Sonochemical degradation of sodium dodecylbenzene sulfonate in aqueous solutions

The sonochemical degradation of sodium dodecylbenzene sulfonate (SDBS) has been studied over a wide concentration range spanning the critical micelle concentration (CMC) of the surfactant. The rate of degradation of SDBS increased linearly with increasing concentration below the CMC of SDBS. Above the CMC, the degradation rate continued to increase but at a much slower rate compared with that below the CMC. It was found that the increasing rate of degradation of SDBS correlated closely with the decrease in the air/water surface tension of the surfactant solutions. The results of this study strongly suggest that the initial step in the degradation process is OH. radical attack onto SDBS molecules adsorbed at the cavitation bubble/solution interface. The sonication of SDBS solutions for extended periods of time (ca. 12 h) led to the generation of gaseous hydrocarbon products, such as methane, ethane, ethylene, and acetylene. It is concluded that further radical attack occurs on the intermediates produced from the initial degradation step. This further degradation pathway is responsible for producing both water-soluble species, and volatile products that are pyrolyzed within the cavitation bubbles.