Novel complexation between ferric ions and nonionic surfactants (Brij) and its visible light activity for CCl₄ degration in aqueous micellar solutions

Wide attentions are recently focused on the use of surfactants for the remediation of contaminated soil and groundwater. UV photolysis has been often studied for the post-treatment of the contaminated surfactant solutions. In this study, we report a novel photolysis system where a recalcitrant perchlorocompound can be degraded in a surfactant solution under visible light (λ>420 nm) illumination: CCl₄ could be successfully dechlorinated in a nonionic surfactant (Brij) solution under visible light. The addition of Fe³⁺ in this surfactant solution enables the visible light induced dechlorination of CCl₄ because Fe³⁺ ions form complexes with the surfactant molecules (carrying the polyoxyethylene group) to act as a visible light sensitizer. A broad UV-Vis absorption band, which is centered around 370 nm and extended into the visible region, appears as a result of this complexation. The generation of this visible light absorption band is observed only in the Brij+Fe³⁺ solution and absent in other surfactant+Fe³⁺ solutions. Accordingly, the visible light induced dechlorination of CCl₄ is significant only in the Brij+Fe³⁺ solution. It is proposed that the Fe(III)-Brij complexing centers are excited by absorbing visible light and subsequently transfer electrons to adjacent CCl₄ molecules confined within the same micelle. Direct evidences for the visible light activation of the Fe³⁺-complexed Brij micelles were obtained from the photocurrent measurement. Effects of various experimental parameters and proposed mechanism for this visible light photochemical process are discussed.