Heterogeneous catalytic ozonation of aqueous reactive dye

The aqueous solution of a model reactive dye, C.I. Reactive Blue 5, was ozonated in the presence of a heterogeneous catalyst, CuS. It was found that CuS was very effective for catalyzing the decolorization so that both treatment time and ozone consumption were significantly reduced. For I g/L of the reactive dye, the stoichiometric ratios of ozone to dye in catalyzed and noncatalyzed ozonations were 2.7 and 10.6 (moles of ozone consumed)/(moles of dye oxidized), respectively, and the optimum catalyst load was 0.4 g/L. Although the noncatalytic ozonation was pseudo-first-order and the apparent pseudo-first-order rate constant declined with initial dye concentration logarithmically, in contrast, the experimental results showed that the catalytic ozonation was pseudo-second-order and the apparent pseudo-second-order rate constant decreased with initial dye concentration semilogarithmically. It was observed that the efficacy of ozone decolorization was higher at low pH and a scavenger test revealed that the amount of free radicals were negligible during ozonation. The experimental data further indicated that increase in temperature would increase the rate of the catalytic ozonation, however, the increment in the rate was not significant beyond 20 degrees C.