According to researchers, the control of the nanoscale structure of membranes is important

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A desalination membrane serves as a filter for salt water: push the water through the membrane, get clean water suitable for agriculture, energy production and even drinking. The process seems simple enough, but it contains intricate intricacies that have amazed scientists for decades – until now.

Researchers from Penn State, the University of Texas at Austin, Iowa State University, Dow Chemical Company and DuPont Water Solutions today (December 31) published an important finding to understand how membranes filter minerals out of water, online. Science. The article will appear on the cover of the print edition, which will be released tomorrow (January 1).

“Despite its use for many years, there is much we do not know about how water filtration membranes work,” said Enrique Gomez, professor of chemical engineering and materials science and engineering at Penn State, who led the research. “We have found that it is important for the production of water production how you control the density distribution of the membrane itself at nanoscale.”

Led by Manish Kumar, associate professor in the Department of Civil, Architectural and Environmental Engineering at UT Austin, the team used multimodal electron microscopy, which combines detailed atomic imaging with techniques that reveal chemical composition to determine that desalination membranes are not consistent in density and mass. The researchers mapped the density variations in polymer film in three dimensions with a spatial resolution of about one nanometer – that is less than half the diameter of a DNA strand. According to Gomez, this technological advancement was the key to understanding the role of density in membranes.

“You can see how some places in your coffee filter are more or less dense,” Gomez said. “In filter membranes it looks the same, but it is not on the nanoscale, and how you control the mass distribution is very important for water filtration.”

This was a surprise, Gomez and Kumar said, as it was previously thought that the thicker the membrane, the less water production. Filmtec, now part of DuPont Water Solutions, which manufactures numerous desalination products, collaborated with the researchers and funded the project because their internal scientists found thicker membranes to be permeable.

The researchers found that the thickness did not matter as much as avoiding high-density regions, or “dead zones”. In a sense, a more consistent density across the membrane is more important than the thickness for maximum water production, according to Gomez.

According to the researchers, this concept could increase membrane efficiency by 30% to 40%, which could lead to more water being filtered with less energy – a possible cost-saving update to current desalination processes.

“Reverse osmosis membranes are used so much for water purification, but there are still many that we do not know about,” Kumar said. “We could not really say how water moves through it, and all the improvements over the last forty years have been made in the dark.”

Reverse osmosis membranes work by applying pressure to one side. The minerals stay there while the water runs through. Although it is more efficient than non-membrane desalination processes, it still requires a tremendous amount of energy, the researchers said, but improving the efficiency of the membranes can reduce the load.

“Freshwater management is becoming a major challenge around the world,” Gomez said. “Deficits, droughts – with increasingly severe weather patterns, are expected to exacerbate the problem. It is extremely important to have clean water available, especially in areas with few resources.”

The team continues to study the structure of the membranes, as well as the chemical reactions involved in the desalination process. They are also investigating how to develop the best membranes for specific materials, such as durable yet tough membranes that can prevent the formation of bacterial growth.

“We continue to push our techniques with more high-performance materials to elucidate the key factors of efficient filtration,” Gomez said.


A biomimetic membrane for desalination of seawater on an industrial scale


More information:
noscale control of internal inhomogeneity increases the transport of water in desalination membranes, Science (2020). DOI: 10.1126 / science.abb8518

Provided by Pennsylvania State University

Quotation: Controlling the nanoscale structure of membranes is the key to clean water, researchers find (2020, 31 December) on 1 January 2021 from https://phys.org/news/2020-12-nanoscale-membranes-key.html

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