Synthesis and Visualization of Entangled 3D Covalent Organic Frameworks with High‐Valency Stereoscopic Molecular Nodes for Gas Separation

Abstract

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.

Efficient Adsorption of Acetylene over CO2 in Bioinspired Covalent Organic Frameworks

“…Notably, the C 2 H 2 /CO 2 uptake ratio of ca. 4 on the two COFs is much higher than that on other COFs, such as ZJUT-2 (1.7) and NKCOF-12 (1.4), and most MOFs, such as MUF-17 (1.2) and MAF-2 (3.7) . The separation selectivities of C 2 H 2 /CO 2 on NUS-71 and NUS-72 were estimated to be 16 and 6.7, respectively (Figure S21), which are much higher than those of COFs like ZJUT-3 (3.2) and 2D sql COF (4.8) but still lower than the benchmark MOFs for C 2 H 2 /CO 2 separation, such as CPL-1-NH 2 (119) and MIL-160 (10) .…”

“…4 on the two COFs is much higher than that on other COFs, such as ZJUT-2 (1.7) and NKCOF-12 (1.4), and most MOFs, such as MUF-17 (1.2) and MAF-2 (3.7) . The separation selectivities of C 2 H 2 /CO 2 on NUS-71 and NUS-72 were estimated to be 16 and 6.7, respectively (Figure S21), which are much higher than those of COFs like ZJUT-3 (3.2) and 2D sql COF (4.8) but still lower than the benchmark MOFs for C 2 H 2 /CO 2 separation, such as CPL-1-NH 2 (119) and MIL-160 (10) . The heats of adsorption ( Q st ) for C 2 H 2 were further calculated to be 32.7 and 30.1 kJ mol –1 on NUS-71 and NUS-72, respectively, which are higher than those for CO 2 (20.6 and 20.8 kJ mol –1 , respectively; Figure S26), indicative of the preferential sorption of C 2 H 2 over CO 2 .…”

Conjugated Three-Dimensional High-Connected Covalent Organic Frameworks for Lithium–Sulfur Batteries

“…3D COFs still remain relatively less explored in comparison with their 2D analogues due to the still limited building blocks and difficulty in solving their more complicated structure . Thus far, only building blocks with 3D tetrahedral ( T d ), − triangular prismatic ( D 3h ), − and cubic ( O h ) , symmetry have been used to fabricate 3D COFs, leading to corresponding materials with extended topologies of ctn , bor , dia , ion , pts , ljh , rra , nbo , tbo , fjh , ffc , acs , ceq , hea , stp , srs , pcb , and bcu , far from their analogous metal-organic frameworks (MOFs) . It is worth noting again that almost all of these 3D building blocks are of nonconjugated nature, resulting in the isolation of nonconjugated 3D COFs with relatively low conductivity.…”

Rationally Fabricating Three-Dimensional Covalent Organic Frameworks for Propyne/Propylene Separation

“…However, to the best of our knowledge, applying COFs for C 3 H 4 /C 3 H 6 separation has not been reported yet. Compared with traditional 2D COFs, which usually possess large and noninterconnected pores, 3D COFs tend to possess more complex microporous structures, interconnected channels, and higher structural robustness and have more accessible active sites, which endow them with higher superiority for gas separation. − In recent years, 3D COFs have attracted increasing interest in the construction of novel topologies and functionalities. − ,,− However, hindered by the limited building blocks and difficulty in structure determination, using 3D COFs for efficient gas separation is still in its infancy. ,, Thus, developing 3D COFs with tailored microporous structures and accessible active sites for gas separation, especially C 3 H 4 /C 3 H 6 separation, is of great significance. To achieve such a goal, there are two feasible design approaches: (1) introducing the specific adsorption sites ,, and (2) forming appropriate pore apertures to enhance the interaction of gas molecules and frameworks …”