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

A detailed investigation of the photochemical and photocatalytic degradatio ns of the indigoid dye AB74 is presented. H2O2 and C-UV light have negligib le 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 isat insulfonic acid, then into aliphatic acids. Under band gap excitation of se miconductors, AB74 undergoes irreversible oxidation too. The photodegradati on kinetics, on various catalysts, are discussed in term of the Langmuir-Hi nshelwood model. H-1 NMR, UV-VIS and FTIR spectroscopic techniques provide an insight into the nature of the photoproducts. It was possible then to pr esent a more complete degradation mechanism than supposed until now. (C) 20 01 Published by Elsevier Science B.V.