Sonochemical degradation of perfluorinated surfactants: Power and multiple frequency effects

• C4 to C8 perfluorinated surfactants are degraded with ultrasound.
• C8 moieties degrade faster under dual frequencies irradiation.
• Rates of degradation are controlled by interfacial bubble water partitioning.

Perfluorosulfonates and carboxylates, C4 to C8 surfactants, are sonolytically degraded primarily at the vapor–water interface of cavitation bubbles. The observed pseudo first-order rate constants for the elimination of the perfluorosurfactants indicate that rates should be proportional to the degree of interfacial bubble–water partitioning. In fact, the sonochemical degradation rates of the more soluble and less hydrophobic perfluorobutane sulfonate, PFBS, and perfluorobutanoate, PFBA, were found to be slower than longer chain analogs due to their greater water solubility compared to the C8 counter parts. The observed degradation rate constants are found to increase with increasing power density. Enhanced degradation rates were observed for the C8 surfactants, PFOS (∼12%) and PFOA (∼23%) under simultaneous irradiation at 20 kHz and 202 kHz at a power combined power density of 250 W L−1.