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

Abstract

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 the ultraviolet (UV) photolysis at 254 nm, and discussed the effects of pH and coexisting chemicals on the VUV photolysis under the coexistence of 100 mM sulfate. The VUV irradiation successfully degraded PFOS, and the degradation rate was 5.5-times higher than that by the UV photolysis. The direct VUV photolysis was inferred to mainly contribute to the PFOS degradation. The PFOS degradation by VUV irradiation was enhanced at the pH less than 2 due to sulfate radicals generated via VUV photolysis of sulfate ions. Consequently, the VUV photolysis was superior to the UV photolysis for PFOS removal on both the removal rate and energy efficiency. However, inorganic chemicals of phosphoric acid and nitric acid strongly inhibited the PFOS degradation probably due to masking PFOS from VUV rays by their VUV absorption. Accordingly, PFOS separation from inorganic materials like phosphate and nitrate will be recommended for application of VUV techniques for PFOS removal. Organic solvent abstraction was inferred to be one of candidates for the PFOS separation in this research.