Xili Cui

Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene

Separating one organic from another Separating closely related organic molecules is a challenge (see the Perspective by Lin).The separation of acetylene from ethylene is needed in high-purity polymer production. Cui et al. developed a copper-based metal-organic framework with hexafluorosilicate and organic linkers designed to have a high affinity for acetylene. These materials, which capture four acetylene molecules in each pore, successfully separated acetylene from mixtures with ethylene. Propane and propylene are both important feedstock chemicals. Their physical and chemical similarity, however, requires energy-intense processes to separate them. Cadiau et al. designed a fluorinated porous metal-organic framework material that selectively adsorbed propylene, with the complete exclusion of propane. Science, this issue pp. 141 and 137; see also p. 121 A copper-based metal-organic framework with hexafluorosilicate linkers can separate acetylene from ethylene. The trade-off between physical adsorption capacity and selectivity of porous materials is a major barrier for efficient gas separation and purification through physisorption. We report control over pore chemistry and size in metal coordination networks with hexafluorosilicate and organic linkers for the purpose of preferential binding and orderly assembly of acetylene molecules through cooperative host-guest and/or guest-guest interactions. The specific binding sites for acetylene are validated by modeling and neutron powder diffraction studies. The energies associated with these binding interactions afford high adsorption capacity (2.1 millimoles per gram at 0.025 bar) and selectivity (39.7 to 44.8) for acetylene at ambient conditions. Their efficiency for the separation of acetylene/ethylene mixtures is demonstrated by experimental breakthrough curves (0.73 millimoles per gram from a 1/99 mixture).

Hydrothermal evolution, optical and electrochemical properties of hierarchical porous hematite nanoarchitectures

Hollow or porous hematite (α-Fe2O3) nanoarchitectures have emerged as promising crystals in the advanced materials research. In this contribution, hierarchical mesoporous α-Fe2O3 nanoarchitectures with a pod-like shape were synthesized via a room-temperature coprecipitation of FeCl3 and NaOH solutions, followed by a mild hydrothermal treatment (120°C to 210°C, 12.0 h). A formation mechanism based on the hydrothermal evolution was proposed. β-FeOOH fibrils were assembled by the reaction-limited aggregation first, subsequent and in situ conversion led to compact pod-like α-Fe2O3 nanoarchitectures, and finally high-temperature, long-time hydrothermal treatment caused loose pod-like α-Fe2O3 nanoarchitectures via the Ostwald ripening. The as-synthesized α-Fe2O3 nanoarchitectures exhibit good absorbance within visible regions and also exhibit an improved performance for Li-ion storage with good rate performance, which can be attributed to the porous nature of Fe2O3 nanoarchitectures. This provides a facile, environmentally benign, and low-cost synthesis strategy for α-Fe2O3 crystal growth, indicating the as-prepared α-Fe2O3 nanoarchitectures as potential advanced functional materials for energy storage, gas sensors, photoelectrochemical water splitting, and water treatment.

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.

Sorting of C4 Olefins with Interpenetrated Hybrid Ultramicroporous Materials by Combining Molecular Recognition and Size-Sieving

C4 olefin separations present one of the great challenges in hydrocarbon purifications owing to their similar structures, thus a single separation mechanism often met with limited success. Herein we report a series of anion-pillared interpenetrated copper coordination for which the cavity and functional site disposition can be varied in 0.2 Å scale increments by altering the anion pillars and organic linkers (GeFSIX-2-Cu-i (ZU-32), NbFSIX-2-Cu-i (ZU-52), GeFSIX-14-Cu-i (ZU-33)), which enable selective recognition of different C4 olefins. In these materials the rotation of the organic linkers is controlled to create a contracted flexible pore window that enables the size-exclusion of specific C4 olefins, while still adsorbing significant amounts of 1,3-butadiene (C4 H6 ) or 1-butene (n-C4 H8 ). Combining the molecular recognition and size-sieving effect, these materials unexpectedly realized the sieving of C4 H6 /n-C4 H8 , C4 H6 /iso-C4 H8 , and n-C4 H8 /iso-C4 H8 with high capacity.

