Design and Development of a Self-Supporting ZIF-62 Glass MOF Membrane with Enhanced Molecular Sieving for High H₂ Separation Efficiency

The purpose of this study was to design and develop a self-supporting glass MOF membrane (GMM) including its design, fabrication under different heat treatment temperatures, analysis of its physical-chemical properties, and assessment of its separation performance. Glass MOFs preserve metal-ligand bonding structures similar to their crystalline counterparts, providing intrinsic gas separation properties alongside the benefits of amorphous materials, including reduced grain boundaries and ease of processing. In this work, ZIF-62 was melted and then cooled to fabricate GMMs using vitrification to enhance molecular sieving. This study systematically examines the impact of varying thermal treatment temperatures (400-475 °C) on the physical and chemical transformations of GMMs, revealing their effects on the porosity, defect formation, and molecular sieving performance through advanced characterization techniques (e.g., solid-state nuclear magnetic resonance (¹³C NMR), X-ray photoelectron spectroscopy (XPS), He pycnometry, and positron annihilation lifetime spectroscopy (PALS)). The optimal GMM exhibits an impressive separation performance, particularly for H₂ separation. The GMM at 4 bar and 25 °C exhibited He, H₂, CO₂, N₂, and CH₄ gas permeations of 576.37, 509.23, 146.07, 3.45, and 2.28 barrer, respectively. The ideal selectivities of H₂/CH₄, CO₂/N₂, CO₂/CH₄, H₂/N₂, and H₂/CO₂ gas pairs were 223.47, 42.37, 64.10, 147.71, and 3.49, respectively, which significantly exceed earlier reported values for ZIF-62 membranes, demonstrating the significant potential for GMMs as high-performance molecular sieve membranes, particularly for H₂ separation. This work by optimizing the vitrification process through systematic temperature control highlights GMM's ability to achieve high selectivity and permeability, positioning it as a promising candidate for industrial gas separation applications.