The role of dissolved oxygen, and of active species generated by photo-induced reactions with oxygen, in the photocatalytic degradation of phenol was investigated using polymer [poly-(fluorene-co-thiophene) with thiophene content of 30%, so-called PFT30] sensitized TiO2 (PFT30/TiO2) under visible light irradiation. The photoluminescent (PL) quantum yield of PFT30/TiO2 was about 30% of that of PFT30/Al2O3, proving that electron transfer took place between the polymer and TiO2. The result that photocatalytic degradation of phenol was almost stopped when the solution was saturated with N-2 proved the importance of O-2. Addition of NaN3, an effective quencher of singlet oxygen (O-1(2)), caused about a 40% decrease in the phenol degradation ratio. Addition of alcohols caused about a 60% decrease in the phenol photodegradation ratio, indicating that the hydroxyl radicals (OH center dot), whose presence was confirmed by electron spin resonance (ESR) spectroscopy, was the predominant active species in aqueous solution. In anhydrous solution, singlet oxygen (O-1(2)) was the predominant species. These results indicate that oxygen plays a very important role in the photocatalytic degradation of phenol. (C) 2008 Elsevier B.V. All rights reserved.