Effects of pH and coexisting chemicals on photolysis of perfluorooctane sulfonate using an excited xenon dimer lamp

Vacuum ultraviolet (VUV) photolysis at the wavelength of 172 nm in a sulfate solution was introduced as a more efficient process for perfluorooctane sulfonate (PFOS) degradation than ultraviolet (UV) photolysis at 254 nm. The effects of pH and coexisting chemicals on VUV photolysis under the coexistence of 100 mM sulfate were investigated. VUV irradiation successfully degraded PFOS, and the degradation rate was 5.5 times higher than by UV photolysis. Direct VUV photolysis was inferred to mainly contribute to PFOS degradation. PFOS degradation by VUV irradiation was enhanced at pH less than 2 due to sulfate radicals generated via VUV photolysis of sulfate ions. Consequently, VUV photolysis was superior to UV photolysis for PFOS removal on both the removal rate and energy efficiency. However, the inorganic chemicals phosphoric acid and nitric acid strongly inhibited PFOS degradation, probably by masking PFOS from VUV rays by their VUV absorption. Accordingly, PFOS separation from inorganic materials such as phosphate and nitrate will be recommended for the application of VUV techniques for PFOS removal. In this research, organic solvent abstraction was inferred to be one of candidates for PFOS separation.