Dye-effect in TiO 2 catalyzed contaminant photo-degradation: Sensitization vs. charge-transfer formalism

Abstract

Anatase TiO 2 surfaces have been treated with 2,4,6-triphenylpyrilium hydrogen sulfate (TPPHS) dye to yield the modified TiO 2/TPPHS surface. The modified TiO 2/TPPHS surface was then supported onto activated carbon (AC) surfaces to yield a new class of catalytic system AC/TiO 2/TPPHS. The catalytic activities of naked TiO 2, TPPHS solution, TiO 2/TPPHS and AC/TiO 2/TPPHS systems were examined in photo-degradation of phenol and benzoic acid in water, using both UV and visible regions. All studied systems showed low catalytic activity when used in the visible region. In UV, the AC/TiO 2/TPPHS showed highest activity, whereas the naked TiO 2 and TPPHS solutions were the least active systems. The dye role, in enhancing activity of modified surfaces in UV degradation of contaminants, is understandable by a charge-transfer catalytic effect rather than a sensitizing effect. AC role is explainable by its ability to adsorb contaminant molecules and bringing them closer to catalytic sites.