College of Engineering, Computing and Applied Sciences

New advances at Clemson University could help degrade toxic chemicals in water


Toxic chemicals that refuse to break down in the environment and have been linked to health problems could be treated with a technology that Ezra Cates is advancing at Clemson University.

Per- and polyfluoroalkyl substances, or PFAS, are man-made chemicals that have been used in a wide variety of commercial products, ranging from water-repellent fabrics and nonstick frying pans to fast-food wrappers and firefighting foams.

Ezra Cates and his students are studying how photocatalysis could remove a group of toxic chemicals from water, a task he said is becoming more urgent.
Ezra Cates and his students are studying how photocatalysis could remove a group of toxic chemicals from water, a task he said is becoming more urgent.

Cates, an assistant professor of environmental engineering, is studying how photocatalysis could remove the chemicals from water. PFAS have contaminated drinking water supplies and groundwater at several sites around the country.

The chemicals don’t break down in the environment, and a growing body of research links them to health problems that include low-infant birth weights, cancer and effects on the immune system, according to the U.S. Environmental Protection Agency.

“It’s becoming pretty urgent, especially considering how widespread it is and how few tools we have to deal with it,” Cates said.

Cates and his team have been using photocatalysis to break down PFAS at Clemson’s L.G. Rich Environmental Research Laboratory. 

In photocatalysis, a suspension of semiconductor particles is added to tainted water, which is then irradiated with ultraviolet light. The light excites the particles, and the reaction reduces the contaminants in the water, Cates said.

Most semiconductors aren’t powerful enough to degrade PFAS, but Cates and his team have found one that is– bismuth phosphate. Even better, it can be used repeatedly with no degradation in performance, he said.

The Cates team has been experimenting with water samples prepared in the lab and groundwater samples provided by the military.

And now the team is expanding its research with the help of a $496,000 early-career grant from the U.S. Environmental Protection Agency.

The funding will allow the team to expand the study to landfill leachate, which poses a new challenge.

When water percolates through a landfill, it picks up organic compounds, Cates said. The challenge will be to get the semiconductor to treat the PFAS rather than mostly reacting with the organic compounds, he said.

A pretreatment before photocatalysis may be necessary, Cates said.

Also as part of the EPA grant, Cates and his team will study perfluorosulfonates, an especially challenging class of PFAS, he said.

“There’s no photocatalysis that’s been demonstrated to degrade this paticular subset of the PFAS,” Cates said. “We have some ideas on how to make that happen and some decent preliminary results. The idea is to ultimately have a catalyst or sequence of systems that can degrade the full range of PFAS contaminants rather than a select few.”

David Freedman, chair of the Department of Environmental Engineering and Earth Sciences, said that Cates is well positioned to tackle the research, an area that he said was urgent and a high priority for the nation.

“Dr. Cates’ work is an important step in identifying the practical approaches to managing PFAS,” Freedman said. “I congratulate him on the grant. It is well deserved.”

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