Effect of Sodium Alkyl Sulfates on Generation of Hydroxyl Radical by Acoustic Cavitation

Abstract

The effect of sodium alkyl sulfates (SAS) on the production of hydroxyl radical (･OH) from collapsing cavitation bubbles generated by irradiation with ultrasound in water was investigated. The surface physicochemical property, that is, dynamic surface tension, elongation of lamellae, and surface viscosity, of the SAS solution was also measured to correlate with the ･OH generation. Sodium dodecyl sulfate (SDS), sodium octyl sulfate (SOS), and sodium ethyl sulfate (SES) were employed as SAS. SAS was added to 0.1 mol/L aqueous disodium terephthalate solution, which is one of the florescence probes to detect ･OH, and was irradiated with ultrasound (47 kHz, 60 W). SDS and SOS prevented the generation of ･OH. However, SES promoted ･OH generation, especially at the low SES concentration. According to the result of dynamic surface tension, the generation of cavitation bubbles was accelerated as follows: SDS＞SOS＞SES≒without SAS. Moreover, the results of elongation of lamellae and surface viscosity demonstrated that the order of stability of cavitation bubbles was SDS＞SOS＞without SAS＞SES. Therefore, these results suggest that the promotion of ･OH generation by SES is associated with accelerated collapse of cavitation bubbles due to reduction in cavitation bubble stability.