Anti-oxidant/pro-oxidant activity of ascorbic acid
Effect in the degradation of Acid Orange 7with H2O2catalyzed by transition metal ions
MARCO PIUMETTI1, FRANCESCA S. FREYRIA1,2, MARCO ARMANDI1,
GUIDO SARACCO1, EDOARDO GARRONE1, BARBARA BONELLI1*
*Corresponding author
1. Department of Applied Science and Technology and INSTM Unit of Torino Politecnico,
Corso Duca degli Abruzzi 24, Politecnico di Torino I-10129 Turin, Italy
2. Department of Chemistry, Massachusetts Institute of Technology,
77 Massachusetts Ave, 02139 Cambridge, MA, USA
Abstract
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.
INTRODUCTION
Ascorbic acid (H2A, Scheme 1) is a molecule of ... ...
