Linking defects, hierarchical porosity generation and desalination performance in metal–organic frameworks

Weibin Liang, Lin Li, Jingwei Hou, Nicholas D. Shepherd, Thomas D. Bennett, Deanna M. D'Alessandro and Vicki Chen - School of Chemistry, The University of Sydney, UNESCO Center for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Department of Materials Science and Metallurgy, University of Cambridge

Composite membranes with defective metal–organic frameworks (MOFs) connect the emerging fields of MOF topological modification, MOF-polymer interfacial engineering and composite material functionalization.

Although defective MOFs can be fabricated via thermal or chemical treatment, the relationship between hierarchical MOF structure and their performance in a polymeric membrane matrix has so far not been investigated. Here we show how a modulator fumarate-based MIL-53(Al) microwave synthesis process results in defective MOFs. This ligand replacement process leads to materials with hierarchical porosity, which creates a higher mesopore volume and Brønsted acidity without compromising the crystalline structure and pH stability. Compared with stoichiometric ratios, increasing the reaction time leads to more effective defect generation. The subsequent incorporation of defective MOFs into polyvinyl alcohol pervaporation membranes can effectively promote the fresh water productivity in concentrated brine treatment, with salt rejection of >99.999%. The membranes also have good long-term operational stability with effective antifouling behavior. We provide evidence that topological engineering of the MOF surface is related to their physical and chemical behaviors in a polymeric matrix, opening up the possibility of MOF defect engineering to realize selective separations, catalysis and sensing within a polymeric matrix.

How Amira-Avizo Software is used

450 SEM images were taken with a magnification of 10 K. Then the collected images were processed with Avizo