Degradation Of Congo Red By Composite Oxidation System Of Anode And Derivative Persulfate

In the anodic oxidation system with sulfate as electrolyte, the generated persulfate can be transformed into sulfate radicals by heating or illumination. The standard redox potential of sulfate radicals is higher than that of the hydroxyl radicals in aqueous solution. As an advanced water treatment oxidant, the sulfate radicals can effectively destruct refractory organics through oxidation and polymerization initiation. If sulfate radicals can be combined with anodic oxidation, and intermittent electricity power supply is used, it will be advantageous to save energy and promote the application of anodic oxidation. This is a great science and applied significances water treatment method.Anodic oxidation and sulphate radical oxidation were combined in the study for degradation of Congo red. The degradation reaction of Congo red and persulfate generation reaction rule were studied in different sodium sulfate concentration, pH values, electric current density, Congo red concentration and electrolytic time. Ti/Sn-Sb- metal oxide coating anode system, Pt anode system and double anode (Pt anode and Ti/Ru-Ir- metal oxide coating anode) system were studied respectively. Pt anode oxidation/heating system, Pt anode oxidation /sunlight system and Pt anode oxidation cooperate with sunlight system were studied in the Pt anode system. Degradation of Congo red by a combined oxidation of Pt anode oxidation cooperate with sunlight system was the most effective. There was a competition relationship between the formation of persulfate and the degradation of Congo red in the anode zone of double anode system. Ti/Ru-Ir-metal oxide coatings anode and Pt-anode were beneficial to the Congo red degradation and persulfate formation, respectively. The degradation rate of Congo red was proportional to Ti/Ru-Ir-metal oxide coatings anode current density and SO42- concentration, but inversely proportional to pH. The formation yield of persulfate was closely related to the current density, SO42-concentration and pH. The most influential factor was the current density.The degradation mechanism of Congo red in anode and persulfate composite oxidation system was also studied. Congo red was degraded into a kind of more stable and photosensitive intermediate material-quinonoids imine. Quinonoids imine can induce photosensitive reaction under visible light to yield singlet oxygen peroxy radical O2·-. C2·- could react with persulphate to generate hydroxyl radicals·OH and sulfate radicals SO4-·, which could promote the further degradation of organics.