A reusable system of natural inspiration that purifies water and builds itself

In nature, the interaction of molecules at the border of different liquids can give rise to new structures. These self-assembling molecules make cell formation possible and are essential for the development of all life on Earth.

They can also be designed to perform specific functions – and now a team of Penn State researchers have taken the opportunity to develop a material that could remove persistent pollutants from water. The researchers recently published their findings in Advanced functional materials.

“We took inspiration from biological systems to see if we can make similar phenomena emerge with non-biological molecules,” said Scott Medina, assistant professor of biomedical engineering and corresponding author of the article.

For their experiment, the researchers chose to incorporate fluorine, an element not widely found in nature, in an amino acid and mix it with a fluorinated oil to guide its molecular organization. The team added fluoridated oil to the water, where it formed a bead made up of droplets of fluorine surrounded by a coating of amino acids. When the researchers inverted the vial to expose the bead to air, the bead’s components rearranged to form a film. Composed of a thin layer of fluorinated oil surrounded by two layers of crystal structures of microscopic amino acids, this film could reorganize in the bead when agitated and carry other fluorinated molecules with it.

“Fluors don’t play well with other people, so if you put them together there are some really strong interactions,” Medina said. “Fluoride contaminants in water want to separate from the water and find other fluorine-rich materials.”

This phenomenon, and the capacity of the compound to switch between a film state and the shape of the ball, aroused the interest of the researchers for a possible capture of the pollutants. Per- and polyfluoroalkylated substances (PFAS) are man-made fluorine-containing chemicals generally used in the manufacture of water repellents or anti-grease products. Their molecular structure allows them to accumulate in environments and the human body permanently.

“Nature has not developed a way to efficiently break down molecules containing fluorine, so these compounds stay on for a long time,” Medina said. “They get into sewage and soil, end up in drinking water and food, and we consume them – and our bodies don’t break them down very well either.”

To test the new compound’s potential for capturing PFAS, the researchers added contaminated water to a plastic container covered with their film of fluorinated amino acids. The film captured the PFAS substances within two hours and was able to retain them for up to 24 hours. From this point on, the film containing PFAS could be stirred to reform into a cohesive bead which could be easily recovered from the now purified water.

The researchers plan to further explore these pollutant extraction capabilities, studying not only water purification, but also the potential for harvesting compounds from the air. With further research into its applications, the fluorinated compound could become a multipurpose contaminant removal tool for use in a variety of settings.

“There are many efforts to investigate the toxicology of PFAS and how to regulate them,” Medina said. “This material could be used to remove PFAS from drinking water and we believe it could be very useful in other areas as well.”