Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas.

Abstract

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure withdiatopology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility(so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was confirmed by gas sorption isotherms and SCXRDstudies, showing that the flexible pore pockets can be opened by C3H8and n-C4H10rather by C2H6and CH4. This leads to notably higher C3H8and n-C4H10uptakes with enhanced selectivities than C2H6over CH4, affording one of the highest n-C4H10/CH4selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-C4H10can induce an obvious framework expansion along with pore-pocket opening to improve n-C4H10uptake and selectivity, while not for C2H6adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.