Effects of initial concentration of LASs on the rates of sonochemical degradation and cavitation efficiency

Abstract

The effect of initial concentration of linear alkylbenzene sulfonate (LAS: p-octylbenzene sulfonate (LAS C 8 ), p-nonylbenzene sulfonate (LAS C 9 ), p-dodecylbenzene sulfonate (LAS C 12 )) on the rate of sonochemical degradation was investigated over a wide concentration range under Ar atmosphere by 200 kHz ultrasonic irradiation. The degradation rate of each LAS increased with increasing initial concentration of LAS and then started to decrease with the different behavior depending on the types of LASs. This result indicated that the cavitation efficiency was gradually changed by their concentrations and the optimum LAS concentrations for their effective degradation existed. The maximum degradation rates were observed at 250 lM of LAS C 12 , 1250 lM of LAS C 9 , and 2500 lM of LAS C 8 , respectively. These optimum concentrations were found to be about four to six times smaller than these critical micelle concentrations (CMCs). It was also found that the maximum degradation rates at the optimum concentrations were observed to be almost linearly correlated with their CMCs. Based on the obtained results, it could be suggested that the micelle formation occurs in the interfacial region of cavitation bubbles during rectified diffusion and this phenomenon reduces the cavitation efficiency. In addition, from the results of the rate of the sonochemical degradation of LASs and the yield of hydrogen peroxide, the existence of thermal gradient in the interfacial region of cavitation bubbles was also confirmed.

Sonochemical degradation of surfactants with different charge types: Effect of the critical micelle concentration in the interfacial region of the cavity

“…It has previously been reported that micelle formation can reduce the cavitation efficiency [20] , [21] . In addition, based on the clear relationship between the maximum degradation rate and cmc for LASs, we suggested that micelles formed in the interfacial region of the cavity by accumulation of the anionic surfactant even when the concentration was less than the cmc and reduced the cavitation efficiency [25] . We then investigated the relation between the maximum degradation rate and the cmc for surfactants with different charge types.…”

“…3 . For comparison, the data for LAS C 9 and C 12 are also plotted [25] . If micelle formation of the surfactant reduced the cavitation efficiency, the degradation rate should reach the maximum value when the initial bulk concentration is the cmc (dashed line in Fig.…”

“…We previously investigated the physicochemical properties of the interfacial region of cavities by sonochemical degradation of anionic surfactants [25] , [26] . We found that the initial degradation rates of linear alkylbenzene sulfonates (LASs) were strongly dependent on their concentrations.…”