Pore-in-Pore Engineering in a Covalent Organic Framework Membrane for Gas Separation.

Covalent organic framework (COF) membranes have emerged as a promising candidate for energy-efficient separations, but the angstrom-precision control of the channel size in the subnanometer region remains a challenge that has so far restricted their potential for gas separation. Herein, we report an ultramicropore-in-nanopore concept of engineering matreshka-like pore-channels inside a COF membrane. In this concept, α-cyclodextrin (α-CD) is in situ encapsulated during the interfacial polymerization which presumably results in a linear assembly (LA) of α-CDs in the 1D nanochannels of COF. The LA-α-CD-in-TpPa-1 membrane shows a high H 2 permeance (∼3000 GPU) together with an enhanced selectivity (>30) of H 2 over CO 2 and CH 4 due to the formation of fast and selective H 2 -transport pathways. The overall performance for H 2 /CO 2 and H 2 /CH 4 separation transcends the Robeson upper bounds and ranks among the most powerful H 2 -selective membranes. The versatility of this strategy is demonstrated by synthesizing different types of LA-α-CD-in-COF membranes.