PHOTOCATALYTIC REDUCTION OF AZO DYES NAPHTHOL BLUE BLACK AND DISPERSEBLUE-79

Photocatalytic reduction of two textile azo dyes, Naphthol Blue Black (NBB) and Disperse Blue 79 (DB79) has been carried out in colloidal WO 3 and TiO2 suspensions. Under bandgap excitation of the semiconductor colloids these dyes undergo irreversible reduction as they react with the trapped electrons. The quantum efficiency for the photocatalytic r eduction of these dyes were 5.4% and 4.8% for NBB and DB79 respectivel y. The kinetics and mechanism of the interfacial charge transfer in th ese colloidal suspension has been elucidated with transient absorption spectroscopy. The reaction between the dye and trapped electrons is d iffusion limited and occurs with rate constants of 1.1 x 10(8) M(-1)s( -1) and 4.0 x 10(7) M(-1)s(-1) for NBB and DB79 respectively.