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Groundbreaking process for creating ultra-selective separation membranes published in Nature

March 15, 2017 - A team of researchers, led by the University of Minnesota, has developed a groundbreaking one-step, crystal growth process for making ultra-thin layers of material with molecular-sized pores. Researchers demonstrated the use of the material, called zeolite nanosheets, by making ultra-selective membranes for chemical separations. These new membranes can separate individual molecules based on shape and size, which could improve the energy-efficiency of chemical separation methods used to make everything from fuels to chemicals and pharmaceuticals. The research is published today in Nature, the world’s most highly cited interdisciplinary science journal.

“Overall, we’ve developed a process for zeolite nanosheet crystal growth that is faster, simpler, and yields better quality nanosheets than ever before,” said Michael Tsapatsis, a University of Minnesota chemical engineering and materials science professor and lead researcher on the study. “Our discovery is another step toward improved energy efficiency in the chemical and petrochemical industries.”

Today, most chemical and petrochemical purification processes are based on heat-driven processes like distillation. These processes are very energy-intensive. For example, chemical separations based on distillation represent nearly 5 percent of the total energy consumption in the United States. Several companies and researchers are developing more energy-efficient separations based on membranes that can separate molecules based on size and shape. One class of these membranes is based on zeolites, silicate crystals that have pores of molecular dimensions. However, the multi-step processes for manufacturing these membranes are costly and difficult to scale up, and commercial production remains a challenge.

In this new discovery, researchers have developed the first-ever, bottom-up process for direct growth of zeolite nanosheets. These nanosheets can be used to make high quality molecular sieve membranes. The new material, is only about five nanometers in thickness, and several micrometers wide (10 times wider than previous zeolite nanosheets). The new nanosheets also grow in a uniform shape making it much easier to make the membranes used in chemical purification.

“With our new material is like tiling a floor with large, uniform tiles compared to small, irregular chips of tile we used to have,” said Mi Young Jeon, a University of Minnesota chemical engineering and materials science Ph.D. graduate and the first author of the study. “Uniform-shaped zeolite nanosheets make a much higher-quality membrane with surprisingly high separation values that can sieve-out impurities.” The researchers’ molecular dynamics calculations also support that separation values in excess of 10000 may be achieved with these nanosheets.

To grow the zeolite nanosheets, researchers begin with seed nanocrystals that, first, double in size and develop facets. The seed crystals then trigger the formation of a twin outgrowth that evolves to become the nanosheet. Nanosheets start to appear from one corner of the seed crystals and then continue to grow, completely encircling the seed to form a faceted nanosheet that is extremely thin and uniform in size and shape. The uniform shape of the crystals came as quite a surprise, when it was first observed four years ago. “In my 25 years of studying zeolite crystal growth, I’d never seen anything like this before,” Tsapatsis said.

In addition to Tsapatsis and Jeon, other key members of the research team include CEMS professor Andre Mkhyoan, chemistry professor J. Ilja Siepmann, postdoctoral researchers Peng Bai and Donghun Kim, Ph.D. candidate Prashant Kumar and Ph.D. graduate Pyung Soo Lee. Other members of the 21-person team include several graduate students and postdoctoral researchers from the University of Minnesota as well as contributors from the U.S. Department of Energy’s Argonne National Laboratory, University of Massachusetts Amherst, and King Abdulaziz University in Saudi Arabia.

To read the full news release and watch a video on this new process, visit the College of Science and Engineering website: https://cse.umn.edu/news-release/researchers-develop-groundbreaking-process-creating-ultra-selective-separation-membranes/

To read the full research paper, entitled “Ultra-selective high-flux membranes from directly synthesized zeolite nanosheets,” visit the Nature website (link below).

Excerpts taken from University of Minnesota news release written by Rhonda Zurn, College of Science and Engineering and Lacey Nygard, University News.

Related Link: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature21421.html

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