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

Presented here is a new,ultramicroporous metal-organic framework (MOF) formulated as [Zn3L2(HCOO)(1.5)] [(CH3)(2)NH2](1.5)center dot 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 N-2, 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 N-2. According to the Toth model, the selectivity of CO2/CH4 and CO2/N-2 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.