Effect of additives on ozone-based decomposition of Reactive Black 5 and Direct Red 28 dyes

In this research, ozonation of Reactive Black 5 (RB5) and Direct Red 28 (DR28) under the presence of Na2SO4 and Na2CO3 used as textile additives was investigated. The effect of these salts on discoloration, degradation dynamics, and the composition of the final compounds were studied. Different systems were evaluated; such as RB5-Na2SO4 (100 g/L), RB5-Na2CO3 (30 g/L), RB5-Na2SO4/Na2CO3 (100 g/ L/30 g/L), and DR28-Na2SO4 (10 g/L, 40 g/L, and 80 g/L) with dye concentrations of 50, 150, and 250 mg/L without pH adjustment. Discoloration of RB5 and DR28 with and without additives was determined by visible and UV (UV-Vis) spectroscopy. Decomposition of the dyes and the dynamics of intermediates and final byproducts were followed by high performance liquid chromatography. The presence of additives accelerated discoloration and decomposition for both dyes (more than 50%). The accumulation of oxalic and formic acids was observed. Possible mechanism schemes of ozonation for both dyes are proposed.