Degree
Doctor of Philosophy (PhD)
Department
Environmental Sciences
Document Type
Dissertation
Abstract
This research investigates the role of pH in activating Environmentally Persistent Free Radicals (EPFRs) and developing sensors to quantify airborne active EPFRs. Model EPFR was synthesized by utilizing copper (Cu) or iron (Fe) as transition metals and monochlorophenol (MCP) as the organic component deposited on the Cab-O-Sil surface. The generation of hydroxyl radicals per EPFR was measured in a buffered solution (pH 5.5–9.0) at 15, 30, 60, 120, 180, and 300 minutes using DMPO spin adducts. The mixed model two-way ANOVA was used for spin-trapping data analysis. A simple linear regression model was fitted in the sensor study. Results indicated that hydroxyl radical formation per EPFR varied significantly with time (p2.5) exhibited trends like synthetic EPFRs, where OH•/EPFR yield increased with time and pH. The lowest radical concentration was observed at pH 5.0 compared to pH 6.0 and 8.0. The reaction order and apparent rate constant were –0.31 and 0.001 rad·EPFR⁻¹·s⁻¹, respectively. EPFR activation to its anionic form was found to be the rate-limiting step dependent on deprotonation in the aqueous medium. Various dyes were evaluated for their response to EPFRs at pH 8.0. Reactive blue showed the highest response, followed by coccine red, congo red, and reactive green, while reactive yellow and indanthrone exhibited no significant response to EPFRs. The results on PM2.5 response on red coccine dye indicated that the ratio of EPFRs measured by the sensor to those measured by Electron Paramagnetic Resonance (EPR) ranged from 0.35 to 2.22. A ratio below 1 implies fewer active radicals or radicals do not present on the PM2.5 surface, whereas a higher ratio suggests surface active radicals. In summary, this study elucidates the influence of pH on EPFR activation in both synthetic and ambient particulates and lays the foundation for developing sensors to monitor and quantify active EPFRs in PM2.5.
Date
3-16-2025
Recommended Citation
Dangal, Prakash, "Role of pH on Environmentally Persistent Free Radicals (EPFRs) Activation, and its Sensor Development" (2025). LSU Doctoral Dissertations. 6693.
https://repository.lsu.edu/gradschool_dissertations/6693
Committee Chair
Lomnicki, Slawo
Included in
Analytical Chemistry Commons, Environmental Chemistry Commons, Environmental Sciences Commons
