Metal-organic frameworks are a recently commercialized class of porous adsorbent materials, which are being thoroughly investigated for implementation in technologies such as gas storage, food preservation, and hydrocarbon separation. It is the design and discovery of new MOF structures with improved stability and heightened functionalities that has accelerated their route to commercialization within the past five years. However, it is also becoming increasingly clear that the development of efficient and economical methodologies for MOF manufacture is an imperative for their adoption on an industrial scale. Mechanochemical and accelerated aging methods are examples of recently developed methodologies which reduce the solvent, high temperatures, and corrosive reagents sometimes associated with traditional solvothermal MOF synthesis. We now demonstrate that the synthesis of high surface area MOFs can be achieved rapidly and efficiently using supercritical carbon dioxide (scCO2) from readily available metal oxides and solid organic linkers. Reacting metal oxides (eg. ZnO) and organic ligands (eg. various imidazoles) in scCO2 results in the rapid (ca. 5 min) and quantitative formation of MOFs such as the prototypical ZIF-8. This work presents a versatile, environmentally-friendly, and virtually solvent-free alternative for MOF synthesis that is scalable to at least 0.5 Kg, and contradicts previous conceptions about the ability for scCO2 to activate highly insoluble metal precursors such as metal oxides.

Clean and scalable synthesis of microporous metal-organic frameworks in supercritical carbon dioxide

256th National Meeting (2018)

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