A microporous zinc–organic framework with Lewis basic pyridyl sites for highly selective C2H2/CH4 and C2H2/CO2 gas separation

Abstract

A new Zn-based metal–organic framework with 8-connected hex topology constructed from bipyridine and carboxylate ligands, namely [Zn(cpna)₃(tmbpy)]_n·4DMF (1) (H₂cpna = 6-(4-carboxyphenyl)nicotinic acid; tmbpy = 3,3′-dimethyl-4,4′-bipyridine), has been synthesized under solvothermal conditions. The Zn-MOF was structurally characterized and retained a good crystal structure after activation (1a), an indication of permanent porosity. 1a exhibits a BET surface of 770 m² g⁻¹ and the maximum aperture of 8.60 Å. Single component adsorption isotherm measurements of C₂H₂, CO₂, CH₄, CO and N₂ on 1a were performed both at 273 K and 298 K, and the selectivities for C₂H₂/CH₄, C₂H₂/CO₂, CO₂/CO, CO₂/CH₄ and CO₂/N₂ were estimated on the basis of the ideal adsorbed solution theory (IAST). 1a shows the uptake of C₂H₂ (3.89 mmol g⁻¹) and CO₂ (3.52 mmol g⁻¹) at 273 K and 100 kPa, respectively. Due to the Lewis basic pyridyl sites inside the channel of the framework, 1a showed good adsorption selectivities for C₂H₂/CH₄(50 : 50) and C₂H₂/CO₂(50 : 50) at 298 K (100 kPa).