Vitrification of non-meltable zeolitic-imidazolate frameworks†

Abstract

The decomposition of porous zeolitic-imidazolate frameworks (ZIFs) poses a significant challenge in discovering new melt-quenched ZIF glasses characterized by high porosity. This challenge has sparked tremendous interest among scientists, driving the pursuit of innovative methods to vitrify non-meltable ZIFs for various applications. Herein, we show a universal approach for synthesizing glasses and foams from non-meltable and porous ZIFs, such as 2D ZIF-7 and 3D ZIF-8, which stand as the most promising porous materials of the ZIF family. This approach is based on the combination of liquid-mediated sequential structure perturbation and post-heat treatment, yielding a variety of highly microporous ZIF foams like glass. The synthesized ZIF foams exhibit superior gas adsorption capacities compared to melt-quenched ones. The as-fabricated membranes based on ZIF foams demonstrate ultrahigh H₂ permeance and good H₂/CH₄ selectivity. In comparison to the melt-quenching technique, our structural perturbation strategy allows for the synthesis of a significantly greater quantity of glasses and foams from a single batch. It greatly broadens the composition range of ZIFs for glass and foam formation. Consequently, this study holds significant potential for upscaling the synthesis of microporous ZIF foams like glass to address a diverse array of applications such as energy storage, gas sorption and separation. Our work provides insight into the formation mechanism of non-melt-quenched glasses.