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Iron powder outperforms activated carbon as adsorbent for PFOS—even when it rusts

PFOS, also known as "forever chemicals," are synthetic compounds popular for several commercial applications, like making products resistant to stains, fire, grease, soil and water. They have been used in non-stick cookware, carpets, rugs, upholstered furniture, food packaging and firefighting foams deployed at airports and military airfields.

PFOS (perfluorooctane sulfonate or perfluorooctane sulfonic acid) are part of the larger class of forever chemicals called PFAS (per- and polyfluoroalkyl substances.) Both types have been linked to a variety of health issues, including liver disease, immune system malfunction, developmental issues and cancer.

Because of their widespread use, PFOS are found in soil, agricultural products and drinking water sources, presenting a health risk. Xiaoguang Meng and Christos Christodoulatos, professors at the Department of Civil, Environmental and Ocean Engineering at Stevens Institute of Technology, and Ph.D. student Meng Ji working in their lab, wanted to identify the most efficient way to remove these toxins from the water.

Most water filters use activated carbon to remove forever chemicals and other contaminants. Activated carbon removes PFOS through a process called adsorption, in which the PFOS molecules stick to the large, porous surface area of the carbon particles as the water flows through them.

However, in the wastewater industry, iron powder—in scientific terms called microscale zero-valent iron or mZVI—is also used to remove contaminants from the effluent. "Iron powder is commonly used for water treatment and wastewater treatment, because it's cheap—it's cheaper than activated carbon," says Meng. They wanted to compare the adsorption potency of iron powder and activated carbon.

They found that iron powder was a better water purifier. "The iron powder was 26 times more effective than activated carbon per unit surface area," says Ji. Researchers outlined their findings in the study titled "Kinetic and Mechanism Study of PFOS Removal by Microscale Zero-Valent Iron from Water," in Environmental Science & Technology on March 19, 2025.

More interestingly, the team found that even when the iron powder rusted from being in the water, its adsorption properties weren't affected much. "The particles' surface is covered by iron oxide, but it's still very active," says Meng—and that's surprising. It means that the oxidized iron still contributes to PFOS removal. The unexpected findings made the study popular with other researchers, Meng says.

Meng and Ji are planning to investigate this phenomenon further. "Now we need to do more research to find out why," Meng says. "Because this is important for the development of large-scale removal technologies."