Effects of sonication on decolorization of C.I. Reactive Red 198 in UV/ZnO system

This study discusses the effects of ultrasound (US) irradiation on the decolorization of C.I. Reactive Red 198 (RR198) in UV/ZnO system. The influences of ZnO dosage, pH and the addition of NaCl or a radical scavenger were evaluated. The decolorization rate of RR198 increased with the ZnO dosage in 0.1-1 g/l and with pH in the UV/ZnO system. US accelerated the decolorization of RR198 in the UV-based system. The enhancement in the presence of NaCl can be attributed to an increase in the partitioning of RR198 upon cavitation implosion in US/ZnO system. At pH 7, the decolorization rate constants of UV/US/ZnO, UV/ZnO, US/ZnO, UV/US and US were 0.0739, 0.0534, 0.0022, 0.0020 and 0.0013 min−1, respectively. The decolorization rate was effectively inhibited by adding 1-butanol to UV/ZnO and UV/US/ZnO systems, suggesting that the main mechanism of RR198 destruction is chemical oxidation by hydroxyl radicals in the bulk liquid. The experimental results revealed that the UV/US/ZnO system cannot only completely decolorize RR198 but can effectively mineralize RR198.