Selective adsorption of CO2/CH4 and CO2/N2 within a charged metal–organic framework

Abstract

Presented here is a new ultramicroporous metal–organic framework (MOF) formulated as [Zn₃L₂(HCOO)_1.5][(CH₃)₂NH₂]_1.5·xDMF, 1 (H₃L = 9-(4-carboxy-phenyl)-9H-carbazole-3,6-dicarboxylic acid), DMF = N,N-dimethylformamide, consisting of an anionic framework and two types of interlaced one-dimensional channels with 0.42 and 0.79 nm diameters respectively, in which the larger channels accommodate protonated dimethylamine as the counter cations. Gas sorption analysis of N₂, CO₂ and CH₄ was investigated and the isotherms exhibit reversible thermodynamic behaviours without hysteresis desorption, evidencing framework rigidity and permanent porosity of solvent-free 1. The synergistic effect of the open ultramicropores and dimethylamine cations may lead to high efficiency separation of CO₂ from CH₄ and N₂. According to the Toth model, the selectivity of CO₂/CH₄ and CO₂/N₂ was calculated to be 96 and 37, respectively. This effort will give rise to a new conception to tailor the charged MOF for high efficiency CO₂ adsorption and separation.