Atomic-Scale Imaging Reveals Secret to Thin Film Strength

In a recent Nature Materials paper, ME Professor Traian Dumitrica and his collaborators report that one-dimensional intergrowths in two-dimensional zeolite nanosheets — as revealed by experiment and atomistic simulations — allow for world-beating xylene separation performance.

An international team of scientists and engineers, led by University of Minnesota Associate Professor K. Andre Mkhoyan and Professor Emeritus Michael Tsapatsis (currently, a Bloomberg Distinguished Professor at Johns Hopkins University) and including ME Professor Traian Dumitrica, have made a discovery that could further advance the use of ultra-thin zeolite nanosheets, which are used as specialized molecular filters. The discovery could improve efficiency in the production of gasoline, plastics, and biofuels.

"The xylene separation process has enormous industrial importance," said Dumitrica. "Improving its performance brings great economic and environmental benefits."

The breakthrough discovery of one-dimensional defects in a two-dimensional structure of porous material (a zeolite called MFI) was achieved using a powerful high-resolution transmission electron microscopy (TEM) on the University of Minnesota Twin Cities campus. By imaging the atomic structure of the MFI nanosheets at unprecedented detail, the researchers found that these one-dimensional defects resulted in a unique reinforced nanosheet structure that changed the filtration properties of the nanosheet dramatically.

Knitting of lines of one zeolite within another has pronounced consequences in the ability of nanosheets to recognize and selectively transport molecules enabling selective separations and catalysis. University of Minnesota Professors Dumitrica (mechanical engineering) and Ilja Siepmann (chemistry) led the simulations to test this pattern and performance. Their findings revealed that the knitted materials are less responsive to stress and more selective in separating molecules based on size and shape.

“Making ultra-selective thin film membranes and hierarchical catalysts by fine tuning the frequency and distribution of intergrowths of porous frameworks is a concept introduced by our research group a decade ago,” said Tsapatsis. “The discovery by TEM of one-dimensional intergrowths in two-dimensional nanosheets and the practical implications suggested by modeling bring the potential of this concept to a new level and suggest new opportunities for targeted synthesis that we have not imagined possible.”

This research was primarily funded by the National Science Foundation, with partial support for certain characterizations and computations by the U.S. Department of Energy and a variety of University of Minnesota partners.