The structural diversity of three-dimensional (3D) covalent organic frameworks (COFs) are limited as there are only a few choices of building units with multiple symmetrically distributed connection sites. To date, 4 and 6-connected stereoscopic nodes with T d , D 3h , D 3d and C 3 symmetries have been mostly reported, delivering limited 3D topologies. We propose an efficient approach to expand the 3D COF repertoire by introducing a high-valency quadrangular prism (D 4h ) stereoscopic node with a connectivity of eight, based on which two isoreticular 3D imine-linked COFs can be created. Low-dose electron microscopy allows the direct visualization of their 2-fold interpenetrated bcu networks. These 3D COFs are endowed with unique pore architectures and strong molecular binding sites, and exhibit excellent performance in separating C 2 H 2 /CO 2 and C 2 H 2 /CH 4 gas pairs. The introduction of highvalency stereoscopic nodes would lead to an outburst of new topologies for 3D COFs.
Adsorptive separation of propylene (C3H6) from propane (C3H8), which could deal with energy-intensive cryogenic distillation technologies, remains challenging due to their similar physiochemical properties. Herein, we present a pure silica zeolite with ordered silanols (OSs), whose crystallographic structure was unraveled by the advanced three-dimensional electron diffraction (3D ED), displaying the highly efficient separation of propylene from propane under ambient conditions. The 3D ED technique enables us to investigate its 8-ring pore opening transformation from the round one to the elliptical one during the removal of organic structure-directing agents. Such unique elliptical 8-ring pore openings can exclude larger-size propane and only adsorb propylene. Its C3H6/C3H8 separation performance is also confirmed by column breakthrough experiments, showing a high dynamic adsorption capacity of 53.36 cm3 g–1 for C3H6 but negligible C3H8 under ambient conditions. The dynamic capacity for C3H6 is superior to that of the well-known pure silica DDR-type zeolite (31.07 cm3 g–1). The density functional theory calculation demonstrates that the adsorbed propylene is distributed in the heart-shaped cavity and has a weak interaction with the OSs.
The structural diversity of three-dimensional (3D) covalent organic frameworks (COFs) are limited as there are only a few choices of building units with multiple symmetrically distributed connection sites. To date, 4 and 6-connected stereoscopic nodes with T d , D 3h , D 3d and C 3 symmetries have been mostly reported, delivering limited 3D topologies. We propose an efficient approach to expand the 3D COF repertoire by introducing a high-valency quadrangular prism (D 4h ) stereoscopic node with a connectivity of eight, based on which two isoreticular 3D imine-linked COFs can be created. Low-dose electron microscopy allows the direct visualization of their 2-fold interpenetrated bcu networks. These 3D COFs are endowed with unique pore architectures and strong molecular binding sites, and exhibit excellent performance in separating C 2 H 2 /CO 2 and C 2 H 2 /CH 4 gas pairs. The introduction of highvalency stereoscopic nodes would lead to an outburst of new topologies for 3D COFs.
Integrating high‐valence metal sites into transition metal‐based oxygen evolution reaction (OER) catalysts turns out to be a prevailing solution to replacing noble metal‐based electrocatalysts. However, stabilizing the thermodynamically unfavorable high‐valence metal sites within the electrocatalyst remains challenging. Hereby, a general strategy is proposed that evokes cooperative geometric and electronic interactions at nanometer coherent interfaces, which effectively stabilizes interfacial high‐valence metal sites within homogeneously distributed heterostructures and significantly enhances electrocatalytic activity. As a proof‐of‐concept study, by derivatizing multicomponent isoreticular hybridized metal–organic frameworks with separated σ‐ or π‐bonded moieties, bimetal Ni–Fe selenides heterostructures with nanoscopic compositional and structural homogeneity are grafted. Such heterostructures entail nanometer‐sized coherent interfaces that accommodate large geometric distortions and cooperatively stabilize the energetically unfavorable Jahn–Teller active electronic states of high‐valence interfacial Ni sites. The presence of high‐valence interfacial Ni sites and associated collective Jahn–Teller distortions greatly facilitate the Ni oxidation cycling through Ni3+/Ni4+ transition and stabilizes the *O key intermediate at Ni‐Se dual sites, both of which synergistically lowers down the overall OER overpotential.
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