Enhancement of the photoinduced electron transfer from cationic dyes to colloidal TiO2 particles by addition of an anionic surfactant in acidic media

The absorption and emission characteristics of a cationic dye rhodamine B (RB) were observed in highly acidic colloidal TiO(2) aqueous solution and the same spectra of synthesized n-hexadecylrhodamine B (C(16)-RB) were also analyzed to get further realization of RE. Since both the TiO(2) surface and the dyes used are positively charged in acidic media, there is almost no adsorption of dye molecules on the surface of TiO(2) particles. By addition of an anionic sodium dodecylbenzensulfonate (DBS) surfactant, the mutual interaction among dyes, DBS and TiO(2) is very strong according to the absorption and emission spectral analysis. Anionic DBS molecules can modify the positively charged TiO(2) surface and make the same positively charged dyes assess to the TiO(2) surface. The distance between the dye and TiO(2) surface can affect the photoinduced electron transfer efficiency from dye molecules to the TiO(2) particles. This is well demonstrated by comparing RB with C(16)-RB by the fluorescence quenching efficiency in the TiO(2)/DBS and the TiO(2)-free systems. The photodegradation of RE in the TiO(2)/DBS system by visible light irradiation under either air-saturated or oxygen-free conditions also verify the conclusion that the dye RE can inject electrons to semiconductor particles much more efficiently after modification of the TiO(2) surface by an anionic surfactant. (C) 1998 Elsevier Science B.V.