Effects of operational parameters on the decolorization of C.I. Reactive Red 198 in UV/TiO2-based systems

The effects of pH, dye concentration, electron acceptor (hydrogen peroxide, persulfate and copper ions) and hydroxyl radical trap (ethanol) on the decolorization of C.I. Reactive Red 198 using a UV/TiO2 system were determined. Decolorization rate increased as the concentration of persulfate ions added increased. The k values followed the order: pH 4 > pH 7 > pH 10 for the UV/TiO2, UV/TiO2/H2O2 and UV/TiO2/Na2S2O8 systems. Hydrogen peroxide, persulfate and copper ions trapped photogenerated electrons and inhibited the recombination of electron/hole pairs in UV/TiO2, thereby accelerating decolorization rate; persulfate ions trapped photogenerated electrons and generated sulfate free radicals. The addition of ethanol inhibited decolorization, suggesting that the predominant decolorization pathway involves hydroxyl radicals and that direct oxidation by photogenerated holes is also significant.