A new type of catalyst could change how we break down some of the most persistent chemicals in the environment.

Researchers at Aarhus University have developed a material that actively weakens the bond between carbon and fluorine – the very bond that makes so-called “forever chemicals”, PFAS, exceptionally stable. In laboratory experiments, the team succeeded in completely degrading the PFAS compound PFOA (perfluorooctanoic acid) within three hours using ultraviolet light and very small amounts of catalyst.

“Instead of using more energy, we try to make the molecule less stable,” says Associate Professor Zongsu Wei. “If we can weaken the bond first, it becomes much easier to break.”

The research is a collaboration between Aarhus University, Stockholm University and the National Center for Materials Sciences in Tunisia, and has been published in the scientific journal Applied Catalysis B: Environment and Energy. 

Designed to destabilise molecules

The catalyst combines bismuth with small amounts of titanium. It is engineered with specific regions on its surface where reactive metal atoms act as chemical “grip points” for PFAS molecules.

When the molecule attaches to these sites, electrons are redistributed. This weakens the carbon–fluorine bond and makes the molecule more susceptible to breakdown.

“It’s a bit like pulling on the molecule so the bond stretches and becomes less stable,” explains Zongsu Wei. “That is what allows us to activate it with light.”

At the same time, the researchers observed that a significant portion of the fluorine is released as free fluoride ions. This is a key indicator that the strong bonds are actually being broken – not just transformed into other compounds.

One of the most striking findings is how little catalyst is required.

At concentrations as low as 5 milligrams per litre, the researchers achieved complete degradation of PFOA. This suggests that performance depends less on the amount of material and more on how it is designed.

“We can see that it is the surface chemistry that drives the process. If we simply add more material, the system actually becomes less efficient because the light cannot penetrate,” says Zongsu Wei.

PFAS: Why they are so difficult to remove

PFAS are a large group of synthetic chemicals designed to resist heat, water and grease. These properties have made them widely used in everything from consumer products to industrial applications – but also extremely difficult to break down.

The challenge lies in their molecular structure. The carbon–fluorine bond is one of the strongest in organic chemistry, which means many existing treatment technologies cannot effectively degrade these substances.

“In many cases, we are not actually eliminating PFAS,” says Zongsu Wei. “We are just moving them from one place to another with traditional filters.”

The new catalyst addresses this challenge by making the molecules chemically more vulnerable before the degradation process begins.

A step towards more effective water treatment

The researchers tested the technology in both pure water and groundwater. In more complex water systems, performance decreases because other substances compete for space on the catalyst surface.

The study also shows that not all PFAS compounds respond equally well, and that the process depends on factors such as pH.

“This is still laboratory research,” Zongsu Wei emphasises. “But it gives us an important insight into how we can design materials that selectively activate very stable molecules.”

The catalyst also demonstrated stability over multiple cycles, indicating potential for reuse.

A new principle for water treatment

The study points to a broader strategy: effectively breaking down persistent pollutants is not just about adding more energy, but about controlling how molecules interact with surfaces.

According to the researchers, the same approach could be applied to other types of hard-to-degrade contaminants.

“If we can control how molecules interact with a surface, we can also begin to control how they break down,” says Zongsu Wei.

Contact

Associate Professor Zongsu Wei
Department of Biological and Chemical Engineering, Aarhus University
Mail: zwei@bce.au.dk
Tel.: +4593522047