Thermoresponsive and xenon-triggered gate-opening in flexible three-dimensional covalent organic framework for selective xenon capture

The development of dynamically responsive soft porous crystals (SPCs) is crucial for advanced gas separation due to their stimuli-triggered structural transitions. Herein, we report a 3D covalent organic framework (FCOF-XJ) constructed from flexible tetrahedral (F-3D-Td) and rigid tetrahedral (3D-Td) building blocks, exhibiting unique temperature-dependent selective adsorption of xenon (Xe). FCOF-XJ features thermoresponsive -O-C-C-C-O- single bonds that enable temperature-dependent conformational switching. The adaptive pore structure of FCOF-XJ enables an Xe-triggered gate-opening effect, with 4 times increase of Xe adsorption and a high Xe/Kr selectivity (36.9 at 298 K, 1 bar) among porous organic materials, surpassing most of metal-organic frameworks (MOFs). Breakthrough experiments reveal a defined high-purity Xe recovery window from Xe/Kr mixtures under non-ideal dynamic conditions, enabled by thermoresponsive pore-gating dynamics. This work establishes a flexible COF platform for thermoresponsive and Xe-selective capture based on guest-triggered framework gating.