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

Nonhydrostatic compression in steps is applied to transform crystalline zeolitic imidazolate framework-62 into glass at room temperature. This method overcomes the limitations of existing approaches. This research reveals the mechanism of this phase transformation, including modifications in porosity, using various techniques, particularly positron annihilation lifetime spectroscopy.

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.

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