Nitrogen-rich porous organic cages with high acetylene storage and separation performance

Abstract

Searching for porous materials that can safely store and efficiently separate acetylene (C₂H₂), a commonly used petrochemical feedstock with highly explosive properties, is a pressing and significant task. Nitrogen-rich porous materials have garnered substantial attention for their ability to interact strongly with acidic C₂H₂. Herein, we report two novel nitrogen-rich porous organic cages (POCs), namely CPOC-107 and CPOC-203, constructed from the same bowl-shaped tetraformylcalix[4]resorcinarene but different nitrogen-rich imidazolium-based diamine synthons. X-ray crystallographic analysis reveals that CPOC-107 adopts a [2 + 4] lantern-shaped structure, whereas CPOC-203 takes on a [3 + 6] triangular prism shape. Moreover, the cages exhibit large cavity volumes of up to 787 ų and high specific surface areas of up to 1202 m² g⁻¹. Owing to their high surface areas and high nitrogen content, both cages exhibit impressive C₂H₂ adsorption capabilities. Specifically, CPOC-107 achieves a remarkable C₂H₂ uptake value of up to 146 cm³ g⁻¹ at 298 K and 1 atm, the highest among those reported for all porous organic materials to date. Moreover, experimental breakthrough tests have confirmed the effective separation of C₂H₂/CO₂ mixtures using the CPOC-107 adsorbent.