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.