Zeolitic imidazole frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs), have demonstrated outstanding potential in membrane separation due to their uniform and fine-tunable pore size, together with structural diversity.^[1] Our research primarily aims to develop scalable and reliable manufacturing methods for synthesizing ZIF-based membranes and use various post-synthetic treatment techniques to tune the membrane performance for various gas mixtures through changes in the effective aperture size or the chemical affinity of the selective ZIF layer.

This presentation includes our recently completed work demonstrating a remarkable modification in membrane properties by organic ligand- or organometallic vapor exposure to the as-formed ZIF-8 membranes. For example, we achieved 5-20-fold increases in selectivity for O₂/N₂, CO₂/CH₄, CO₂/N₂, and H₂/CH₄ mixtures following treatment with 2-aminobenzimidazole vapors at 180 °C for 40 min.^[2] On the other hand, when treated with manganese (II) acetylacetonate (Mn(acac)₂) vapors, ZIF-8 membranes exhibited a distinct tuning behavior depending upon the treatment temperatures: selectivity increases for i) propylene over propane from 31 to 210 at 165 °C for 30 min and for ii) smaller gas pairs of H₂/CH₄ from 14.6 to 242, CO₂/N₂ 2.4 to 29, and O₂/N₂ of 2.9 to 7.5, respectively, at 175 °C for 30 min.^[3]

In addition, we will introduce a relatively fast (less than one minute) electron beam exposure approach employed to alter ZIF-8 membrane properties, leading to an increase in CO₂/N₂ and CO₂/CH₄selectivities by factors of 3.8 and 3.2, respectively.^[4]

At the end of the presentation, it will be briefly discussed in our recent collaborative work regarding a systematic investigation through computer modeling and IR adsorption studies on variations in both gas adsorption and diffusion behavior of the ZIF-8 structure (e.g., cell shape and size), resulting from confinement within a substrate or exposure to high pressure feeds.

Mikio Hayashi

Appearances