Enhancement of the catalytic activity of TiO2 by using activated carbon in the photocatalytic degradation of cytarabine

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 O3. The presence of non-oxidized (S, M, and W) and oxidized (WH2O2WH2O2, WHNO3WHNO3, WO3-30WO3-30, WO3-120WO3-120) 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 WH2O2WH2O2, WHNO3WHNO3, WO3-30WO3-30, and WO3-120WO3-120 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 (WO3-30WO3-30 and WO3-120WO3-120) 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 and eaq− radicals with acid sites of the activated carbons are responsible for the increased photocatalytic activity of TiO2. The interaction between eaq− and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to ketones generating H2O2 which can be decomposed into HO radicals and, subsequently, the ketones generated can be transformed into an alcoholic superficial group generating additional HO radicals.

. Adding activated carbon to the system considerably increased the photocatalytic cytarabine removal; the percentage removal was highest with the UV/TiO2/WO3-120UV/TiO2/WO3-120 system and decreased in the order: UV/TiO2/WO3-120>UV/TiO2/WO3-30>UV/TiO2/S>UV/TiO2/M>UV/TiO2/W>UV/TiO2/WH2O2>UV/TiO2/WHNO3>UV/TiO2UV/TiO2/WO3-120>UV/TiO2/WO3-30>UV/TiO2/S>UV/TiO2/M>UV/TiO2/W>UV/TiO2/WH2O2>UV/TiO2/WHNO3>UV/TiO2. It is important to note that in the absence of TiO2 those activated carbons samples did not increased the cytarabine photodegradation rate.Figure optionsDownload as PowerPoint slideResearch highlights
► This study analyzed the photocatalytic degradation of cytarabine in the presence of both TiO2 and activated carbon.
► The improvement with activated carbons WH2O2WH2O2, WHNO3WHNO3, WO3-30WO3-30, and WO3-120WO3-120 was mainly due to interactions between acid sites of the carbons and the radical species generated from the TiO2 photoactivation.
► The presence of radical scavengers demonstrated that the interactions of HO and eaq− radicals with acid sites of the activated carbons.
► The interaction between eaq− and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to cetones.