Two zinc metal–organic framework isomers based on pyrazine tetracarboxylic acid and dipyridinylbenzene for adsorption and separation of CO2 and light hydrocarbons

Abstract

Two highly porous metal–organic framework isomers Zn₂(TCPP)(DPB) (1 and 2, H₄TCPP = 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine and DPB = 1,4-di(pyridin-4-yl)benzene) were successfully synthesized using different solvents and acid species to adjust the topologies of these two MOFs. Both of them were constructed by paddlewheel Zn₂(COO)₄, TCPP⁴⁻, and DPB ligands. In compound 1, the Zn₂(COO)₄ paddlewheel units were fitted together by the TCPP⁴⁻ ligands to form two-dimensional layers, which were further connected by DPB ligands as pillars to construct a two-fold catenated 3D framework. In compound 2, the cross-linkage of Zn₂(COO)₄ paddlewheel units and TCPP⁴⁻ ligands resulted in a three-dimensional framework of Zn-TCPP, in which DPB ligands coordinated to two axial vertical dinuclear Zn₂(COO)₄. Both activated MOFs exhibited permanent porosity with high BET areas (1324 m² g⁻¹ for 1 and 1247 m² g⁻¹ for 2) and possessed narrow pore size distributions (0.93 nm for 1 and 1.02 nm for 2). Moreover, the adsorption behaviors of the two activated MOFs for CO₂ and light hydrocarbons (C1, C2, and C3) at low pressure were evaluated and favorable selectivity was proven for C₃H₈/C₃H₆ over CH₄. These two MOF materials reported in this study for selective CO₂ and light hydrocarbon capture have immense potential applications for environmental protection.