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.