Photodegradation of the aminoazobenzene acid orange 52 by three advanced oxidation processes: UV/H2O2 UV/TiO2 and VIS/TiO2 - Comparative mechanistic and kinetic investigations

This paper presents the results obtained from the oxidation of the aminoazo benzene dye AO52 by the UV/H2O2, UV/TiO2 and VIS/TiO2 systems. In the forme r case, we investigated the formation of first by-products by means of GC/M S, HPLC and H-1 NMR. spectroscopy. We conclude that hydroxyl radicals are a dded to aromatic rings in the ipso position with respect to the sulfonate g roup or to the azo-linkage-bearing carbon. The reaction of the inorganic ra dical with the N,N-dimethylamino substituent, leading to demethylation, add s to the multiplicity of the possible pathways. Degradation by the UV/TiO2 system is pH dependent. Whereas hydroxyl radicals are the main oxidative ag ent in neutral and alkaline solutions, positive hole-induced oxidation comp etes with the reduction of the protonated dye molecules in acid media. More over, FTIR spectroscopy of AO52/TiO2 wafers provided an insight to the natu re of the photoproducts. This process is very efficient since only ultimate breakdown products, i.e. aliphatic acids and inorganic salts, are detected . Similar results were obtained using visible light as the irradiation sour ce in the case of wafers whereas in heterogeneous solutions, the dye seems to be resistant to degradation. (C)2000 Elsevier Science S.A. All rights re served.