Nanopore Technology Could Mean Cheaper Desalination
Researchers at the University of Illinois have revealed that a thin film of molybdenum disulfide could transform seawater into freshwater at dramatically reduced cost.
Current desalination technology relies on reverse osmosis, which involves forcing seawater through plastic filters. The filters allow water to pass, but virtually nothing else, leaving the salt behind. But the thick filters require high water pressure, which increases the energy cost. They are also prone to clogging.
Using computer modeling, the Illinois team tested numerous surfaces and found that a thin sheet of molybdenum disulfide riddled with tiny holes, or nanopores, can pass high volumes of water but screen out salt and other impurities. Because of the way the material functions, high water pressures are not required.
A nanopore is a tiny hole in a thin membrane, typically just big enough to allow a single molecule of DNA to pass through.
“I’m very hopeful that this work can help the designers of desalination plants,” said Amir Barati Farimani, who worked on the study as a graduate student at Illinois and is now a postdoctoral fellow at Stanford University. “This type of thin membrane can increase return on investment because they are much more energy efficient.”
A study on their research was published in October in the journal Nature Communications.
The material works because a molybdenum disulfide molecule has one molybdenum atom sandwiched between two sulfur atoms. A sheet of MoS2, then, has sulfur coating either side with the molybdenum in the center.
The researchers found that creating a pore in the sheet that left an exposed ring of molybdenum around the center of the pore created a nozzle-like shape that drew water through the pore.
The molybdenum disulfide attracts water, then the sulfur on the other side pushes it away, which allows a much higher rate of water to pass through the pore.
In addition to these chemical properties, the single-layer sheets have the advantages of thinness, requiring much less energy, which in turn dramatically reduces operating costs. Molybdenum disulfide also is a robust material, so even a very thin sheet can withstand high water pressures and volumes.
The researchers are now establishing collaborations to experimentally trial molybdenum disulfide for desalination and test its rate of clogging of the pores. The Air Force Office of Scientific Research, the National Science Foundation and the Beckman Institute supported the research.
October Conservation Results Out Today
The State Water Resources Control Board at a meeting today will reveal October water conservation progress by California’s urban water agencies, and the results are expected to be less than stellar.
That’s because cooler temperatures reduced the need for landscape irrigation. Because this is the largest sector of urban water use, it’s an easy area in which to find savings. As a result, this year’s October comparison with the benchmark of 2013 will be about indoor water consumption, where water savings are much harder to come by.
Felicia Marcus, chair of the water board, revealed in an interview with the Associated Press that October conservation progress has declined, although she would not disclose by how much.
“I think people have gotten the message,” Marcus said. “Californians are continuing to understand that they need to save water.”
California’s 411 large urban water agencies are under orders to cut water use by 25 percent in the 12 months ending with February 2016. Initial efforts were poor, with savings reaching only into the 10–12 percent range in the spring. By summer, Californians got the message and savings reached 27 percent in June, 31 percent in July, 27 percent in August and 26 percent in September.
But because of the slow start and declines expected in the cooler fall and winter months, it is possible the state will miss the 25 percent goal on average.
Today’s water board meeting is at 9 a.m. in Sacramento. A live webcast and audiocast are available.
Top image: A computer model of a nanopore in a single-layer sheet of molybdenum disulfide shows that high volumes of water can pass through the pore using less pressure than standard plastic membranes. Salt water is shown on the left, fresh water on the right. (University of Illinois)