Decolouration of azo dyes by radicals generated from KSO automatically in homogeneous aqueous solutions.

In this work, at 15 °C and 25 °C, authors study the decolouration reactions (or degradation reactions or oxidation reactions) of 0.10 mM azo dyes (methyl orange and congo red) by (1) KSO and (2) Co/KSO, expounding the roles of KSO and Co: KSO can oxidize azo dyes automatically in water by radicals; Co has catalysis for oxidation of KSO, whether Co is from CoSO or Co(NO), CoCl, CoAc. The decolouration degree of azo dyes in all systems quickens with the increase of the initial concentration of KSO and the reaction temperature. In the presence and absence of Co, comparative experiments are done between the oxidation of KSO and oxone, KSO shows weaker oxidation than oxone. The decolouration reaction of methyl orange (MO) in the system of (0.10 mM MO + 2.00 mM KSO) accords with the second order reaction, the reaction rate constants are 4.789 Mmin at 15 °C and 5.894 Mmin at 25 °C respectively, the activation energy E is 14813 J/mol, and Arrhenius equation is  = 2.328 exp[-14813/(RT)].