This study analyzed the photocatalytic degradation of cytarabine in the presence of both TiO2 and activated carbon. Three commercial activated carbons denominated as S, M, and W were used in this study. Activated carbon W was oxidized with H2O2, HNO3, or O-3. The presence of non-oxidized (S. M, and W) and oxidized (W-H2O2, W-HNO3, WO3-30, WO3-120) activated carbon enhanced the degradation of cytarabine. The improvement with activated carbons S. M, and W was mainly attributable to their high adsorption capacity of cytarabine, whereas the improvement with activated carbons W-H2O2, W-HNO3, WO3-30, and WO3-120 was mainly due to interactions between acid sites of the carbons and the radical species generated from the TiO2 photoactivation. Activated carbon samples oxidized with ozone (WO3-30 and WO3-120) had more acid groups on their surface and yielded 20% and 32% additional degradation percentage of cytarabine, respectively. The presence of radical scavengers such as thiourea, t-butanol, and nitrate ions demonstrated that the interactions of HO center dot and e(aq)(-) radicals with acid sites of the activated carbons are responsible for the increased photocatalytic activity of TiO2. The interaction between e(aq)(-) and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to ketones generating H2O2 which can be decomposed into HO center dot radicals and, subsequently, the ketones generated can be transformed into an alcoholic superficial group generating additional HO center dot radicals. (C) 2011 Elsevier B.V. All rights reserved.