Photodegradation of C.I. Reactive Red 2 in UV/TiO2-based systems: Effects of ultrasound irradiation

This investigation elucidated the decolorization of C.I. Reactive Red 2 (RR2) in US/TiO2, UV/TiO2 and UV/US/TiO2 systems and evaluated the effect of ultrasound (US) irradiation in photocatalysis. The effects of RR2 concentration, temperature and the addition of NaCl, Na2S2O8 and radical scavenger were determined. The decolorization reactions obeyed the pseudo-first-order kinetics in all tested systems. In US-related systems, the decolorization rate of RR2 declines as RR2 concentration increases. At pH 7, the decolorization rates followed the order UV/US/TiO2 (0.94 h−1) > UV/TiO2 (0.85 h−1) > US/TiO2 (0.25 h−1). The promotion efficiencies of adding NaCl in US/TiO2, UV/TiO2 and UV/US/TiO2 systems were 16%, 18% and 29%, respectively. The decolorization rate increased with the temperature; additionally, the decolorization rate in UV/US/TiO2/Na2S2O8 exceeded that in UV/US/TiO2. The inhibition of RR2 decolorization by adding 1-butanol reveals that the primary decolorization pathway involves hydroxyl radicals, and that direct oxidation by photogenerated holes is probably important in the UV/TiO2-based system. After 120 min of the reaction, the TOC degradation efficiencies of UV/TiO2 and UV/US/TiO2 systems were 47% and 63%, respectively.