"Fluorines don’t play well with others, so if you put them together there are very strong interactions. Fluorinated contaminants in water want to separate themselves from the water and find other fluorine-rich matter."Scott Medina, Penn State
In nature, the interaction of molecules at the boundary of different liquids can give rise to new structures. These self-assembling molecules make cell formation possible and are instrumental to the development of all life on Earth.
They can also be engineered to perform specific functions — and now a team of Penn State researchers has leveraged this opportunity to develop a material that could remove persistent pollutants from water. The researchers report their work in a paper in Advanced Functional Materials.
"We took inspiration from biological systems to see if we can get similar phenomena to emerge with non-biological molecules," said Scott Medina, assistant professor of biomedical engineering at Penn State and corresponding author of the paper.
For their experiment, the researchers opted to incorporate fluorine, an element not commonly found in nature, into an amino acid and then mix it with a fluorinated oil to guide its molecular organization. When the team added this fluorinated oil to water, it formed a bead comprised of a fluorine droplet surrounded by an amino acid coating.
On exposing the bead to air, the researchers found that the bead’s components rearranged themselves to form a film. Composed of a thin layer of fluorinated oil surrounded by two layers of microscopic amino acid crystalline structures, this film would revert back to the bead when agitated — and take other fluorinated molecules with it.
"Fluorines don’t play well with others, so if you put them together there are very strong interactions," Medina said. "Fluorinated contaminants in water want to separate themselves from the water and find other fluorine-rich matter."
This phenomenon, and the compound’s capacity to switch between a film state and the bead shape, sparked the researchers’ interest in using it for pollutant capture. Per- and polyfluoroalkyl substances (PFAS) are artificial chemicals containing fluorine, typically used in the manufacture of water- or grease-repellent products. Their molecular structure allows them to accumulate in environments and the human body — permanently.
"Nature hasn’t evolved ways to break down fluorine-containing molecules efficiently, so these compounds stick around for a long time," Medina said. "They enter wastewater and soil, make their way into drinking water and food, and we consume them — and our bodies don’t degrade them very well, either."
To test the new compound’s potential for capturing PFAS, the researchers added contaminated water to a plastic container coated with their fluorinated amino acid film. The film captured the PFAS substances in the water within two hours and was able to hold them for up to 24 hours. If agitated during this time, the film would reform itself into a cohesive bead that could be easily collected from the now-purified water.
The researchers plan to explore these pollutant extraction capabilities further, investigating not only water purification but also the potential to harvest compounds from air. With further research into its applications, this fluorinated compound could become a multi-use contaminant removal tool in a variety of settings.
"There’s a lot of effort being placed into investigating the toxicology of PFAS and how to regulate them," Medina said. "This material could be implemented to remove PFAS from drinking water — and we think it could have a lot of utility in other areas as well."
This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.