Cu(I)-cluster-based covalent organic frameworks with open metal sites and tuned microporosity for efficient C2H2/CO2 separation.

Incorporating open metal sites into covalent organic frameworks (COFs) offers a promising strategy to enhance acetylene (C2H2) and carbon dioxide (CO2) separation performance. Herein, we report two Cu(I)-cluster-based COFs, Cu-HAPB and Cu-HABPB, with kgd topology and distinct pore apertures, constructed from a C3-symmetric trinuclear copper cluster and C6-symmetric linkers of different sizes. Both materials integrate the structural tunability of COFs with the strong binding capability of metal sites. Notably, Cu-HAPB, featuring smaller pores, exhibits a superior C2H2/CO2 selectivity of 6.23 at 298 K and 1 bar, outperforming most reported COFs. GCMC simulations reveal that exposed Cu(I) sites act as primary adsorption centers, strengthening C2H2 binding via π-complexation. Dynamic breakthrough experiments further confirm its efficient separation performance. This work highlights the synergistic effect of open metal sites and pore size regulation in designing high-performance COFs for C2H2/CO2 separation.