Abstract:The use of coumarin dyes adsorbed on titanium dioxide (TiO2, P25) successfully extended the photocatalytic UV response of TiO2 toward visible light region. The hydrogenation of acetophenone (AP) using TiO2 modified with coumarin dyes proceeded with good chemical efficiencies under visible light irradiation. The role of sacrificial reagents on this dye-sensitized system is also reported.

Phenothiazine dyes, methylene blue, new methylene blue, azure A, and azure B, photosensitized the oxidation of nicotinamide adenine dinucleotide (NADH), an important coenzyme in the living cells, through electron transfer. The reduced forms of these phenothiazine dyes, which were produced through electron extraction from NADH, underwent reoxidation to the original cationic forms, leading to the construction of a photoredox cycle. This reoxidation process was the rate-determining step in the photoredox cycle. The electron extraction from NADH using phenothiazine dyes can trigger the chain reaction of the NADH oxidation. Copper ions enhanced the photoredox cycle through reoxidation of the reduced forms of phenothiazine dyes. New methylene blue demonstrated the highest photooxidative activity in this experiment due to the fast reoxidation process. Electron-transfer-mediated oxidation and the role of endogenous metal ions may be important elements in the photosterilization mechanism.