Purifying dirty water is an age-old problem that has become more urgent as the global population grows, and water contains more and different kinds of pollutants. Over time, filters have evolved—from simple sieves that strain out sand and dirt to advanced membranes that selectively remove harmful chemicals and dissolved salts.
William Phillip, Rooney Family Collegiate Chair of Engineering, and his W.A.T.E.R. Lab have developed a charge-patterned mosaic membrane (CMM) that separates substances based on their charged ions. Separating ions is important not only for cleaning water, but also for recycling resources, since it can target specific chemicals or ions accurately.
Their results were published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).
“Our membranes rely on the way molecules interact or their electrical charges to separate them more effectively,” said Phillip. “This approach could make it possible to tackle difficult problems, such as recovering valuable metals from electronic waste or extracting nutrients from wastewater—something traditional membranes struggle to do.”
Mixed salts, a common byproduct in industrial wastewater, are notoriously difficult to remove using conventional filters because their ions carry different charges. Mathematical models and computer simulations enabled the team to predict, and then confirm with experiments, that by fine-tuning the patterns of charges on the membrane, they could make salts move in very specific ways.
The team’s inkjet-printed membrane with its pattern of positive or negative charges could be tuned to hold certain salts back—concentrating them on one side of the membrane to make them recoverable—or to reject them entirely, cleaning them out of sensitive systems such as power plants and pharmaceutical production.
“Our approach isn’t a one-size-fits-all solution,” said Phillip. “The insights we’ve gained suggest that we can design patterns to calibrate selectivity and permeability—all based on our specific goals.”
This work was made possible with support from the NSF through the Advanced Manufacturing Program.
—Karla Cruise, Notre Dame Engineering