Simultaneous Removal Of Acid Orange 7 And Cr（VI） From Aqueous Solution By Ti O₂ Based Photoelectrocatalytic Technique System

Cr(VI), a common carcinogenic substance, its toxicity is 100 times than that of Cr(III). High color, high CODcr, poor biodegradability and complex components are generally characteristics of dyes wastewater. However, Cr(VI) and dyes are identified as coexistence pollutants in many industrial wastewaters, such as leather, dyes and other industrial wastewaters. Many previous researches demonstrated that photoelectrocatalytic technique system not only could degrade many difficult biodegradation organic pollutants from wastewaters, but also could reduce heavy metal ions with a high state. Usually, the degradation of organic pollutants or reduction of heavy metal ions by photoelectrocatalytic technique system has been individually investigated. Therefore, in this paper, Ti O2 based photoelectrocatalytic technique system has been adopted to remove acid orange 7 and Cr(VI) simultaneously, and the affecting factors and reaction mechanism have been investigated.In this paper, the treatment methods and research progress of chromium-containing wastewater, dyes wastewater and inorganic-organic compound pollution have been analyzed. The simultaneous removal of acid orange 7 and Cr(VI) by Ti O2 based photoelectrocatalytic technique system were systematically investigated. Experimental results showed that a higher simultaneous removal efficiency have been observed, and 95.9 % acid orange 7 and 89.4% Cr(VI) could be removed after 120 min with acid orange 7 initial concentration 20 mg/L, Cr(VI) initial concentration 10 mg/L, initial p H value 2, constant current value 3.5 m A and the surface area of the cathode(Ti mesh) 55 mm×40 mm.The intermediate products of acid orange 7 and Cr(VI) were analyzed by IC, FT-IR and GC/MS, the removal mechanism of acid orange 7 and Cr(VI) by Ti O2 based photoelectrocatalytic technique system was respectively investigated. The experimental results showed that Cr(VI) was removed due to reduction of photoinduced electrons, a much consumption of H+ during the reaction, resulting in a increase in p H, but the solution was always acidic, no precipitation was observed, and the concentration of total chromium remained unchanged. Degradation of acid orange 7 begins from falling of a sulfonic acid group from the benzene ring, the released N2 or NH3 is mainly derived from N of the molecule, only a few portion form NO3-. Some intermediate products such as coumarin, phthalic acid, etc are observed, and then, these intermediate products are degraded into oxalic acid as a small molecular organic acid after a series of oxidation reactions, and finally are completely mineralized to CO2 and H2 O.