Inverse and highly selective separation of CO2/C2H2 on a thulium–organic framework

Abstract

The selective removal of CO₂ impurities from C₂H₂ is important but extremely difficult due to their very similar physical properties and almost identical kinetic diameters. In this work, a hydro-stable 3D porous thulium(III)–organic framework, {[Tm₂(OH-bdc)₂(μ₃-OH)₂(H₂O)₂]·11H₂O}_n (1) (OH-H₂bdc = 2,5-dihydroxyterephthalic), functionalized with hydroxyl groups and aqua ligands with an ecu topology is constructed. The activation of 1 at different temperatures realizes two novel porous MOFs (1a and 1a′) with channels of 6.2 × 9.3 and 6.3 × 9.3 Ų and 6.3 × 10.6 and 9.3 × 12.2 Ų, respectively. 1a and 1a′ show distinctly different ability to separate a CO₂/C₂H₂ mixture. As compared with the poor CO₂/C₂H₂ separation performance of 1a′, 1a shows an excellent capability to selectively capture CO₂ from CO₂/C₂H₂ based on the results of single-component adsorption isotherm and breakthrough experiments. The CO₂ and C₂H₂ uptakes on 1a are 5.83 mmol g⁻¹ and 2.01 mmol g⁻¹ at 298 K and 1 bar, respectively. More importantly, 1a achieves a high selectivity for CO₂ over C₂H₂ with an IAST selectivity of 17.5 at 298 K and 1 bar. Furthermore, 1a exhibits good reusability in CO₂/C₂H₂ separation. To the best of our knowledge, 1a represents the first example of lanthanide-based MOFs for CO₂/C₂H₂ separation.