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

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 Å3. 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.