Illustration showing how a composite material containing sheets of boron nitride (lattice of blue and silver balls) and nanoparticles of titanium dioxide (gray spheres) uses long-wave ultraviolet energy in sunlight to photocatalyse the breakdown of PFOA into carbon dioxide, fluorine and minerals. Credit: M.S. Wong/Rice University
Key Points
- Newly created boron nitride-titanium dioxide composites can degrade about 99% of PFOA in water.
- The research team exploited the power of the sun’s rays to catalyze the breakdown of PFOA.
- Growing regulatory pressure to set PFOA standards demands new and cost-efficient methods of removing the chemical from water.
Just two years after discovering that boron nitride, a commercially available powder commonly used in cosmetics, can destroy the forever chemical PFOA in just a few hours when exposed to UV light, Rice University chemical engineers have improved upon their design.
The 2020 discovery saw boron nitride destroy 99% of perfluorooctanoic acid (PFOA) in water samples within just a few hours once 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 Michael Wong, chemical and bioengineering professor at Rice. “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 to 400 nanometers. It’s what causes suntans and sunburns, and it’s plentiful in the sun rays that reach Earth. Building off the accessibility of long-wave UV, Wong and his team created a composite of boron nitride and titanium dioxide that is activated by UV-A.
In their new study, published in Chemical Engineering Journal, they showed the UV-A-powered composites destroyed PFOA about 15 times faster than plain titanium dioxide photocatalysts.
In outdoor experiments using plastic water bottles under natural sunlight, the team found that the boron nitride-titanium dioxide composites could degrade about 99% of PFOA in deionized water in less than 3 hours. In salty water, that process took about 9 hours.
PFOA is one of the most prevalent perfluoroalkyl and polyfluoroalkyl substances (PFAS), also called forever chemicals since they do not degrade easily. Mounting evidence suggests PFOA is harmful to human health. Some U.S. states have even set limits on PFOA contamination in drinking water, and in March 2021, the Environmental Protection Agency announced plans to develop federal standards.
Wong said his team is assessing how well its composite photocatalyst works for breaking down other PFAS.
Information provided by Rice University.