Facile Synthesis of 20‐nm‐Thick ZIF‐67 Films for Hydrogen Sieving Using β‐Co(OH) ₂ Precursor Nanosheets

Zeolitic imidazolate framework-67 (ZIF-67) is an important class of nanoporous materials for high-performance membranes for gas separation, offering uniform-sized gas-selective pores. However, the fabrication of high-quality sub-100-nm-thick ZIF-67 membranes, critical for high-performance separation, has remained elusive. Herein, we report a facile strategy to fabricate ∼20-nm-thick ZIF-67 membranes. We identify a simple and rapid route to prepare ∼1-nm-thick β-Co(OH)₂ nanosheets as a precursor to ZIF-67. Highly dispersed β-Co(OH)₂ nanosheets are synthesized via a one-pot reaction at room temperature in just 1 h using ultradilute cobalt and linker concentrations in water. The resulting high-aspect-ratio nanosheets yield compact coating on porous polymeric supports. Well-intergrown ZIF-67 membranes are prepared by thermal treatment of nanosheets in the presence of a linker and exhibit attractive hydrogen sieving performance at elevated temperatures (up to 250 °C). This approach provides a scalable and versatile platform for hydrogen separation for applications such as precombustion carbon capture.