Shape-based molecular separation

Scientists have created permeable thin, microporous films to separate molecules by cross-linking cyclodextrins — sugar-based organic molecules.

The films can be used to make a filtration membrane that can adapt to shapes and segregate molecules accordingly, 10 times faster than available commercial membranes, a feature that is potentially useful for industrial applications¹. 

“The films, made of container-shaped molecules, have cavities which can be exploited to make membranes with high permeability and selectivity,” says lead author Luis Francisco Villalobos from the King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia.

Their high permeability — 47 times higher than that of flat films — is partly due to their ‘crumbled’ structures. Molecules in a solvent were able to travel very quickly through the cavities or intermolecular spaces in the film.  

To test their sensitivity to molecule shape, the scientists exposed the films to a mixture of rhodamine B and protoporphyrin IX, two different neutral molecules of similar molecular weight, in methanol. The films allowed 97% of the cylindrically shaped rhodamine B molecules to pass through while retaining 90% of the spherically shaped protoporphyrin IX molecules.

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