Optimized nanospace of coordination isomers with selenium sites for acetylene separation

Abstract

The safe storage and separation of acetylene (C₂H₂) is difficult and essential, due to its explosive properties and wide usage for various industrial products. With a generally low energy cost, highly efficient adsorption separation has been considered as a promising solution. Taking advantage of the inbuilt nature of a tunable pore space, a porous coordination polymer (NTU-56) was prepared from a selenium-containing carboxylate ligand and Cu²⁺ ions. Triggered by water at different temperatures, NTU-56 transformed into two other porous frameworks (NTU-57 and NTU-58) with different topologies and pore environments. Single-component gas adsorption experiments showed that this new group of porous isomers featured systematically varied adsorption selectivity for C₂H₂/CO₂, two gases that have extremely similar molecular sizes and boiling points. More interestingly, among the isomers, NTU-58, a rare 2D, flexible, and water-stable framework, has the highest C₂H₂ uptake (60 cm³ g⁻¹) and C₂H₂/CO₂ selectivity (13.9, 1/1, v/v, 1 bar) at 273 K, derived from the synergetic effect of the unique pore sizes (4.5 and 5.5 Å) and pore surface polarity, where the Cu²⁺ and selenium sites are exposed for preferred C₂H₂ interactions. Efficient and recyclable C₂H₂/CO₂ separation was also confirmed via breakthrough experiments, even with wet feed-gas.