Modulation of porosity, melting and glass formation in zeolitic imidazolate frameworks

Abstract

The phase transition of metal–organic frameworks (MOFs) from a crystalline to a liquid and a glassy state represents a promising avenue for the development of a novel class of amorphous materials. In contrast to their crystalline counterparts, liquid and glassy MOFs exhibit excellent processability, a highly advantageous property for industrial applications where the formation of specific shapes, such as pellets or thin films, is often a prerequisite. Furthermore, unlike conventional glasses, the utilization of coordination chemistry allows for the implementation of rational design concepts, thereby facilitating the fine-tuning of the desired properties. In this thesis, Solvent-assisted linker exchange (SALE) as a versatile method for the preparation of melt-quenched MOF glasses from proto typical MOFs, such as ZIF-8. Two additional organic linkers are incorporated into the non-meltable ZIF-8, yielding high-entropy linker-exchanged ZIF-8 derivatives that undergo a phase transition from crystalline to liquid and glassy states upon thermal treatment. This strategy opens new pathways for creating meltable and glass-forming MOFs from the extensive pool of non-meltable MOFs documented in the literature. Moreover, Post-synthetic ball-milling (PSBM) is explored as a suitable alternative to melt-quenching in MOF glass formation. MOFs can be transformed into glasses in just 5 minutes by mechanical milling at room temperature. This PSBM method can also transform crystalline MOFs in the glassy state that do not melt due to low thermal stability. This approach broadens the spectrum of potential applications, paving the way for the development of multifunctional MOF glass composites and expanding their use into more diverse fields. Additionally, Single-component glass-ceramics (SCGC) explored from a Cd-based MOF exhibit unique structural and thermal properties. Upon reheating the Cd-based MOF glass, it undergoes partial recrystallization into a single component glass-ceramic state with potentially enhanced mechanical properties — a feature not observed in previous melt-quenched MOF glasses. Overall, this thesis offers new insights into the porosity of MOF glasses, their formation mechanism, the preparation of MOF glass-ceramics and a generic method for the mechanochemical preparation of MOF glasses.