Ultrafast Synthesis of a Metal Organic Framework (MOF) Critical for New CO2 Uptake Technology

Lorenzo MASERATI, Lawrence Berkeley National Laboratory - USA

Exponential increase in greenhousegas emission in the last decades put pressure on the searching for a feasible technology for CO2 capture and storage. To provide alternatives to the existing, too costly technologies, many materials have been investigated. In recent years, the develop of a new class of materials called metal-organic frameworks (MOFs) paved the way for molecular engineering and construction of porous materials.
Among several MOFs tested, M2(dobpdc) and their diamine modified derivatives have shown exceptional promise as materials for energy-efficient CO2 capture. Currently limiting their expedient production is the observation by us and others that reaction times in excess of 12 h are required when preparing M2(dobpdc).
We report an exceptionally rapid synthesis of high quality M2(dobpdc) where (dobpdc = 4,4′-dioxido-3,3′-bip henyldicarboxylate) (also called expanded MOF-74). This (pseudo)halide-free route avoids the generation of acidic by-products otherwise inherent to conventional M2(dobpdc) syntheses; as a result, the reaction time needed decreases significantly — in some cases, by several orders of magnitude. We show that M2(dobpdc) formation proceeded via a dissolution-precipitation mechanism. Through our analysis of Metal Oxide (MO) precursor morphology, surface area, and composition-dependent etch rate, we determined that MO dissolution is rate-limiting. Notably, then, scaling the dimensions of the MO precursor to nanoscopic dimensions allows these MOFs to be prepared in high quality in mere minutes without residual MO. As a penultimate demonstration, we synthesized Zn2(dobpdc) MOFs from 7 nm ligand-stripped ZnO colloidal nanocrystals (NCs) in less than 1 minute.

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