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Northwestern Chemists Develop New Methods to Remove Toxins from Drinking Water

New materials target perfluorochemicals, chloroform, and dioxane pollutants

Mike M. McMahon | September 25, 2019
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Researchers at Northwestern University recently unveiled two new classes of materials designed to remove several toxic contaminants from drinking water. Developed in the lab of Will Dichtel, Robert L. Letsinger Professor of Chemistry at Northwestern’s Weinberg College of Arts and Sciences, the materials have been shown to greatly reduce the prevalence of perfluorinated pollutants, chloroform, and dioxane—all chemicals that have been linked to serious public health concerns including birth defects and cancer.

Research related to perfluorinated pollutant removal was published in the journal Angewandte Chemie while findings on chloroform and dioxane extraction appeared in the Journal of the American Chemical Society.

Removing Perfluorinated Pollutants

Perfluorochemicals are a family of synthetic chemicals that have been used for decades to make products that resist heat, oil, stains, grease, and water. Common uses include nonstick cookware, stain-resistant fabrics, and coatings for packaging such as milk cartons. The chemical structures of perfluorochemicals make them extremely resistant to degradation in the environment. Scientists have found that they accumulate in the food chain and are associated with several negative health effects including types of cancer and complications related to pregnancy and childbirth.

“Unfortunately, these chemicals have been used throughout the world and a very large amount of people have been exposed to them, often through drinking water,” says Dichtel. “Most recent estimates say that roughly 50 million Americans have been affected by perfluorinated pollutants, and that number could be higher.”
William Dichtel, Robert L. Letsinger Professor of Chemistry at Northwestern

We’re talking about one part-per-trillion, which is roughly equivalent to a couple drops of water in an Olympic-size swimming pool.”

Will Dichtel
Robert L. Letsinger Professor of Chemistry at Northwestern

In order to keep drinking water safe for public consumption, perfluorinated pollutants should be kept at extremely low levels. “We’re talking about one part-per-trillion, which is roughly equivalent to a couple drops of water in an Olympic-size swimming pool,” Dichtel explains.

To address this challenge, the Dichtel Lab has developed a polymer from a sugar derivative called cyclodextrin, whose molecules form a cup-like shape that is slightly larger than those of the pollutants, allowing them to fit inside. The researchers also built positive charges into the material, which has an added benefit.

“Most perfluorinated surfactant compounds of greatest present concern happen to be negatively charged. By adding a positive charge to the polymer, we can more selectively attract these negatively charged pollutants,” says Max Klemes, a PhD candidate in the Dichtel Lab at Northwestern and lead author on the Angewandte Chemie publication. “The combination of the molecular shape and the surface charge of our material allows these pollutants to bind very strongly.”

Another advantage of the material is that it can be reused, which is difficult to do with current methods that primarily rely on activated carbon to remove pollutants.

Targeting Chloroform and Dioxane Pollutants

In addition to tackling perfluorochemicals, the Dichtel Lab has developed another type of material aimed at removing a different class of harmful pollutants from drinking water. For this material, they set their sights on chloroform and dioxane—two chemicals that have been linked to increased risk of cancer and other adverse health effects.

Chloroform is formed when chlorine—a disinfectant that must be added to drinking water to kill disease-causing pathogens—interacts with organic matter in water systems. Dioxane is a chemical used in building materials, degreasers, and other industrial processes that often makes its way into water supplies through leaking underground storage tanks at hazardous waste sites or discharges from manufacturing facilities.

“Chloroform and dioxane are pretty small molecules—much too small for the cyclodextrin material we used to remove perfluorinated pollutants,” says Dichtel.

Using a similar conceptual idea, the research team designed a material that had different receptors specifically tailored for these two pollutants. Luke Skala, a PhD candidate in Dichtel’s lab and lead author for the Journal of the American Chemical Society publication, found his inspiration for the material from chemistry research conducted decades ago.

“I was looking through a supramolecular chemistry textbook and noticed that the synthesis of one particular receptor that’s known to bind things like chloroform was very similar to the types of bonds we form all the time with our polymers,” explains Skala. “It shows that you can use inspiration from older supramolecular chemistry knowledge to design new adsorbents. And if you can do that, this strategy should be able to be applied to all types of pollutants—not just chloroform and dioxane.”

In terms of next steps, Dichtel and his team are exploring the commercial viability of their new materials. In 2016, Dichtel co-founded CycloPure, Inc., which is commercializing adsorbents based on his research group’s discoveries for removing organic pollutants and problematic per- and polyfluorinated alkyl substances (PFAS) from water. The researchers are also interested in figuring out new methods for repurposing or permanently destroying the toxic pollutants after they have been extracted from water.

The research at Northwestern was supported by the Center for Sustainable Polymers, a National Science Foundation (NSF) supported Center for Chemical Innovation (CHE-1413862). Research on PFAS removal was conducted in collaboration with professor Damian Helbling of the School of Civil and Environmental Engineering at Cornell University. The work at Cornell was previously supported by the NSF (CHE-1541820) and more recently by the Strategic Environmental Research and Development Program (ER18-1026). Skala is supported by the NSF Graduate Research Fellowship under grant DGE-1842165.