Ultrahigh and Selective SO2 Uptake in Inorganic Anion‐Pillared Hybrid Porous Materials

The efficient capture of SO2 is of great significance in gas-purification processes including flue-gas desulfurization and natural-gas purification, but the design of porous materials with high adsorption capacity and selectivity of SO2 remains very challenging. Herein, the selective recognition and dense packing of SO2 clusters through multiple synergistic host-guest and guest-guest interactions by controlling the pore chemistry and size in inorganic anion (SiF62- , SIFSIX) pillared metal-organic frameworks is reported. The binding sites of anions and aromatic rings in SIFSIX materials grasp every atom of SO2 firmly via Sδ+ ···Fδ- electrostatic interactions and Oδ- ···Hδ+ dipole-dipole interactions, while the guest-guest interactions between SO2 molecules further promote gas trapping within the pore space, which is elucidated by first-principles density functional theory calculations and powder X-ray diffraction experiments. These interactions afford new benchmarks for the highly efficient removal of SO2 from other gases, even if at a very low SO2 concentration. Exceptionally high SO2 capacity of 11.01 mmol g-1 is achieved at atmosphere pressure by SIFSIX-1-Cu, and unprecedented low-pressure SO2 capacity is obtained in SIFSIX-2-Cu-i (4.16 mmol g-1 SO2 at 0.01 bar and 2.31 mmol g-1 at 0.002 bar). More importantly, record SO2 /CO2 selectivity (86-89) and excellent SO2 /N2 selectivity (1285-3145) are also achieved. Experimental breakthrough curves further demonstrate the excellent performance of these hybrid porous materials in removing low-concentration SO2 .

A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Propyne/propylene (C3 H4 /C3 H6 ) separation is a critical process for the production of polymer-grade C3 H6 . However, optimization of the structure of porous materials for the highly efficient removal of C3 H4 from C3 H6 remains challenging due to their similar structures and ultralow C3 H4 concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF62- = SIFSIX, NbOF52- = NbOFFIVE) can serve as highly selective C3 H4 traps for the removal of trace C3 H4 from C3 H6 . Especially, it is revealed that the pyrazine-based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1-0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single-molecule trap for C3 H4 molecule. The pyrazine-based single-molecule trap enables extremely high C3 H4 uptake under ultralow concentration (2.65 mmol g-1 at 3000 ppm, one C3 H4 per unit cell) and record selectivity over C3 H6 at 298 K (>250). The single-molecule binding mode for C3 H4 within ultramicroporous material is validated by X-ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion-pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C3 H4 (1000 ppm on SIFSIX-3-Ni, and 10 000 ppm on SIFSIX-2-Cu-i) from C3 H6 .

An amino-coordination metal-organic framework for highly selective C2H2/CH4 and C2H2/C2H4 separations through the appropriate control of window sizes

The efficient separation of C2H2 versus C2H4 and CH4 to obtain high-purity C2H2 and C2H4 is of significance for making full, economic use of these raw chemicals. Herein, an amino-coordination microporous metal–organic framework ZJU-198, ZnL·DMF (ZJU = Zhejiang University, L = (2E,2E′)-3,3′-(5-amino-1,3-phenylene)diacrylic acid, DMF = N,N′-dimethylformamide), has been demonstrated as a valuable adsorbent for C2H2/C2H4 and C2H2/CH4 separations. The activated ZJU-198a exhibits moderate C2H2 uptakes (99.4 cm3 cm−3 for 273 K and 98.4 cm3 cm−3 for 298 K under 1.0 bar) and moderately high C2H2/C2H4 selectivity (5.8 to 7.7 at 273 K and 4.8 to 7.2 at 298 K). Specifically, the C2H2/CH4 selectivity of ZJU-198a reaches up to 497.9 and 391.1 at 273 K and 298 K, respectively. To the best of our knowledge, the C2H2/CH4 selectivity coefficients of ZJU-198a at both 298 K and 273 K are the highest values among the reported metal–organic frameworks, meaning that there is bright potential for ZJU-198a in hydrocarbon storage and separation.