up of [Bi₂O₂]²⁺ layers, show an efficient charge separation and, thus, high photocatalytic activities. To explore a possible synergetic effect of bismuth metallic nodes combined with the electron-rich linker squarate, Bi₂O₂(C₄O₄) or IEF-3 (an IMDEA Energy framework) was hydrothermally prepared and adequately characterized. As determined from the X-ray structure, [Bi₂O₂]²⁺ layers are interconnected by squarate ligands, having a pronounced effect of the 6s² lone pair on the bismuth local environment. IEF-3 shows high thermal and chemical robustness at industrially relevant model aggressive media. A large panel of physicochemical methods were applied to recognize IEF-3 as an UV-absorbing n-type semiconductor, showing a photocurrent response comparable to that of α-Bi₂O₃, offering further possibilities for tuning its electrochemical properties by modifying the ligand. In this way, the well-known compositional and structural versatility of coordination polymers may be applied in the future to fine-tune metal-organic semiconductor systems.

Separation of Xe from Kr with Record Selectivity and Productivity in Anion-Pillared Ultramicroporous Materials by Inverse Size-Sieving

The separation of xenon/krypton (Xe/Kr) mixture is of great importance to industry, but the available porous materials allow the adsorption of both, Xe and Kr only with limited selectivity. Herein we report an anion-pillared ultramicroporous material NbOFFIVE-2-Cu-i (ZU-62) with finely tuned pore aperture size and structure flexibility, which for the first time enables an inverse size-sieving effect in separation along with record Xe/Kr selectivity and ultrahigh Xe capacity. Evidenced by single-crystal X-ray diffraction, the rotation of anions and pyridine rings upon contact of larger-size Xe atoms adapts cavities to the shape/size of Xe and allows strong host-Xe interaction, while the smaller-size Kr is excluded. Breakthrough experiments confirmed that ZU-62 has a real practical potential for producing high-purity Kr and Xe from air-separation byproducts, showing record Kr productivity (206 mL g^-1 ) and Xe productivity (42 mL g^-1 , in desorption) as well as good recyclability.

Adsorptive Separation of Acetylene from Ethylene in Isostructural Gallate-Based Metal-Organic Frameworks

The separation of acetylene from ethylene is of paramount importance in the purification of chemical feedstocks for industrial manufacturing. Herein, an isostructural series of gallate-based metal-organic frameworks (MOFs), M-gallate (M=Ni, Mg, Co), featuring three-dimensionally interconnected zigzag channels, the aperture size of which can be finely tuned within 0.3 Å by metal replacement. Controlling the aperture size of M-gallate materials slightly from 3.69 down to 3.47 Å could result in a dramatic enhancement of C₂ H₂ /C₂ H₄ separation performance. As the smallest radius among the studied metal ions, Ni-gallate exhibits the best C₂ H₂ /C₂ H₄ adsorption separation performance owing to the strongest confinement effect, ranking after the state-of-the-art UTSA-200a with a C₂ H₄ productivity of 85.6 mol L^-1 from 1:99 C₂ H₂ /C₂ H₄ mixture. The isostructural gallate-based MOFs, readily synthesized from inexpensive gallic acid, are demonstrated to be a new top-performing porous material for highly efficient adsorption of C₂ H₂ from C₂ H₄ .