Single-Molecule Traps in Covalent Organic Frameworks for Selective Capture of CH from CH-Rich Gas Mixtures.

Removing trace amounts of acetylene (CH) from ethylene (CH)-rich gas mixtures is vital for the supply of high-purity CH to the chemical industry and plastics sector. However, selective removal of CH is challenging due to the similar physical and chemical properties of CH and CH. Here, we report a "single-molecule trap" strategy that utilizes electrostatic interactions between the one-dimensional (1D) channel of a covalent organic framework (denoted as COF-1) and CH molecules to massively enhance the adsorption selectivity toward CH over CH. CH molecules are immobilized via interactions with the O atom of C=O groups, the N atom of C≡N groups, and the H atom of phenyl groups in 1D channels of COF-1. Due to its exceptionally high affinity for CH, COF-1 delivered a remarkable CH uptake of 7.97 cm/g at 298 K and 0.01 bar, surpassing all reported COFs and many other state-of-the-art adsorbents under similar conditions. Further, COF-1 demonstrated outstanding performance for the separation of CH and CH in breakthrough experiments under dynamic conditions. COF-1 adsorbed CH at a capacity of 0.17 cm/g at 2,000 s/g when exposed to 0.5 ml/min CH-rich gas mixture (99% CH) at 298 K, directly producing high-purity CH gas at a rate of 3.95 cm/g. Computational simulations showed that the strong affinity between CH and the single-molecule traps of COF-1 were responsible for the excellent separation performance. COF-1 is also robust, providing a promising new strategy for the efficient removal of trace amounts of CH in practical CH purification.