Amine-modified Mg-MOF-74/CPO-27-Mg membrane with enhanced H2/CO2 separation

•Amination of the open metal sites in Mg-MOF-74 leads to retardation of CO2 and doubles the selectivity for H2/CO2 separation.•The size of Mg-MOF-74 crystals in membrane can be reduced after optimization of synthesis solution.•Only by using MgO as seeds, a dense and continuous Mg-MOF-74 layer could be obtained.•The selectivity of the Mg-MOF-74 membrane for H2/CO2 is far above the Robeson bound.

Mg-MOF-74 has attracted intense attention due to its high CO2 uptake ability. In this work, a new strategy by using magnesium oxide as seeds was developed to synthesize a dense, defect-free Mg-MOF-74 membrane with hydrogen-selectivity. The mixed gas separation factor of H2/CO2 mixture could be improved by the post-modification of the Mg-MOF-74 membrane with ethylenediamine, since the modification with amine groups enhanced the strong adsorption of CO2 molecules, which reduces the permeance of CO2. The separation factors for both as-synthesized and amino-functionalized Mg-MOF-74 membranes reduce gradually with increasing temperature. After amination of the open Mg sites, the separation performance of the Mg-MOF-74 membrane was remarkably enhanced, and the H2/CO2 selectivity increased from 10.5 to 28 at room temperature.

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