Photodegradation of Surfactants. XVIII. Total Organic Carbon Measurements in the TiO2-Assisted Photomineralization of Surfactants.

Abstract

Anionic (DBS), cationic (CTAB, BTDAC, C 12 -PC), non-ionic (C 12 E 5 , N-DHA) and amphoteric (C 12 -betaine, C 12 -amidobetaine, C 12 -HAA) surfactants were photodegraded in TiO 2 semiconductor suspensions under UV irradiation. Dependence of the rate of photodegradation on the chemical structure was investigated based on temporary variation of total organic carbon (TOC) in photodegraded solution. Differences in the photocatalytic effect of other metal-oxide catalysts such as ZnO, WO 3 , TiO 2 (anatase or rutile), TiO 2 (UV-100) and TiO 2 (T-805) were also examined. TiO 2 (anatase) and ZnO showed superior catalytic activity. TOC decreased with increase in irradiation time, since the surfactants were oxidized with the consequent evolution of CO 2 gas. TOC in solution after sonication without exposure to UV was less than that of the starting solution, indicating that surfactant to be preadsorbed on the TiO 2 surface. The rate of photodegradation of the anionic surfactants was greater than for the non-ionic, cationic and amphoteric surfactants. The increase in concentration caused decrease in the photodegradation rate. From the results of laser flash photolysis using colloidal TiO 2 and benzene sulfonate (BS), the surfactant is implicated in the scavenging of the charge carrier, thereby producing either a ground-state BS + cation radicals or.OH adducts with the benzene ring of BS.