Photocatalysis at solid/liquid interfaces-photooxidation of mixed aqueous surfactants at the TiO₂/H₂O interface

A series of anionic (DBS, SDS), non-ionic (C12E8, NPE-9), and cationic (HTAB, BDDAC) surfactant systems were examined alone and in a variety of combinations to assess the influence of co-habitation of two different types in the overall photodegra-dation of mixed aqueous surfactant solutions. The process was monitored by UV spectroscopy, total organic carbon (TOC) analyses, and surface tension measurements prior to and subsequent to UV illumination of the surfactant solutions in the presence of TiO2 particles. Results indicate that after about 3 to 4 hr of irradiation, more than ca. 90% of the mixed surfactant system was degraded as attested by the TOC remaining in the solution phase. As well, contrary to the stand-alone case, the photodegradation of the cationic surfactants was enhanced in the mixed systems as a result of positive charge neutralization by the other surfactant component. This study provides an overall strategy to minimize pollution caused by intentional or unintentional discharges of surfactants into water bodies.