Discerning the inefficacy of hydroxyl radicals during perfluorooctanoic acid degradation

Hassan Javed; Cong Lyu; Ruonan Sun; Danning Zhang; Pedro J J Alvarez

doi:10.1016/j.chemosphere.2020.125883

Discerning the inefficacy of hydroxyl radicals during perfluorooctanoic acid degradation

Chemosphere. 2020 May:247:125883. doi: 10.1016/j.chemosphere.2020.125883. Epub 2020 Jan 10.

Authors

Hassan Javed¹, Cong Lyu², Ruonan Sun³, Danning Zhang⁴, Pedro J J Alvarez⁵

Affiliations

¹ NSF Engineering Research Center for Nanotechnology Enabled Water Treatment (NEWT), USA; Dept. of Chemistry, Rice University, Houston, TX, 77005, USA.
² Key Lab of Groundwater Resources and Environment, Jilin University, Changchun, PR China.
³ Dept. of Civil and Environmental Engineering, Rice University, Houston, TX, 77005, USA.
⁴ NSF Engineering Research Center for Nanotechnology Enabled Water Treatment (NEWT), USA; Dept. of Civil and Environmental Engineering, Rice University, Houston, TX, 77005, USA.
⁵ NSF Engineering Research Center for Nanotechnology Enabled Water Treatment (NEWT), USA; Dept. of Chemistry, Rice University, Houston, TX, 77005, USA; Dept. of Civil and Environmental Engineering, Rice University, Houston, TX, 77005, USA. Electronic address: alvarez@rice.edu.

PMID: 31978654
DOI: 10.1016/j.chemosphere.2020.125883

Abstract

Perfluorooctanoic acid (PFOA) is a recalcitrant contaminant of emerging concern, and there is growing interest in advanced oxidation processes to degrade it. However, there is ambiguity in the literature about the efficacy of hydroxyl radicals (OH) for degrading PFOA. Here, we resolve this controversy by comparing PFOA degradation by UV photolysis (254 nm, 6 × 10^-6 E/L.s) versus UV + H₂O₂, which produces OH. We optimized OH production in a UV + H₂O₂ system using nitrobenzene (NB) as a OH probe, but even under optimized conditions (i.e., 5 g/L H₂O₂), no significant difference occurred in PFOA removal by UV photolysis (21.1 ± 0.4%) versus UV + H₂O₂ (19.7 ± 0.7%) after 1-day treatment. Both treatments also resulted in similar daughter by-product concentrations and defluorination efficiencies (9.5 ± 1.7% for UV photolysis and 6.8 ± 1.0% for UV + H₂O₂), which indicates that OH is ineffective towards PFOA degradation and infers that other degradation mechanisms that are independent of OH production should be explored.

Keywords: Advanced oxidation process (AOP); Defluorination; Hydroxyl radicals; Perfluorooctanoic acid (PFOA); Photolysis.

MeSH terms

Caprylates / chemistry*
Fluorocarbons / chemistry*
Hydrogen Peroxide
Hydroxyl Radical
Models, Chemical*
Oxidation-Reduction
Photolysis
Ultraviolet Rays
Water Pollutants, Chemical / chemistry*

Substances

Caprylates
Fluorocarbons
Water Pollutants, Chemical
Hydroxyl Radical
perfluorooctanoic acid
Hydrogen Peroxide