Oxidation Degradation of Rhodamine B in Aqueous by UV/S2O82- Treatment System

The UV photolysis of persulfate (S2O82-) is a novel advanced oxidation technologies (AOTs), which leads to the formation of strong oxidizing radicals, sulfate radicals (SO4 center dot-). The effect of oxidant S2O82- concentration, initial dye concentration, initial pH of solution, and various inorganic anions (Cl-, H2PO4-, and HCO3-) were investigated using Rhodamine B (RhB), a kind of xanthene dye, as a model pollutant. With the increase of oxidant S2O82-, more SO4 center dot- produced to attack RhB molecules and result in the increase of RhB degradation. While the improvement was not sustained above a critical value, beyond which degradation rate does not increase. Initial pH of solution had great effect on the RhB degradation rate during UV/S2O82- system. SO4 center dot- is rather stable in acidic solutions, while increasing system pH results in the transformation of SO4 center dot- to (OH)-O-center dot. The effects of three inorganic anions (Cl-, H2PO4-, and HCO3-) all had some negative effect on the degradation of RhB. Based on the RhB solution changes of the UV-vis absorption intensity during the UV/S2O82- treatment, decolorization of RhB accompanied the destruction of aromatic ring structures of RhB molecules.