Does hydrogen peroxide really accelerate TiO2 UV-C photocatalyzed decolouration of azo-dyes such as Reactive Orange 16?

Abstract A comparison of UV-C initiated decolourations of the anionic azo-dye Reactive Orange 16 by H 2 O 2 , by anatase TiO 2 (PC500), and by H 2 O 2 /TiO 2 is reported. The decolouration rates induced by H 2 O 2 , by TiO 2 and by H 2 O 2 /TiO 2 , were compared in order to determine whether H 2 O 2 /TiO 2 was more beneficial than either H 2 O 2 or TiO 2 alone. UV-C photolyses H 2 O 2 to form hydroxyl radicals. UV-C can also initiate hydroxyl radical formation at the surface of TiO 2 , and in this study the photocatalytic conditions were chosen to enhance hydroxyl radical formation. In both cases the hydroxyl radicals lead to decolouration of the azo-dye Reactive Orange 16. Decolouration by irradiation of H 2 O 2 /TiO 2 was ∼5 times faster than by the TiO 2 photocatalyzed reaction but slower than that caused by irradiation of H 2 O 2 alone. Thus, the relative order of decolouration rates is: UV-C/TiO 2 2 /H 2 O 2 2 O 2 . Estimates of the absorption of UV by both H 2 O 2 and H 2 O 2 /Reactive Orange 16 solutions are used to show that this order is a consequence of the photonic efficiency of H 2 O 2 photolysis being ten to a hundred times larger than the photonic efficiency of hydroxyl radical generation at the surface of TiO 2 .

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