Modifying a partial corn-sql layer-based (3,3,3,3,4,4)-c topological MOF by substitution of OH− with Cl− and its highly selective adsorption of C2 hydrocarbons over CH4

Abstract

Modifying VNU-18 (a MOF with a partial cone-sql layer pillared by the chains of pillars decorated with OH⁻) by substitution of OH⁻ with Cl⁻, a new isoreticular structure, [Cu₆(L)₅·(Cl⁻)₂·H₂O·4DMF]·4DMF·6(H₂O) (SNNU-Bai67, SNNU-Bai = Shaanxi Normal University Bai's group), has been successfully synthesized. Furthermore, we deeply investigated the selective C2 hydrocarbon separation properties of SNNU-Bai67 and VNU-18 by single-component gas adsorption experiments, breakthrough experiments and simulation studies. They exhibit highly selective adsorption for C2 hydrocarbons over CH₄ compared to many reported MOFs for the separation of C2 hydrocarbons from CH₄, due to the suitable pore sizes of the partial corn sql-layer built from the isophthalic acid analogy and Cu-paddlewheel units. Interestingly, with the counterion of OH⁻ in VNU-18 tuned by Cl⁻ in SNNU-Bai67, the adsorption uptake values of C2 hydrocarbons were apparently improved by 15.0% for C₂H₂, 20.4% for C₂H₄ and 25.3% for C₂H₆, respectively, while the IAST selectivities of C2 hydrocarbons/CH₄ were still nearly the same, which may be because the synergistic effect of interactions of H_C2/1⋯O_COO, H_C2/1⋯N/C_Py, H_Py⋯C_C2, π⋯π or H_C2⋯C_C2 between the gas molecules and the framework is enhanced by the weaker polarity of Cl⁻ decorating the framework.