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

## TL;DR

Researchers developed a simple method to make ultra-thin ZIF-67 membranes for efficient hydrogen separation at high temperatures.

## Contribution

A facile and scalable method to synthesize ∼20-nm-thick ZIF-67 membranes using β-Co(OH)₂ nanosheets as a precursor.

## Key findings

- Highly dispersed β-Co(OH)₂ nanosheets were synthesized in 1 hour at room temperature.
- ZIF-67 membranes showed excellent hydrogen sieving performance up to 250°C.
- The method enables scalable fabrication of sub-100-nm-thick membranes for gas separation.

## Abstract

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.

We report that highly dispersed β‐Co(OH)2 nanosheets (∼1‐nm‐thick) could be synthesized via a one‐pot reaction of ultradilute precursors (Co(NO3)2 + 2‐methyimidazole (HmIm) + H2O system) at room temperature in just 1 h. By using thin coatings of the as‐synthesized β‐Co(OH)2 nanosheets as self‐sacrificial templates, ∼20‐nm‐thick ZIF‐67 membranes could be fabricated in a facile way. The prepared ZIF‐67 membranes demonstrated attractive H2 sieving performance at elevated temperatures (up to 250 °C).