Researchers find that nanomembrane-scale control of membranes is essential for clean water

A desalination membrane acts 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 complex complexities that have puzzled scientists for decades – until now.

Researchers at Penn State, Texas University of Austin, Iowa State University, Dow Chemical Company and DuPont Water Solutions published today (December 31) a key breakthrough in understanding how membranes filter minerals from water in Science. The article will be presented on the cover of the print edition, which will be published tomorrow (January 1).

“Despite their use for many years, we don’t know much about how water filtration membranes work,” said Enrique Gomez, a professor of chemical engineering and materials science and engineering at Penn State who led the research. “We’ve found that how you control the density distribution of the membrane itself at the nanoscale is really important for water production performance.”

Co-led by Manish Kumar, an associate professor in the Department of Civil, Architectural and Environmental Engineering at UT Austin, the team used multimodal electron microscopy, which combines detailed atomic-scale imaging with techniques that reveal chemical composition, to determine those membranes. desalination plant. they are inconsistent in density and mass. The researchers mapped the density variations of the 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 progress has been essential in understanding the role of membrane density.

“You can see how some places are more or less dense in a coffee filter just by the eyes,” Gomez said. “In filter membranes, it looks uniform, but it’s not at the nanomural level, and how you control the mass distribution is really important for water filtration performance.”

This was a surprise, Gomez and Kumar said, because previously it was believed that the thicker the membrane, the less water production. Filmtec, now part of DuPont Water Solutions, which produces many desalination products, collaborated with the researchers and funded the project, as scientists inside found that the thicker membranes proved to be more permeable.

Researchers have found that thickness does not matter as much as avoiding extremely dense regions at the nanomic level or dead zones. In a sense, a more consistent density across the membrane is more important than thickness to maximize water production, according to Gomez.

This understanding could increase the efficiency of the membrane by 30% to 40%, according to the researchers, resulting in more filtered water with less energy – a potential cost-saving upgrade to current desalination processes.

“Reverse osmosis membranes are so widely used for water purification, but there are still many things we don’t know,” Kumar said. “I couldn’t really tell how the water was moving through them, so all the improvements over the last 40 years have been essentially in the dark.”

Reverse osmosis membranes work by applying pressure to one side. Minerals remain there as water passes through. Although it is more efficient than membrane-free desalination processes, it still requires a huge amount of energy, the researchers said, but improving the efficiency of membranes could reduce this burden.

“Managing freshwater is becoming a crucial challenge around the world,” Gomez said. “Lack, drought – as severe weather conditions increase, this problem is expected to become even more significant. It is extremely important to have clean water available, especially in low-resource areas.”

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

“We continue to push our techniques with better materials in order to elucidate the crucial factors of efficient filtration,” Gomez said.