Low‐Temperature Melting and Glass Formation of the Zeolitic Imidazolate Frameworks ZIF‐62 and ZIF‐76 through Ionic Liquid Incorporation

Abstract

Hybrid glass formation offers a potential route for processing metal‐organic frameworks (MOFs) in bulk shapes, however, only a small number of MOFs have proven to be meltable. For the non‐meltable zeolitic imidazolate framework ZIF‐8, ionic liquid (IL) incorporation has recently been found to reduce the melting temperature to below the thermal decomposition temperature, thus, enabling the formation of IL@ZIF‐8 glasses. Here, the effect of IL incorporation on the enthalpic response of some zeolitic imidazolate frameworks (ZIFs) and other MOFs upon heating is reported. For ZIF‐62, ZIF‐67, ZIF‐76, and MIL‐68, the accessibility of the metal site and MOF porosity govern the meltability of IL@MOF composites. IL incorporation enables the formation of ZIF‐76 glasses, and significantly reduces the melting temperature of ZIF‐62 but does not seem to facilitate the melting of ZIF‐67 or MIL‐68 (before thermal decomposition). Although the thermal stability limit of the IL plays an important role in governing the melting window of the IL@MOF composite, by careful selection of the melting temperature, thermal decomposition and compositional changes upon melting can be avoided to a greater extent. IL incorporation seems to offer a more universal route for melting MOFs, but requires careful adaption to the specific MOF architecture.

Precise control over gas transporting channels in zeolitic imidazolate framework glasses

“…For example, ZIF-76 needs a melt of ZIF-62 or TIF-4 as a mediator, making it difficult to determine the exact material porosity after melt-quenching (15). Surface-mediated melting through imidazole-based ionic liquids is another option, which helps to transform ZIF-8 into a glass, and also helps to melt ZIF-76 (16).…”

Functions and applications of emerging metal–organic-framework liquids and glasses

“…45 Besides, other alternative approaches like pressure, mechanical milling and chemical treatment can also induce a direct crystal-to-glass transformation of MOFs. 16,46–48…”

“…45 Besides, other alternative approaches like pressure, mechanical milling and chemical treatment can also induce a direct crystal-to-glass transformation of MOFs. 16,[46][47][48] Investigation of the structures of MOF liquids and glasses is essential in order to understand the phase transformation and their functionalities. Phase transition or recombination of the coordination bonds in the framework of MOFs generally occurs at 200 to 500 1C, leading to the structural damage and making MOFs thermally less stable than many inorganic materials.…”

Metal Organic Framework Glasses: A New Platform for Electrocatalysis?

“…Recently, some new MOF glasses have been prepared by new ideas and methods. The method of ionic liquid incorporation was used to prepare IL@ZIF‐8 glass, which solved the problem that ZIF‐8 could not be prepared into glass [57] . Other researchers doped ZIF‐8 into ZIF‐62 to prepare glass [58] .…”