Photo-induced oxidative synergistic degradation of mixed anionic/cationic surfactant systems in aqueous dispersions. A detailed study of the DBS/HTAB system

The TiO2-photoassisted degradations of the anionic dodecylbenzenesulfonate (DBS) and cationic hexadecyltrimethylammonium (HTAB) surfactants have been examined in aqueous media along with the cationic/anionic 1:1 binary complexes of DBS/HTAB. The processes were monitored by surface tension measurements, total organic carbon (TOC) assays and carbon dioxide evolution. The degradation of the anionic surfactant was significantly involved in prior adsorption of the species on the positively charged metal-oxide particle surface. By contrast, the degradation of the cationic surfactant was rather limited owing to the lack of adsorption on the TiO2 surface under the same conditions. An adsorption model is proposed for the binary complexes on the metal-oxide surface.