Degradation of alkylphenol ethoxylate surfactants in water with ultrasonicirradiation

During the last years, many efforts have been devoted to the elimination of alkylphenol ethoxylate surfactants from aqueous systems. In this paper, th e sonochemical degradation of aqueous solutions of Triton X-100 was perform ed at an ultrasonic frequency of 358 kHz and an applied power of 50 W. Anal ysis of the reaction products by HPLC-ES-MS suggests that the hydrophobic a lkyl chain is the preferential site for oxidation. Alkylphenol, or short-ch ain ethoxylated phenols, were not generated as byproducts. To verify this h ypothesis, the sonochemical degradation of the corresponding alkylphenols ( e.g., tert-octylphenol) was performed under the same conditions; in these c ases, similar rate constants and products were observed. These results diff er from those reported for the biodegradation of alkylphenol ethoxylates. A substantial increase in the rate constant was observed for the degradation of Triton X-100 below its critical micelle concentration. This observation indicates that micelle formation serves to effectively isolate the free su rfactant monomers from the water-air interface of the oscillating cavitatio n bubbles, thus decreasing the overall efficiency of the sonochemical proce ss. The hydrophobic tail of the molecule is no longer exposed directly to t he bubble "hot spot" when it is pointed into the core of the micelles.