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 rhodamin e B (RB) were observed in highly acidic colloidal TiO2 aqueous solutio n and the same spectra of synthesized n-hexadecylrhodamine B (C-16-RB) were also analyzed to get further realization of RE. Since both the T iO2 surface and the dyes used are positively charged in acidic media, there is almost no adsorption of dye molecules on the surface of TiO2 particles. By addition of an anionic sodium dodecylbenzensulfonate (DB S) surfactant, the mutual interaction among dyes, DBS and TiO2 is very strong according to the absorption and emission spectral analysis. An ionic DBS molecules can modify the positively charged TiO2 surface and make the same positively charged dyes assess to the TiO2 surface. The distance between the dye and TiO2 surface can affect the photoinduced electron transfer efficiency from dye molecules to the TiO2 particles . This is well demonstrated by comparing RB with C-16-RB by the fluore scence quenching efficiency in the TiO2/DBS and the TiO2-free systems. The photodegradation of RE in the TiO2/DBS system by visible light ir radiation under either air-saturated or oxygen-free conditions also ve rify the conclusion that the dye RE can inject electrons to semiconduc tor particles much more efficiently after modification of the TiO2 sur face by an anionic surfactant. (C) 1998 Elsevier Science B.V.