Single-Molecule Traps in Covalent Organic Frameworks for Selective Capture of C 2 H 2 from C 2 H 4 -Rich Gas Mixtures.

Removing trace amounts of acetylene (C 2 H 2 ) from ethylene (C 2 H 4 )-rich gas mixtures is vital for the supply of high-purity C 2 H 4 to the chemical industry and plastics sector. However, selective removal of C 2 H 2 is challenging due to the similar physical and chemical properties of C 2 H 2 and C 2 H 4 . 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 C 2 H 2 molecules to massively enhance the adsorption selectivity toward C 2 H 2 over C 2 H 4 . C 2 H 2 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 C 2 H 2 , COF-1 delivered a remarkable C 2 H 2 uptake of 7.97 cm 3 /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 C 2 H 2 and C 2 H 4 in breakthrough experiments under dynamic conditions. COF-1 adsorbed C 2 H 2 at a capacity of 0.17 cm 3 /g at 2,000 s/g when exposed to 0.5 ml/min C 2 H 4 -rich gas mixture (99% C 2 H 4 ) at 298 K, directly producing high-purity C 2 H 4 gas at a rate of 3.95 cm 3 /g. Computational simulations showed that the strong affinity between C 2 H 2 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 C 2 H 2 in practical C 2 H 4 purification.