Catalyst destroys PFOA with sunlight

Researchers from Rice University have improved their catalyst, which destroys PFOA in just a few hours of ultraviolet light exposure, by creating a composite of boron nitride and titanium dioxide.

July 26, 2022

2 min read

Chemical engineers from Rice University, Texas, have improved their design for a light-powered catalyst that rapidly breaks down perfluorooctanoic acid (PFOA), one of the world’s problematic “forever chemical” pollutants.

Michael Wong and his students made the surprising discovery in 2020 that boron nitride, a commercially available powder that’s commonly used in cosmetics, could destroy 99 percent of PFOA, or perfluorooctanoic acid, in water samples within just a few hours when it was exposed to ultraviolet light with a wavelength of 254 nanometers.

“That was great because PFOA is an increasingly problematic pollutant that’s really hard to destroy,” said Wong, corresponding author of a study about the redesigned catalyst in Chemical Engineering Journal. “But it was also less than ideal because the boron nitride was activated by short-wave UV, and the atmosphere filters out almost all of the short-wave UV from sunlight. We wanted to push as much as possible boron nitride’s ability to access energy from other wavelengths of sunlight.”

Long-wave UV, or UV-A, has wavelengths ranging from about 315-400 nanometers. Boron nitride is a semiconductor, and isn’t activated by UV-A. Titanium dioxide, a common ingredient in sunscreen, is a semiconductor that is activated by UV-A, and it had even been shown to catalyze the breakdown of PFOA, albeit very slowly, when exposed to UV-A.

So Wong and study co-lead authors Bo Wang, Lijie Duan and Kimberly Heck decided to create a composite of boron nitride and titanium dioxide that married the best features of the individual catalysts. In their new study, they showed the UV-A powered composites destroyed PFOA about 15 times faster than plain titanium dioxide photocatalysts.

By analyzing photocurrent response measurements and other data, Wong’s team learned how its semiconductor composite harvested UV-A energy to break apart PFOA molecules in water. In outdoor experiments using plastic water bottles under natural sunlight, they found the boron nitride-titanium dioxide composites could degrade about 99 percent of PFOA in deionized water in less than three hours. In salty water, that process took about nine hours.

Mounting evidence suggests PFOA is harmful to human health. Some U.S. states have set limits on PFOA contamination in drinking water, and in March 2021 the Environmental Protection Agency announced plans to develop federal standards.