Evaluating the sensitizing effect on the photocatalytic decoloration of dyes using anatase-TiO₂

This work tries to clarify the contribution of the dye-sensitizing effect on the photocatalytic decoloration of dyes dissolved in aqueous media using an anatase TiO₂ (A-TiO₂) photocatalyst. The photocurrent-voltage (J-V) curves of a typical dye-sensitized solar cell (DSSC) with the A-TiO₂ photoanodes adsorbed with various dyes, including methylene blue (MB), orange G (OG), rhodamine B (RhB), metanil yellow (MY), acid black 24 (AB24), and N719, are employed to demonstrate the sensitizing characteristics of dyes on A-TiO₂. Unlike RhB, the MB, OG, MY, and AB24 cannot work as the photo-sensitizer on A-TiO₂ from the J-V curves of DSSCs, reasonably due to the unmatched band position between dyes and A-TiO₂. In the photocatalytic decoloration test of these dyes on A-TiO₂ in aqueous media, dye adsorption onto A-TiO₂ becomes the key factors affecting the photocatalytic decoloration rate because the generation of oxidants species (e.g., O2-, OH• or photo-excited holes) occurs on the A-TiO₂ surface. The contribution of dye-sensitizing on the photocatalytic decoloration of RhB is negligible since the dye-sensitizing/electron-injection/dye-regeneration cycle cannot be completed in the degradation media while adsorbed RhB molecules are unstable when few photo-generated electrons have been injected into the conduction band of A-TiO₂, probably leading to the decomposition of RhB.