Responsive membranes — materials that change properties in response to different conditions — can sustainably and economically filter pollutants from water, according to Rollie Mills, Ph.D., formerly with the University of Kentucky Superfund Research Center. Mills described how his research aimed to treat water contaminated with chemicals, like PFAS, at the Karen Wetterhahn Memorial Award Lecture, March 12.

PFAS are a large group of stable compounds that can leach into water and persist for many years. These chemicals have been linked to many health issues. Existing methods to remove PFAS from water, such as activated carbon or nanofiltration, have drawbacks that limit widespread usefulness.

“Activated carbon requires high temperatures to renew, making it less sustainable,” said Mills. “On the other hand, methods like nanofiltration can be expensive to use.”

Developing a responsive filter

Mills wanted to develop a flexible filter that was not only efficient and affordable but could also be easily and sustainably reused. He created a specialized membrane coated with a thermo-responsive polymer that could attract or repel PFAS depending on the temperature.

“At temperatures above 35 degrees Celsius, about the temperature of a hot summer’s day, the membrane can attract and capture PFAS from the water,” explained Mills. “Then, at lower temperatures, the material will repel PFAS and allow us to clean and reuse the filter.”

Mills also tested flexible membrane filters that could be used to remove other contaminants in different environments. He incorporated the thermo-responsive polymer into a membrane that could degrade polychlorinated biphenyls (PCBs) and found that the new filter could capture and destroy PCBs more efficiently than the membrane alone. Additionally, Mills found that light could be used to stimulate and heat membranes, introducing the possibility of using sunlight to treat contaminated water.

“As a result of this research, we’ve patented three devices and methods for removing PFAS from water, and we can definitely widen the technology more,” said Mills.

He says that, in addition to PFAS and PCBs, membrane filters could also be used to remove a range of pollutants, including trichloroethylene and volatile organic compounds.

More applications of membranes

In addition to creating membranes for filtering water contaminants, Mills developed an aerosol filter that can neutralize COVID-19 viral particles. The filter, which can be placed in N95 masks, contains enzymes that deactivate disease-causing proteins on the virus within 30 seconds. The membranes are also long-lasting and are capable of degrading viral particles for weeks after their initial use.

According to Mills, his research shows the potential of membranes to filter contaminants from both air and water.

“The membrane platform is very flexible and adaptable,” said Mills. “It really has the potential to help with so many emerging problems in the world.”