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Thursday, 07 February 2013

MOF balls: hollow microstructures built with fast-drying “spray-paint”

In Nature Chemistry, ICN team led by ICREA Prof Daniel Maspoch reports spray-dry fabrication of Metal-Organic Framework (MOF) nanocrystals that self-assemble into superstructures

ICN researchers Arnau Carné, Dr Imaz Imaz and Dr Mary Cano, led by NANOup Group Leader and ICREA Professor Daniel Maspoch, have just published an article in Nature Chemistry describing a spray-drying method to create Metal-Organic Framework (MOF) nanocrystals that self-assemble into hollow superstructures of microscale dimensions. The article is entitled “A spray-drying strategy for synthesis of nanoscale metal–organic frameworks and their assembly into hollow superstructures”.MOFs are a diverse class of porous materials comprising one or more metal components, and one or more organic components, arranged in complex patterns. They have garnered much attention for their amenability to numerous applications involving storage, catalysis and separation. As such, nanoscale MOFs have been proposed as potential drug delivery vectors, contrast agents, sensors or gas entrapment scaffolds.  However, methods for reliable nanoscale MOF synthesis, in which the precise patterning of the structure is intimately linked to its functional capacity, have been limited.

Prof Maspoch and co-workers devised a unique take on spray-drying, a technique which has already been used by other researchers to fabricate other types of materials.  In the ICN team’s method, MOF precursor solutions are sprayed through a specialised nozzle to create atomised droplets which instantly react to form MOF nanocrystals, which go on to self-assemble into hollow, highly-ordered superstructures of microscale dimensions (diameter: < 5 microns).

They were able to obtain a diverse array of MOF superstructures by selectively controlling the precursor solutions as well as the spray-drying parameters (time, temperature, solvent, etc.). After synthesising these superstructures, they characterised them by Electron Microscopy, among other methods, verifying the regular patterning of the outer shell as well as the empty core of each type. Furthermore, they were able to encapsulate other functional substances inside the MOF superstructures. Lastly, they broke the superstructures apart by sonication to obtain highly pure MOF nanocrystals.The ICN team have a patent pending on the methods described in the article (European Union application number EP 11183773.8; filed 27 October 2011).According to Prof Maspoch, “Our methodology can be easily tailored to create custom MOF microstructures and highly sophisticated composites for a desired application involving specific cargo, so the possibilities for industry are basically endless.”ICN’s NANOup Group is currently pursuing the controlled assembly of higher-order supramolecular materials for applications in biomedicine, storage and separation, and pollutant removal, among others.

To access the article “A spray-drying strategy for synthesis of nanoscale metal–organic frameworks and their assembly into hollow superstructures”, click here.