| The persulphate oxidation method was a new advanced oxidation technology, came forth recently. Persulfate could be divided into peroxymonosulfate and peroxysulphate. The organic could be thoroughly degraded using the common persulphate oxidation method, which was similar to Fenton method. For example, a relatively stable reddish brown substance was formed during acid Congo red degradation. Its formation causes the lower decolorization rates and TOC removal rates. It was necessary to study the sunlight/persulphate method for to overcome this drawback, and compare to Fenton method.It has been proved that sunlight/Fe2+/S2O82-method is superior to UV/Fe2+/S2O82-method in the process of acidic Congo red degradation. By using simulated sunlight/Fe2+/S2O82-method, the decoloring rate of acidic Congo red(50μmol/L) was up to100%after60min reaction and the TOC removal rate of acidic Congo red was up to80.4%after120min reaction, by using UV/Fe2+/S2O82-method, the decoloring rate of acidic Congo red got to99%after120min reaction while the TOC removal rate of acidic Congo red reached69.6%after120min reaction. It was necessary to study the degradation mechanism of acidic Congo red in sunlight/persulphate system for making clear the reason why sunlight method is superior to UV method.In this study, acidic Congo red was chosen as the model contamination to study the degradation rate in sunlight/Fe2+/peroxysulphate, sunlight/Fe2+/peroxymonosulfate and sunlight/Fenton system, and the effects of pH, the initial concentrations of Fe(II), oxidant on the degradation efficiencies of Congo red in sunlight were studied. The results have proven that regardless of whether sunlight or UV light the degradation rate of acidic Congo red as follow:peroxysulphate> peroxysulphate>hydrogen peroxide; sunlight/Fe2+/persulphate was superior to UV/Fe2+/persulphate and sunlight Fenton was superior to UV/Fenton method.The reason of why simulated sunlight/Fe2+/S2O82-method was superior than UV/Fe2+/S2O82-one was as follow:The results showed that the intermediate materials ofQuinonoids imine class could be generated in the process of degradation, and Quinonoids imine class has photosensitivity and is more sensitive to visible light; Quinonoids imine class is induced photosensitive reaction under visible light, which yielded singlet oxygen1O2and peroxy radical O2·-. O2·-can promote the generation of hydroxyl radicals·OH and sulfate radicals SO4-· in acidic condition, which can cause more active material to be produced in this system. |
