Efficient photocatalytic degradation of Safranin O by integrating solar-UV/TiO 2 /persulfate treatment: Implication of sulfate radical in the oxidation process and effect of various water matrix components

Abstract

Abstract In this work, the degradation of Safranin O (SO), a cationic dye pollutant, by integrating UV/TiO 2 /PPS treatment (PPS: potassium persulfate) was found to be more efficient than UV/TiO 2 and UV/PPS individual binary systems. The complete removal of SO by the integrated system was achieved after only 25 min, whereas 22, 39, 83 and 97% of SO remained in the solutions with UV/TiO 2 , UV/PPS, UV and PPS separated systems. Moreover, the combination of UV/TiO 2 and UV/PPS exhibited a synergistic effect. A complete systematic study of SO removal by UV/TiO 2 /PPS system was carried out by assessing the effect of operating parameters, additives and several complex matrices. Chemical probes experiments showed that both OH and SO 4 − radicals contribute efficiently in the degradation of the dye by the UV/TiO 2 /PPS system. It was found that the degradation of the dye did not obey first-order kinetics law. The initial degradation rate increased significantly with the increase of initial dye and PPS concentrations, catalyst loading, liquid temperature and solution pH. Salts such as KNO 3 and Na 2 CO 3 enhanced notably the degradation of the dye probably by the formation of secondary radicals, such as CO 3 − , NO 2 and NO 3 , which participate in the oxidation reactions. Humic acid, as natural organic matter, decreased the efficiency of the integrated process toward the removal of SO. The conversion yield of SO by the UV/TiO 2 /PPS process was improved when the experiments was performed in natural mineral water, making this process as a promising technique for treating contaminated real natural waters. However, the very high quantity of salts present in seawater alters the reaction of radicals with the dye molecules resulting in lower degradation rate.