Soft Crystal Design for Discriminatory Gate Effect on Inverse Selective CO2/C2H2 Separation

Abstract

One-step purification of acetylene (C₂H₂) from carbon dioxide (CO₂) using CO₂-selective adsorbents is urgently needed but strategically challenging due to their similar physicochemical properties. In this work, we designed a series of isostructural flexible porous coordination polymers (PCPs) modulating the gate-opening pressure for C₂H₂ through linker substitution, preserving high CO₂ uptake at low pressure, and enabling a customizable inverse selectivity of CO₂/C₂H₂. By exploring both pillar and capping ligand substitutions, we found that pillar-ligand substitution in the PCPs allows rational control of the gate-opening behavior for C₂H₂ to achieve highly selective adsorption of CO₂ while discriminating C₂H₂, achieving high CO₂/C₂H₂ uptake ratio (8.5) and selectivity (232.5), which are comparable to other benchmark materials. Furthermore, dynamic breakthrough experiments suggest that our PCPs effectively achieve an inverse CO₂/C₂H₂ separation at 298 K and 1 bar. Consequently, high-purity C₂H₂ (>99.5%) could be obtained from the CO₂/C₂H₂ mixture through a simple one-step column purification. Combining crystallographic structural analyses, we found that the significant structural deformation differences after pillar-ligand substitution compared with capping ligand substitution can rationally control the gate-opening behavior. This simple design strategy allows for reasonable control of the gating behavior of porous materials.