What question did this study set out to answer?

The research aims to characterize the behavior of EPFRs and how pH influences hydroxyl radical production.

March 19, 2026Environmental Science & Technology1 citations

pH-Dependent Activation of EPFRs and Kinetics of Hydroxyl Radical Generation

PDPrakash Dangal LKLavrent Kanchatryan QYQingzhao Yu

Key Points

The research aims to characterize the behavior of EPFRs and how pH influences hydroxyl radical production.
Utilized a model EPFRs system with copper oxide and 2-monochlorophenol on amorphous silica.
Measured hydroxyl radical production across a pH range of 5.5-9.0 during redox cycling intervals.
Developed a kinetic model to analyze the pH-dependent formation rate of hydroxyl radicals.
Confirmed that lower pH enhances the stability of EPFRs, while higher pH boosts redox activity.
Observed a significant increase in hydroxyl radical yield at pH levels above 7.4 (<i>p</i> < 0.001).
The developed kinetic model accurately described hydroxyl radical generation, indicating an inverse relationship with proton concentration.

Abstract

Environmentally Persistent Free Radicals (EPFRs) pose potential environmental and health risks, yet their behavior remains insufficiently characterized. This study investigates the influence of pH on EPFRs activation during redox cycling, focusing on their capacity to generate hydroxyl radicals (•OH). We hypothesized and confirmed that EPFRs environmental stability is enhanced under low pH conditions, whereas higher pH accelerates their redox activity. A model EPFRs system was employed, consisting of 0.25% copper oxide (CuO) as the transition metal center and 2-monochlorophenol (MCP) as the organic precursor, supported on amorphous silica (Cabosil). Hydroxyl radical production was quantified via DMPO spin trapping across a buffered pH range of 5.5-9.0 at redox cycling intervals of 15, 30, 60, 120, 180, and 300 min. Results revealed that •OH yield per EPFRs (•OH/EPFR) was significantly different on both pH and time (p < 0.001), with substantially higher ratios observed at pH values above 7.4. A kinetic model describing the pH-dependent •OH formation rate was developed, showing excellent agreement with experimental data. The model suggests that hydroxyl radical generation by EPFRs is inversely proportional to proton concentration, exhibiting pseudo-first-order kinetic behavior. These findings suggest that EPFRs persist under acidic environmental conditions but become highly reactive at physiological pH, thereby increasing their potential to produce reactive oxygen species.

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