Photochemical and heterogeneous photocatalytic degradation of waste vinylsulphone dyes: A case study with hydrolyzed Reactive Black 5

Aqueous solutions of hydrolyzed Reactive Black 5 (RB5) dye, a well-known surrogate for non-biodegradable azo dyes, were photochemically and photocatalytically treated by employing the H₂O₂/UV-C and TiO₂/UV-A advanced oxidation systems, respectively. The observed effects of reaction pH, oxidant dose and initial dyestuff concentration were used to explain the OH· induced color disappearance kinetics empirically. Accordingly, the waste dyestuff solutions could be completely decolorized (k_{d, max}=0.155min^-1; H₂O₂/UV-C system) and effectively mineralized (k_{TOC, max}=0.01min^-1; H₂O₂/UV-C system), with an average overall TOC removal of 78% after 120min advanced oxidation at the specified optimized reaction conditions. The treatment via H₂O₂/UV-C was mainly governed by OH· type oxidation rather than direct UV-C or UV-A photolysis, and the bleaching effect of the TiO₂/UV-A process could be successfully fitted to the empirical Langmuir-Hinshelwood (L-H) kinetic model (k_L-H=4.47mgl^-1min^-1; K_L-H=2.01lmg^-1).