Significantly enhanced separation using ZIF-8 membranes by partial conversion of calcined layered double hydroxide precursors

Significantly enhanced H₂/CH₄ (ca. 80) selectivity was realized by effective suppression of the framework flexibility of a prepared ZIF-8 membrane. Initially a ZnO buffer layer consisting of 20 nm-sized ZnO-nanoparticle aggregates was fabricated by controlled calcination of a ZnAl-NO₃ layered double hydroxide membrane. Owing to its high chemical reactivity, the ZnO buffer layer was partially converted into a well-intergrown ZIF-8 membrane with a certain penetration depth upon solvothermal treatment with ligands. Our method may represent a new concept for the design of advanced MOF membranes with high selectivity. There is still space for improvement: Alleviation of the framework flexibility enables significantly enhanced gas selectivity of pure ZIF-8 membranes, which is realized by partial conversion of calcined ZnAl-NO₃ layered double hydroxide precursor membranes under solvothermal conditions. This study represents a new concept for designing advanced MOF membranes.