Concurrent Manipulation of Out-of-Plane and Regional In-Plane Orientations of NH2-UiO-66 Membranes with Significantly Reduced Anisotropic Grain Boundary and Superior H2/CO2 Separation Performance

Preferred orientation has proven to exert a significant impact on the gas separation performance of metal-organic framework membranes. Nevertheless, realizing three-dimensional orientation control remains a challenging issue. In this study, well-intergrown NH₂-UiO-66 membranes with both (111) out-of-plane and regional in-plane orientations were prepared by combining oriented deposition of seeds and solvothermal epitaxial growth. Dynamic air-liquid interface-assisted self-assembly method was employed to organize uniform octahedral-shaped NH₂-UiO-66 seeds into closely packed monolayers with (111) out-of-plane and regional in-plane orientations, whereas the use of ZrS₂ as the zirconium precursor during the solvothermal epitaxial growth was found indispensible for sealing the intercrystalline gaps while preserving the preferred orientation inherited from seed layers. In addition, compared with solvothermal heating, employing microwave heating led to poor intergrowth between neighboring NH₂-UiO-66 crystals because of a lower dielectric loss factor of the reaction medium. Gas permeation results indicated that the prepared NH₂-UiO-66 membranes exhibited H₂/CO₂ selectivity up to 5.5 times higher than their counterparts with random and/or mere out-of-plane orientations as well as H₂ permeability 14.5 times higher than NH₂-MIL-125(Ti) membranes with mere out-of-plane orientation under similar operating conditions.