Compression-Induced Amorphization of ZIF-62 Leading to Formation of Porous Glass: Overcoming the Limitations of Current Methods

Porous hybrid glasses-based on metal-organic frameworks (MOFs) have garnered significant interest in gas separation, due to their excellent processing ability, porosity, and grain boundary-free properties. Melt-quenching and mechanical vitrification are the currently used methods to transform crystalline MOFs into glasses. However, research is still ongoing to make the formation process of MOFs-based porous glasses easier, scalable, and energy efficient. A simple and scalable process overcoming the limitations of the existing methods to form glass of an extensively studied MOF, i.e., zeolitic imidazolate framework-62 (ZIF-62) is reported. Ball milling and melt-quenching are widely explored methods for ZIF-62 glass formation. ZIF-62 undergoes reversible amorphization (nonglassy phase) at very high hydrostatic pressure at ambient temperature. The present study demonstrates that successive nonhydrostatic compression at lower pressures irreversibly transforms crystalline ZIF-62 into an amorphous phase having glassy characteristics. The pore network characteristics and local structure of the compression-induced phase are compared with the melt-quenched ZIF-62. X-ray absorption spectroscopy confirms an identical local structure of both the glasses. Positron annihilation lifetime spectroscopy measurements show that the compression-induced glassy phase exhibits a higher number density of smaller pores compared to the melt-quenched glass which exhibits lower number density of larger pores.