Photochemical and photocatalytic degradation of an indigoid dye: a case study of acid blue 74 (AB74)

A detailed investigation of the photochemical and photocatalytic degradations of the indigoid dye AB74 is presented. H2O2 and C-UV light have negligible effect when they are used on their own. However, joint UV/H2O2 treatment more efficiently decomposes this organic compound. Surprisingly, reaction order depends strongly on the initial dye concentration On the other hand, H-1 NMR analysis reveals that the original dye is first converted into isatinsulfonic acid, then into aliphatic acids. Under band gap excitation of semiconductors, AB74 undergoes irreversible oxidation too. The photodegradation kinetics, on various catalysts, are discussed in term of the Langmuir-Hinshelwood model. H-1 NMR, UV-VIS and FTIR spectroscopic techniques provide an insight into the nature of the photoproducts. It was possible then to present a more complete degradation mechanism than supposed until now. (C) 2001 Published by Elsevier Science B.V.