Zinc-imidazole-based metal-organic framework nanosheet membrane for H₂/O₂ separation

Abstract Metal-organic framework (MOF) nanosheets are promising candidates for molecular sieve because of their structural diversity and minimized mass transfer barrier. However, design of appropriate MOF nanosheets and preparation of high-performance MOF nanosheet-based membranes, especially for gas separation, remains great challenges. Structural degradation may simultaneously occur with conventional exfoliation method, which has hindered its widespread application in high-performance molecular sieve membrane preparation. Even if nanosheets could be stacked, grain boundaries would form between the nanosheets, which could be applied to liquid separation but not to gas separation. To address these challenges, we applied bottom-up growth of Zn2(benzimidazole)4 nanosheet to fabricate defect-free membranes. Zn2(benzimidazole)4 is composed of benzimidazole-zinc tetrahedral units and layers are connected by van der Waals interaction. At first, the Zn2(benzimidazole)4 nanosheets were deposited onto a porous support to prepare gutter layer. Next, Zn-based amorphous layer was coated on the gutter layer and crystallized by benzimidazole vapor treatment. Highly oriented Zn2(benzimidazole)4 nanosheet based membranes were fabricated by anisotropically controlling crystallization. The prepared Zn2(benzimidazole)4 nanosheet-based membranes show separation performance in hydrogen purification with H2/O2 ideal separation factor of 11.6 and H 2 permeance of 5650 GPU.