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.
Chenhan Zhang,Jiahui Yan,Taotao Ji,Dongying Du,Yanwei Sun,Liangliang Liu,Xiongfu Zhang,Yi Liu
Preferred orientation represents a main concern for microstructure control and performance optimization of MOF membranes. To date, it remains a challenging task to precisely control preferred orientation of ZIF-8 membrane. Herein, we prepared highly (110)-oriented ZIF-8 membrane by oriented secondary growth. Among various elements, preparation of uniform ZIF-8 nanosheet seeds through thermal conversion of identically shaped ZIF-L precursors, spin-coating-assisted oriented deposition of (110)-oriented ZIF-8 seed layer, and controlled in-plane secondary growth at low temperature were found crucial for obtaining well-intergrown (110)-oriented ZIF-8 membrane whose H 2 /CO 2 ideal selectivity exceeded H 2 /N 2 and H 2 /CH 4 under ambient conditions, owing to preferential CO 2 adsorption capacity of not only PEI but also ZIF-8 nanosheets compared with their bulk counterparts. Our research highlighted the significance of preferred orientation regulation in tailoring the gas permeation behavior of MOF membranes.
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