# Unlocking large-area free-standing MOF-glasses for molecular sieving gas separation membranes

## TL;DR

Researchers developed a method to create large, crack-free MOF-glass membranes that can efficiently separate gases like methane.

## Contribution

A step-by-step method to fabricate large, free-standing MOF-glass membranes with sharp molecular sieving properties.

## Key findings

- Crack-free ZIF-62 MOF-glass membranes were successfully fabricated using optimized processing steps.
- The membranes exhibit exceptionally sharp methane molecular sieving with low permeability.
- SEM-EDX analysis confirmed the homogeneous and boundary-free structure of the MOF-glass.

## Abstract

Membranes from MOF glasses hold significant promise for gas separations due to the absence of grain boundary diffusion, liquid processibility, and tunability. The inherent high viscosity of MOF melts renders them prone to cracking and further handling, and their propensity to densify at high temperatures and long time in molten state severely limits their upscaling potential. A solution to overcome these limitations is demonstrated by selecting suitable materials that fit the thermal and mechanical behaviour to MOF-glass, enabling processing and making of large, crack-free MOF-glass sheets. This is demonstrated on the example of the well-known MOF-glass former ZIF-62. By optimizing each step of the process – from melting to performance testing – we successfully fabricate a crack-free, self-supported ZIF-62 glass membrane. The microstructure is investigated using microscopy as well as SEM-EDX analysis, confirming homogeneous boundary-free MOF-glass, while gas permeation experiments prove the applicability of MOF-glass as gas separation membrane. The membrane exhibits exceptionally sharp methane molecular sieving cut-off with such low permeability that gas chromatography is unable to detect CH4. We conclude this work by giving a brief outlook of the remaining challenges and perspectives for MOF glasses, envisioning transferability of our approach to other glass-forming systems and their scaling perspectives.

The unique properties of membranes made from MOF glasses suggest their potential for precise molecular-sieving separations. In this work, the authors present a step-by-step method to fabricate large, free-standing MOF glass membranes capable of sharply excluding methane.