Water Science and Technology (Dec 2021)

Dependency of the photocatalytic and photochemical decomposition of per- and polyfluoroalkyl substances (PFAS) on their chain lengths, functional groups, and structural properties

  • Nusrat Chowdhury,
  • Srinivas Prabakar,
  • Hyeok Choi

DOI
https://doi.org/10.2166/wst.2021.458
Journal volume & issue
Vol. 84, no. 12
pp. 3738 – 3754

Abstract

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This study reports the removal of per- and polyfluoroalkyl substances (PFAS) in water using various photocatalytic and photochemical processes. PFAS were chosen, based on chain lengths, functional groups, and structural properties: four perfluorocarboxylic acids (PFCAs), including perfluorooctanoic acid (PFOA), three perfluorosulfonic acids (PFSAs), including perfluorooctanesulfonic acid (PFOS), hexafluoropropylene oxide dimer (GenX), and 6:2 fluorotelomer sulfonate (6:2 FTS), and dependency of the photocatalytic decomposition of PFAS on their properties was investigated. Oxidants and reductants were introduced to study the photochemical decomposition of PFAS, and reactive species and reaction byproducts were identified to elucidate the decomposition mechanism of PFAS. Some notable findings include: long chain PFCAs (95% in 48 h) and 6:2 FTS (100%) were removed via chemical decomposition in TiO2/UVC while GenX (37%), long chain PFSAs (60%), short chain PFSAs (0–10%) and short chain PFCAs (5–18%) were removed via physical adsorption. Sulfate radicals generated with persulfate (PS) played an important role in decomposing PFCAs (60–90%). Sulfite activated by UVC worked for defluorination of PFOA (75%) and PFOS (80%). PFOA was removed faster by UVC/sulfite > UVC/TiO2/sulfite ≈ UVC/TiO2/PS ≥ UVC/PS > UVC/TiO2 while PFOS was removed faster by UVC/sulfite ≫ UVC/TiO2/sulfite ≈ UVC/TiO2/PS ≈ UVC/TiO2 ≫ UVC/PS. Susceptibility of PFAS to the chemical reactions could be explained by their properties and the reactive species produced in each system. HIGHLIGHTS TiO2 photocatalytic/photochemical decomposition of nine different PFAS was compared.; TiO2/UV removed PFAS via physical adsorption and/or chemical decomposition.; Sulfate radicals generated with S2O82− played a major role in decomposing PFCAs.; Sulfite activated by UV worked significantly for defluorination of PFAS.; Overall susceptibility of PFAS to the chemical reactions was explained.;

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