Turning a weak process into a strong one
PFOA is a widely used perfluorinated compound valued for its durability, but its strong carbon fluorine bonds make it extremely hard to break down once it reaches the environment. Traditional advanced oxidation processes based on ultraviolet light and powerful oxidants often require high temperatures, large doses of chemicals, or long treatment times to partially degrade these molecules.
In the new work, the research team tested several UV based redox systems and found that a standard UV persulfate setup could only achieve 27 percent defluorination of PFOA after 24 hours under mild conditions. When they added a small amount of formic acid, a cheap and common organic acid, defluorination jumped to 89 percent over the same period.
Radical "hand off" unlocks faster defluorination
The key lies in how radicals are generated and transformed in the system. Under UV light, persulfate produces strong oxidizing radicals, but these species tend to attack the carboxyl end of PFOA rather than cleaving its robust carbon fluorine backbone.
"With formic acid, we essentially turn an oxidative system into a powerful reductive one that can finally open up the carbon fluorine chain," says corresponding author Dongmei Zhou of Nanjing University. Electron paramagnetic resonance measurements and quenching experiments showed that the oxidizing radicals react with formic acid to form carbon dioxide radical anions, which are strongly reducing and become the main agents that strip fluorine atoms from PFOA.
Simple chemistry, big impact
The study also compared methanol as an alternative organic additive and confirmed that both additives can generate reductive radicals, but the carbon dioxide radical from formic acid has a more negative reduction potential and delivers higher defluorination efficiency. Under identical conditions, the UV–persulfate–formic acid system outperformed UV–persulfite and UV–hydrogen peroxide setups, particularly in acidic solutions.
"PFOA prefers to accept electrons rather than be oxidized, so reductive radicals give us a much more efficient pathway for breaking its bonds," explains first author Changyin Zhu. The team showed that the method remained effective even at higher PFOA concentrations, still achieving around 55 percent defluorination at 200 micromolar, which exceeds many conventional Fenton and persulfate treatments.
Role of pH, oxygen, and coexisting substances
Acidic conditions proved crucial for performance, with the best results at pH 2.5 and reduced efficiency at neutral and alkaline pH. The authors attribute this to both electrostatic effects between charged species and the way acidity promotes productive encounters between PFOA and the carbon dioxide radicals.
The system worked best under oxygen free conditions because dissolved oxygen readily scavenges the reductive radicals that drive defluorination. Common anions such as sulfate, bicarbonate, and nitrate moderately enhanced the process by helping to overcome electrostatic repulsion, whereas nitrite and natural organic matter such as humic acid strongly suppressed performance by consuming key radicals.
Toward practical PFAS remediation
By relying on inexpensive persulfate and formic acid, the approach offers a comparatively simple and potentially scalable route to tackle PFOA and related PFAS in contaminated water. The only primary byproduct of formic acid oxidation is carbon dioxide, which reduces concerns about secondary pollution compared with many other radical generating additives.
"This study shows that carefully steering radical pathways with a small organic acid can unlock far more efficient destruction of stubborn fluorinated pollutants," says Zhou. The researchers suggest that similar carbon dioxide radical based strategies could be extended to other perfluorinated compounds, opening new avenues for treating PFAS contaminated sites.
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Journal reference: Zhu C, Zhang Q, Wang X, Zhou D. 2025. Synergistic enhancement by formic acid in the oxidation system for perfluorooctanoic acid defluorination: efficiency and mechanism. Environmental and Biogeochemical Processes 1: e013
https://www.maxapress.com/article/doi/10.48130/ebp-0025-0012
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About the Journal:
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
