image: (a) EPR analysis of UV/PS/FA, UV/PS, and UV/FA systems. (b) Free radical quenching experiments. Reaction conditions: PFOA = 20 µM, initial pH of 2.5, anaerobic environment. (a) PS = 2 mM, FA = 15 mM, DMPO = 100 mM, reaction time = 5 min, anaerobic environment. (b) PS = 4 mM, FA = 2 mM, MV2+ = 10 mg/L, CCl4 = 10 µM, Cr(VI) = 1 mM.
Credit: The authors
By introducing a small amount of formic acid into a UV-activated persulfate system, the researchers transformed an inefficient oxidation process into a highly effective defluorination pathway, increasing fluorine removal from 27% to nearly 90% within 24 hours. The key lies in redirecting reactive chemistry to generate carbon dioxide radical anions, strongly reductive species capable of attacking PFOA’s notoriously stable carbon–fluorine bonds.
PFOA belongs to a broader class of per- and polyfluoroalkyl substances (PFAS) that have been widely used in textiles, firefighting foams, packaging, electroplating, and other industrial applications. Their exceptional chemical stability makes them valuable in products—but also means they persist in the environment, accumulate in organisms, and pose risks to liver function, immune systems, and reproduction. As a result, PFAS contamination has become a global concern, with urgent demand for effective remediation technologies. Existing treatment methods face major trade-offs. Advanced oxidation processes using persulfate or hydrogen peroxide can degrade PFAS, but typically require extreme conditions such as high temperatures, high oxidant doses, or intense energy input. Advanced reduction approaches based on hydrated electrons are highly effective but rely on costly photosensitizers and may generate problematic byproducts. A low-cost, energy-efficient, and scalable alternative has remained elusive.
A study (DOI: 10.48130/ebp-0025-0010) published in Environmental and Biogeochemical Processes on 05 December 2025 by Dongmei Zhou’s team, Nanjing University, offers a low-cost, energy-efficient route for treating recalcitrant perfluorinated contaminants in water and provides new mechanistic insight into how oxidative systems can be engineered for targeted reductive degradation.
Using a systematic comparison of UV-coupled redox systems combined with mechanistic probing and parameter optimization, the study first evaluated how different radical pathways influence the defluorination of PFOA. Three representative UV-activated systems—UV/SO₃²⁻, UV/persulfate (PS), and UV/H₂O₂—were examined to distinguish reductive versus oxidative degradation routes, followed by targeted modification of the UV/PS system through the addition of small-molecule organic additives (formic acid and methanol). Radical species were identified using electron paramagnetic resonance (EPR) spectroscopy and selective quenching experiments, while the effects of PFOA loading, PS and formic acid concentrations, solution pH, dissolved oxygen, coexisting anions, and natural organic matter were systematically investigated. The results show that reductive systems intrinsically outperform oxidative ones in cleaving PFOA’s strong C–F bonds: UV/SO₃²⁻ achieved 67% defluorination in 24 h via hydrated electrons, whereas UV/PS and UV/H₂O₂ reached only 27% and 18%, respectively. Introducing formic acid fundamentally altered the UV/PS chemistry, boosting defluorination to 89% by converting sulfate and hydroxyl radicals into highly reductive CO₂•⁻ radicals, as directly confirmed by EPR. Quenching tests demonstrated that suppressing CO₂•⁻ nearly eliminated defluorination, identifying it as the dominant reactive species. CO₂•⁻ proved more effective than alcohol radicals due to its stronger reduction potential, explaining the superior performance of UV/PS/FA over UV/PS/MeOH. Defluorination efficiency declined at higher PFOA concentrations due to radical competition and short-chain PFAS formation but remained superior to conventional oxidation even at 200 µM. Optimal performance occurred at moderate PS and formic acid dosages, under acidic and oxygen-free conditions. Common anions such as sulfate, bicarbonate, and nitrate slightly enhanced degradation by mitigating electrostatic repulsion, whereas nitrite and natural organic matter strongly inhibited defluorination by scavenging reactive radicals.
This strategy avoids extreme temperatures, high-energy inputs, and expensive reagents, relying instead on UV light, persulfate, and a low-cost organic acid. The findings also establish carbon dioxide radical anions as a powerful yet underexplored tool for PFAS remediation. More broadly, the work shows that oxidation-based systems can be deliberately redirected toward reductive chemistry, opening new design principles for treating pollutants that resist conventional approaches.
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References
DOI
Original Source URL
https://doi.org/10.48130/ebp-0025-0012
Funding Information
This work was supported by grants from the National Natural Science Foundation of China (Grant Nos 22176091, 42377010), and the State Key Laboratory of Water Pollution Control and Green Resource Recycling Foundation (Grant No. PCRRF25048).
About Environmental and Biogeochemical Processes
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.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Synergistic enhancement by formic acid in the oxidation system for perfluorooctanoic acid defluorination: efficiency and mechanism
Article Publication Date
5-Dec-2026
COI Statement
The authors declare that they have no competing interests.