The Science

Whether making a plastic coating or fuel, saving energy reduces costs. A vital target for cost savings is separating chemicals that are slightly different from each other. Nearly every processing industry must separate chemicals. Scientists created a rigid material with ultra-small pores with diameter less than 7Å, (less than one-millionth the diameter of a human hair) that are ultra selective based on size. The pores enable scientists to design films that can differentiate between similarly sized molecules based on small differences in a molecule’s shape.

The Impact

Membranes are separation agents. Scalable, efficient membranes reduce the cost and the environmental impact of producing vital commodities. How? The best membranes use a fraction of the energy of traditional approaches. This study shows how a material with ultra small pores can be scaled to separate large quantities of molecules effectively by allowing an efficient sorting process based on size.


Materials with rigid ultra small micropores provide selectivity that controls the motion of individual molecules to improve separation between similarly sized molecules by making it difficult for the “chubby ones” to get through. Next-generation membranes based on these advanced materials overcome the deficiencies of conventional polymers to separate alkanes and alkenes, natural gases, and isomers. Additionally, these next-generation membranes will achieve solute-solute discrimination in organic solvents, which was also a problem for conventional methods. Mass-producing molecular-scale separators must be economical. The key is to use hollow fibers with selective thin layers using an advanced version of the process to make textile fibers like those used to make inexpensive clothes. The advanced version of this technology relies upon hundreds of “spinnerets” to produce the fibers in parallel and then collect them into a holder. When the fibers are extruded and contact air, a skin forms—like it does when glue is in contact with air. Because these advanced materials are scalable, scientists can create molecularly selective membranes that could provide large payoffs in reducing carbon dioxide emissions and energy consumption for a more sustainable future.


W.J.K. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences (grant DE-FG02-04ER15510). Additional support was provided by the Roberto C. Goizueta Chair for Excellence in Chemical Engineering and Georgia Research Alliance Eminent Scholar in Membranes awards.


W.J. Koros and C. Zhang, “Materials for next-generation molecularly selective synthetic membranesExternal link.” Nature Materials 16, 289-297 (2017). [DOI: 10.1038/nmat4805]

Journal Link: Nature Materials 16, 289-297 (2017). [DOI: 10.1038/nmat4805]