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 to 100% after 60min reaction and the TOC removal rate of acidic Congo red was up to 80.4% after 120min reaction, by using UV/Fe2+/S2O82- method, the decoloring rate of acidic Congo red got to 99% after 120min reaction while the TOC removal rate of acidic Congo red reached 69.6% after 120min reaction. The degradation mechanism of acidic Congo red was studied in the simulated sunlight /Fe2+/S2O82- system. The results showed that the intermediate materials of Quinonoids 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 oxygen 1O2 and 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 .

Key words: sulfate radical, persulfate, sunlight, Congo red