Photocatalytic degradation of commercial azo dyes

Seven azo dyes were photocatalytically degraded in TiO2 suspension. Their degradation rates were compared with disappearance and TOC elimination rates. It was demonstrated that diazo dye is less degradable than monoazo and the order of photocatalytic degradation rates was in approximate agreement with that of ozonation rates cited from literature. Major intermediates identified are aromatic amine, phenolic compounds and several organic acids. It was indicated from this study that in the photocatalytic degradation of azo dye the disappearance proceeds through both oxidation and reduction, whereas TOC is eliminated predominantly by oxidation. (C) 1999 Elsevier Science Ltd. All rights reserved.