Perfluorinated surfactant chain-length effects on sonochemical kinetics

Area of Science:

• Environmental Chemistry
• Physical Chemistry
• Chemical Engineering

Background:

• Perfluorochemicals (PFCs) are persistent environmental contaminants.
• Understanding their degradation pathways is crucial for remediation.
• Sonolysis offers a potential method for PFC removal.

Purpose of the Study:

• Investigate sonochemical degradation kinetics of short-chain PFCs (PFBA, PFBS, PFHA, PFHS).
• Evaluate the influence of chain length on PFC partitioning at the air-water interface.
• Compare degradation rates with longer-chain PFCs (PFOS, PFOA).

Main Methods:

• Surface tension measurements to determine air-water interface partitioning coefficients (KeqPF) and maximum surface concentrations (Gamma(max)PF).
• Sonolytic degradation experiments across a range of ultrasonic frequencies (202–1060 kHz).
• Kinetic analysis using pseudo-first-order models.

Main Results:

• Air-water interface partitioning (KeqPF) increased with decreasing chain length (PFHS < PFHA < PFBS < PFBA).
• Maximum surface concentrations (Gamma(max)PF) showed minimal chain length dependence.
• Sonolytic degradation rates followed pseudo-first-order kinetics at dilute concentrations.
• Degradation rate constants for PFHX peaked at 358 kHz, while PFBX peaked at 610 kHz.
• PFHX degradation rates were comparable to PFOX, but PFBX degradation was slower, correlating with their water solubility and film stability.

Conclusions:

• PFC degradation rates are influenced by chain length and interfacial properties.
• Ultrasonic enhancement of adsorption to the bubble-water interface occurs at dilute concentrations.
• Shorter-chain PFCs like PFBS and PFBA exhibit slower sonochemical degradation due to less stable surface films.
• Sonolysis shows potential for PFC remediation, with optimal frequencies varying by compound class.