Optimizing Pore Space for Flexible-Robust Metal-Organic Framework to Boost Trace Acetylene Removal

Abstract

Isoreticular principle has been employed to realize a flexible-robust metal-organic framework (MOF) with extended pore structure for the adsorptive removal of trace acetylene from ethylene under ambient conditions. The substitution from zinc(II) to copper(II) of high coordination distortion leads to elongated Cu-F bonds that expand the closed pore cavities in the prototypical MOF from 3.5 × 3.9 × 4.1 to 3.6 × 4.3 × 4.2 ų. The optimal cavity size together with strong binding sites thus endows the new Cu analogue to possess open pore space accessible for trace C₂H₂ within a substantial low-pressure range while excluding C₂H₄ molecules, as validated by gas isotherms and single-crystal structure of its partially C₂H₂-loading phase. In contrast to the Zn prototype, at 298 K and 1.0 bar, the guest-free Cu analogue shows significant C₂H₂ uptake increase with a total capacity of 4.57 mmol g^-1, and gains an over two orders of magnitude jump in IAST selectivity for C₂H₂/C₂H₄ (1/99, v/v). These results are higher than the benchmark MOFs for molecular sieving of C₂H₂/C₂H₄, leading a high C₂H₄ productivity of 14.9 mmol g^-1. Crystallography studies, molecular modeling, selectivity evaluation, and breakthrough experiments have comprehensively demonstrated this flexible-robust MOF as an efficient adsorbent for C₂H₂/C₂H₄ separation.