Spontaneous formation of amorphous precursors and their vapour-induced crystallisation into zeolitic imidazolate frameworks.

In this study, a solvent-minimised synthesis method for ZIF-8 was developed based on vapour-induced crystallisation from a metal-organic ligand amorphous precursor that spontaneously forms under ambient conditions. An amorphous network was first formed by simply mixing a metal salt and an organic ligand without the use of a solvent. Subsequent exposure of the amorphous precursor to 1-butanol vapour induced its crystallisation into ZIF-8. Because the precursor is fluid and mouldable prior to crystallisation, it can be deposited and shaped into different morphologies, including particulate and continuous coatings. Variation of the metal source, imidazolate ligand, and amount of added 1-butanol revealed their respective roles in amorphous precursor formation and morphology control. As the crystallisation step requires only a limited amount of organic solvent supplied in vapour form, this approach may reduce liquid-solvent consumption compared with conventional solution-based MOF synthesis. This work provides a versatile route for the morphology-controlled synthesis of ZIF-based materials through spontaneously formed amorphous precursors.