Anti-oxidant/pro-oxidant activity of ascorbic acid
Effect in the degradation of Acid Orange 7with H2O2catalyzed by transition metal ions
The effect of incubating mesoporous TiO2, with or without Fe3+ or V5+, in ascorbic acid (H2A) solutions before the catalytic oxidation in the dark with H2O2 of Acid Orange 7 was studied; the results were compared to the same reaction without H2A pretreatment. With a short incubation time, H2A irreversibly adsorbs on the TiO2 surface, depleting the related activity, so that pure TiO2 becomes inactive, and reduces surface ions to Fe2+ and V3+ species, so that the pristine reaction mechanisms (slow Fe3+-catalysed Fenton and stoichiometric oxidation by V5+ to V4+) are replaced by fast Fenton reactions. With long incubation times, H2A reacts with dissolved O2 to form 2,3-diketo-L-gulono-δ-lactone and has a detrimental effect on the catalytic activity.