Visible light sensitization of TiO2 nanoparticles by a dietary pigment, curcumin, for environmental photochemical transformations

Abstract

The use of curcumin, an active ingredient of turmeric powder (a dye component in curry), as a TiO₂ photo-sensitizer was investigated in terms of the photochemical and photoelectrochemical (PEC) properties. Owing to its strong visible light absorption and strong surface complexation, the curcumin-sensitized TiO₂ composite exhibited notable activities for the photochemical degradation of organic compounds, the reduction of chromate (Cr(VI)), and the generation of OH radicals and H₂O₂ through the reduction of O₂ under visible light (λ > 420 nm). Various spectroscopic methods confirmed the anchoring of curcumin on TiO₂ and the photochemical and PEC properties of curcumin/TiO₂ were compared with those of TiO₂ sensitized by a ruthenium complex (RuL₃) that has been frequently employed as a visible light sensitizer. Curcumin/TiO₂ exhibited consistently higher photochemical and PEC activities than RuL₃/TiO₂ over a wide pH range in an aquatic environment. These results confirm the practical viability of using a natural food dye, curcumin, as an efficient, eco-friendly, and cheap photo-sensitizer of TiO₂ for solar environmental applications. However, it should be noted that curcumin on TiO₂ like other dye sensitizers is degraded as a result of the sensitizing reactions in water and should be considered as a sensitizing reagent, not a photocatalyst.